Shaft connection structure, motor with speed reducer, electric power steering device, and steering unit for steer-by-wire

Abstract

To provide a shaft connection structure that can absorb an alignment error, can connect a pair of shafts without increasing the number of components, and can shorten the entire length of a connection part.SOLUTION: A male spline connection part 76 provided at the rear end part of an upper output shaft 73, which is formed by forming a plurality of male spline teeth 78 on the outer surface of a hemispherical convex part 77, and a female spline connection part 21 provided at the front end part of a lower shaft 19, which is formed by forming a plurality of female spline teeth 23 on the inner surface of a hemispherical concave part 22, are connected by inserting the hemispherical convex part 77 into the hemispherical concave part 22 and spline-engaging each of the male spline teeth 78 and each of the female spline teeth 23.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to a shaft connection structure for connecting a pair of shafts. The present invention also relates to a motor with a speed reducer, an electric power steering device, and a steering unit for steer-by-wire, each having the shaft connection structure.

Background Art

[0002] An electric power steering device that uses an electric motor as an auxiliary power source is widely used to reduce the force with which a driver operates a steering wheel. In addition, in an electric power steering device, in order to reduce the size of the electric motor, the electric motor is also used in combination with a worm speed reducer.

[0003] In a motor with a speed reducer that combines an electric motor and a worm speed reducer, in order to increase the output torque of the electric motor, the motor output shaft of the electric motor and the worm that constitutes the worm speed reducer are connected so as to be able to transmit torque.

[0004] As described in, for example, Japanese Patent Application Laid-Open No. 2016-2926 (Patent Document 1), a structure in which a motor output shaft and a worm are connected using a joint member (coupling) is widely known.

[0005] According to the structure described in Japanese Patent Application Laid-Open No. 2016-2926, even when a so-called alignment error occurs in which the central axis of the motor output shaft and the central axis of the worm do not match, the alignment error can be absorbed by elastic deformation of the joint member or the like. Therefore, even when an alignment error occurs, torque can be transmitted between the motor output shaft and the worm. In addition, generation of abnormal noise can also be suppressed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] In the structure described in Japanese Patent Application Laid-Open No. 2016-2926, a joint member for connecting a motor output shaft and a worm is composed of three parts: a first rotating element fixed to the end of the motor output shaft, a second rotating element fixed to the end of the worm, and an intermediate element disposed between the first rotating element and the second rotating element. For this reason, the number of parts of the motor with a speed reducer increases, which causes an increase in cost. Further, since a joint member is interposed between the motor output shaft and the worm, the overall length of the connection portion becomes long, and the motor with a speed reducer, and thus, the electric power steering device is likely to be enlarged.

[0008] The above problems are not specific to the connection portion between the motor output shaft and the worm, but are problems that can similarly occur in the connection portion between a pair of shafts connected so as to be able to transmit torque.

[0009] The present invention has been made to solve the above problems, and is capable of absorbing an alignment error, connecting a pair of shafts to each other without increasing the number of parts, and shortening the overall length of the connection portion. An object of the present invention is to provide a shaft connection structure, a motor with a speed reducer provided with this shaft connection structure, an electric power steering device, and a steering unit for steer-by-wire.

MEANS FOR SOLVING THE PROBLEMS

[0010] The shaft connection structure of the present invention includes a male spline connection portion provided at an end of a first shaft and a female spline connection portion provided at an end of a second shaft. The male spline connection portion is formed by forming a plurality of male spline teeth on an outer surface of a partial spherical convex portion. The female spline connection portion is formed by forming a plurality of female spline teeth on an inner surface of a partial spherical concave portion. The partial spherical concave portion is open only to one end face of the second shaft. The inner diameter of the partial spherical concave portion gradually decreases in a curved manner from the opening toward the inner part, and the female spline teeth are formed on the entire inner surface in the axial direction. The outer diameter of the partial spherical convex portion gradually decreases in a curved manner from the base end portion toward the tip end portion, and the male spline teeth are formed on the entire outer surface in the axial direction. In the shaft connection structure of the present invention, the partial spherical convex portion is inserted inside the partial spherical concave portion, and the male spline teeth and the female spline teeth are spline-engaged with each other, thereby connecting the first shaft and the second shaft so that torque can be transmitted. Note that the partial spherical convex portion includes not only a convex portion (spherical segment convex portion) having a spherical segment-shaped outer surface formed by cutting a sphere (including an ellipsoid) with one plane as shown in FIG. 29(A), but also a convex portion (frustum-shaped convex portion) having a frustum-shaped outer surface formed by cutting a sphere with two parallel planes as shown in FIG. 29(B). The spherical segment convex portion has a cross-sectional arcuate shape and a dome-shaped convex curved surface with a rounded tip on the outer surface. On the other hand, the frustum-shaped convex portion has a cross-sectional substantially isosceles trapezoid shape and a strip-shaped convex curved surface on the outer surface. Among the spherical segment-shaped convex portions, those having a hemispherical outer surface formed by cutting the sphere near the center are particularly referred to as hemispherical convex portions. The partial spherical concave portion includes not only a concave portion (spherical segment concave portion) having a spherical segment-shaped inner surface formed by cutting a sphere (including an ellipsoid) with one plane, but also a concave portion (frustum-shaped concave portion) having a frustum-shaped inner surface formed by cutting a sphere with two parallel planes. Among the spherical segment-shaped concave portions, those having a hemispherical inner surface formed by cutting the sphere near the center are particularly referred to as hemispherical concave portions.

[0011] In one aspect of the shaft connection structure of the present invention, the male spline connection portion can be configured by forming a plurality of the male spline teeth on the outer surface of the hemispherical convex portion, and the female spline connection portion can be configured by forming a plurality of the female spline teeth on the inner surface of the hemispherical concave portion. Alternatively, in one aspect of the shaft connection structure of the present invention, the male spline connection portion can be configured by forming a plurality of the male spline teeth on the outer surface of the frustum-shaped convex portion, and the female spline connection portion can be configured by forming a plurality of the female spline teeth on the inner surface of the frustum-shaped concave portion.

[0012] In one aspect of the shaft connection structure of the present invention, at least one of the male spline connection portion and the female spline connection may be covered with a coating layer made of synthetic resin. Alternatively, a buffer member made of an elastic material can be disposed between the male spline connection portion and the female spline connection portion.

[0013] In one aspect of the shaft connection structure of the present invention, the outer diameter of the portion of the first shaft adjacent to the male spline connection portion can be made smaller than the outer diameter of the male spline connection portion.

[0014] The motor with a speed reducer of the present invention includes a worm speed reducer and an electric motor. The worm speed reducer has a worm and a worm wheel. The electric motor has a motor output shaft. In the motor with a speed reducer of the present invention, the end of the worm and the end of the motor output shaft can be connected by the shaft connection structure of the present invention. In this case, the male spline connection portion can be provided at the end of the motor output shaft, and the female spline connection portion can be provided at the end of the worm. Alternatively, the female spline connection portion can be provided at the end of the motor output shaft, and the male spline connection portion can be provided at the end of the worm.

[0015] The electric power steering apparatus of the present invention includes the motor with a speed reducer of the present invention.

[0016] The steering unit for steer-by-wire of the present invention includes, for example, a steering shaft that constitutes a position adjustment device, and a reaction force output shaft, and a reaction force generation device for applying a steering reaction force to the steering wheel. In the steering unit for steer-by-wire of the present invention, the end of the steering shaft and the end of the reaction force output shaft can be connected in a torque-transmittable manner by the shaft connection structure of the present invention. In this case, the end of the steering shaft may be provided with the male spline connection portion, and the end of the reaction force output shaft may be provided with the female spline connection portion. Alternatively, the end of the steering shaft may be provided with the female spline connection portion, and the end of the reaction force output shaft may be provided with the male spline connection portion.

[0017] The steer-by-wire steering unit of the present invention includes, for example, a steering shaft that constitutes a position adjusting device, and a reaction force applying motor that has a motor output shaft and applies a steering reaction force to a steering wheel. In the steer-by-wire steering unit of the present invention, the end of the steering shaft and the end of the motor output shaft can be connected so as to be torque-transmittable by the shaft connection structure of the present invention. In this case, the end of the steering shaft may be provided with the male spline connection portion, and the end of the motor output shaft may be provided with the female spline connection portion. Alternatively, the end of the steering shaft may be provided with the female spline connection portion, and the end of the motor output shaft may be provided with the male spline connection portion.

Advantages of the Invention

[0018] According to the present invention, it is possible to absorb alignment errors, connect a pair of shafts to each other without increasing the number of parts, shorten the total length of the connection portion, and realize a shaft connection structure, a motor with a speed reducer provided with this shaft connection structure, an electric power steering device, and a steer-by-wire steering unit.

Brief Description of the Drawings

[0019]

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[0020] [First Example of the Embodiment] The first example of the embodiment will be described with reference to FIGS. 1 to 14. In this example, the shaft connection structure of the present invention is applied to a steer-by-wire type steering device. In the following description, the front-rear direction means the front-rear direction of the vehicle, the up-down direction means the up-down direction of the vehicle, and the width direction means the width direction of the vehicle.

