JP2007161165A - Power transmission mechanism and electric power steering device installing the mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase motive power transmittable between a rotation shaft 29 and a worm shaft 27 and to easily generate misalignment of axes of both shafts 29, 27. <P>SOLUTION: An elastic ring 49a with a tooth is spline-engaged between a male spline part 47b provided on the rotation shaft 29 and a female spline part 48a provided on the worm shaft 27. The respective teeth of the respective spline parts 47b, 48a are overlapped in a circumferential direction in the state that the elastic ring 49a with the tooth is provided between both spline parts 47b, 48a. Outer shapes of cross section shapes of the tooth surfaces opposed to each other of the respective teeth of the male spline part 47b and inner teeth 51a provided on the elastic ring 49a with the tooth are made different. Thereby, clearances 63, 63 are provided between the tooth surfaces opposed to each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is, for example, incorporated in a steering apparatus of an automobile and uses an output of an electric motor as auxiliary power, thereby reducing the force required for a driver to operate a steering wheel, and the electric power steering apparatus The present invention relates to an improvement of a power transmission mechanism incorporated in an electric power steering device or the like.

  A power steering device is widely used as a device to reduce the force required for the driver to operate the steering wheel when giving a steering angle to the steered wheels (usually the front wheels except for special vehicles such as forklifts) Has been. In addition, an electric power steering apparatus that uses an electric motor as an auxiliary power source in such a power steering apparatus has begun to spread in recent years. The electric power steering device can be made smaller and lighter than the hydraulic power steering device, has advantages such as easy control of the magnitude (torque) of auxiliary power and less power loss of the engine. FIG. 13 schematically shows an example of a conventionally known basic configuration of such an electric power steering apparatus.

  This electric power steering apparatus is provided with a speed reducer 4 between a steering shaft 2 having a steering wheel 1 fixed to a base end portion (upper end portion in FIG. 13) and an electric motor 3, and the power of the electric motor 3 is supplied. The transmission can be transmitted to the steering shaft 2 via the speed reducer 4. When the steering shaft 2 is rotated by operating the steering wheel 1 in order to give a steering angle to the steering wheel 14, the torque sensor 5 detects the rotation direction and torque of the steering shaft 2, and the detection signal is sent to the controller. Send to 6. Based on this detection signal, the controller 6 energizes the electric motor 3 and rotates the steering shaft 2 in the same direction as the rotation direction based on the operation of the steering wheel 1 via the speed reducer 4. As a result, the tip end portion (the lower end portion in FIG. 13) of the steering shaft 2 rotates with a torque larger than the torque based on the force applied from the steering wheel 1. The distal end portion of the steering shaft 2 is transmitted to the input shaft 10 of the steering gear 9 through the universal joints 7 and 7 and the intermediate shaft 8. The input shaft 10 rotates the pinion 11, pushes and pulls the tie rod 13 through the rack 12, and gives a desired steering angle to the steered wheel 14. As is clear from this explanation, the force required for the driver to operate the steering wheel 1 to give the steering angle to the steered wheel 14 is applied from the electric motor 3 to the steering shaft 2 via the speed reducer 4. It becomes small as much as the auxiliary power applied.

  In the case of such an electric power steering apparatus, a worm speed reducer composed of a worm shaft and a worm wheel has been generally used as the speed reducer 4 provided between the steering shaft 2 and the electric motor 3. Yes. The rotating shaft of the electric motor 3 and the input shaft constituting the speed reducer 4 are formed by spline engagement between a male spline portion provided on one of these shafts and a spline portion provided on the other. In general, the spline engaging portions are connected so as to be able to transmit power.

  However, when a worm reducer is used as the reducer 4, if the inevitable backlash existing between the tooth surfaces of the worm shaft worm and the worm wheel increases, the tooth surfaces strongly collide with each other, An annoying rattling noise can occur. For example, when a vibration load is applied to the steering shaft 2 from the wheel side due to a rough road surface, an unpleasant rattling sound is generated due to the presence of the backlash. For these reasons, in recent years, an elastic force imparting means is provided between the gear housing constituting the worm speed reducer and the worm shaft, and the elastic force imparting means imparts the elastic force in the direction toward the worm wheel to the worm shaft. However, it is considered to suppress the backlash (reduce or reduce it to 0) and suppress the occurrence of the rattling noise.

  However, when the generation of the rattling noise is suppressed by the configuration provided with such elasticity applying means, the spline mechanism provided between these two shafts is used to incline the worm shaft with respect to the rotating shaft of the electric motor 3. There is a possibility that a part of each tooth constituting the joint is beaten. On the other hand, when the rigidity of both the male and female spline parts constituting the spline engaging part is increased, the teeth can be prevented from being beaten, but the tooth surfaces of these spline parts are It is easy to generate a rattling noise between the two. For this reason, in order to suppress the occurrence of rattling noise while enabling the inclination of the worm shaft with respect to the rotation shaft of the electric motor 3, the gap between the two spline portions provided on both the shafts is strictly regulated. However, it is necessary to carry out difficult work such as management, which causes an increase in cost of the electric power steering apparatus.

[Description of Prior Invention]
In view of such circumstances, the inventors of the present invention previously invented a first example of the prior invention of an electric power steering apparatus incorporating a power transmission mechanism as shown in FIGS. Application No. 2004-353558). In the case of the power transmission mechanism of the first example of the prior invention shown in FIGS. 14 to 19 and the electric power steering apparatus incorporating the same, a female spline portion 48 provided at the end of the worm shaft 27, and an electric motor An elastic toothed ring 49, part of which is made of an elastic material, is provided between the male spline portion 47 provided on the 28 rotating shaft 29, and the shafts 27, 29 are connected to each other via the elastic toothed ring 49. Power transmission between them is possible. Next, this structure will be described in detail.

  The electric power steering apparatus includes a steering shaft 2 having a steering wheel 1 fixed to a rear end (right end in FIG. 14), a steering column 15 through which the steering shaft 2 can be inserted, and an auxiliary torque applied to the steering shaft 2. And an assist device 16 for imparting.

  The steering shaft 2 is formed by combining an outer shaft 17 provided on the rear end side (right side in FIG. 14) of the vehicle and an inner shaft 18 provided on the front end side (left side in FIG. 14) so that transmission of rotational force is possible. Become. Further, the inner shaft 18 connects a first inner shaft 22 provided on the rear end side of the vehicle and a second inner shaft 23 provided on the front end side by a torsion bar 24 (FIG. 15). A front end portion (left end portion in FIG. 14) of the steering column 15 is coupled and fixed to a rear end surface (right end surface in FIG. 14) of the gear housing 21 supported by a part of the vehicle body 19. The front end portion of the inner shaft 18 is inserted into the gear housing 21 and protrudes from the front end surface of the gear housing 21. The front end portion of the inner shaft 18 projecting from the front end surface and the input shaft 10 of the steering gear 9 are connected via the universal joints 7 and 7 and the intermediate shaft 8 so that power can be transmitted. . Further, a pinion 11 (see FIG. 13) is fixed to the input shaft 10, and the pinion 11 is meshed with a rack 12 (see FIG. 13). Accordingly, as the steering shaft 2 rotates, the tie rods 13 and 13 are pushed and pulled through the rack 12 to give a desired steering angle to the steered wheels 14 (see FIG. 10).

  As shown in FIGS. 15 to 19, the assist device 16 includes a worm wheel 26, a worm shaft 27, elasticity applying means 31 that applies elasticity to the worm shaft 27, an electric motor 28, and a power transmission mechanism 30. And a torque sensor 5 and a controller 6 (see FIG. 13). Of these, the worm wheel 26 is externally fitted and fixed to an intermediate portion of the second inner shaft 23 provided on the front end side of the inner shaft 18. The elastic force imparting means 31 includes a stepped cylindrical bearing holder 32, first and second ball bearings 33 and 34, a swing shaft 35, a coil provided on the inside of the gear housing 21, respectively. And a spring 36. The worm wheel 26 and the worm shaft 27 are provided inside the gear housing 21, and the worm 37 provided at an intermediate portion of the worm shaft 27 and the worm wheel 26 are engaged with each other. The worm shaft 27 and the worm wheel 26 constitute the worm speed reducer 20. The worm shaft 27 corresponds to the driven shaft described in the claims.

  The torque sensor 5 is a torque applied from the steering wheel 1 to the steering shaft 2 based on the relative rotation direction and the relative rotation amount of the first and second inner shafts 22 and 23 based on the twist of the torsion bar 24. The direction and magnitude of the signal are detected, and a signal (detection signal) representing the detected value is sent to the controller 6. In response to the detection signal, the controller 6 sends a drive signal to the electric motor 28 to generate auxiliary torque with a predetermined magnitude in a predetermined direction.

