JP2016074379A - Electrically-driven type power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure capable of suppressing worm teeth from being displaced in a direction perpendicular to a direction of engagement between the worm teeth and a worm wheel and an axial direction of a worm shaft while suppressing a tooth hitting sound from being generated at an engagement part between the worm teeth and worm wheel even when the worm wheel rotates in either direction.SOLUTION: An energizing member 24 constituting energizing means 21 is arranged in such a state that a modulus of section associated with a direction of a bisector between a vector of engagement reaction force applied to a worm shaft 6a when a worm wheel is rotated in one direction and a vector of engagement reaction force when the worm wheel is rotated in the other direction is minimum and a modulus of section associated with a direction perpendicular to the direction of the bisector and the axial direction of the worm shaft 6a is maximum. Then the energizing member 24 is elastically deformed to press a tip-side bearing 9a toward the worm wheel 4 as to the direction of the bisector.SELECTED DRAWING: Figure 2

Description

  The electric power steering device that is the subject of the present invention is used as a steering device for an automobile. By using an electric motor as an auxiliary power source, it is possible to reduce the force required for the driver to operate the steering wheel. It is intended. The present invention relates to a technique for suppressing the generation of an unpleasant noise called a rattling noise in a worm type reduction gear portion constituting such an electric power steering apparatus.

  Power steering devices are widely used as devices for reducing 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). It is used. 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 configured to be smaller and lighter than the hydraulic power steering device, and can easily control the magnitude (torque) of the auxiliary power and has less power loss of the engine. .

  Various structures of the electric power steering device are known, but in any structure, the steering rotating shaft that is rotated by the operation of the steering wheel and gives a steering angle to the steered wheel as it rotates, Auxiliary power of the electric motor is applied through a speed reducer. In general, a worm type speed reducer is used as the speed reducer. In the case of an electric power steering device using a worm-type speed reducer, a worm that is rotationally driven by the electric motor and a worm wheel that rotates together with the steering rotation shaft are engaged with each other, and auxiliary power of the electric motor is supplied to the worm-type power steering device. It can be transmitted to the rotating shaft for steering.

  For example, Patent Document 1 describes an electric power steering device as shown in FIGS. The electric power steering apparatus is configured to rotatably support a front end portion of a steering shaft 2, which is a steering rotation shaft, which is rotated in a predetermined direction by a steering wheel 1, inside the housing 3. A worm wheel 4 is fixed to the front end. The worm wheel 4 is engaged with the worm teeth 5 provided at the intermediate portion in the axial direction of the worm shaft 6 that is rotationally driven by the electric motor 7. 8, the front end portion is also rotatably supported inside the housing 3 by the front end side bearing 9.

  In a worm type reduction gear formed by meshing the worm wheel 4 and the worm tooth 5, inevitable backlash usually exists at the meshing portion between the worm wheel 4 and the worm tooth 5. This backlash is caused not only by a dimensional error or an assembly error of each member constituting the worm type speed reducer, but also by wear of the tooth surfaces of the worm wheel 4 and the worm tooth 5. In particular, in recent years, since there is a tendency to increase the auxiliary power, the amount of wear increases and backlash is more likely to occur. In any case, when backlash is present in the meshing portion, the meshing portion is uncomfortable when changing the rotation direction of the steering shaft 2 or when rotational vibration is applied to the steering shaft 2 from the wheel side. There is a possibility of rattling noise.

  Therefore, in the case of the illustrated structure, the worm shaft 6 is swung around the base end side bearing 8 in order to eliminate backlash at the meshing portion between the worm wheel 4 and the worm teeth 5. Thus, the worm teeth 5 are urged toward the worm wheel 4.