[0021] [Overall Configuration of the Steering Device] The steering device 1 of this example is a steer-by-wire type steering device. As shown in the overall configuration in FIG. 1, the steering device 1 includes a steering unit 3 to which a steering wheel 2 is attached, a steering unit 5 that steers a pair of steering wheels 4, and a control device (ECU) 6. The steering device 1 has a linkless structure in which the steering unit 3 and the steering unit 5 are not mechanically connected but electrically connected.

[0022] The steering unit 3 measures the operation of the steering wheel 2 by the driver using a torque sensor 75 (see FIG. 5) and a steering angle sensor (not shown), and outputs the measurement result to the control device 6. Various signals indicating the driving situation, such as the steering torque measured by the torque sensor 75, the steering angle measured by the steering angle sensor, the vehicle speed, the yaw rate, and the acceleration, are input to the control device 6. Based on various signals indicating the driving situation, the control device 6 drives the steering actuator 7 provided in the steering unit 5. As a result, a linear motion member such as a rack shaft or a screw shaft is displaced in the width direction, and a pair of tie rods 8 are pushed and pulled to apply a steering angle to the pair of steering wheels 4.

[0023] Further, the control device 6 controls the drive of a reaction force applying motor 58 (see FIG. 3) of a reaction force generating device 10 described later provided in the steering unit 3 based on various signals indicating driving conditions such as steering torque, steering angle, vehicle speed, etc., and applies a steering reaction force corresponding to the driving condition to the steering wheel 2.

[0024] 〔Steering Unit〕 Next, the steering unit 3, which is a characteristic part of the steering device 1 in this example, will be described. The steering unit 3 includes a position adjusting device 9 for adjusting the position of the steering wheel 2 and a reaction force generating device 10 for applying a steering reaction force to the steering wheel 2.

[0025] The position adjusting device 9 and the reaction force generating device 10 are each sub-assembled and connected to each other by two connection parts. Specifically, as shown in FIGS. 4 and 5, the position adjusting device 9 and the reaction force generating device 10 arranged in front of the position adjusting device 9 are connected only at two places, namely a power connection part 11 and a housing connection part 12. Therefore, the steering unit 3 in this example is assembled by connecting the position adjusting device 9 and the reaction force generating device 10 at two places, namely the power connection part 11 and the housing connection part 12. In particular, in this example, the connection structure of the power connection part 11 has features. A detailed description of the connection structure of the power connection part 11 will be given after the descriptions of the position adjusting device 9 and the reaction force generating device 10 respectively.

[0026] 〈Position Adjusting Device〉 The position adjusting device 9 has a function of adjusting each of the front-rear position and the up-down position of the steering wheel 2. In other words, the position adjusting device 9 includes a telescopic mechanism for adjusting the front-rear position of the steering wheel 2 and a tilt mechanism for adjusting the up-down position of the steering wheel 2 respectively.

[0027] The position adjustment device 9 includes a steering shaft 13, a steering column 14, a lower telescopic actuator 15, an upper telescopic actuator 16, and a tilt actuator 17.

[0028] 《Steering Shaft》 The steering shaft 13 is configured to be able to expand and contract in its entire length, and is rotatably supported inside the steering column 14 by using a plurality (three in the illustrated example) of rolling bearings 18a to 18c. A steering wheel 2 is attached to the rear end of the steering shaft 13. The steering shaft 13 is formed by spline-engaging a lower shaft 19 disposed on the front side and a hollow cylindrical upper shaft 20 disposed on the rear side so as to be able to transmit torque and allow relative displacement in the axial direction.

[0029] 《Female Spline Connection Portion》 The front end of the lower shaft 19 is provided with a female spline connection portion 21 that constitutes a power connection portion 11 capable of torque transmission with the reaction force generating device 10. Therefore, in this example, the steering shaft 13 (lower shaft 19) corresponds to the second shaft described in the claims.

[0030] As shown in FIG. 11, the female spline connection portion 21 has a hemispherical female spline structure formed by forming a plurality of female spline teeth 23 on the inner surface of a hemispherical concave portion 22 that opens on the front end face of the lower shaft 19. The hemispherical concave portion 22 has an inner diameter that curves and becomes smaller from the opening to the inner part (the central part of the inner surface), and the inner part is located on the central axis of the lower shaft 19. The plurality of female spline teeth 23 are arranged at equal intervals in the circumferential direction and are formed in the radial direction from the inner part of the hemispherical concave portion 22 toward the opening edge. Note that the hemispherical concave portion 22 only needs to have a concave shape in which the inner diameter curves and becomes smaller from the opening to the inner part. Therefore, the hemispherical concave portion 22 includes not only a complete hemispherical shape in which the depth dimension from the opening to the inner part is half of the inner diameter of the opening, but also a substantially hemispherical shape, a semi-elliptical spherical shape, and a substantially semi-elliptical spherical shape that is not a complete semi-elliptical spherical shape.

[0031] "Steering Column" The steering column 14 is configured to be telescopically extendable in its overall length and is supported by a vehicle body (not shown). The steering column 14 includes a bracket 24 and a column main body 25. Note that the steering column 14 in this example has a two-stage telescopic structure in order to ensure a large amount of telescopic displacement in the front-rear direction.

[0032] The bracket 24 is for supporting the column main body 25 on the vehicle body, and includes a fixed bracket 26 fixed to the vehicle body and a displacement bracket 27 supported so as to be relatively displaceable in the front-rear direction with respect to the fixed bracket 26.

[0033] The fixed bracket 26 includes a substantially rectangular flat plate-shaped fixing plate portion 28 and a substantially U-shaped fixed-side support frame 29. The fixing plate portion 28 is fixed to the vehicle body using a plurality of mounting bolts 30. The fixed-side support frame 29 is provided at the front end of the fixing plate portion 28 and connects the end portions on both sides in the width direction of the fixing plate portion 28.

[0034] The displacement bracket 27 includes a displacement plate portion 31 disposed so as to overlap the lower surface of the fixing plate portion 28 and a substantially U-shaped displacement-side support frame 32. The displacement plate portion 31 is supported using a linear guide 80 (see FIG. 3) so as to be relatively displaceable in the front-rear direction with respect to the fixing plate portion 28. The displacement-side support frame 32 is provided at the rear end of the displacement plate portion 31 and connects the end portions on both sides in the width direction of the displacement plate portion 31. Among the pair of left and right support wall portions 33 constituting the displacement-side support frame 32, a screw shaft (not shown) of a tilt feed screw device 56 constituting the tilt actuator 17 is rotatably supported on the inner surface of one of the support wall portions 33 with the axial direction oriented in the vertical direction.

[0035] As shown in FIG. 4, the column body 25 is generally configured in a substantially cylindrical shape and is arranged with its axial direction oriented in the front-rear direction. The column body 25 includes an outer column 34 disposed at an intermediate portion in the front-rear direction, a lower inner column 35 fitted inside the front side portion of the outer column 34, and an upper inner column 36 fitted inside the rear side portion of the outer column 34.

[0036] The outer column 34 is supported so as to be movable in the vertical direction with respect to the displacement bracket 27. The rear side portion of the outer column 34 passes through the inside of the displacement side support frame 32 that constitutes the displacement bracket 27 in the front-rear direction. A nut (not shown) of a tilt feed screw device 56 that constitutes the tilt actuator 17 is pivotally supported on the outer peripheral surface of the rear side portion of the outer column 34. The outer column 34 has a slit 37 (see FIG. 4) extending in the front-rear direction at an intermediate portion in the front-rear direction of the lower surface. The outer column 34 has screw holes 38 at a plurality of locations on its outer peripheral surface. A screw plug 39 made of a material with a low coefficient of friction such as polyacetal (POM) is screwed into each of the screw holes 38.

[0037] The lower inner column 35 is fitted inside the front side portion of the outer column 34 so as to be relatively displaceable in the front-rear direction. The tip of the screw plug 39 screwed into the screw hole 38 provided in the outer column 34 is pressed against the outer peripheral surface of the lower inner column 35. Thereby, rattling of the lower inner column 35 with respect to the outer column 34 is suppressed. The lower inner column 35 includes a cylindrical portion 40 disposed inside the outer column 34 and a first housing connection portion 41 fitted and supported at the front end of the cylindrical portion 40.

[0038] 《First Housing Connection Portion》 The first housing connection portion 41 includes a cylindrical first connection cylinder portion 42 fitted inside the front end of the cylindrical portion 40, and a first connection plate portion 43 that is outward flange-shaped and substantially rectangular flat plate-shaped and bends radially outward from the front end of the first connection cylinder portion 42. Each of the corner portions of the first connection plate portion 43 is provided with a first through hole 44 penetrating in the front-rear direction. The first housing connection portion 41 is disposed inside the fixed-side support frame 29. Note that the first through hole 44 can be merely a through hole or a threaded hole. Since the first housing connection portion 41 is disposed at the front end of the column body 25 in a state before connecting the position adjusting device 9 and the reaction force generating device 10, it functions as a cover when incorporating or assembling the position adjusting device 9, and can suppress foreign matter from entering the inside of the column body 25.