  The distal end portion (right end portion in FIGS. 15 to 17) of the rotating shaft 29 of the electric motor 28 and the proximal end portion (left end portion in FIGS. 15 to 17) of the worm shaft 27 are driven by the power transmission mechanism 30. Are connected to each other. The power transmission mechanism 30 includes a male spline portion 47 (FIGS. 15 to 17) provided at the distal end portion of the rotating shaft 29 and a female spline portion 48 (FIGS. 15 to 17) provided at the proximal end portion of the worm shaft 27. And an elastic toothed ring 49 provided between the two spline portions 47 and 48. The rotary shaft 29 corresponds to the drive shaft recited in the claims, and both end portions are rotatably supported by a case 38 constituting the electric motor 28 by third and fourth ball bearings (not shown). is doing. A rotor (not shown) facing the stator is provided at the intermediate portion of the rotating shaft 29.

  As shown in detail in FIG. 19, the elastic toothed ring 49 includes an outer tooth 50 that engages with the female spline portion 48 on the outer peripheral surface and an inner surface that engages with the male spline portion 47 on the inner peripheral surface. Each of the teeth 51 has a substantially cylindrical shape. Such an elastic toothed ring 49 includes external tooth element portions 54 projecting to the outer diameter side at a plurality of circumferentially equidistant positions on the outer peripheral surface of the main body 52 formed of a synthetic rubber, which is an elastic material. Similarly, inner tooth element portions 55 and 55 projecting toward the inner diameter side are formed over the entire length in the axial direction at a plurality of equally spaced circumferential positions on the inner peripheral surface.

  Further, a woven fabric 56a such as a nylon canvas is provided on the outer diameter side surface of each external tooth element portion 54, 54 and the outer peripheral surface of the main body portion 52 between these external tooth element portions 54, 54. It is stuck in a continuous state over the entire circumference of the outer peripheral surface. The external teeth 50 are configured by the external tooth element portions 54 and 54 and the portion of the woven fabric 56a covering the outer diameter side surfaces of the external tooth element portions 54 and 54. Further, a woven fabric 56b such as a nylon canvas is provided on the inner diameter side surface of each of the internal tooth element portions 55, 55 and between the inner peripheral element portions 55, 55 on the inner peripheral surface of the main body portion 52. Affixed over the entire circumference of the inner peripheral surface. The internal teeth 51 are constituted by the internal tooth element portions 55 and 55 and a portion of the woven fabric 56b covering the inner diameter side surfaces of the internal tooth element portions 55 and 55. With this configuration, the outer teeth 50 and the inner teeth 51 are provided on the outer diameter side and the inner diameter side of the elastic toothed ring 49, respectively. In the case of the illustrated example, the positions and numbers of the external tooth element portions 54 and 54 and the internal tooth element portions 55 and 55 in the circumferential direction are set to the external tooth element portions 54 and 54 and the internal tooth element portions 54 and 54. The tooth element portions 55 and 55 are matched with each other.

  Of the elastic toothed ring 49 configured as described above, the external teeth 50 are engaged with the female spline portion 48, and the internal teeth 51 are engaged with the male spline portion 47, respectively. The distal end portion of the rotary shaft 29 and the proximal end portion of the worm shaft 27 are connected so that the relative rotation of the shafts 29 and 27 is impossible. With this configuration, the worm shaft 27 rotates together with the rotating shaft 29.

  On the other hand, the bearing holder 32 is provided inside the gear housing 21, and the worm shaft 27 is rotatably supported inside the bearing holder 32. In the bearing holder 32, a large-diameter cylindrical portion 39 and a small-diameter cylindrical portion 40 that are concentric with each other are connected by a step portion 41. The bearing holder 32 is supported on the inner side of the gear housing 21 by a swing shaft 35 supported by the gear housing 21 so as to freely swing around the swing shaft 35. Further, the base end portion (the left end portion in FIGS. 15 to 17) of the worm shaft 27 is rotatably supported by the first ball bearing 33 inside the large diameter cylindrical portion 39 of the bearing holder 32. . The tip of the worm shaft 27 (the right end in FIGS. 15 to 17) is rotatably supported by the second ball bearing 34 inside the small diameter cylindrical portion 40 of the bearing holder 32.

  Further, an elastic ring 43 is provided between the outer peripheral surface of the distal end portion of the small diameter cylindrical portion 40 and the inner peripheral surface of the concave hole 42 provided in the inner surface of the gear housing 21. Further, a through hole 44 that penetrates both the inner and outer peripheral surfaces is formed in a part in the circumferential direction of the intermediate portion in the longitudinal direction of the small diameter cylindrical portion 40, and the worm wheel 26 and the worm shaft are passed through the through hole 44. 27 worms 37 are engaged with each other.

  Further, a concave hole 45 is formed in a part in the circumferential direction of the outer peripheral surface of the large-diameter cylindrical portion 39 constituting the bearing holder 32, and between the bottom surface of the concave hole 45 and the inner surface of the gear housing 21, A coil spring 36 is provided. The coil spring 36 imparts radial elasticity to the base end portion of the worm shaft 27 via the bearing holder 32 and the first ball bearing 33. With this configuration, the worm shaft 27 is elastically oscillated and displaced in the direction toward the worm wheel 26 around the oscillating shaft 35. Then, the distance between the central axes of the second inner shaft 23 and the worm shaft 27 to which the worm wheel 26 is fitted and fixed is elastically reduced, and the teeth between the worm 37 and the worm wheel 26 are elastically contracted. The surfaces come into contact with each other with a preload applied. With this configuration, it is possible to suppress the occurrence of rattling noise at the meshing portions of both the members 37 and 26.

  In the case of the power transmission mechanism of the first example of the present invention and the electric power steering apparatus incorporating the power transmission mechanism configured as described above, the female spline portion 48 provided on the worm shaft 27 and the rotating shaft of the electric motor 28 are provided. An elastic toothed ring 49 is provided between the male spline portion 47 provided on 29. For this reason, it is possible to prevent the tooth surfaces of the male and female spline portions 47 and 48 from directly colliding with each other, and it is possible to prevent the generation of noise due to the collision between the tooth surfaces. In addition, external teeth 50, which are external tooth elements 54 and 54 made of synthetic rubber, are provided on the outer diameter side of the elastic toothed ring 49, and partly on the inner diameter side of the elastic toothed ring 49. Is provided with internal teeth 51 which are internal tooth element portions 55, 55 made of synthetic rubber. For this reason, it is possible to reduce annoying noise caused by the contact between the tooth surfaces of the male and female spline portions 47 and 48 and the tooth surfaces of the inner tooth 51 and the outer tooth 50 of the elastic toothed ring 49, Or disappear. Further, it is not necessary to reduce the bending rigidity between the rotating shaft 29 and the worm shaft 27 of the electric motor 28 in order to suppress the generation of this annoying abnormal noise.

  In addition, since the internal tooth element portions 55 and 55 and the external tooth element portions 54 and 54 are made of synthetic rubber, which is an elastic material, inevitable dimensions existing in the male and female spline portions 47 and 48. The error can be easily absorbed to some extent by the inner teeth 51 and the outer teeth 50, and the size management and the assembly work can be easily performed. For this reason, an increase in the cost of the power transmission mechanism and the electric power steering apparatus incorporating the same can be suppressed to some extent.

  As a result, according to the structure of the first example of the prior invention shown in FIGS. 14 to 19 described above, without increasing the cost or reducing the bending rigidity between the rotating shaft 29 and the worm shaft 27, The generation of annoying noises can be suppressed. In the case of the structure shown in FIGS. 14 to 19 described above, synthetic rubber is used as an elastic material constituting the main body portion 52 of the elastic toothed ring 49, but instead of this synthetic rubber, Elastomers other than synthetic rubber, synthetic resins, and the like can also be used.

  However, in the case of the structure of the first example of the above-described prior invention, there is still room for improvement in terms of increasing the power that can be transmitted between the rotating shaft 29 and the worm shaft 27. Under such circumstances, the inventor of the present invention invented the second example of the prior invention of the power transmission mechanism as shown in FIG. 20 prior to the present invention. Next, a second example of the prior invention will be described. In the second example of the prior invention, the structure of the electric power steering device other than the power transmission mechanism 30a is the same as that of the first example of the prior invention shown in FIGS. In the case of the power transmission mechanism 30a of the second example of the present invention, the positions of the outer teeth 50a and the inner teeth 51a of the elastic toothed ring 49a in the circumferential direction are different from each other (the phases are shifted). That is, the elastic toothed ring 49a includes a main body 62 integrally formed in a cylindrical shape by an elastic material such as synthetic rubber, and a pair of woven fabrics 56a and 56b such as a nylon canvas. Of these, the main body portion 62 has external teeth element portions 54a and 54a having arc-shaped cross sections provided at a plurality of circumferentially equidistantly spaced locations (six locations in the illustrated example) located at the outer diameter side end portions, A plurality of inner tooth element portions 55a, 55a having a circular arc cross section provided at a plurality of circumferentially equidistantly spaced locations (six locations in the illustrated example) located at the inner diameter side end portion The connecting portions 61 and 61 are alternately connected in the circumferential direction. The entire elastic toothed ring 49a is formed in a cylindrical shape. In addition, the woven fabrics 56a and 56b are attached to the outer peripheral surface and the inner peripheral surface of the elastic toothed ring 49a over the entire circumference. And the external teeth 50a that are spline-engaged with the female spline portion 48a provided on the worm shaft 27 are constituted by the external tooth element portions 54a, 54a and the portions near the outer peripheral surface of the connecting portions 61, 61. ing. Further, the inner spline element 47a provided on the rotary shaft 29 of the electric motor 28 is spline-engaged by the inner tooth element portions 55a, 55a and the inner peripheral surface portions of the connection portions 61, 61. The teeth 51a are configured. Because of this configuration, the top portion (tooth tip surface) of the external tooth 50a of the elastic toothed ring 49a and the top portion (tooth tip surface) of the internal tooth 51a are shifted from each other in the circumferential direction, and the external tooth 50a The top of the inner teeth 51a faces the root of the inner teeth 51a, and the top of the inner teeth 51a faces the bottom of the outer teeth 50a in the radial direction.