  For this reason, in the case of the illustrated structure, a holding recess 10 is provided inside the housing 3 around the tip of the worm shaft 6, and the holder 11 is held and fixed inside the holding recess 10. Yes. Further, an outer ring constituting the distal end side bearing 9 is fitted and fixed to the holder 11, and an annular bush 12 made of an elastic material is fitted and fixed to the inner ring constituting the distal end side bearing 9. Then, the portion near the tip of the worm shaft 6 is loosely inserted into the bush 12 so that the portion near the tip of the worm shaft 6 can be rotated with respect to the holder 11 and moved in the distance from the worm wheel 4. I support it. In addition, a preload pad 13 is placed on the inner side of the holding recess 10 adjacent to the axially outer side (right side in FIG. 7) of the holder 11, and the meshing direction between the worm wheel 4 and the worm teeth 5 (FIG. 7). In the vertical direction). At the same time, the tip of the worm shaft 6 is inserted into a through hole provided at the center of the preload pad 13 so as to allow relative rotation with respect to the preload pad 13 without any radial backlash. The tip of the worm shaft 6 is pressed toward the worm wheel 4 through the preload pad 13 by the elastic force of the coil spring 14 spanned between the preload pad 13 and the holder 11. . As a result, the worm shaft 6 is swung about the base end side bearing 8 to urge the worm teeth 5 toward the worm wheel 4, so that the worm teeth 5, the worm wheel 4, The backlash of the meshing portion is suppressed, and the occurrence of rattling noise is suppressed at this meshing portion.

  As described above, in the case of the electric power steering apparatus shown in FIGS. 6 and 7, the preload pad 13 is placed inside the holding recess 10 and the meshing direction of the worm wheel 4 and the worm tooth 5 (see FIG. 7 in order to enable the displacement in the meshing direction to be performed smoothly, the meshing direction between the preload pad 13 and the stationary member existing therearound is provided. In addition, a minute guide gap is provided in each direction perpendicular to the axial direction of the worm shaft 6 (front and back direction in FIG. 7). For this reason, the preload pad 13 can be displaced in the perpendicular direction (front and back direction in FIG. 7) by the amount of the guide gap inside the holding recess 10. Accordingly, the worm teeth 5 can also be displaced in the direction perpendicular to the worm wheel 4.

  On the other hand, the meshing reaction force applied to the worm shaft 6 from the meshing portion of the worm wheel 4 and the worm tooth 5 includes not only the component in the meshing direction (vertical direction in FIG. 7) but also the perpendicular direction (FIG. 7). This point will be described below with reference to FIGS.

As shown in FIGS. 8 and 9, when the driving force is transmitted from the worm shaft 6 to the worm wheel 4 by rotationally driving the worm shaft 6, a meshing reaction force is applied from the worm wheel 4 to the worm shaft 6. Note that the magnitude of the driving force applied to the worm shaft 6 is the same between the case shown in FIG. 8 and the case shown in FIG. 9, but the rotational directions of the driving force are opposite to each other. . Therefore, the worm wheel 4 rotates in the opposite direction between the case shown in FIG. 8 and the case shown in FIG. In such a state, the worm wheel 4 and the worm teeth 5 are engaged with the worm wheel 4 from the worm wheel 4 with respect to the worm shaft 6 in the three directions x, y, and z in FIGS. An apparent meshing reaction force having components of F _x , F _y , and F _z is added. Of these component forces F _x , F _y , F _z , F _x , F _z means that the worm wheel 4 rotates in one direction {direction shown by arrow A in FIG. 8A) as shown in FIG. In the case and the case where the worm wheel 4 rotates in the other direction (the direction indicated by the arrow B in FIG. 9A) as shown in FIG. 9, the directions are opposite to each other.