[0039] The upper-side inner column 36 is fitted inside the rear side portion of the outer column 34 so as to enable relative displacement in the front-rear direction. The tip of a screw plug 39 screwed into a threaded hole 38 provided in the outer column 34 is pressed against the outer peripheral surface of the upper-side inner column 36. Thereby, rattling of the upper-side inner column 36 with respect to the outer column 34 is suppressed.

[0040] 〈Lower-side telescopic actuator〉 The lower-side telescopic actuator 15 is disposed so as to span between the fixed bracket 26 and the displacement bracket 27 that constitute the bracket 24, and displaces the displacement bracket 27 in the front-rear direction with respect to the fixed bracket 26. Thereby, the outer column 34 and the lower-side inner column 35 that constitute the column body 25 are relatively displaced in the front-rear direction, and the column body 25 is expanded and contracted.

[0041] The lower-side telescopic actuator 15 includes a lower-side telescopic motor 45 and a lower-side feed screw device 46.

[0042] The lower telescopic motor 45 is supported and fixed on the side surface in the width direction of the fixed side support frame 29 that constitutes the fixed bracket 26 with the motor output shaft (not shown) facing in the vertical direction.

[0043] As shown in FIG. 3, the lower feed screw device 46 includes a lower screw shaft 47 and a lower nut 48. The lower screw shaft 47 is arranged with its axial direction facing the front-rear direction, and is rotationally driven by the lower telescopic motor 45 via a speed reduction mechanism such as a worm speed reducer (not shown). The lower screw shaft 47 is supported by the fixed bracket 26 so as to be rotatable only. The lower nut 48 is screwed onto the lower screw shaft 47 and is supported by the side surface in the width direction of the displacement bracket 27. That is, the lower telescopic actuator 15 rotates the lower telescopic motor 45 to displace the lower nut 48 in the axial direction of the lower screw shaft 47, thereby relatively displacing the outer column 34 in the front-rear direction with respect to the lower inner column 35.

[0044] 〈Upper Telescopic Actuator〉 The upper telescopic actuator 16 is arranged so as to span between the outer column 34 and the upper inner column 36 that constitute the column body 25, and displaces the upper inner column 36 in the front-rear direction with respect to the outer column 34. Thereby, the column body 25 is expanded and contracted.

[0045] The upper telescopic actuator 16 includes an upper telescopic motor 49 and an upper feed screw device 50.

[0046] The upper telescopic motor 49 is supported below the front end of the outer column 34 with the motor output shaft (not shown) facing in the width direction.

[0047] As shown in Fig. 3, the upper feed screw device 50 includes an upper screw shaft 51 and an upper nut 52. The upper screw shaft 51 is arranged with its axial direction facing the front-rear direction, and is rotationally driven by an upper telescopic motor 49 via a speed reduction mechanism such as a worm speed reducer (not shown). The upper screw shaft 51 is supported by the outer column 34 so as to be rotatable only. The upper nut 52 is screwed onto the upper screw shaft 51 and is supported on the lower surface of the upper inner column 36 via a connector member 53. The connector member 53 is arranged inside the slit 37 of the outer column 34 and is fixed to the lower surface of the upper inner column 36. That is, the upper telescopic actuator 16 rotates the upper telescopic motor 49 to displace the upper nut 52 in the axial direction of the upper screw shaft 51, thereby relatively displacing the upper inner column 36 in the front-rear direction with respect to the outer column 34.

[0048] 〈Tilt Actuator〉 The tilt actuator 17 is arranged so as to span between the displacement-side support frame 32 constituting the displacement bracket 27 and the outer column 34, and displaces the outer column 34 in the vertical direction with respect to the displacement bracket 27. Further, as will be described later, a reaction force generating device 10 connected to the front side of the position adjusting device 9 is rotatably supported by a pair of pivot bolts 54 arranged in the width direction with respect to the fixed-side support frame 29. Thereby, the column body 25 can be swung in the vertical direction around the pivot bolt 54 with respect to the bracket 24.

[0049] The tilt actuator 17 includes a tilt motor 55 and a tilt feed screw device 56.

[0050] The tilt motor 55 is fixed to one support wall portion 33 constituting the displacement-side support frame 32 with its motor output shaft (not shown) facing the front-rear direction.

[0051] The tilt feed screw device 56 includes a tilt screw shaft (not shown) and a tilt nut. The tilt screw shaft is arranged with its axial direction facing the vertical direction, and is rotationally driven by a tilt motor 55 via a speed reduction mechanism such as a worm speed reducer (not shown). The tilt screw shaft is supported by one support wall portion 33 so as to be rotatable only. The tilt nut is screwed onto the tilt screw shaft and is pivotally supported on the side surface in the width direction of the outer column 34. That is, the tilt actuator 17 rotates the tilt motor 55 to displace the tilt nut in the axial direction of the tilt screw shaft, thereby relatively displacing the outer column 34 in the vertical direction with respect to the displacement bracket 27.

[0052] 《Method for Adjusting the Position of the Steering Wheel》 To adjust the front-rear position of the steering wheel 2 by the position adjustment device 9 in this example, the lower telescopic actuator 15 is driven to relatively displace the displacement bracket 27 in the front-rear direction with respect to the fixed bracket 26, and the outer column 34 is relatively displaced in the front-rear direction with respect to the lower inner column 35, or / and the upper telescopic actuator 16 is driven to relatively displace the upper inner column 36 in the front-rear direction with respect to the outer column 34. Thereby, while expanding and contracting the entire length of the steering column 14 and expanding and contracting the entire length of the steering shaft 13, the front-rear position of the steering wheel 2 is adjusted. After adjusting the front-rear position of the steering wheel 2 to a desired position, the driving of the lower telescopic actuator 15 or / and the upper telescopic actuator 16 is stopped.

[0053] To adjust the vertical position of the steering wheel 2 by the position adjustment device 9 in this example, the tilt actuator 17 is driven to displace the rear portion of the outer column 34 in the vertical direction with respect to the displacement bracket 27. Thereby, the steering shaft 13 rotatably supported inside the column main body 25 is swung to adjust the vertical position of the steering wheel 2. After adjusting the vertical position of the steering wheel 2 to a desired position, the driving of the tilt actuator 17 is stopped.

[0054] Incidentally, the adjustment of the front - rear position and the up - down position of the steering wheel 2 can be performed simultaneously or independently (before and after in time).

[0055] 〈Reaction force generating device〉 The reaction force generating device 10 is disposed in front of the position adjusting device 9 and is connected to the position adjusting device 9 by a power connection portion 11 and a housing connection portion 12. The reaction force generating device 10 is controlled by the control device 6 and applies a steering reaction force of a magnitude and direction corresponding to the driving conditions such as the steering angle and vehicle speed of the steering wheel 2 to the steering wheel 2.

[0056] The reaction force generating device 10 includes a gear housing 57, a reaction force applying motor 58, a worm reducer 59, and a reaction force output shaft 60.

[0057] As shown in FIG. 9, the gear housing 57 includes a lower - side housing 61, an upper - side housing 62, and a second housing connection portion 63. The lower - side housing 61, the upper - side housing 62, and the second housing connection portion 63 are connected in the front - rear direction by bolts 81 in a state before connecting the reaction force generating device 10 to the position adjusting device 9. The lower - side housing 61 integrally includes a cup - shaped worm accommodating portion 65 and a cylindrical worm wheel accommodating portion 66. The upper - side housing 62 is formed in a cylindrical shape and is fixed to the rear side of the worm wheel accommodating portion 66. Both side portions in the width direction of the upper - side housing 62 are rotatably supported by a pair of pivot bolts 54 with respect to the fixed - side support frame 29.

[0058] 《Second housing connection portion》 The second housing connection portion 63 closes the opening at the rear side of the upper housing 62, and has a cylindrical second connection cylinder portion 67 and a second connection plate portion 68 which is outward flange-shaped and substantially rectangular flat plate-shaped and bends radially outward from the front end portion of the second connection cylinder portion 67. Second through holes 69 penetrating in the front-rear direction are provided at respective corner portions of the second connection plate portion 68. In this example, among the lower housing 61 and the upper housing 62, auxiliary through holes (not shown) penetrating in the front-rear direction are provided at portions (in the illustrated example, two upper positions) that coincide with the second through holes 69. For this reason, in a state where the lower housing 61, the upper housing 62, and the second housing connection portion 63 are connected in the front-rear direction by bolts 81 to form the gear housing 57, the second through holes 69 and the auxiliary through holes are continuous in the front-rear direction and become one continuous hole 79. Note that the second through holes 69 can be mere through holes or can be threaded holes. The lower housing 61 and the upper housing 62 are connected to each other by bolts 87 inserted through the auxiliary through holes from the front side toward the rear side.

[0059] The reaction force applying motor 58 is supported and fixed to the worm accommodating portion 65 constituting the gear housing 57. The rotation of the reaction force applying motor 58 is transmitted to the steering shaft 13 via the worm reducer 59, the reaction force output shaft 60, and the power connection portion 11.

[0060] The worm reducer 59 includes a worm 70 and a worm wheel 71. The worm 70 is rotatably supported inside the worm accommodating portion 65 and is connected to a motor output shaft (not shown) of the reaction force applying motor 58. The worm wheel 71 is disposed inside the lower housing 61 and is externally fitted to a lower side output shaft 72 (described later) constituting the reaction force output shaft 60.