  Further, the top portion of the external tooth 50a is brought close to the tooth bottom surface of the internal tooth 51a, and the top portion of the internal tooth 51a is brought close to the tooth bottom surface of the external tooth 50a in the diameter direction of the elastic toothed ring 49a. The bottom portion of the inner tooth 51a is positioned closer to the outer diameter side of the elastic toothed ring 49a than the bottom portion of the outer tooth 50a. Each tooth of the male spline portion 47a is provided with the elastic toothed ring 49a between the male spline portion 47a provided on the rotating shaft 29 and the female spline portion 48a provided on the worm shaft 27. And the teeth of the female spline part 48a are overlapped (overlapped) in the circumferential direction of the male and female spline parts 47a, 48a. For example, when a virtual circle concentric with the elastic toothed ring 49a shown by a two-dot chain line a in FIG. 20 is considered, each tooth of the male spline portion 47a and the female spline portion 48a are arranged on the circumference of the virtual circle. Each tooth is present.

  In the case of the structure of the second example of the prior invention shown in FIG. 20, the male spline portion 47a provided on the rotating shaft 29 and the female spline portion 48a provided on the worm shaft 27 as described above. With the elastic toothed ring 49a in between, the teeth of the male spline portion 47a and the teeth of the female spline portion 48a are overlapped in the circumferential direction of the male and female spline portions 47a, 48a. Yes. On the other hand, in the case of the structure of the first example of the prior invention shown in FIG. 19 described above, the tooth bottom portion of the outer tooth 50 is positioned on the outer side in the diameter direction than the tooth bottom portion of the inner tooth 51. In the case of such a conventional structure, when power is transmitted between the rotating shaft 29 of the electric motor 28 and the worm shaft 27, the inner diameter side portion and the outer diameter side portion of the elastic toothed ring 49 are circumferentially connected. A large shearing force may be applied to the elastic toothed ring 49 by applying forces in directions opposite to each other in the direction.

  On the other hand, in the case of the structure of the second example of the prior invention shown in FIG. 20, the teeth of the male and female spline portions 47a and 48a are connected in the circumferential direction of both the spline portions 47a and 48a. Therefore, even when power is transmitted between the rotating shaft 29 and the worm shaft 27, it is possible to prevent a large shearing force from being applied to the elastic toothed ring 49a. In the case of the structure of the second example of the prior invention, the elastic material constituting the elastic toothed ring 49a is used to transmit both power between the shafts 29 and 27. The elastic toothed ring 49a to which compression force is mainly applied is more than the elastic toothed ring to which mainly shearing force is applied, although it is compressed between the teeth adjacent to each other in the circumferential direction of the spline portions 47a and 48a. Are not easily damaged (durability is easy to ensure). Therefore, the power that can be transmitted between the shafts 29 and 27 can be increased. Moreover, in the case of the structure of the second example of the prior invention, the top of the external tooth 50a and the top of the internal tooth 51a are displaced in the circumferential direction, and the bottom of the internal tooth 51a is It is located on the outer side in the diameter direction than the tooth bottom of the tooth 50a. For this reason, the radial dimension of the elastic toothed ring 49a can be reduced to some extent, and the power transmission mechanism 30a can be downsized.

  However, in the case of the power transmission mechanism 30a of the second example of the prior invention shown in FIG. 20 described above, at least the female spline portion 48a provided on the worm shaft 27 and the male spline provided on the rotating shaft 29 of the electric motor 28. Each tooth of the female spline portion 48a and the external tooth 50a of the elastic toothed ring 49a that is spline-engaged with each other face each other (contact with each other) in a state where the elastic toothed ring 49a is provided between the portions 47a. ) The external shapes of the cross-sectional shapes of the tooth surfaces are the same. And it is trying not to produce a clearance gap between these mutually facing tooth surfaces. In addition, the external shapes of the cross-sectional shapes of the tooth surfaces of the male spline portion 47a and the teeth 51a of the elastic toothed ring 49a that are spline-engaged with the teeth are opposite to each other and are opposite to each other. In order to prevent gaps from occurring between the tooth surfaces. In the case of the second example of the prior invention as described above, the escape portion (gap portion) when the elastic toothed ring 49a is elastically deformed between the female spline portion 48a and the male spline portion 47a is formed in this intermediate portion. not exist. For this reason, it becomes difficult to sufficiently absorb the deviation (diameter mismatch or inclination) between the central axes of the worm shaft 27 and the rotary shaft 29 by the elastic deformation of the elastic toothed ring 49a. That is, there is a problem that the rigidity of the elastic toothed ring 49a becomes very high, and the allowable amount with respect to the deviation between the central axes of the two shafts 27 and 29 becomes very small. As described above, when the allowable amount with respect to the deviation between the central axes of the two shafts 27 and 29 is very small, the worm wheel 26 (see FIGS. 15 and 16) constituting the worm speed reducer 20 and the worm shaft 27 are arranged. In order to suppress backlash with the worm (see FIG. 15), when the elastic force is applied to the worm wheel 26 via the worm shaft 27, the elastic force cannot be sufficiently applied. This leads to an unpleasant noise (gap sound) or a deterioration in the steering feeling of the steering wheel 1 (see FIGS. 13 and 14).

In the case of the first example of the prior invention shown in FIGS. 11 to 19, the tooth surfaces of the internal teeth 51 and the external teeth 50 of the elastic toothed ring 49 are the same as in the case of the second example of the prior invention. The outer shapes of the cross-sectional shapes are the same as the outer shapes of the cross-sectional shapes of the tooth surfaces of the male spline portion 47 and the female spline portion 48, respectively. However, in the case of the first example of the prior invention, the circumferential positions of the outer teeth 50 and the inner teeth 51 of the elastic toothed ring 49 are made to coincide with each other, and each tooth of the female spline portion 48 The teeth of the male spline portion 47 are not overlapped (not overlapped) in the circumferential direction. In the case of the first example of such a prior invention, since the thickness in the radial direction of the elastic toothed ring 49 can be increased at the portion coinciding with the tops of the outer teeth 50 and the inner teeth 51 in the circumferential direction, The displacement between the central axes of the shaft 27 and the rotating shaft 29 can be absorbed to some extent by the elastic deformation of the elastic toothed ring 49. For this reason, problems such as the generation of abnormal noise and the deterioration of the steering feeling of the steering wheel 1 are less likely to occur than in the case of the second example of the prior invention. On the other hand, in the case of the second example of the prior invention shown in FIG. 20, the radial thickness of the elastic toothed ring 49a is different from the case of the first example of the prior invention. It becomes small (thin) in many parts. For this reason, it becomes difficult to sufficiently absorb the shift between the central axes of the worm shaft 27 and the rotary shaft 29 by the elastic deformation of the elastic toothed ring 49a. In the case of the second example of such a prior invention, an unpleasant noise is more likely to occur and the steering feeling of the steering wheel 1 is more likely to deteriorate than in the case of the first example of the prior invention. There is a lot of room for improvement.
Note that there are Patent Documents 1 to 3 as prior art documents related to the present invention.

JP 2002-211141 A JP 2005-69470 A International Publication No. 2005/012748

  In view of such circumstances, the present invention can increase the power that can be transmitted between the drive shaft and the driven shaft by overlapping each tooth of the male and female spline portions in the circumferential direction. In addition, the invention has been invented to realize a structure that can easily cause a shift between the central axes of these two axes.

Of the power transmission mechanism of the present invention and the electric power steering apparatus incorporating the power transmission mechanism, the power transmission mechanism described in claim 1 is the same as the power transmission mechanism of each example of the prior invention shown in FIGS. In addition,
A power transmission mechanism that is provided between a drive shaft and a driven shaft and transmits power between the two shafts, and includes a female spline portion, a male spline portion, and an elastic toothed ring. .
Of these, the female spline portion is provided on the inner peripheral surface of the end portion of one of the two shafts.
The male spline portion is provided on the outer peripheral surface of the end portion of the other shaft of the two shafts.
The elastic toothed ring has external teeth that are spline-engaged with the female spline portion on its outer peripheral surface, and inner teeth that are spline-engaged with the male spline portion on its inner peripheral surface. The elastic toothed ring is integrally provided with a plurality of external tooth element portions and internal tooth element portions each made of an elastic material on the outer diameter side and the inner diameter side.
The elastic toothed ring includes not only a cylindrical shape as a whole but also a cylindrical shape as a whole. The elastic toothed ring is not only made of an elastic material as a whole, but also made by attaching a woven fabric to at least one of the outer peripheral surfaces of the main body made of elastic material. Including.