On the other hand, when the distance between the meshing portion and the swing center o of the worm shaft 6 in the radial direction of the worm shaft 6 is d ₆ , the moment M having a magnitude of d ₆ · F _x is Acts on the shaft 6. Therefore, when the distance between the meshing portion and the swing center o in the axial direction of the worm shaft 6 is L ₆ , a force F _r having a magnitude of M / L ₆ based on the moment M is This acts in the radial direction of the worm shaft 6 (upward in FIG. 8, downward in FIG. 9). This force F _r is in the opposite direction between the case shown in FIG. 8 and the case shown in FIG. For this reason, the magnitude of the actual force F _y ′ acting in the y direction in consideration of the moment M acting on the worm shaft 6 from the worm wheel 4 at the meshing portion is shown in FIG. It becomes small when rotating in one direction (F _y ′ = F _y −F _r ), and becomes large when rotating in the other direction shown in FIG. 9 (F _y ′ = F _y + F _r ). Therefore, the actual resultant force F ′ of the meshing component force in the y and z directions acting on the meshing portion becomes small as shown by the arrow C in FIG. 10 when the worm wheel 4 rotates in one direction, When the worm wheel 4 rotates in the other direction, the worm wheel 4 becomes larger as indicated by an arrow D in the figure. As can be seen from the direction of the resultant force F ′, the meshing reaction force applied to the worm shaft 6 from the meshing portion is the same as that of the worm wheel 4, regardless of which direction the worm wheel 4 rotates. The meshing direction with the worm teeth 5 (vertical direction in FIGS. 8 to 10) and the direction perpendicular to the axial direction of the worm shaft 6 {the front and back directions in FIGS. 8A and 9A, FIG. It can be seen that the components related to B) and FIGS. 9B and 10 in the horizontal direction} are included.

Therefore, in the case of the above-described conventional electric power steering apparatus, when a meshing reaction force is applied from the meshing portion to the worm shaft 6, the meshing reaction force is based on the component in the direction perpendicular to the meshing force (front and back direction in FIG. 7). Thus, the worm tooth 5 is displaced in the direction perpendicular to the worm wheel 4. For this reason, when rotational vibration is applied to the steering shaft 2 from the wheel side, the worm teeth 5 may vibrate in the perpendicular direction at the meshing portion, and an annoying rattling noise may be generated.
In the conventional electric power steering apparatus described above, the worm teeth 5 are urged toward the worm wheel 4, and the direction of this urging is the same as the rotation direction of the worm wheel. No particular consideration is given to the difference in direction and magnitude of the meshing reaction force applied to the worm shaft from the meshing portion due to the difference.

Japanese Patent No. 4381024

  In view of the circumstances as described above, the present invention suppresses the occurrence of rattling noise at the meshing portion between the worm tooth and the worm wheel when the worm wheel rotates in any direction, and the worm tooth and the worm. It was invented to realize a structure that can suppress the occurrence of rattling noise at the meshing portion by suppressing the displacement of the worm tooth with respect to the meshing direction with the wheel and the direction perpendicular to the axial direction of the worm shaft. Is.

The electric power steering apparatus of the present invention includes a housing, a rotating shaft for steering, a worm wheel, a worm shaft, a base end side bearing, a tip end side bearing, an electric motor, and an urging means.
Of these, the steering rotation shaft is rotatably provided with respect to the housing, and is rotated by operation of the steering wheel. As such a rotating shaft for steering, for example, the steering shaft 2, the intermediate shaft 15, and the input shaft (pinion shaft) 17 of the steering gear unit 16 in the structure shown in FIG.
The worm wheel is supported concentrically with the steering rotation shaft inside the housing, and rotates together with the steering rotation shaft.
The worm shaft has a worm tooth at an intermediate portion in the axial direction, and the worm tooth meshes with the worm wheel.
The base end side bearing rotatably supports the base end portion of the worm shaft with respect to the housing.
The tip side bearing supports the tip of the worm shaft rotatably with respect to the housing.
In the electric motor, the distal end portion of the output shaft is engaged with the proximal end portion of the worm shaft so that rotational force can be transmitted.
The urging means swings the worm shaft around the base end portion (for example, the base end side bearing) or the intermediate portion of the worm shaft, so that the worm teeth are moved to the worm wheel. Energize towards.