[0061] The reaction force output shaft 60 is arranged with its axial direction facing the front-rear direction and is rotatably supported inside the gear housing 57 via a plurality (two in the illustrated example) of rolling bearings 82a and 82b. The reaction force output shaft 60 includes a lower side output shaft 72, an upper side output shaft 73, and a torsion bar 74. The lower side output shaft 72 and the upper side output shaft 73 are arranged coaxially with each other and are connected to each other via the torsion bar 74. Around the upper side output shaft 73, a torque sensor 75 for measuring the steering torque input from the driver to the steering wheel 2 is arranged. The rear end portion of the upper side output shaft 73 protrudes rearward from the second connection cylinder portion 67 that constitutes the second housing connection portion 63.

[0062] 《Male spline connection portion》 At the rear end portion of the upper side output shaft 73, a male spline connection portion 76 is provided, which constitutes a power connection portion 11 capable of torque transmission with the position adjusting device 9. Therefore, in this example, the reaction force output shaft 60 (upper side output shaft 73) corresponds to the first shaft described in the claims.

[0063] As shown in FIG. 10, the male spline connection portion 76 has a hemispherical male spline structure formed by forming a plurality of male spline teeth 78 on the outer surface of a hemispherical convex portion 77 provided at the rear end portion of the upper side output shaft 73. The hemispherical convex portion 77 has an outer diameter that gradually decreases in a curved manner from the base end portion (skirt portion) toward the tip end portion (top portion), and the tip end portion is located on the central axis of the upper side output shaft 73. The plurality of male spline teeth 78 are arranged at equal intervals in the circumferential direction and are formed in the radial direction from the tip end portion to the base end portion of the hemispherical convex portion 77. In this example, the male spline connection portion 76 is covered with a coating layer made of a synthetic resin having a low friction coefficient, such as polyamide resin. Note that the hemispherical convex portion 77 may have a convex shape in which the outer diameter gradually decreases in a curved manner from the base end portion to the tip end portion. Therefore, the hemispherical convex portion 77 is not limited to a perfect hemispherical shape in which the length dimension from the base end portion to the tip end portion is 1 / 2 of the outer diameter at the base end portion, and includes a substantially hemispherical shape that is not a perfect hemispherical shape, a semi-elliptical spherical shape, and a substantially semi-elliptical spherical shape that is not a perfect semi-elliptical spherical shape.

[0064] In order to apply a steering reaction force to the steering wheel 2 by the reaction force generating device 10, for example, the reaction force applying motor 58 is driven by the control device 6 based on various signals indicating driving conditions such as steering torque, steering angle, and vehicle speed. The rotation of the reaction force applying motor 58 is transmitted to the reaction force output shaft 60 via the worm reducer 59, and is applied to the steering wheel 2 as a steering reaction force via the power connection portion 11 that connects the upper side output shaft 73 and the lower shaft 19.

[0065] In this example, the position adjusting device 9 and the reaction force generating device 10 as described above are connected at two locations, namely, the power connection portion 11 and the housing connection portion 12.

[0066] 〈Power connection portion〉 The power connection portion 11 is formed by directly connecting a female spline connection portion 21 provided at the front end portion of the lower shaft 19 constituting the position adjusting device 9 and a male spline connection portion 76 provided at the rear end portion of the upper side output shaft 73 constituting the reaction force generating device 10 by spline engagement. Therefore, the power connection portion 11 has a connection structure with a spline structure.

[0067] Specifically, as shown in FIG. 12(B), the tip of the hemispherical convex portion 77 constituting the male spline connection portion 76 is inserted into the hemispherical concave portion 22 constituting the female spline connection portion 21, and each of the plurality of female spline teeth 23 provided on the inner surface of the hemispherical concave portion 22 and each of the plurality of male spline teeth 78 provided on the outer surface of the hemispherical convex portion 77 are alternately arranged in the circumferential direction and engaged with each other to achieve spline engagement. In this example, since the male spline connection portion 76 is covered with a coating layer made of synthetic resin, the female spline teeth 23 and the male spline teeth 78 are spline-engaged via the coating layer.

[0068] Also, in this example, the outer surface of the hemispherical convex portion 77 constituting the male spline connection portion 76 is pressed against the inner surface of the hemispherical concave portion 22 constituting the female spline connection portion 21 in the rearward (axial direction) via the coating layer.

[0069] The power connection portion 11 connects the steering shaft 13 (lower shaft 19) and the reaction force output shaft 60 (upper output shaft 73) in a torque-transmittable manner based on the engagement between the female spline teeth 23 and the male spline teeth 78 and the frictional force acting between the inner surface of the hemispherical concave portion 22 and the outer surface of the hemispherical convex portion 77.

[0070] In this example, in the power connection portion 11, the outer surface of the hemispherical convex portion 77 constituting the male spline connection portion 76 is pressed rearward against the inner surface of the hemispherical concave portion 22 constituting the female spline connection portion 21. Therefore, in order to prevent the lower shaft 19 provided with the female spline connection portion 21 from being displaced rearward, a displacement prevention structure is separately provided.

[0071] In this example, as shown in FIG. 13, a rolling bearing 18a for rotatably supporting the lower shaft 19 with respect to the lower inner column 35 is used to prevent the rearward displacement of the lower shaft 19. Specifically, a locking groove 83 is formed at a position adjacent to the front side of the portion of the outer peripheral surface of the lower shaft 19 where the rolling bearing 18a is externally fitted, and a bevel-shaped retaining ring 84 having a tapered surface is locked to the locking groove 83. Further, Lower side inner column 35 an annular protrusion 86 projecting radially inward is provided at a position adjacent to the rear side of the portion of the inner peripheral surface of the inward flange-shaped annular wall portion 85 provided on the inner peripheral surface of Lower side inner column 35 where the rolling bearing 18a is internally fitted. Thereby, the rearward pressing force acting on the lower shaft 19 is supported by the lower inner column 35 via the retaining ring 84 and the rolling bearing 18a.

[0072] 〈Housing connection part〉 The housing connection part 12 is formed by connecting a first housing connection part 41 provided at the front end of the lower inner column 35 constituting the position adjusting device 9 and a second housing connection part 63 provided at the rear side part of the gear housing 57 constituting the reaction force generating device 10 with a plurality of (four in the illustrated example) connection bolts 64 (see FIG. 5). Therefore, the housing connection part 12 has a bolt connection structure.

[0073] Specifically, the first connection plate portion 43 constituting the first housing connection portion 41 and the second connection plate portion 68 constituting the second housing connection portion 63 are overlapped without a gap in the front-rear direction, and a connection bolt 64 inserted from the rear side toward the front side is inserted into the first through hole 44 provided in the first connection plate portion 43 and the second through hole 69 (continuous hole 79) provided in the second connection plate portion 68, thereby coupling the first connection plate portion 43 and the second connection plate portion 68. Further, in this example, when the first connection plate portion 43 and the second connection plate portion 68 are overlapped in the front-rear direction, the second connection cylinder portion 67 is fitted into the first connection cylinder portion 42 in an inro fitting manner. In this example, such a housing connection portion 12 connects the lower side inner column 35 constituting the position adjustment device 9 and the gear housing 57 constituting the reaction force generating device 10 in the front-rear direction. Also, in this example, such a housing connection portion 12 is disposed in the vicinity of the power connection portion 11, that is, slightly forward of the power connection portion 11.

[0074] In the present example as described above, even when a so-called alignment error occurs in the power connection portion 11 where the central axis of the lower shaft 19 and the central axis of the upper output shaft 73 do not coincide, the alignment error can be absorbed (allowed). That is, in this example, the power connection portion 11 is configured by inserting a hemispherical convex portion 77 constituting the male spline connection portion 76 into a hemispherical concave portion 22 constituting the female spline connection portion 21 and spline-engaging a female spline tooth 23 provided on the inner surface of the hemispherical concave portion 22 and a male spline tooth 78 provided on the outer surface of the hemispherical convex portion 77. Therefore, the alignment error can be absorbed by displacing the hemispherical convex portion 77 inside the hemispherical concave portion 22 while the female spline tooth 23 and the male spline tooth 78 are in spline engagement. Further, the power connection portion 11 can absorb not only the alignment error generated during the connection operation between the lower shaft 19 and the upper output shaft 73 but also the alignment error generated during the use (operation) of the steering device 1.

[0075] Therefore, according to the connection structure of the power connection portion 11 in this example, even when an alignment error occurs, torque can be transmitted between the steering shaft 13 and the reaction force output shaft 60. Further, it is possible to prevent the generation of abnormal noise and the reduction of transmission efficiency due to the alignment error. Further, even when the hemispherical concave portion 22 and the hemispherical convex portion 77 are twisted, torque can be efficiently transmitted between the steering shaft 13 and the reaction force output shaft 60.