In particular, among the power transmission mechanisms of the present invention, in the power transmission mechanism described in claim 1,
The teeth of the female spline part and the teeth of the male spline part are overlapped in the circumferential direction of the male and female spline parts, and at least one of the male and female spline parts Cross-sectional outer shape of each tooth and an imaginary plane perpendicular to the central axis of the tooth surfaces facing each other, with the internal teeth or external teeth provided on the elastic tooth ring, which are spline-engaged with each one of these teeth By making these different from each other, a gap is provided between the tooth surfaces facing each other.

  Preferably, as described in claim 2, in the configuration described in claim 1, the teeth of at least one of the male and female spline portions, and the teeth of the one, Of the tooth surfaces facing each other with the internal teeth or external teeth provided on the elastic toothed ring engaged with the spline, one is a curved surface and the other is a flat surface.

The electric power steering apparatus according to claim 3 is:
The rotation shaft of the electric motor and the input shaft constituting the speed reducer are coupled so as to be able to transmit power by the power transmission mechanism as described above.

Furthermore, the electric power steering apparatus according to claim 4 is:
The output shaft of the speed reducer or the rotating shaft of the electric motor and the ball nut are coupled to each other by a power transmission mechanism as described above so that power can be transmitted.

  In the case of the power transmission mechanism of the present invention as described above and the electric power steering apparatus incorporating the same, an elastic toothed ring is provided between the female spline part and the male spline part. For this reason, it is possible to prevent the tooth surfaces of both the male and female spline parts from directly abutting each other as in the examples of the prior invention shown in FIGS. It is possible to prevent the generation of abnormal noise. Further, a plurality of external tooth elements made of elastic material are provided on the outer diameter side of the elastic toothed ring, and a plurality of internal tooth elements made of elastic material are provided on the inner diameter side of the elastic toothed ring. For this reason, it is possible to reduce or eliminate annoying noise caused by the contact between the tooth surfaces of both the male and female spline portions and the tooth surfaces of the internal and external teeth of the elastic toothed ring. Further, it is not necessary to reduce the bending rigidity of the drive shaft and the driven shaft in order to suppress the generation of this annoying abnormal noise.

  Moreover, since each of the internal tooth element portions and each external tooth element portion are made of an elastic material, the inevitable dimensional errors existing in both the male and female spline portions can be easily absorbed by the elastic toothed ring, Dimension management and assembly work can be performed easily. For this reason, it is possible to suppress an increase in cost of the power transmission mechanism and the electric power steering apparatus incorporating the same. Therefore, it is possible to suppress the generation of annoying noise without increasing the cost and reducing the bending rigidity of the drive shaft and the driven shaft. In addition, when a woven fabric is applied to the outer peripheral surface and the inner peripheral surface of the elastic toothed ring, it is possible to effectively prevent the elastic material from tearing and the tooth surface from coming off.

  In particular, in the case of the present invention, each tooth of the female spline portion provided on one of the drive shaft and the driven shaft and each tooth of the male spline portion provided on the other shaft are The power transmission mechanism can be downsized because these spline portions are overlapped (overlapped) in the circumferential direction. Further, when power is transmitted between the drive shaft and the driven shaft, it is possible to prevent a large shearing force from being applied to the elastic toothed ring. When transmitting power between the two shafts, the compression force is applied to a part of the elastic toothed ring that exists between the teeth adjacent to each other in the circumferential direction of the male and female spline parts. However, the elastic toothed ring to which the compressive force is mainly applied is less likely to be damaged than the elastic toothed ring to which the shearing force is mainly applied (durability is easily ensured). For this reason, the power (allowable transmission power) that can be transmitted between the drive shaft and the driven shaft can be increased. For this reason, it is not necessary to increase the size of the structure.

  In addition, in the case of the present invention, the teeth of at least one of the male and female spline portions and the internal or external teeth provided on the elastic toothed ring that are spline-engaged with the one of the teeth. The gaps are provided between the tooth surfaces facing each other by making the outer shapes of the cross-sectional shapes with respect to the virtual plane orthogonal to the central axis of the tooth surfaces facing each other different from each other. For this reason, a relief portion of the elastic toothed ring when the elastic toothed ring is elastically deformed between the male and female spline portions can be provided in this portion. Therefore, the tolerance for the deviation (radial mismatch and inclination) between the central axes of the drive shaft and the driven shaft can be increased. As a result, according to the present invention, it is possible to increase the power that can be transmitted between the drive shaft and the driven shaft, and it is possible to easily cause a shift between the central axes of these two shafts. For example, the driven shaft is a worm shaft, the driving shaft is a rotating shaft of an electric motor, and this worm shaft is elastically pressed against the worm wheel by means of elastic force imparting to suppress the generation of abnormal noise. Even in this case, by making the worm shaft easy to incline with respect to the drive shaft, it is possible to more effectively suppress the generation of abnormal noise and to improve the steering feeling of the steering wheel more effectively.

  When power is transmitted from the drive shaft to the driven shaft, force is applied to the elastic toothed ring from both shafts from both sides in the rotational direction. This elastic toothed ring is circularly moved by both male and female spline parts. By being pressed in the circumferential direction and elastically deformed, the tooth surfaces of the inner and outer teeth of the elastic toothed ring and the tooth surfaces of both the male and female spline portions come into contact with each other in a sufficiently large area. For this reason, the surface pressure applied to the elastic toothed ring can be sufficiently reduced, and the durability of the elastic toothed ring can be sufficiently ensured.

[First example of embodiment of the present invention]
1 and 2 show a first example of an embodiment of the present invention corresponding to claims 1 and 3. The power transmission mechanism of this example and the electric power steering apparatus incorporating the power transmission mechanism can transmit power between the rotating shaft 29 of the electric motor 28 that is a driving shaft and the worm shaft 27 that is a driven shaft. The structure of the power transmission mechanism 30a is devised. In this example, the structure and operation of the electric power steering apparatus excluding the power transmission mechanism 30a are the same as those of the first example of the prior invention shown in FIGS. 14 to 19 and the previous invention shown in FIG. The same as in the case of the second example. For this reason, the illustrations and explanations regarding the equivalent parts of the first and second examples of the prior invention are omitted or simplified, and the following description will focus on the characteristic parts of this example.

  In the case of this example, a male spline portion 47b provided on the outer peripheral surface of the distal end portion of the rotating shaft 29 of the electric motor 28 that is a drive shaft, and a female provided on the inner peripheral surface of the proximal end portion of the worm shaft 27 that is a driven shaft. The power transmission mechanism 30a is constituted by the spline portion 48a and the elastic toothed ring 49a provided between the male and female spline portions 47b and 48a. In the case of this example, the structure is the same as that of the second example of the previous invention shown in FIG. 20 except for the shape of the tooth surface of each tooth of the male spline portion 47b.

  That is, in the case of this example, the elastic toothed ring 49b is entirely cylindrical with an elastic material such as an elastomer such as synthetic rubber or synthetic resin, as in the case of the second example of the previous invention shown in FIG. And a pair of woven fabrics 56a and 56b (see FIG. 20) attached to the outer peripheral surface and the inner peripheral surface of the main body portion 62 over the entire circumference. In FIG. 1 and FIG. 2, the illustration of the woven fabrics 56a and 56b is omitted for the sake of simplification. However, in the first example of the embodiment of the present invention, the prior invention shown in FIG. The woven fabrics 56a and 56b are provided similarly to the case of the second example (the same applies to the second to eighth examples of the embodiment of the present invention shown in FIGS. 3 to 10 described later). Of these woven fabrics 56a and 56b, the actual outer shape of the outer peripheral surface of the outer woven fabric 56a is the same as the outer shape of the outer peripheral surface of the elastic toothed ring 49b shown in FIGS. I'm doing it. Moreover, the outer shape of the cross-sectional shape of the actual inner peripheral surface of the woven fabric 56b on the inner diameter side coincides with the outer shape of the cross-sectional shape of the inner peripheral surface of the elastic toothed ring 49b shown in FIGS.