Particularly, in the case of the electric power steering apparatus according to the present invention, the front end side bearing is externally supported by a front end portion of the outer peripheral surface of the worm shaft with respect to the worm teeth.
The biasing means includes a bearing holder, a support member, and a biasing member.
Of these, the bearing holder is externally fitted to the outer peripheral surface of the distal end side bearing with a gap provided between the outer peripheral surface thereof and the inner peripheral surface of the housing.
The support member is for supporting the urging means with respect to the housing, and is disposed in a portion opposite to the electric motor from the bearing holder with respect to the length direction of the worm shaft. And supported by the housing.
The urging member is in a state where both ends thereof are coupled to the support member and the bearing holder (one end coupled to the support member and the other end coupled to the bearing holder). Of the meshing reaction force applied to the worm shaft from the meshing portion between the worm wheel and the worm teeth when the worm wheel (the steering wheel) rotates in one direction, the worm wheel is in a virtual plane orthogonal to the worm shaft. The vector of the component force (component force F ′ indicated by one of the arrows C and II in FIG. 10) and the meshing reaction force applied to the worm shaft from the meshing portion when rotated in the other direction. Of these, the direction of the bisector of the vector of the component force (component force F ′ indicated by the other arrow of arrow c and arrow 2 in FIG. 10) in a virtual plane orthogonal to the worm axis Regarding The tip bearing is directed toward the worm wheel and biased based on its own elasticity.
In addition, the section modulus of the urging member in the direction of the bisector is smaller than the section modulus in the direction perpendicular to the direction of the bisector and the axial direction of the worm shaft. It has been.

When carrying out the present invention as described above, in addition, as in the invention described in claim 2, the biasing member is in a state where the section modulus in the direction of the bisector is the smallest. Can be placed.
Further, when the present invention as described above is carried out, as in the invention described in claim 3, the biasing member is arranged in the direction of the bisector and the axial direction of the worm shaft. It is also possible to arrange them in a state where the section modulus in the direction perpendicular to each becomes the largest.
Further, when the present invention as described above is carried out, in addition, as in the invention described in claim 4, the worm shaft engages with the worm wheel and the worm teeth from the meshing portion of the worm wheel and the worm teeth. When the tip side bearing or the bearing holder comes into contact with the inner peripheral surface of the housing, further displacement of the tip side bearing can be restricted.

  In the case of the electric power steering apparatus of the present invention configured as described above, the elastic member constituting the biasing means is configured such that when the worm wheel (steering wheel) rotates to one side, the worm wheel and the worm tooth Of the meshing reaction force applied to the worm shaft from the meshing portion, the vector of the component force in a virtual plane orthogonal to the worm shaft and the meshing reaction applied to the worm shaft from the meshing portion when rotated in the other direction. Of the force, with respect to the direction of the bisector with the vector of the component force in a virtual plane perpendicular to the worm axis, the tip side bearing is directed toward the worm wheel and biased based on its own elasticity. Yes. In addition, the elastic member has a smaller section modulus in the direction of the bisector of the elastic member than a section modulus in a direction perpendicular to the direction of the bisector and the axial direction of the worm shaft. It is provided in the state. For this reason, the elastic member can be easily elastically deformed in the direction of the bisector with respect to the reaction force applied to the worm shaft from the meshing portion regardless of the rotation direction of the worm wheel. As a result, the impact force generated in the meshing portion can be relaxed, and the generation of abnormal noise in the portion can be more effectively suppressed.

  Further, in the case of the present invention, the section modulus of the elastic member with respect to the direction of the bisector and the direction perpendicular to the axial direction of the worm shaft is greater than the section modulus with respect to the direction of the bisector. It is getting bigger. For this reason, the elastic member can be made difficult to elastically deform in directions perpendicular to the direction of the bisector and the axial direction of the worm shaft. As a result, at the meshing portion, the worm teeth are prevented from being displaced with respect to the worm wheel in directions perpendicular to the direction of the bisector and the axial direction of the worm shaft, Generation of rattling noise at the meshing portion can be prevented.