[0076] In addition, since the surface of the male spline connection portion 76 is covered with a coating layer made of synthetic resin, rattling between the male spline teeth 78 and the female spline teeth 23 can be suppressed. Further, it is possible to prevent the generation of abnormal noise due to metal contact between the male spline connection portion 76 and the female spline connection portion 21. When implementing the present invention, instead of the male spline connection portion 76, the female spline connection portion 21 can also be covered with a coating layer made of synthetic resin, or both the male spline connection portion 76 and the female spline connection portion 21 can be covered with a coating layer made of synthetic resin. Further, without providing a coating layer made of synthetic resin, a buffer member (damper member) made of an elastic material such as rubber or elastomer can be disposed between the female spline connection portion and the male spline connection portion.

[0077] In addition, the power connection portion 11 in this example directly connects the female spline connection portion 21 and the male spline connection portion 76 without using a joint member or a joint member. Therefore, the steering shaft 13 and the reaction force output shaft 60 can be connected so as to be able to transmit torque without increasing the number of parts. Further, the overall length (axial length) of the power connection portion 11 can be shortened. Therefore, it is possible to prevent the dimensions of the steering unit 3 in the front-rear direction from becoming large.

[0078] Furthermore, the power connection portion 11 of this example can connect the female spline connection portion 21 and the male spline connection portion 76 by simply inserting the hemispherical convex portion 77 constituting the male spline connection portion 76 inside the hemispherical concave portion 22 constituting the female spline connection portion 21. Therefore, the connection operation between the female spline connection portion 21 and the male spline connection portion 76 and the connection operation between the first housing connection portion 41 and the second housing connection portion 63 can be performed simultaneously. Also, when connecting the first housing connection portion 41 and the second housing connection portion 63, since the second connection cylinder portion 67 is inrolled and fitted to the first connection cylinder portion 42, it is also possible to easily achieve positioning in the diameter direction (radial direction) between the female spline connection portion 21 and the male spline connection portion 76.

[0079] In the illustrated example, the steering shaft 13 is rotatably supported inside the steering column 14 by three rolling bearings 18a to 18c, and a reaction force output shaft 60 that is torque-transmittably connected to the power connection portion 11 with respect to the steering shaft 13 is rotatably supported inside the gear housing 57 by two rolling bearings 82a and 82b. However, regarding the rolling bearing 18b provided between the outer peripheral surface of the front end of the upper shaft 20 and the inner peripheral surface of the front end of the upper inner column 36 among the three rolling bearings 18a to 18c that rotatably support the steering shaft 13, it can be omitted if a rolling bearing 18a that functions as a displacement prevention mechanism is provided. In this way, if the rolling bearing 18b is omitted, the cost of the steering unit 3 can be reduced.

[0080] Also, in this example, the outer column 34 is fitted to the lower inner column 35 so as to allow relative displacement in the front-rear direction, and the upper inner column 36 is fitted to the outer column 34 so as to allow relative displacement in the front-rear direction, thereby making the column body 25 have a two-stage telescopic structure. Therefore, while sufficiently ensuring the telescopic amount of the entire length of the steering column 14, it is possible to prevent the axial dimensions of the lower screw shaft 47 and the upper screw shaft 51 from becoming excessive.

[0081] In addition, the position adjustment device 9 in this example can adjust the position of the steering wheel 2 in the front-rear direction by either the lower telescopic actuator 15 or the upper telescopic actuator 16. Therefore, even if a malfunction such as a failure occurs in either one of the lower telescopic actuator 15 and the upper telescopic actuator 16, the position of the steering wheel 2 can be adjusted by the other actuator.

[0082] Furthermore, since the position adjustment device 9 in this example can drive the lower telescopic actuator 15 and the upper telescopic actuator 16 simultaneously, the adjustment speed of the front-rear position of the steering wheel 2 can be improved compared to a position adjustment device equipped with only one actuator.

[0083] [Second Example of the Embodiment] The second example of the embodiment will be described with reference to FIGS. 15 to 18. In this example, the same components as those in the first example of the embodiment are denoted by the same reference numerals as in the first example of the embodiment, and detailed descriptions thereof are omitted.

[0084] In this example, the lower shaft 19a is divided into a connection shaft 88 and a main shaft 89, and these connection shaft 88 and main shaft 89 are connected by a shaft coupling 90 to form a connection structure.

[0085] The connection shaft 88 is provided with a female spline connection portion 21 at its front end. Similar to the first example of the embodiment, the female spline connection portion 21 is spline-engaged with a male spline connection portion 76 provided at the rear end of the reaction force output shaft 60 (upper output shaft 73) of the reaction force generating device 10 so as to be able to transmit torque. In the illustrated example, the upper output shaft 73 is provided with a constricted portion 118 having an outer diameter smaller than the outer diameter of the base end portion of the male spline connection portion 76 at a position adjacent to the front side of the male spline connection portion 76.

[0086] The connecting shaft 88 includes, at its rear end, a first shaft portion 91 having a cylindrical outer peripheral surface. The main shaft 89 includes, at its front end, a second shaft portion 92 having a cylindrical outer peripheral surface. Notches, key grooves, etc. for preventing rotation can be formed in a part of the circumferential direction of the outer peripheral surface of each of the first shaft portion 91 and the second shaft portion 92.

[0087] The shaft coupling 90 includes a first transmission member 93 connected to the first shaft portion 91 so as not to be relatively rotatable, a second transmission member 94 connected to the second shaft portion 92 so as not to be relatively rotatable, and an intermediate member 95 disposed between the first transmission member 93 and the second transmission member 94 and transmitting torque between the first transmission member 93 and the second transmission member 94.

[0088] The first transmission member 93 has an insertion hole 96a penetrating axially through its central portion and has cutouts 97a extending radially at two positions in the circumferential direction. Further, the first transmission member 93 is provided with protrusions 98a protruding axially at a plurality of positions in the circumferential direction. To connect the first transmission member 93 to the first shaft portion 91, the first shaft portion 91 is inserted into the insertion hole 96a, and a screw member (not shown) disposed in a part of the circumferential direction of the first transmission member 93 is tightened using a tool (not shown). Thereby, by reducing the circumferential width of the cutout 97a and reducing the inner diameter of the insertion hole 96a, the first transmission member 93 is connected to the first shaft portion 91.

[0089] The second transmission member 94 has an insertion hole 96b penetrating axially through its central portion and has cutouts 97b extending radially at two positions in the circumferential direction. Further, the second transmission member 94 is provided with protrusions 98b protruding axially at a plurality of positions in the circumferential direction. To connect the second transmission member 94 to the second shaft portion 92, the second shaft portion 92 is inserted into the insertion hole 96b, and a screw member (not shown) disposed in a part of the circumferential direction of the second transmission member 94 is tightened using a tool (not shown). Thereby, by reducing the circumferential width of the cutout 97b and reducing the inner diameter of the insertion hole 96b, the second transmission member 94 is connected to the second shaft portion 92.

[0090] The intermediate member 95 is made of an elastic material, for example, and is configured in an annular shape. The intermediate member 95 is provided with annular portions 99a and 99b on both axial sides. The annular portion 99a is provided with first engagement holes (not shown) into which the protrusion portions 98a provided on the first transmission member 93 can be inserted at a plurality of locations in the circumferential direction. The annular portion 99b is provided with second engagement holes (not shown) into which the protrusion portions 98b provided on the second transmission member 94 can be inserted at a plurality of locations in the circumferential direction.

[0091] In this example, since the lower shaft 19a has a connection structure in which the lower connection shaft 88 and the upper main shaft 89 are connected via the shaft coupling 90, the alignment error generated between the lower shaft 19a and the reaction force output shaft 60 can be absorbed not only by the power connection portion 11 but also by the shaft coupling 90. Regarding other configurations and effects, they are the same as those in the first example of the embodiment.

[0092] [Third Example of the Embodiment] The third example of the embodiment will be described with reference to FIG. 19. In this example, the same components as those in the first example of the embodiment are denoted by the same reference numerals as those in the first example of the embodiment, and detailed descriptions thereof are omitted.

[0093] The power connection portion 11a in this example is configured by spline-engaging a male spline connection portion 76a provided at the front end of the lower shaft 19b and a female spline connection portion 21a provided at the rear end of the upper output shaft 73a. That is, in the power connection portion 11a of this example, the front and rear positions of the male spline connection portion and the female spline connection portion are opposite to those of the power connection portion 11 in the first example of the embodiment.

[0094] In this example, a hemispherical convex portion 77a is provided at the front end of the lower shaft 19b, and a plurality of male spline teeth 78a are formed on the outer surface of the hemispherical convex portion 77a. Further, a hemispherical concave portion 22a is provided at the rear end of the upper output shaft 73a, and a plurality of female spline teeth 23a are formed on the inner surface of the hemispherical concave portion 22a. Then, the hemispherical convex portion 77a constituting the male spline connection portion 76a is inserted into the hemispherical concave portion 22a constituting the female spline connection portion 21a, and each of the plurality of female spline teeth 23a provided on the inner surface of the hemispherical concave portion 22a and each of the plurality of male spline teeth 78a provided on the outer surface of the hemispherical convex portion 77a are spline-engaged. In this example, the lower shaft 19b and the upper output shaft 73a are connected by such a power connection portion 11a so as to be able to transmit torque.