  As in the case of the second example of the prior invention shown in FIG. 20, the main body 62 has a plurality of circumferentially equidistant positions (six in the illustrated example) located at the outer diameter side end. The external tooth element portions 54a and 54a having a circular arc cross section provided in a state extending over the entire length in the axial direction, and a plurality of circumferentially equidistantly spaced locations (six locations in the illustrated example) located on the inner diameter side end portion. It is provided with internal tooth element portions 55a and 55a having a circular arc cross section provided in a state extending over the entire length in the axial direction. And each said external tooth element part 54a, 54a and each internal tooth element part 55a, 55a are alternately continued regarding the circumferential direction via the some connection part 61, 61 provided in the radial direction center part. It is integrally molded in the state. Further, the outer tooth 50a is constituted by the outer diameter side woven fabric 56a, the outer tooth element portions 54a, 54a to which the woven fabric 56a is adhered, and the portions near the outer peripheral surface of the connecting portions 61, 61. is doing. Further, the inner tooth 51a is constituted by the inner diameter side woven fabric 56b, the inner tooth element portions 55a and 55a to which the woven fabric 56b is adhered, and the portions near the inner peripheral surface of the connecting portions 61 and 61. is doing.

Further, with respect to the radial direction of the elastic toothed ring 49a, the bottom of the external tooth 50a is the top (tooth tip surface) of the internal tooth 51a, and the bottom of the internal tooth 51a is the top of the external tooth 50a (tooth). The front) is approaching each. And the tooth bottom part of the said inner tooth 51a is located in the diameter direction outer side of the said elastic toothed ring 49a rather than the tooth bottom part of the said outer tooth 50a. Accordingly, the diameter d _{1 of the} pitch circle passing through each bottom of the inner tooth 51a is larger than the diameter d _{2 of the} pitch circle passing through each bottom of the outer tooth 50a (d ₁ > d ₂ ).

  The elastic toothed ring 49a configured as described above is configured such that the external teeth 50a are engaged with the female spline portion 48a and the internal teeth 51a are engaged with the male spline portion 47b by spline engagement. It is provided between the spline portions 47b and 48a. And the front-end | tip part of the rotating shaft 29 of the said electric motor 28 and the base end part of the worm shaft 27 are connected by the said elastic toothed ring 49a so that relative rotation of these both shafts 29 and 27 is impossible. For this reason, the worm shaft 27 rotates together with the rotating shaft 29.

  Further, in the state where the elastic toothed ring 49a is provided between the male spline portion 47b and the female spline portion 48a, the teeth of the male spline portion 47b and the teeth of the female spline portion 48a are connected to the male, The female spline portions 47b and 48a are overlapped (overlapped) in the circumferential direction. Therefore, for example, when a virtual circle concentric with the elastic toothed ring 49a shown by a two-dot chain line A ′ in FIG. 1A is considered, each of the male spline portions 47b is arranged on the circumference of the virtual circle. There are teeth and each tooth of the female spline portion 48a.

Furthermore, in the case of this example, each tooth of the male spline portion 47b and each tooth of the internal tooth 51a provided on the elastic toothed ring 49a that is spline-engaged with each tooth are provided with this elastic tooth. Out of the cross-sectional shapes related to the virtual plane orthogonal to the central axis of the ring 49a, the external shapes (tooth surface shapes) of the cross-sectional shapes of the tooth surfaces facing each other are different from each other. That is, in the case of this example, the pressure angle α ₂ of the tooth surface of each tooth of the inner tooth 51a provided on the elastic toothed ring 49a is the same in almost all the portions extending from the tooth tip portion to the tooth root portion. respect are we to tooth surfaces facing the internal teeth 51a, the pressure angle alpha ₁ of the tooth tip portion near the tooth surfaces of the teeth of the male spline portion 47b, the pressure angle of the tooth root portion near alpha ₂ (Α ₁ > α ₂ ). In addition, regarding the internal teeth 51a and the male spline portion 47b, the external shapes of the cross-sectional shapes of the tooth surfaces facing each other are different from each other. As a result, the gaps 63 and 63 (see FIG. 1) are provided between the tooth surfaces of the teeth close to the teeth of the inner teeth 51a and the tooth surfaces of the teeth of the male spline portion 47b. (B)) is provided.

  In the case of the power transmission mechanism 30b of this example configured as described above and the electric power steering apparatus incorporating this power transmission mechanism 30b, the case of each example of the prior invention shown in FIGS. Similarly, generation of annoying noise can be suppressed without increasing the cost or reducing the bending rigidity between the rotating shaft 29 and the worm shaft 27 of the electric motor 28.

  In particular, in the case of this example, the teeth of the female spline portion 48a provided on the worm shaft 27 and the teeth of the male spline portion 47b provided on the rotating shaft 29 are connected to the male and female spline portions 47b. , 48a are overlapped (overlapped) in the circumferential direction. For this reason, the dimension of the power transmission part in the diameter direction can be reduced, and the power transmission mechanism 30b can be downsized. Further, when power is transmitted between the rotating shaft 29 and the worm shaft 27, it is possible to prevent a large shearing force from being applied to the elastic toothed ring 49a. When power is transmitted between the shafts 29 and 27, the circumferential direction of the elastic toothed ring 49a existing between the teeth adjacent to each other in the circumferential direction of the male and female spline portions 47b and 48a. Although the compressive force is applied to a plurality of places, the elastic toothed ring 49a to which the compressive force is mainly applied is less likely to be damaged than the elastic toothed ring to which the shear force is mainly applied (it is easy to ensure durability). . For this reason, the power (allowable transmission power) that can be transmitted between the rotating shaft 29 and the worm shaft 27 can be increased. For this reason, it is not necessary to increase the size of the structure.

  In addition, in the case of this example, the teeth of the male spline portion 47b and the inner teeth 51a provided on the elastic toothed ring 49a are opposed to each other on the central axis of the elastic toothed ring 49a. On the other hand, by making the outer shapes (tooth surface shapes) of the cross-sectional shapes orthogonal to the orthogonal virtual plane different from each other, between the tooth surfaces of the teeth of the internal teeth 51a facing each other and the tooth surfaces of the teeth of the male spline portion 47b. Clearances 63 and 63 are provided. For this reason, the escape portion of the elastic toothed ring 49a when the elastic toothed ring 49a is elastically deformed between the male and female spline portions 47b, 48a can be provided in this portion. Therefore, the allowable amount with respect to the deviation (radial mismatch and inclination) between the central axes of the rotating shaft 29 of the electric motor 28 and the worm shaft 27 can be increased. As a result, according to this example, the power that can be transmitted between the rotary shaft 29 and the worm shaft 27 can be increased, and the center axes of the shafts 29 and 27 can be easily displaced. Therefore, as in this example, the worm shaft 27 is elastically pressed against the worm wheel 26 by the elastic force applying means 31 (see FIGS. 15 and 16), thereby suppressing the backlash and suppressing the generation of annoying abnormal noise. Even in such a case, by making the worm shaft 27 easily inclined with respect to the rotating shaft 29, it is possible to more effectively suppress the generation of abnormal noise and to steer the steering wheel 1 (see FIGS. 13 and 14). The feeling can be improved more effectively.

  As shown in FIG. 2, when power is transmitted from the rotary shaft 29 to the worm shaft 27, the elastic toothed ring 49a is rotated from both the shafts 29, 27 in the direction of rotation (in the direction of arrow B in FIG. 2). Although force is applied from both sides, the elastic toothed ring 49a is pressed in the circumferential direction by the male and female spline portions 47b and 48a and elastically deformed, whereby the inner teeth 51a and the outer teeth of the elastic toothed ring 49a are externally deformed. The tooth surfaces of the teeth 50a and the tooth surfaces of both the male and female spline portions 47b and 48a are in contact with each other in a sufficiently large area at portions facing each other in the circumferential direction. For this reason, the surface pressure applied to the elastic toothed ring 49a can be kept sufficiently low, and the durability of the elastic toothed ring 49a can be sufficiently ensured.

[Second example of the embodiment of the present invention]
Next, FIG. 3 shows a second example of the embodiment of the present invention, which also corresponds to claims 1 and 3. In the case of this example, unlike the case of the first example shown in FIGS. 1 and 2 described above, the pressure angle β ₂ of the tooth surface of each tooth of the male spline portion 47a provided on the rotating shaft 29 of the electric motor 28 is set. The pressure angle β _{1 of the} portion near the tooth tip of the tooth surface of the inner tooth 51b of the elastic toothed ring 49b is set to be the same in almost the entire range from the tooth root portion to the tooth tip portion. The pressure angle β _{2 at the} side portion is increased (β ₁ > β ₂ ). The tooth surfaces of the male spline portion 47a and the internal teeth 51b provided on the elastic toothed ring 49b are opposed to a virtual plane orthogonal to the central axis of the elastic toothed ring 49b. By making the external shapes of the cross-sectional shapes different from each other, between the tooth surface of the tooth tip portion of each tooth of the internal teeth 51b facing each other and the tooth surface of the tooth base portion of each tooth of the male spline portion 47a, Clearances 64 and 64 are provided.

In the case of this example configured as described above, the power that can be transmitted between the rotating shaft 29 of the electric motor 28 and the worm shaft 27 can be increased as in the case of the first example described above. Deviations between the central axes of the shafts 29 and 27 can be easily generated.
Other configurations and operations are the same as those in the case of the first example shown in FIGS. 1 and 2 described above.