The fragmentary sectional view equivalent to the aa section of Drawing 6 showing the 1st example of an embodiment of the invention. The b section enlarged view of FIG. The perspective view which takes out and shows only an urging means. The figure seen from the front side of FIG. 3 which takes out and shows only an urging means. The figure for demonstrating about the arrangement | positioning aspect of the elastic member which comprises a biasing means. The partially cut side view which shows an example of a prior art structure. The aa expanded sectional view of FIG. (A) is a schematic sectional view and (B) is a cc sectional view of (A) for explaining the direction of the meshing reaction force applied from the worm wheel to the worm shaft when the electric motor is rotationally driven in a predetermined direction. (A) is a schematic cross-sectional view and (B) is a d- in (A) for explaining the direction of the meshing reaction force applied from the worm wheel to the worm shaft when the electric motor is rotated in the direction opposite to the predetermined direction. d sectional drawing. The same figure as FIG. 8 (B) which shows the meshing reaction force of the two directions added to a worm shaft from a worm wheel when an electric motor is rotationally driven in both directions.

  An example of an embodiment of the present invention will be described with reference to FIGS. The feature of the electric power steering apparatus of this example is that the structure of the biasing means 21 that biases the tip of the worm shaft 6a toward the worm wheel 4 is devised. Since the structure and operation of the other parts are almost the same as those of the conventional structure shown in FIGS. 6 and 7, the illustration and explanation of the equivalent parts are omitted or simplified. The explanation will be focused on. 7 and FIG. 1 of the present example are different in the mounting direction of the electric motor 7 with respect to the housing 3a. This point is appropriately changed in design according to the automobile to be installed. This has nothing to do with the features of the present invention.

  Also in this example, the worm shaft 6a has worm teeth 5 at the axially intermediate portion, and the worm shaft 6a is engaged at both ends in the axial direction with the worm teeth 5 meshed with the worm wheel 4. The proximal end portion on the side closer to the electric motor 7 out of the portion, the distal end portion on the side farther away from the electric motor 7 by the proximal end bearing 8a which is a ball bearing such as a single row deep groove type or a four-point contact type, The front end bearing 9a, which is a single row deep groove type ball bearing, is rotatably supported by the housing 3a. The base end side bearing 8a supports the worm shaft 6a with respect to the housing 3a so as to be able to be slightly displaced.

  On the other hand, the front end side bearing 9a is externally supported by a small diameter portion 18 provided at the front end portion of the worm shaft 6a. Therefore, in the case of this example, the inner ring 19 constituting the distal end side bearing 9a is externally fixed to the small diameter portion 18 by an interference fit. Further, a holding recess 10a having a cylindrical inner peripheral surface having a larger diameter than the outer peripheral surface of the outer ring 20 constituting the front end side bearing 9a is provided in the peripheral portion of the front end side bearing 9a inside the housing 3a. One end of the holding recess 10a in the axial direction (the left end in FIGS. 1 and 2) is opened to the outside of the housing 3a. The one-end opening of the holding recess 10a is closed by a support member 23 that constitutes an urging means 21 described later.

  Further, an urging means 21 is assembled to the peripheral portion of the distal end side bearing 9a inside the holding recess 10a. The biasing means 21 elastically biases the tip of the worm shaft 6a toward the worm wheel 4 via the tip bearing 9a. As a result, the worm shaft 6a is swung around the base end side bearing 8a to urge the worm teeth 5 toward the worm wheel 4 so that the worm teeth 5 and the worm wheel 4 The backlash of the meshing part is eliminated. Such a biasing means 21 includes a bearing holder 22, a support member 23, and a biasing member 24. 1 and 2, only the bearing holder 22 is shown in cross section for the convenience of explanation with respect to the urging means 21.