[0095] Furthermore, in this example, the male spline teeth 78a constituting the male spline connection portion 76a provided at the front end of the lower shaft 19b and the male spline teeth 100 for telescopic adjustment provided in the range from the rear end to the middle portion of the outer peripheral surface of the lower shaft 19b are made continuous in the front-rear direction. In other words, the male spline teeth 100 for telescopic adjustment are formed by extending to the front end of the lower shaft 19b. For this reason, the lower shaft 19b is provided with male spline teeth over the entire axial length of the outer peripheral surface.

[0096] In this example as described above, the male spline teeth 100 for telescopic adjustment and the male spline teeth 78a constituting the male spline connection portion 76a can be machined simultaneously. For this reason, it is possible to reduce the number of processing steps and reduce the cost of the steering unit 3. Regarding other configurations and operational effects, they are the same as those in the first example of the embodiment.

[0097] [Fourth Example of the Embodiment] For the fourth example of the embodiment, it will be described with reference to FIGS. 20 to 21. In this example, the shaft connection structure of the present invention is applied to an electric power steering apparatus. Also in this example, the same components as those in the first example of the embodiment are denoted by the same reference numerals as those in the first example of the embodiment, and detailed descriptions thereof are omitted.

[0098] The steering apparatus 1a of this example is an electric power steering apparatus of a column assist type. The steering apparatus 1a includes a steering wheel 2, a steering shaft 13a, a steering column 14a, a pair of universal joints 101a and 101b, an intermediate shaft 102, a steering gear unit 103, a pair of tie rods 8, and an electric assist device 104.

[0099] The steering wheel 2 is attached to the rear end portion of the steering shaft 13a rotatably supported inside the steering column 14a. The front end portion of the steering shaft 13a is inserted inside a housing 105 fixed to the front end portion of the steering column 14a, and is connected to an output shaft 106 via a torsion bar 117.

[0100] The rotation of the output shaft 106 is transmitted to the pinion shaft 107 of the steering gear unit 103 via a pair of universal joints 101a and 101b and the intermediate shaft 102. Then, by converting the rotation of the pinion shaft 107 into a linear motion of a rack shaft (not shown), the pair of tie rods 8 are pushed and pulled to impart a steering angle to the steered wheels.

[0101] The electric assist device 104 is configured to reduce the force required for the driver to operate the steering wheel 2, and includes a torque sensor (not shown) disposed around the output shaft 106, an ECU (not shown), and a motor 108 with a speed reducer.

[0102] The motor 108 with a speed reducer includes a worm speed reducer 109 and an electric motor 110.

[0103] The worm reducer 109 includes a worm 111 and a worm wheel 112. The worm 111 has both end portions in the axial direction rotatably supported with respect to the housing 105 by a pair of rolling bearings 113 (only one is shown in FIG. 21). The worm 111 has worm teeth 114 at an intermediate portion in the axial direction. The worm wheel 112 is externally fitted to the output shaft 106 and is rotatably supported with respect to the housing 105 by a rolling bearing (not shown). The worm wheel 112 has worm wheel teeth 115 meshing with the worm teeth 114 on its outer peripheral surface.

[0104] The electric motor 110 is driven and controlled by the ECU and has a motor output shaft 116.

[0105] In this example, the connection structure of the power connection portion 11b between the motor output shaft 116 and the worm 111 is devised. That is, at the tip of the motor output shaft 116, a female spline connection portion 21b is provided, in which a plurality of female spline teeth 23b are formed on the inner surface of the hemispherical recess 22b. Also, at the base end portion of the worm 111, a male spline connection portion 76b is provided, in which a plurality of male spline teeth 78b are formed on the outer surface of the hemispherical protrusion 77b. Then, the hemispherical protrusion 77b constituting the male spline connection portion 76b is inserted into the hemispherical recess 22b constituting the female spline connection portion 21b, and each of the plurality of female spline teeth 23b provided on the inner surface of the hemispherical recess 22b is spline-engaged with each of the plurality of male spline teeth 78b provided on the outer surface of the hemispherical protrusion 77b. Thereby, the motor output shaft 116 and the worm 111 are connected so as to be able to transmit torque. In this example, the worm 111 corresponds to the first shaft described in the claims, and the motor output shaft 116 corresponds to the second shaft described in the claims.

[0106] In the present example as described above, the motor output shaft 116 and the worm 111 can be connected so as to be able to transmit torque without increasing the number of parts. Further, the overall length of the power connection portion 11b can be shortened, and an increase in the size of the motor 108 with a speed reducer, and thus the steering device 1a can be prevented. Also, the alignment error between the motor output shaft 116 and the worm 111 can be absorbed.

[0107] Conventionally, in order to support the worm so as to be swingable, a pair of axial dampers have been arranged on both axial sides of a rolling bearing that rotatably supports the proximal end portion of the worm. However, in the present example, since the distal end portion of the motor output shaft 116 and the proximal end portion of the worm 111 are connected via the power connection portion 11b as described above, the axial damper arranged on the electric motor 110 side can be omitted, and it is sufficient to arrange a resin axial damper 128 only between the flange portion 127 provided at the axial intermediate portion of the outer peripheral surface of the worm 111 and the rolling bearing 113. Therefore, according to the present example, the size reduction of the motor 108 with a speed reducer can be achieved. Regarding other configurations and operational effects, they are the same as those in the first example of the embodiment.

[0108] [Modification of the Fourth Example of the Embodiment] A modification of the fourth example of the embodiment will be described with reference to FIG. 22. Also in this example, the shaft connection structure of the present invention is applied to an electric power steering device, and the connection structure of the power connection portion 11c between the motor output shaft 116a and the worm 111a is devised.

[0109] That is, in the power connection portion 11c of the present example, the positional relationship between the male spline connection portion and the female spline connection portion provided at the distal end portion of the motor output shaft 116a and the proximal end portion of the worm 111a is reversed from that in the fourth example of the embodiment.

[0110] In this example, a male spline connection portion 76c is provided at the tip of the motor output shaft 116a, where a plurality of male spline teeth 78c are formed on the outer surface of the hemispherical convex portion 77c. Further, a female spline connection portion 21c is provided at the base end portion of the worm 111a, where a plurality of female spline teeth 23c are formed on the inner surface of the hemispherical concave portion 22c. Then, the hemispherical convex portion 77c constituting the male spline connection portion 76c is inserted into the hemispherical concave portion 22c constituting the female spline connection portion 21c, and each of the plurality of female spline teeth 23c provided on the inner surface of the hemispherical concave portion 22c is spline-engaged with each of the plurality of male spline teeth 78c provided on the outer surface of the hemispherical convex portion 77c. Thereby, the motor output shaft 116a and the worm 111a are connected so as to be able to transmit torque. In this example, the worm 111a corresponds to the second shaft described in the claims, and the motor output shaft 116a corresponds to the first shaft described in the claims.

[0111] Further, a biasing member 129 is provided around the tip-side portion of the worm 111a. Thereby, the tip of the worm 111a is biased in a direction approaching the worm wheel 112.

[0112] In the present example as described above, it is possible to align the center O of the rolling bearing 113 that rotatably supports the base end portion of the worm 111a with the axial position of the spline engagement portion between the male spline teeth 78c and the female spline teeth 23c. For this reason, the worm 111a can be swung with the center O of the rolling bearing 113 as a fulcrum. Thereby, it becomes possible to efficiently function the biasing member 129 provided on the tip side of the worm 111a. Therefore, the worm teeth 114 can be biased toward the worm wheel teeth 115 by the biasing member 129, and the backlash at the meshing portion between the worm teeth 114 and the worm wheel teeth 115 can be reduced. As a result, it is possible to suppress the generation of tooth striking noise at the meshing portion between the worm teeth 114 and the worm wheel teeth 115.

[0113] In addition, since the power connection portion 11c is configured by inserting a hemispherical convex portion 77c inside the hemispherical concave portion 22c, it is possible to suppress an increase in the axial dimension of the power connection portion 11c, and the speed reduction motor 108 can be downsized. Regarding other configurations and operational effects, they are the same as those in the first example and the fourth example of the embodiment.

[0114] [Fifth Example of the Embodiment] The fifth example of the embodiment will be described with reference to FIG. 23. In this example, the same components as those in the first example of the embodiment are denoted by the same reference numerals as those in the first example of the embodiment, and detailed descriptions thereof are omitted.

[0115] In this example, among the upper output shaft 73a, the outer diameter of the axial intermediate portion adjacent to (connected to) the male spline connection portion 76 is made smaller than the outer diameter of the male spline connection portion 76 (hemispherical convex portion 77). In other words, the upper output shaft 73a is provided with a constricted portion 118 having a smaller diameter than the male spline connection portion 76 at a portion adjacent to the front side of the male spline connection portion 76. For this reason, in this example, the shape of the rear side portion of the upper output shaft 73a is made substantially mushroom-shaped.

[0116] In this example as described above, as shown in FIG. 23(C), even when an alignment error occurs in which the central axis of the upper output shaft 73a and the central axis of the lower shaft 19 do not coincide, the front end surface of the lower shaft 19 can be made less likely to interfere with the outer peripheral surface of the upper output shaft 73a. For this reason, the alignment error can be sufficiently absorbed. Further, in this example, even when the central axis of the upper output shaft 73a and the central axis of the lower shaft 19 do not coincide, it is possible to prevent the intersection position of the central axis of the upper output shaft 73a and the central axis of the lower shaft 19 from shifting.