[Third example of the embodiment of the present invention]
Next, FIG. 4 shows a third example of the embodiment of the present invention, which also corresponds to claims 1 and 3. In the case of this example, unlike the cases described above, the teeth of the male spline portion 47a provided on the rotating shaft 29 of the electric motor 28 and the internal teeth 51a provided on the elastic toothed ring 49a are mutually connected. The external shapes of the cross-sectional shapes of the opposing tooth surfaces with respect to a virtual plane orthogonal to the central axis of the elastic toothed ring 49a are the same. Instead, in the case of this example, each tooth surface of the female spline portion 48b provided on the worm shaft 27 and each tooth of the external tooth 50a provided on the elastic toothed ring 49a are opposed to each other. The outer shapes of the cross-sectional shapes related to the virtual plane orthogonal to the central axis of the elastic toothed ring 49a are different from each other. For this reason, in the case of this example, the pressure angle γ ₁ at the tooth tip portion of the tooth surface of each tooth of the female spline portion 48b is made larger than the pressure angle γ ₂ at the tooth base portion. (Γ ₁ > γ ₂ ). In contrast, the pressure angle γ ₁ of the tooth surface of each tooth of the external tooth 50a of the elastic toothed ring 49a is the same in almost all ranges from the tooth root portion to the tooth tip portion. And thereby, the clearance gaps 65 and 65 are provided between the tooth | gear surface of the tooth tip near part of the external tooth 50a which mutually opposes, and the tooth surface of the tooth | gear base part of each tooth | gear of the female spline part 48b. That is, in the case of the above-described first and second examples, the gaps 63 and 64 (see FIGS. 1 to 3) between the inner peripheral surfaces of the elastic toothed rings 49a and 49b and the male spline portions 47b and 47a of the rotating shaft 29. In the case of this example, clearances 65 and 65 are provided between the outer peripheral surface of the elastic toothed ring 49a and the female spline portion 48b of the worm shaft 27.

Also in the case of this example configured as described above, the relief portion of the elastic toothed ring 49a when the elastic toothed ring 49a is elastically deformed between the male and female spline portions 47a and 48b, Can be provided. Therefore, as in the case of the first and second examples described above, it is possible to increase the tolerance for the deviation between the central axes of the rotating shaft 29 of the electric motor 28 and the worm shaft 27. Therefore, according to the present example, the power that can be transmitted between the rotary shaft 29 and the worm shaft 27 can be increased, and the center axes of the shafts 29 and 27 can be easily displaced. As a result, even when the worm shaft 27 is elastically pressed against the worm wheel 26 (see FIGS. 15 and 16) as in this example, the backlash is suppressed to a small level and the generation of annoying noise is suppressed. By making the worm shaft 27 easy to incline with respect to the rotating shaft 29, it is possible to more effectively suppress the generation of abnormal noise and to make the steering feeling of the steering wheel 1 (see FIGS. 13 to 14) more effective. Can be improved.
Since other configurations and operations are the same as those of the first example shown in FIGS. 1 and 2 described above, the same parts are denoted by the same reference numerals, and redundant description is omitted.

[Fourth Example of the Embodiment of the Present Invention]
Next, FIG. 5 shows a fourth example of the embodiment of the present invention, which also corresponds to claims 1 and 3. In the case of this example, unlike the case of the third example shown in FIG. 4 described above, the pressure angle δ ₂ of the tooth surface of each tooth of the female spline part 48a provided on the worm shaft 27 is changed from the tooth base part to the tooth part. It is the same in almost all areas over the front. On the other hand, the pressure angle δ ₁ of the tooth tip portion of the tooth surface of each of the external teeth 50b of the elastic toothed ring 49c is made larger than the pressure angle δ ₂ of the tooth tip portion (δ). ₁ > δ ₂ ). As a result, the teeth of the female spline portion 48a and the teeth of the external teeth 50b provided on the elastic toothed ring 49c are opposed to each other on the central axis of the elastic toothed ring 49c. On the other hand, by making the outer shapes of the cross-sectional shapes related to the orthogonal virtual planes different from each other, the tooth surface near the tooth tip of the external tooth 50b facing each other and the tooth surface near the tooth root of each tooth of the female spline portion 48a A gap 66 is provided between them.

In the case of this example configured as described above, the power that can be transmitted between the rotating shaft 29 of the electric motor 28 and the worm shaft 27 is increased as in the case of the third example shown in FIG. In addition, the center axes of these shafts 29 and 27 can be easily displaced.
Since other configurations and operations are the same as in the case of the third example shown in FIG. 4 described above, the same parts are denoted by the same reference numerals, and redundant description is omitted.

[Fifth example of the embodiment of the present invention]
Next, FIGS. 6-7 has shown the 5th example of embodiment of this invention corresponding to Claims 1-3. In the case of this example, in the structure of the first example shown in FIGS. 1 and 2 described above, the tooth surface of each tooth of the male spline portion 47c provided on the rotation shaft 29 of the electric motor 28 The outer shape of the cross-sectional shape related to the virtual plane orthogonal to the central axis is a composite curve formed by continuously connecting only a plurality of curves having different curvature centers. Further, the radial intermediate portions of the tooth surfaces on both sides in the circumferential direction of each tooth of the male spline portion 47c are projected in a convex shape toward both sides in the circumferential direction from the tooth surfaces near the both ends in the radial direction. In contrast, in the free state of the elastic toothed ring 49a, almost all of the tooth surfaces on both sides in the circumferential direction of the inner teeth 51a of the elastic toothed ring 49a extending from the base end portion to the tip end portion. Are provided with flat surface portions 67 and 67 which are inclined with respect to a virtual plane including the central axis of the elastic toothed ring 49a. The pressure angles at the flat surface portions 67 and 67 of these teeth are the same in the entire range from the proximal end portion to the distal end portion. Further, the flat surface portions 67 and 67 of the inner teeth 51a and the convex curved surfaces protruding on both sides in the circumferential direction of the teeth of the male spline portion 47c are opposed to each other and brought into contact with each other. As a result, gaps 68, 68 are provided between the tooth surfaces near the radial ends of each tooth of the internal teeth 51a facing each other and the tooth surfaces near the radial ends of each tooth of the male spline portion 47c. It is done.

  In the case of this example, a radial gap 69 is provided between the tip surface (top) of each tooth of the male spline portion 47c and the bottom of the inner tooth 51a of the elastic toothed ring 49a. . However, the tip surface (top) of each tooth of the male spline portion 47c and the tooth bottom portion of the inner tooth 51a of the elastic toothed ring 49a can be brought into contact with each other. Further, in the state where the radial gap 69 is provided, between the tooth surfaces on both sides in the circumferential direction of each tooth of the male spline portion 47c and the tooth surfaces on both sides in the circumferential direction of the inner teeth 51a of the elastic toothed ring 49a. The gaps 68 and 68 can be eliminated.

  In the case of this example configured as described above, as in the case of the first and second examples shown in FIGS. 1 to 3, the teeth of the male spline portion 47c and the elastic toothed ring 49a are provided. Gaps 68 and 69 are provided between the tooth surfaces facing each other of the provided internal teeth 51a. For this reason, when the elastic toothed ring 49a is elastically deformed between the male spline part 47c and the female spline part 48a provided on the worm shaft 27, a relief part of the elastic toothed ring 49a is provided in this part. I can do things.

As shown in FIG. 7, when power is transmitted from the rotary shaft 29 to the worm shaft 27, the elastic toothed ring 49a is rotated from both the shafts 29, 27 in the direction of rotation (the direction indicated by the arrow C in FIG. 7). Although force from both sides is applied, the elastic toothed ring 49a is pressed in the circumferential direction by the male and female spline portions 47c and 48a and elastically deformed, so that the inner teeth 51a and the outer teeth of the elastic toothed ring 49a are externally deformed. The tooth surface of the tooth 50a and the tooth surfaces of both the male and female spline portions 47c and 48a are in contact with each other with a sufficiently large area. For this reason, the surface pressure applied to the elastic toothed ring 49a can be kept sufficiently low, and the durability of the elastic toothed ring 49a can be sufficiently ensured.
Since other configurations and operations are the same as those in the first example shown in FIGS. 1 and 2 described above, the same parts are denoted by the same reference numerals, and redundant description is omitted.