  Of these, the bearing holder 22 is made of an elastomer such as metal, synthetic resin, or rubber, and has a bottomed cylindrical shape including a holder cylindrical portion 25 and a holder bottom portion 26. In the holder cylindrical portion 25, the inner diameter of the inner peripheral surface and the outer diameter of the outer peripheral surface do not change over the entire length in the axial direction. The holder bottom portion 26 closes an opening on one end side (left side in FIGS. 1 and 2) of the holder cylindrical portion 25 in the axial direction. Such a bearing holder 22 constitutes the front end side bearing 9a with the holder cylindrical portion 25 in a state where a clearance is provided over the entire circumference between the outer peripheral surface and the inner peripheral surface of the holding recess 10a. The outer ring 20 is assembled in a state of being fitted and fixed to the outer peripheral surface. Such a bearing holder 22 is displaced in a direction in which the worm shaft 6a moves away from the worm wheel 4 on the basis of the meshing reaction force applied to the worm shaft 6a from the meshing portion of the worm wheel 4 and the worm tooth 5. In this case, the outer peripheral surface of the holder cylindrical portion 25 and the inner peripheral surface of the holding recess 10a are in contact with each other, so that further displacement of the worm shaft 6a is restricted. Depending on the shape of the bearing holder 22, when the worm shaft 6a is displaced as described above, the outer peripheral surface of the outer ring 20 constituting the distal end side bearing 9a is directly connected to the inner peripheral surface of the holding recess 10a. It is also possible to configure such that the displacement of the worm shaft 6a beyond that is restricted by contacting.

  The support member 23 is for supporting the biasing means 21 with respect to the housing 3a. Such a support member 23 is made of metal or synthetic resin, and has a bottomed cylindrical shape including a fitting cylinder portion 27 and a bottom portion 28. The fitting cylinder portion 27 has a cylindrical shape in which the inner diameter of the inner peripheral surface and the outer diameter of the outer peripheral surface do not change over the entire length in the axial direction. The bottom portion 28 closes the opening portion on the other axial end side (the right side in FIGS. 1 and 2) of the fitting tube portion 27. Such a support member 23 is assembled in a state where the outer peripheral surface of the fitting tube portion 27 is fitted and fixed to a large-diameter groove 29 formed on the inner peripheral surface of one end portion of the holding concave portion 10a over the entire circumference. ing.

  The urging member 24 is made of an elastomer such as rubber, and includes a long side 30 having a length dimension a, a middle side 31 having a length dimension b, and a short side 32 having a length dimension c. (A> b> c). Such an urging member 24 has one end portion (left end portion in FIGS. 1 to 3) in the axial direction of the worm shaft 6a on the other side surface (right side surface in FIGS. 1 to 3) of the bottom portion 28 of the support member 23. Similarly, the other end portion (the right end portion in FIGS. 1 to 3) is coupled and fixed to one side surface (the left side surface in FIGS. 1 to 3) of the holder bottom portion 26 of the bearing holder 22.

Further, the urging member 24 is configured such that when the worm wheel 4 {steering wheel 1 (see FIG. 6)} is rotated to one side, the worm shaft from the meshing portion between the worm wheel 4 and the worm teeth 5. of meshing reaction force exerted on the 6a, the the vector of the in force component _F'1 to the virtual plane orthogonal to the worm shaft 6a, meshing likewise applied from the engagement portion when rotated in the other to the worm shaft 6a anti Among the forces, the section modulus with respect to the direction of the bisector L _B {see FIG. 5 (a)} between the worm shaft 6 a and the vector of the component force F ′ ₂ in a virtual plane perpendicular to the worm shaft 6 a is the smallest, and direction and is arranged in a state in which the section modulus becomes the largest with respect to perpendicular directions {direction indicated by α in Fig. 5 (b)} with respect to the axial direction of the worm shaft 6a of the bisector force L _B To have. Specifically, the biasing member 24, the in parallel with the bisector L _B, provided as the short sides 32 of the biasing member 24 is located with {see FIG. 5 (b)} the in parallel with the respective perpendicular direction (alpha direction) with respect to the axial direction of direction and the worm shaft 6a of the bisector L _B, as long sides 30 of the biasing member 24 is disposed Provided {see FIG. 5B}.