[0117] Further, in this example, as shown in (B) of FIG. 23, a space 130 is provided between the tip of the male spline connection portion 76 (hemispherical convex portion 77) and the bottom of the female spline connection portion 21 (hemispherical concave portion 22) without bringing them into contact with each other. Therefore, this space 130 can also be used as a grease reservoir. Regarding other configurations and effects, they are the same as those in the first example of the embodiment.

[0118] [Modification of the Fifth Example of the Embodiment] A modification of the fifth example of the embodiment will be described with reference to FIG. 24.

[0119] In the fifth example of the embodiment, as shown in (B) of FIG. 23, with the male spline connection portion 76 (hemispherical convex portion 77) inserted inside the female spline connection portion 21 (hemispherical concave portion 22), most of the base end portion 131 of the male spline connection portion 76 (the range surrounded by the two-dot chain line in (A) of FIG. 23) where the outer diameter of the male spline teeth 78 is constant protrudes (is exposed) axially from the female spline connection portion 21. Therefore, in the fifth example of the embodiment, the base end portion 131 of the male spline connection portion 76 hardly contributes to torque transmission. Thus, in this example, as shown in FIG. 24, a portion where the outer diameter of the male spline teeth 78 is constant is omitted from the male spline connection portion 76d provided at the rear end of the upper output shaft 73b. In other words, the male spline teeth 78d constituting the male spline connection portion 76d change in outer diameter curvilinearly over the entire axial length.

[0120] In this example as described above, compared with the structure of the fifth example of the embodiment, the axial dimension of the male spline connection portion 76d can be shortened. Note that the structure of this example can be applied not only to the connection portion between the steering shaft and the reaction force output shaft, but also, for example, to the connection portion between the worm and the motor output shaft. Regarding other configurations and effects, they are the same as those in the first and fifth examples of the embodiment.

[0121] [Sixth Example of the Embodiment] A sixth example of the embodiment will be described with reference to FIG. 25. In this example, the same components as those in the first example of the embodiment are denoted by the same reference numerals as in the first example of the embodiment, and detailed descriptions thereof are omitted.

[0122] In this example, the position adjusting device 9a that constitutes the steering unit 3a is a manual position adjusting device instead of an electric position adjusting device having the structure of the first example of the embodiment. The position adjusting device 9a can adjust the front-rear position and the up-down position of the steering wheel 2 (see FIG. 1). Inside the steering column 119, the steering shaft 120 is rotatably supported via a pair of rolling bearings 18d and 18e.

[0123] In order to enable adjustment of the front-rear position of the steering wheel 2, the steering column 119 is fitted to the outer column 121 arranged on the lower side and the inner column 122 arranged on the upper side so as to be relatively displaceable in the front-rear direction, and the overall length is configured to be extendable and retractable. Further, the steering shaft 120 is fitted to the inner shaft 123 arranged on the lower side and the outer shaft 124 arranged on the upper side so as to be torque-transmittable and relatively displaceable in the front-rear direction, and the overall length is configured to be extendable and retractable. In this example, a rolling bearing 18d is arranged between the outer column 121 and the inner shaft 123, and a rolling bearing 18e is arranged between the inner column 122 and the outer shaft 124.

[0124] In order to enable adjustment of the up-down position of the steering wheel 2, the front end portion of the outer column 121 and the like are pivotally supported with respect to the vehicle body by a tilt shaft (not shown) arranged in the width direction, and the rear side portion of the outer column 121 is supported so as to be displaceable in the up-down direction with respect to a support bracket 125 fixed to the vehicle body. Note that, in order to adjust the position of the steering wheel 2, an adjustment lever (not shown) is operated, and the position of the steering wheel 2 is manually adjusted in a state where the tightening force of the outer column 121 by the support bracket 125 is reduced.

[0125] In this example, a reaction force applying motor 58a that constitutes a reaction force generating device 10a is directly fixed to the front end of an outer column 121 that constitutes a position adjusting device 9a having the above-described configuration. And, a male spline connection portion 76 provided at the tip (rear end) of a motor output shaft 126 of the reaction force applying motor 58a is directly connected to a female spline connection portion 21 provided at the front end of an inner shaft 123 so as to be torque-transmittable by spline engagement. Specifically, the front half of a hemispherical convex portion 77 that constitutes the male spline connection portion 76 is inserted into a hemispherical concave portion 22 that constitutes the female spline connection portion 21, and each of a plurality of female spline teeth 23 provided on the inner surface of the hemispherical concave portion 22 and each of a plurality of male spline teeth 78 provided on the outer surface of the hemispherical convex portion 77 are alternately arranged in the circumferential direction and meshed with each other, thereby achieving spline engagement. Thus, in this example, the steering unit 3a is configured in a direct drive method. Note that, in this example, the motor output shaft 126 of the reaction force applying motor 58a corresponds to the first shaft described in the claims, and the inner shaft 123 corresponds to the second shaft described in the claims.

[0126] According to the steering unit 3a of this example as described above, compared with the structure of the first example of the embodiment, a plurality of members such as a worm reducer can be omitted. For this reason, cost reduction and weight reduction can be achieved by reducing the number of parts. Regarding other configurations and operational effects, they are the same as those of the first example of the embodiment.

[0127] [Seventh Example of the Embodiment] The seventh example of the embodiment will be described with reference to FIGS. 26 to 28. In this example, the same reference numerals as those in the first example of the embodiment are given to the same components as those in the first example of the embodiment, and detailed descriptions thereof are omitted.

[0128] In this example, the structure of the power connection portion 11d is changed from the structures of the first to sixth examples of the embodiment. Specifically, the structure of the male spline connection portion 76e provided at the rear end portion of the upper output shaft 73c and the structure of the female spline connection portion 21d provided at the front end portion of the lower shaft 19c are changed from the structures of the first to sixth examples of the embodiment.

[0129] As shown in FIG. 26, the male spline connection portion 76e is a spherical frustum-shaped male spline structure in which a plurality of male spline teeth 78e are formed on the outer surface of a spherical frustum-shaped convex portion 132 provided at the rear end portion of the upper output shaft 73. The spherical frustum-shaped convex portion 132 has a shape in which the tip portion of the hemispherical convex portion is flat, and the outer diameter gradually decreases in a curved manner from the base end portion toward the tip portion. Note that the spherical frustum-shaped convex portion refers to a convex portion having a spherical frustum-shaped outer surface formed by cutting a sphere with two parallel planes, as shown in FIG. 29(B). In other words, the spherical frustum-shaped outer surface can also be referred to as a belt-shaped convex curved surface. Further, the spherical frustum-shaped convex portion has a substantially isosceles trapezoidal cross-sectional shape. In this example, a partially spherical convex curved portion 133 is provided at the tip portion of the spherical frustum-shaped convex portion 132, but the convex curved portion 133 can also be omitted. The plurality of male spline teeth 78e are arranged at equal intervals in the circumferential direction and are formed in the radial direction on the outer surface of the spherical frustum-shaped convex portion 132. In this example, the male spline connection portion 76e is covered with a coating layer made of a synthetic resin having a low coefficient of friction, such as polyamide resin.

[0130] Also, as shown in FIG. 27, the female spline connection portion 21d is a spherical frustum-shaped female spline structure in which a plurality of female spline teeth 23d are formed on the inner surface of a spherical frustum-shaped concave portion 134 opened at the front end surface of the lower shaft 19c. The spherical frustum-shaped concave portion 134 has a shape in which the bottom portion of the hemispherical concave portion is flat, and the inner diameter gradually decreases in a curved manner from the opening portion toward the back side. In this example, a partially spherical concave curved portion 135 is provided at the bottom portion of the spherical frustum-shaped concave portion 134, but the concave curved portion 135 can also be omitted. The plurality of female spline teeth 23d are arranged at equal intervals in the circumferential direction and are formed in the radial direction on the inner surface of the spherical frustum-shaped concave portion 134.

[0131] In this example, as shown in Fig. 28(A), the entire frustum-shaped convex portion 132 that constitutes the male spline connection portion 76e is inserted into the frustum-shaped concave portion 134 that constitutes the female spline connection portion 21d, and each of the plurality of female spline teeth 23d provided on the inner surface of the frustum-shaped concave portion 134 is spline-engaged with each of the plurality of male spline teeth 78e provided on the outer surface of the frustum-shaped convex portion 132. In this example, since the male spline connection portion 76e is covered with a coating layer made of synthetic resin, the female spline teeth 23d and the male spline teeth 78e are spline-engaged via the coating layer. Further, the convex curved portion 133 provided at the tip of the frustum-shaped convex portion 132 is inserted inside the concave curved portion 135 provided at the bottom of the frustum-shaped concave portion 134.

[0132] In this example, as shown in Fig. 28(B), when a so-called alignment error occurs in which the central axis of the lower shaft 19c and the central axis of the upper output shaft 73c do not match, the alignment error can be absorbed by displacing the frustum-shaped convex portion 132 inside the frustum-shaped concave portion 134 while the female spline teeth 23d and the male spline teeth 78e are spline-engaged.