[Sixth example of embodiment of the invention]
Next, FIG. 8 shows a sixth example of the embodiment of the present invention, which also corresponds to claims 1 to 3. In the case of this example, unlike the case of the fifth example shown in FIGS. 6 to 7 described above, the tooth surfaces on both sides in the circumferential direction of each tooth of the male spline portion 47a provided on the rotating shaft 29 of the electric motor 28, Flat surface portions 70 and 70 which are inclined with respect to a virtual plane including the central axis of the elastic toothed ring 49a are provided in almost all portions extending from the proximal end portion to the distal end portion. The pressure angles at the flat surface portions 70 of these teeth are the same in the entire range from the base end portion to the tip end portion. Further, in the free state of the elastic toothed ring 49d, the tooth surface on both sides in the circumferential direction of each tooth of the inner tooth 51c of the elastic toothed ring 49d relates to a virtual plane orthogonal to the central axis of the elastic toothed ring 49d. The outer shape of the cross-sectional shape is a composite curve formed by continuously connecting a plurality of curves having different curvature centers. In addition, the radially intermediate portions of the tooth surfaces on both sides in the circumferential direction of each tooth of the inner tooth 51c are projected in a convex shape toward both sides in the circumferential direction rather than the portions near both ends in the radial direction. And the flat surface parts 70 and 70 provided in each tooth | gear of the said male spline part 47a and the convex curved surface which protruded in the circumferential direction both sides of each said tooth | gear 51c are made to oppose and contact. As a result, gaps 71a and 71b are provided between the tooth surfaces near the both ends in the radial direction of each tooth of the internal teeth 51c facing each other and the tooth surfaces near the both ends in the radial direction of each tooth of the male spline portion 47a. It is done.
Since other configurations and operations are the same as in the case of the fifth example shown in FIGS. 6 to 7 described above, the same parts are denoted by the same reference numerals and redundant description is omitted.

[Seventh embodiment of the present invention]
Next, FIG. 9 shows a seventh example of the embodiment of the present invention, which also corresponds to claims 1 to 3. In the case of this example, unlike the case of the fifth to sixth examples shown in FIGS. 6 to 8 described above, the tooth surface of each tooth of the male spline portion 47a provided on the rotating shaft 29 of the electric motor 28 and the elastic tooth The outer shapes of the cross-sectional shapes in the direction perpendicular to the central axis of the elastic toothed ring 49a with the tooth surfaces of the inner teeth 51a provided on the attached ring 49a are the same. Instead, in the case of this example, the outer shapes of the cross-sectional shapes of the tooth surfaces of the teeth of the female spline portion 48c provided on the worm shaft 27 with respect to the virtual plane orthogonal to the central axis of the worm shaft 27 are mutually connected. A compound curve is formed by continuously connecting only a plurality of curves having different curvature centers. Further, the radial intermediate portions of the tooth surfaces on both sides in the circumferential direction of each tooth of the female spline portion 48c are projected in a convex shape toward both sides in the circumferential direction rather than the portions near both ends in the radial direction. On the other hand, the elastic toothed ring 49a is provided on almost all of the tooth surfaces on both sides in the circumferential direction of each tooth of the external teeth 50a provided on the elastic toothed ring 49a. Are provided with flat surface portions 72 and 72 which are inclined with respect to a virtual plane including the central axis. The pressure angles at the flat surface portions 72, 72 of these teeth are the same in the entire range from the proximal end portion to the distal end portion. Further, the flat surface portions 72, 72 of the external teeth 50a and the convex curved surfaces projecting on both sides in the circumferential direction of the teeth of the female spline portion 48c are opposed to and in contact with each other. As a result, gaps 73a and 73b are provided between the tooth surfaces near the both ends in the radial direction of each tooth of the external teeth 50a facing each other and the tooth surfaces near the both ends in the radial direction of each tooth of the female spline portion 48c. It is done.

  In the case of this example, a radial gap is provided between the tip surface (top) of each tooth of the female spline portion 48c and the bottom of the external tooth 50a of the elastic toothed ring 49a. However, the tip surface (top) of each tooth of the female spline portion 48c and the tooth bottom portion of the external tooth 51a of the elastic toothed ring 49a can be brought into contact with each other. Further, in the state where the radial gap is provided, between the tooth surfaces on both sides in the circumferential direction of each tooth of the female spline portion 48c and the tooth surfaces on both sides in the circumferential direction of the external teeth 50a of the elastic toothed ring 49a. The gaps 73b and 73b can be eliminated.

In the case of this example configured as described above, as in the case of the third example shown in FIG. 4, the external teeth provided on the teeth of the female spline portion 48c and the elastic toothed ring 49a are provided. Clearances 73a and 73b are provided between the tooth surfaces facing each other and the teeth of 50a. For this reason, the escape portion of the elastic toothed ring 49a when the elastic toothed ring 49a is elastically deformed between the male and female spline portions 47a and 48c can be provided in this portion.
Since other configurations and operations are the same as in the case of the third example shown in FIG. 4 described above, the same parts are denoted by the same reference numerals and redundant description is omitted.

[Eighth Example of the Embodiment of the Present Invention]
Next, FIG. 10 shows an eighth example of the embodiment of the present invention, which also corresponds to claims 1 to 3. In the case of this example, unlike the case of the seventh example shown in FIG. 9 described above, the proximal end portion to the distal end portion of the tooth surface on both sides in the circumferential direction of each tooth of the female spline portion 48a provided on the worm shaft 27. The flat surface portions 74, 74 that are inclined with respect to the virtual plane including the central axis of the worm shaft 27 are provided in almost all portions. The pressure angles at the flat surface portions 74, 74 of these teeth are the same in the entire range from the proximal end portion to the distal end portion. On the other hand, the outer shape of the cross-sectional shape related to the virtual plane orthogonal to the central axis of the elastic toothed ring 49e of the tooth surfaces on both sides in the circumferential direction of each tooth of the external teeth 50c provided on the elastic toothed ring 49e A composite curve is formed by continuously connecting a plurality of curves having different curvature centers. Further, the radial intermediate portions of the tooth surfaces on both sides in the circumferential direction of each tooth of the external tooth 50c are projected in a convex shape toward both sides in the circumferential direction rather than the portions near both ends in the radial direction. And the flat surface parts 74 and 74 of the said female spline part 48a and the convex curved surface which protruded in the circumferential direction both sides of the tooth surface of each said external tooth 50c are made to oppose and contact. As a result, gaps 75a and 75b are provided between the tooth surfaces of the external teeth 50c facing each other at both ends in the radial direction of the teeth and the tooth surfaces at the ends of the female spline portion 48a in the radial direction. It is done.
Since other configurations and operations are the same as those in the case of the seventh example shown in FIG. 9 described above, the same parts are denoted by the same reference numerals, and redundant description is omitted.

[Ninth example embodiment of the present invention]
Next, FIGS. 11 to 12 show a ninth example of the embodiment of the invention corresponding to claims 1, 3 and 4. In the case of the electric power steering apparatus of this example, unlike the above-described examples, the auxiliary torque of the electric motor 28 is applied to the steering shaft 2 (see FIGS. 13 to 15) via the worm reducer. Absent. In the case of this example, a so-called rack-assist type electric power steering apparatus that applies auxiliary torque of the electric motor 28 to the rack 12 via a helical gear type reduction gear 80 and a ball screw mechanism 81 is provided. The present invention is applied. That is, in the case of this example, the electric motor 28 is provided on the side of the rack 12. Further, the rotary shaft 29 of the electric motor 28 is connected to the input shaft 82 of the helical gear type reduction gear 80, and the output gear 83 serving as the output shaft of the reduction gear 80 and the ball nut 84 are connected to each other. ing. The output gear 83 and the ball nut 84 are provided so as to be fitted around the rack 12. A plurality of balls 87, 87 are provided between an inner diameter side ball screw groove 85 provided on a partial outer peripheral surface of the rack 12 and an outer diameter side ball screw groove 86 provided on the inner peripheral surface of the ball nut 84. It is provided to roll freely. The ball nut 84 is supported only rotatably with respect to the housing 88. The rack 12 supports only the axial displacement with respect to the housing 88.

  When the steering wheel 1 (see FIGS. 13 and 14) is operated with such a rack-assist type electric power steering device, a torque sensor (not shown) provided around the steering shaft 2 or the pinion 11 is used for this steering. The direction and magnitude of torque applied to the shaft 2 or the pinion 11 are detected. Then, the controller 6 (see FIG. 13) energizes the electric motor 28 based on the signal input from the torque sensor, and rotates the ball nut 84 via the speed reducer 80. The rack 12 is displaced in the axial direction by the rotation of the ball nut 84.

  In particular, in the case of this example, a female spline portion 48d provided on the inner peripheral surface of the distal end portion of the rotating shaft 29 of the electric motor 28 and one end portion of the input shaft 82 of the speed reducer 80 (the left end portion of FIGS. 11 to 12). ) Between the male spline portion 47d provided on the outer peripheral surface, an elastic toothed ring 49a similar to the case of the first example of the embodiment shown in FIGS. By 49a, the said rotating shaft 29 and the input shaft 82 are couple | bonded so that motive power can be transmitted. The teeth of the male spline portion 47d and the female spline portion 48d are overlapped in the circumferential direction of both the spline portions 47d and 48d. As in the case of the first example of the embodiment shown in FIGS. 1 and 2, the teeth of the male spline portion 47d and the internal teeth 51a provided on the elastic toothed ring 49a are mutually connected. The outer shapes of the cross-sectional shapes of the opposing tooth surfaces with respect to a virtual plane orthogonal to the central axis are different from each other. And thereby, the clearance gap is provided between the tooth surface of each tooth of the internal tooth 51a which mutually opposes, and the tooth surface of each tooth of the male spline part 47d.