State biasing means 21 having such a structure described above, based on the elastic force of the biasing member 24, the distal end side bearing 9a, and biased toward the worm wheel 4 with respect to the bisector L _B direction Thus, it is assembled to the housing 3a and the worm shaft 6a (tip bearing 9a). In this example, the urging member is made of an elastomer such as rubber, but it can also be made of metal or synthetic resin. Further, the shape of the biasing member is not limited to the rectangular plate shape of this example.

The component force F ′ ₁ is, for example, as shown in FIG. 5A with respect to a direction {z direction in FIG. 5A) perpendicular to the meshing direction and the axial direction of the worm shaft 6. It exists in the range of 90 ° to 135 ° counterclockwise. On the other hand, the component force F ′ ₂ exists in the range of 0 ° to 45 ° counterclockwise in FIG. 5A with respect to the perpendicular direction {z direction in FIG. 5A, for example]. . When each of the component forces F ′ ₁ and F ′ ₂ are in the above-described range, the biasing member 24 has the long side with respect to the perpendicular direction {z direction in FIG. 5A}. 30 is arranged in a state inclined by 0 ° to 45 ° when the clockwise direction is positive.

In the case of the electric power steering apparatus of this example configured as described above, the elastic member 24 constituting the urging means 21 is used when the worm wheel 4 (the worm wheel 1) is rotated to one side. the said worm wheel 4 of the meshing reaction force exerted on the worm shaft 6a from the meshing portion between the worm teeth 5, a vector of at component force _F'1 in a virtual plane perpendicular to the worm shaft 6a, likewise other from the engagement portion when rotated within the meshing reaction force exerted on the worm shaft 6a, the in component force _F'2 in a virtual plane perpendicular to the worm shaft 6a of the bisector L _B between the vector Regarding the direction, the front end side bearing 9a is directed toward the worm wheel 4 and urged based on its own elasticity. Further, the biasing member 24, the section modulus with respect to the direction of the bisector L _B are disposed in smallest state. Therefore, regardless of the direction of rotation of the worm wheel 4, relative to the reaction force applied to said worm shaft 6a from the engagement portion on the basis of this rotation, the elastic member 24 in the direction of the bisector L _B It can be easily elastically deformed. As a result, the impact force generated in the meshing portion can be relaxed, and the generation of abnormal noise in the portion can be more effectively suppressed.

And in this embodiment, the biasing member 24, the direction and the section modulus for each perpendicular direction (alpha direction) with respect to the axial direction of the worm shaft 6a of the bisector L _B becomes the largest state It is arranged with. For this reason, the elastic member 24 can be hardly elastically deformed in the α direction. As a result, it is possible to prevent the worm teeth 5 from being displaced in the α direction with respect to the worm wheel 4, thereby preventing occurrence of rattling noise at the meshing portion.