[0133] In this example as described above, the axial dimension of the power connection portion 11d composed of the male spline connection portion 76e and the female spline connection portion 21d can be shortened. Therefore, the size of the entire device can be reduced. Further, in this example, since the male spline teeth 78e are formed on the outer surface of the frustum-shaped convex portion 132 and the female spline teeth 23d are formed on the inner surface of the frustum-shaped concave portion 134, compared with the case where the male spline teeth are formed on the outer surface of the hemispherical convex portion and the female spline teeth are formed on the inner surface of the hemispherical concave portion as in the structure of the first example of the embodiment, the meshing length of the spline engagement portion can be shortened. For this reason, the occurrence of undulation noise, which is likely to occur when the meshing length is long, can be effectively prevented. Also, since the meshing length can be shortened, the absorption of alignment can be increased. That is, the inclination between the upper output shaft 73c and the lower shaft 19c can be increased. For other configurations and effects, they are the same as those in the first example of the embodiment.

[0134] As described above, the embodiments of the present invention have been explained. However, the present invention is not limited to this, and can be appropriately modified without departing from the technical idea of the invention. In addition, the structures of the respective examples of the embodiment can be implemented in appropriate combinations as long as there is no contradiction.

[0135] When implementing the present invention, as long as the partial spherical convex portion can be displaced inside the partial spherical concave portion while the female spline teeth and the male spline teeth are in spline engagement, the shapes of the partial spherical convex portion and the partial spherical concave portion, as well as the numbers and shapes of the male spline teeth and the female spline teeth, are not limited to the structures of the respective examples of the embodiment. In addition, when implementing the present invention, the male spline engaging portion and the female spline engaging portion can also be implemented in the opposite structure to that of the respective examples of the embodiment.

[0136] In addition, when implementing the present invention, the types of the first shaft and the second shaft that can be connected by the shaft connection structure of the present invention are not limited to the shafts described in the respective examples of the embodiment. Also, the reduction gear motor of the present invention is not limited to the reduction gear motor constituting the electric power steering device described in the fourth example and the modified example of the embodiment, and can also be applied to a reduction gear motor such as a reaction force generating device constituting a steer-by-wire type steering device, or a reduction gear motor provided in other devices.

[0137] In addition, when implementing the present invention, the position adjusting device combined with the reaction force generating device is not limited to the electric type position adjusting device as shown in the first example of the embodiment, and a manual type position adjusting device as shown in the sixth example of the embodiment can also be adopted.

Explanation of Reference Numerals

[0138] 1, 1a Steering device 2 Steering wheel 3, 3a Steering unit 4 Steering wheel 5 Steering unit 6 Control device 7 Steering actuator 8 Tie rod 9, 9a Position adjusting device 10, 10a Reaction force generating device 11, 11a, 11b, 11c, 11d Power connection part 12 Housing connection part 13, 13a Steering shaft 14, 14a Steering column 15 Lower telescopic actuator 16 Upper telescopic actuator 17 Tilt actuator 18a - 18e Rolling bearing 19, 19a, 19b, 19c Lower shaft 20 Upper shaft 21, 21a, 21b, 21c, 21d Female spline connection part 22, 22a, 22b, 22c Hemispherical recess 23, 23a, 23b, 23c, 23d Female spline teeth 24 Bracket 25 Column body 26 Fixed bracket 27 Displacement bracket 28 Fixed plate part 29 Fixed - side support frame 30 Mounting bolt 31 Displacement plate part 32 Displacement - side support frame 33 Support wall part 34 Outer column 35 Lower - side inner column 36 Upper - side inner column 37 Slit 38 Threaded hole 39 Screw plug 40 Cylindrical part 41 First housing connection part 42 First connection cylinder part 43 First connection plate part 44 First through-hole 45 Lower side telescopic motor 46 Lower side feed screw device 47 Lower side screw shaft 48 Lower side nut 49 Upper side telescopic motor 50 Upper side feed screw device 51 Upper side screw shaft 52 Upper side nut 53 Connector member 54 Pivot bolt 55 Tilt motor 56 Tilt feed screw device 57 Gear housing 58, 58a Reaction force applying motor 59 Worm reducer 60 Reaction force output shaft 61 Lower side housing 62 Upper side housing 63 Second housing connection part 64 Connection bolt 65 Worm housing part 66 Worm wheel housing part 67 Second connection cylinder part 68 Second connection plate part 69 Second through-hole 70 Worm 71 Worm wheel 72 Lower side output shaft 73, 73a, 73b, 73c Upper side output shaft 74 Torsion bar 75 Torque sensor 76, 76a, 76b, 76c, 76d, 76e Male spline connection part 77, 77a, 77b, 77c Hemispherical convex part 78, 78a, 78b, 78c, 78d, 78e Male spline teeth 79 Continuous hole 80 Linear guide 81 Bolt 82a, 82b Rolling bearing 83 Locking groove 84 Stop ring 85 Annular wall portion 86 Annular protrusion 87 Bolt 88 Connecting shaft 89 Main shaft 90 Shaft coupling 91 First shaft-like portion 92 Second shaft-like portion 93 First transmission member 94 Second transmission member 95 Intermediate member 96a, 96b Insertion hole 97a, 97b Notch 98a, 98b Protrusion 99a, 99b Ring portion 100 Male spline teeth 101a, 101b Universal joint 102 Intermediate shaft 103 Steering gear unit 104 Electric assist device 105 Housing 106 Output shaft 107 Pinion shaft 108 Motor with reducer 109 Worm reducer 110 Electric motor 111, 111a Worm 112 Worm wheel 113 Rolling bearing 114 Worm teeth 115 Worm wheel teeth 116, 116a Motor output shaft 117 Torsion bar 118 Constricted portion 119 Steering column 120 Steering shaft 121 Outer column 122 Inner column 123 Inner shaft 124 Outer shaft 125 Support bracket 126 Motor output shaft 127 flange 128 axial damper 129 biasing member 130 space 131 base end portion 132 truncated spherical convex portion 133 convex curved portion 134 truncated spherical concave portion 135 concave curved portion

Claims

1. A male spline connection portion provided at an end of a first shaft, wherein a plurality of male spline teeth are formed on an outer surface of a partially spherical convex portion; and A female spline connection portion provided at an end of a second shaft, wherein a plurality of female spline teeth are formed on an inner surface of a partially spherical concave portion, and The partially spherical concave portion is open only at one end surface of the second shaft, The inner diameter of the partially spherical concave portion becomes curvilinearly smaller from the opening toward the inner part, and the female spline teeth are formed over the entire axial direction of the inner surface thereof, The outer diameter of the partially spherical convex portion becomes curvilinearly smaller from the base end portion toward the tip end portion, and the male spline teeth are formed over the entire axial direction of the outer surface thereof, By inserting the partially spherical convex portion inside the partially spherical concave portion and spline-engaging each of the male spline teeth with each of the female spline teeth, the first shaft and the second shaft are connected so as to be torque-transmittable, A shaft connection structure.

2. The male spline connection portion is formed by forming a plurality of the male spline teeth on an outer surface of a hemispherical convex portion, The female spline connection portion is formed by forming a plurality of the female spline teeth on an inner surface of a hemispherical concave portion, The shaft connection structure according to claim 1.

3. The male spline connection portion is formed by forming a plurality of the male spline teeth on an outer surface of a frustum-of-a-sphere convex portion, The female spline connection portion is formed by forming a plurality of the female spline teeth on an inner surface of a frustum-of-a-sphere concave portion, The shaft connection structure according to claim 1.

4. The shaft connection structure according to any one of claims 1 to 3, wherein at least one of the male spline connection portion and the female spline connection portion is covered with a coating layer made of synthetic resin.

5. The shaft connection structure according to any one of claims 1 to 4, wherein an outer diameter of a portion of the first shaft adjacent to the male spline connection portion is smaller than an outer diameter of the male spline connection portion.

6. A worm reducer having a worm and a worm wheel; and An electric motor having a motor output shaft, and An end of the worm and an end of the motor output shaft are connected so as to be torque-transmittable by the shaft connection structure according to any one of claims 1 to 5, A motor with a reducer.

7. The male spline connection portion is provided at an end of the motor output shaft, The female spline connection part is provided at the end of the worm. The motor with a speed reducer according to claim 6. **Claim 8** An electric power steering apparatus comprising the motor with a speed reducer according to claim 6 or claim 7. **Claim 9** A steering shaft, A reaction force generating device for applying a steering reaction force to a steering wheel having a reaction force output shaft, and The end of the steering shaft and the end of the reaction force output shaft are connected so as to be torque transmissible by the shaft connection structure according to any one of claims 1 to 5. A steer-by-wire steering unit. **Claim 10** A steering shaft, A reaction force applying motor for applying a steering reaction force to a steering wheel having a motor output shaft, and The end of the steering shaft and the end of the motor output shaft are connected so as to be torque transmissible by the shaft connection structure according to any one of claims 1 to 5. A steer-by-wire steering unit.

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