  Furthermore, a female spline portion 48e provided on the output gear 83 of the speed reducer 80, and a male spline portion 47e formed on the small diameter cylindrical portion 90 provided on one end portion (the left end portion in FIGS. 11 to 12) of the ball nut 84; In the meantime, an elastic toothed ring 49a similar to the case of the first example of the embodiment shown in FIGS. The elastic geared ring 49a connects the output gear 83 and the ball nut 84 so that power can be transmitted. The teeth of the male spline portion 47e and the female spline portion 48e are overlapped in the circumferential direction of both the spline portions 47e and 48e. Furthermore, as in the case of the first example of the embodiment shown in FIGS. 1 and 2, the teeth of the male spline portion 47e and the internal teeth 51a provided on the elastic toothed ring 49a are mutually connected. The outer shapes of the cross-sectional shapes of the opposing tooth surfaces with respect to a virtual plane orthogonal to the central axis are different from each other. And thereby, the clearance gap is provided between the tooth surface of each tooth of the internal tooth 51a which mutually opposes, and the tooth surface of each tooth of the male spline part 47e.

  Also in this example, the elastic toothed rings 49a and 49a are provided in some of the power transmission parts, the tooth surfaces of the internal teeth 51a of these elastic toothed rings 49a and 49a, and the teeth The external shapes of the cross-sectional shapes with respect to the virtual plane orthogonal to the central axis of the tooth surfaces of the male spline portions 47d and 47e facing the surface are different from each other. For this reason, the power that can be transmitted by each power transmission section can be increased, and the center axes of the rotary shaft 29 and the input shaft 82 of the electric motor 28 and the center axes of the output gear 83 and the ball nut 84 are shifted. Can be easily generated. Therefore, even if a manufacturing error or an assembly error occurs in the rotating shaft 29 and the input shaft 82, and the output gear 83 and the ball nut 84, the rotating shaft 29 and the input shaft 82, and the output gear 83 and the ball The nut 84 can be combined more easily, and assemblability can be secured better. In the scope of the present invention, instead of the elastic toothed ring 49a, the elastic toothing used in the second, fourth, sixth and eighth examples of the embodiment shown in FIGS. The ring 49b to 49e is adopted, or the structure having the female spline portions 48b and 48c similar to the third and seventh examples of the embodiment shown in FIGS. 4 and 9 is adopted. Of course, a structure having the same male spline portion 47c as that of the fifth example of the embodiment shown in FIGS.

  Although not shown, the rack assist type electric power steering apparatus has an electric motor having a rotating shaft of the electric motor and a rotating shaft of the ball nut in addition to the structure shown in FIGS. In addition to being provided around the rack so as to be positioned on the same axis, the rotating shaft of the electric motor and the ball nut may be directly connected without a reduction gear. Even in the electric power steering apparatus having such a structure, the same structure as the power transmission mechanism 30a of the first to eighth examples described above can be adopted for the power transmission part between the rotating shaft of the electric motor and the ball nut.

  In the case of each example described above, a pair of woven fabrics 56a and 56b (refer to FIG. 20) are pasted on the outer peripheral surfaces of the elastic main body 62 inside the elastic toothed rings 49a to 49e. It is supposed to be worn. However, the power transmission mechanism of the present invention is not limited to the structure using the elastic toothed rings 49a to 49e provided with the woven fabrics 56a and 56b. For example, the present invention may be a structure using one of the pair of woven fabrics 56a and 56b in which one woven fabric 56a (or 56b) or both woven fabrics 56a and 56b are omitted as the elastic toothed ring. Can be implemented. For example, the elastic toothed ring may be composed only of an elastic material such as an elastomer such as synthetic rubber or a synthetic resin.

The figure similar to FIG. 20 which shows the power transmission mechanism of the 1st example of embodiment of this invention. (A) (b) is a figure which shows the state which transmits motive power to the worm shaft from the rotating shaft of an electric motor, respectively in Fig.1 (a) (b). The figure similar to FIG. 1 which shows the power transmission mechanism of the 2nd example of embodiment of this invention. The figure similar to FIG. 1 which shows the power transmission mechanism of the 3rd example. The figure similar to FIG. 1 which shows the power transmission mechanism of the 4th example. The figure similar to FIG. 1 which shows the power transmission mechanism of the 5th example. (A) (b) is a figure which shows the state which transmits motive power to the worm shaft from the rotating shaft of an electric motor, respectively by Fig.6 (a) (b). The figure similar to FIG. 1 which shows the power transmission mechanism of the 6th example of embodiment of this invention. The figure similar to FIG. 1 which shows the power transmission mechanism of the 7th example. The figure similar to FIG. 1 which shows the power transmission mechanism of the 8th example. The fragmentary sectional view which shows the rack assist type electric power steering apparatus of the 9th example. The A section expanded sectional view of FIG. BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the whole structure of one example of the electric power steering apparatus used as the object of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway view showing an electric power steering apparatus according to a first example of the present invention invented prior to the present invention. The fragmentary sectional view of the BB part of FIG. The elements on larger scale of FIG. The C section enlarged view of FIG. DD sectional drawing. The figure which expands the EE cross section of FIG. 17 about the power transmission mechanism of the 1st example of the prior invention invented prior to this invention. The power transmission mechanism of the said 2nd example is shown, (a) is a figure similar to FIG. 19, (b) is the elements on larger scale of (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Electric motor 4 Reduction gear 5 Torque sensor 6 Controller 7 Universal joint 8 Intermediate shaft 9 Steering gear 10 Input shaft 11 Pinion 12 Rack 13 Tie rod 14 Steering wheel 15 Steering column 16 Assist device 17 Outer shaft 18 Inner Shaft 19 Car body 20 Worm speed reducer 21 Gear housing 22 First inner shaft 23 Second inner shaft 24 Torsion bar 26 Worm wheel 27 Worm shaft 28 Electric motor 29 Rotating shaft 30, 30a Power transmission mechanism 31 Elasticity applying means 32 Bearing holder 33 First ball bearing 34 Second ball bearing 35 Oscillating shaft 36 Coil spring 37 Worm 38 Case 39 Large diameter cylindrical portion 40 Small diameter cylindrical portion 41 Step portion 42 Recessed hole 43 Sex ring 44 through-hole 45 concave hole 47, 47a to 47e male spline part 48, 48a to 48e female spline part 49, 49a to 49e elastic toothed ring 50, 50a to 50c outer tooth 51, 51a to 51c inner tooth 52 body part 54, 54a External tooth element portion 55, 55a Internal tooth element portion 56a, 56b Woven cloth 61 Connection portion 62 Main body portion 63 Clearance 64 Clearance 65 Clearance 66 Clearance 67 Flat surface portion 68 Clearance 69 Clearance 70 Flat surface portion 71a, 71b Clearance 72 Flat surface portion 73a, 73b Clearance 74 Flat surface portion 75a, 75b Clearance 80 Reducer 81 Ball screw mechanism 82 Input shaft 83 Output gear 84 Ball nut 85 Inner diameter side ball screw groove 86 Outer diameter side ball screw groove 87 Ball 88 Housing 90 Small diameter cylindrical portion

Claims (4)

A power transmission mechanism provided between the drive shaft and the driven shaft for transmitting power between the two shafts;
A female spline portion provided on the inner peripheral surface of the end of one of these shafts, a male spline portion provided on the outer peripheral surface of the end of the other shaft, and an outer surface that engages with the female spline portion. An elastic toothed ring having teeth on its outer peripheral surface and inner teeth on its inner peripheral surface that engage with the male spline portion on its inner peripheral surface. The elastic toothed ring is provided on the outer diameter side and the inner diameter side. In the power transmission mechanism in which a plurality of external tooth element portions and internal tooth element portions each made of an elastic material are integrally provided,
The teeth of the female spline part and the teeth of the male spline part are overlapped in the circumferential direction of the male and female spline parts, and at least one of the male and female spline parts Cross-sectional outer shape of each tooth and an imaginary plane perpendicular to the central axis of the tooth surfaces facing each other, with the internal teeth or external teeth provided on the elastic tooth ring, which are spline-engaged with each one of these teeth A power transmission mechanism characterized in that a gap is provided between the tooth surfaces facing each other by differentiating each other.   Of the tooth surfaces facing each other, each tooth of at least one of the male and female spline portions and the internal or external tooth provided on the elastic toothed ring that is spline-engaged with the one tooth. The power transmission mechanism according to claim 1, wherein one is a curved surface and the other is a flat surface.   An electric power steering apparatus in which a rotating shaft of an electric motor and an input shaft constituting a speed reducer are coupled by a power transmission mechanism according to claim 1 or 2 so as to enable transmission of power.   An electric power steering device in which an output shaft of a reduction gear or a rotating shaft of an electric motor and a ball nut are coupled to each other by a power transmission mechanism according to claim 1 or 2 so as to be able to transmit power.

Images