When implementing the electric power steering apparatus of the present invention, the material and shape of the urging member constituting the urging means are not limited to the material and shape of the above-described embodiment, and can be employed. For example, a metal or a synthetic resin can be adopted as the material. In addition, the urging member can be configured by stacking a plurality of plate-like members instead of an integral member, or by combining a plurality of bar-like members.
The arrangement of the urging member is not limited to the arrangement of the embodiment described above, and when the worm wheel is rotated to one side, it is applied to the worm shaft from the meshing portion between the worm wheel and the worm teeth. meshing of the reaction force, and a vector of in component force _F'1 an imaginary plane orthogonal to the worm shaft, also among from the engagement portion when rotated in the other meshing reaction force exerted on the worm shaft, the worm section modulus with respect to the direction of the bisector L _B between the vector of at component force _F'2 to a virtual plane orthogonal to the axis, the axial direction of direction and the worm shaft of the bisector L _B Various modes that are smaller than the section modulus with respect to a direction perpendicular to each other are included in the technical scope of the present invention. That is, when carrying out the present invention, as the urging member, at least, the section modulus with respect to the direction of the bisector L _B, with respect to the direction and the axial direction of the worm shaft of the bisector L _B In this case, a shape that can vary the section modulus in the direction perpendicular to each other is adopted.
Further, the present invention can be applied to various structures in which the worm shaft is supported so as to be swingable with respect to the housing with a part of the worm shaft as a fulcrum. That is, the structure of the portion that supports the worm shaft so as to be swingable with respect to the housing is not limited to the structure of the above-described embodiment.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3, 3a Housing 4 Worm wheel 5 Worm tooth | gear 6, 6a Worm shaft 7 Electric motor 8, 8a Base end side bearing 9, 9a Front end side bearing 10, 10a Holding recessed part 11 Holder 12 Bush 13 Preload pad 14 Coil spring 15 Intermediate shaft 16 Steering gear unit 17 Input shaft 18 Small diameter portion 19 Inner ring 20 Outer ring 21 Biasing means 22 Bearing holder 23 Support member 24 Biasing member 25 Holder cylindrical portion 26 Holder bottom portion 27 Fitting cylinder portion 28 Bottom portion 29 Large diameter Groove 30 Long side 31 Middle side 32 Short side

Claims (4)

A housing;
A rotating shaft for steering that is rotatably provided to the housing and is rotated by an operation of a steering wheel;
A worm wheel that is supported concentrically with the steering rotation shaft inside the housing and rotates with the steering rotation shaft;
A worm shaft having a worm tooth in the middle in the axial direction and meshing the worm tooth with the worm wheel;
A base end bearing that rotatably supports the base end of the worm shaft with respect to the housing;
A tip-side bearing that rotatably supports the tip of the worm shaft with respect to the housing;
An electric motor in which the distal end portion of the output shaft is engaged with the proximal end portion of the worm shaft so as to transmit the rotational force;
Biasing means for biasing the worm teeth toward the worm wheel by swinging the worm shaft;
An electric power steering apparatus comprising:
The tip side bearing is externally supported by the tip side part of the outer peripheral surface of the worm shaft with respect to the worm teeth,
The biasing means includes a bearing holder, a support member, and a biasing member,
Of these, the bearing holder is externally fitted to the outer peripheral surface of the front end side bearing with a gap provided between the outer peripheral surface thereof and the inner peripheral surface of the housing.
The support member is for supporting the urging means with respect to the housing, and is disposed in a portion opposite to the electric motor from the bearing holder with respect to the length direction of the worm shaft. , Supported by the housing,
When the worm wheel rotates in one direction with both end portions thereof coupled to the support member and the bearing holder, the urging member moves from the meshing portion of the worm wheel and the worm tooth to the worm shaft. Of the meshing reaction force applied, the worm shaft out of the meshing reaction force applied to the worm shaft from the meshing portion when rotated in the other direction, and the vector of the component force in a virtual plane orthogonal to the worm shaft. With respect to the direction of the bisector with the vector of the component force in a virtual plane orthogonal to the point, the tip side bearing is directed toward the worm wheel and biased based on its own elasticity,
The section modulus of the urging member with respect to the direction of the bisector is smaller than the section modulus with respect to the direction of the bisector and the direction perpendicular to the axial direction of the worm shaft. An electric power steering device characterized by that.   2. The electric power steering apparatus according to claim 1, wherein the biasing member is disposed in a state in which a section modulus with respect to a direction of the bisector is minimized.   The urging member is arranged in a state in which a section modulus with respect to a direction perpendicular to the direction of the bisector and the axial direction of the worm shaft is maximized. The electric power steering apparatus described in any one of the items.   When a meshing reaction force is applied to the worm shaft from the meshing portion of the worm wheel and the worm tooth, the tip side bearing or the bearing holder is brought into contact with the inner peripheral surface of the housing, so that The electric power steering device according to any one of claims 1 to 3, wherein the displacement of the tip side bearing is regulated.

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