JP2008195310A - Electric power steering device - Google Patents

Abstract

To facilitate assembly work, a backlash of a spline engaging portion 19 between a spline shaft portion 14 and a spline hole 13 is secured to some extent, and the rotation direction of an electric motor is converted. To achieve a structure that can suppress the rattling noise that occurs at the moment.
A preload applying member made of an elastic material is installed between an inner peripheral surface of the spline hole and an outer peripheral surface of the spline shaft portion. The preload applying member 20 includes an annular base portion 21 fitted and supported in a locking groove 23 formed on the outer peripheral surface of the spline shaft portion 14, and a tongue piece 22 protruding in the axial direction from the base portion 21. 22. These tongue pieces 22 are sandwiched between the circumferential side surface of the female spline teeth 17 and the circumferential side surface of the male spline teeth 18 in an elastically compressed state.
[Selection] Figure 2

Description

  The electric power steering apparatus according to the present invention is used as a steering apparatus for an automobile, and uses an electric motor as auxiliary power to reduce the force required for the driver to operate the steering wheel. is there. The present invention suppresses the generation of unpleasant noise called rattling noise at the spline engaging portion between the output shaft of the electric motor and the worm shaft of the speed reducer constituting such an electric power steering apparatus. It was invented with the intention of realizing such a structure.

  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.

  Various structures of the electric power steering apparatus are known. In any structure, the electric motor is attached to the rotating shaft that is rotated by the operation of the steering wheel and gives a steering angle to the steered wheel as the wheel rotates. Auxiliary power is applied through a speed reducer. In general, a worm reducer is used as the reducer. In the case of an electric power steering device using a worm speed reducer, a worm that is rotationally driven by the electric motor and a worm wheel that rotates together with the rotating shaft are engaged with each other, and auxiliary power of the electric motor is applied to the rotating shaft. Communicate freely. However, in the case of a worm reducer, if no measures are taken, it is called a rattling sound when changing the rotation direction of the rotating shaft based on the backlash existing in the meshing portion of the worm and the worm wheel. Unpleasant noise may occur.

  Conventionally, as described in Patent Documents 1 to 3, it is considered that the worm is elastically pressed toward the worm wheel by an elastic member such as a spring as a structure that can suppress the generation of such rattling noise. ing. 8 to 9 show an example of the electric power steering apparatus described in Patent Document 2 among them. A front end portion of a steering shaft 2 that is a rotating shaft that is rotated in a predetermined direction by the steering wheel 1 is rotatably supported inside the housing 3, and the worm wheel 4 is fixed to this portion. The worm teeth 5 that mesh with the worm wheel 4 are provided in the axially intermediate portion of the worm shaft 6, and both ends of the worm 8 that is rotationally driven by the electric motor 7 have a pair of rolling bearings 9 a such as a deep groove ball bearing, 9b is rotatably supported in the housing 3. Further, a pressing piece 10 is externally fitted to a portion protruding from the rolling bearing 9 a at the tip of the worm shaft 6, and an elastic member such as a coil spring 11 is provided between the pressing piece 10 and the housing 3. Yes. The coil spring 11 presses the worm teeth 6 toward the worm wheel 4 through the pressing piece 10. With such a configuration, backlash between the worm teeth 6 and the worm wheel 4 is suppressed, and generation of the rattling noise is suppressed.

  In the case of the conventional structure as described above, it is possible to suppress the occurrence of the rattling noise at the meshing portion between the worm tooth 5 and the worm wheel 4, but the tip of the output shaft 12 of the electric motor 7 and the worm The rattling noise generated at the joint with the base end of the shaft 6 cannot be suppressed. This point will be described below. A spline hole 13 is formed in the base end portion of the worm shaft 6 so that the tip end portion of the output shaft 12 of the electric motor 7 and the base end portion of the worm shaft 6 can be freely transmitted. It forms in the state opened to the base end surface of the axis | shaft 6. FIG. A spline shaft portion 14 is formed at the tip of the output shaft 12. The spline shaft portion 14 and the spline hole 13 are spline-engaged so that the output shaft 12 and the worm shaft 6 are freely coupled to transmit rotational force. The “spline” in the present specification and claims includes what is called “serration” with a fine pitch.

  If the spline shaft portion 14 and the spline hole 13 are in spline engagement with no circumferential clearance (without backlash), the distal end portion of the output shaft 12 and the proximal end portion of the worm shaft 6 No rattling noise is generated at the coupling part (spline engaging part). However, in the actual case, a backlash exists in the spline engaging portion. The backlash of the spline engaging portion is necessary so that the work of spline engaging the spline shaft portion 14 and the spline hole 13 can be easily performed. Further, as long as the center axis of the output shaft 12 and the center axis of the worm shaft 6 are slightly deviated from each other, it is necessary to rotate the output shaft 12 so that the spline engaging portion is not distorted. The backlash is also necessary to prevent the torque from increasing.

  However, when there is backlash in the spline engaging portion, at the moment when the rotation direction of the electric motor 7 is changed, the circumferential side surface of the male spline teeth provided on the outer peripheral surface of the spline shaft portion 14; The circumferential side surface of the female spline tooth provided on the inner peripheral surface of the spline hole 13 collides with vigor, and the rattling noise is generated. Such a rattling noise becomes more prominent as the backlash becomes larger. Conventionally, the backlash has been reduced to the extent that the spline engaging portion can be assembled. However, if this backlash is reduced, it becomes difficult to insert the spline shaft portion 14 into the spline hole 13 accordingly, the assembling workability is lowered, and the manufacturing cost of the electric power steering apparatus is increased. Further, unless the assembly accuracy between the output shaft 12 and the worm shaft 6 is increased, the problem of the torque increase due to the galling is likely to occur, which also increases the manufacturing cost of the electric power steering apparatus. On the other hand, in Patent Document 4, an elastic body such as an O-ring is provided between the outer peripheral surface of the spline shaft portion and the inner peripheral surface of the spline hole so that the spline tooth tip and the tooth bottom collide with force. The invention to prevent is described. However, the structure of the invention described in Patent Document 4 cannot suppress the rattling noise that occurs at the moment when the rotation direction of the electric motor is changed as described above.

JP 2000-43739 A JP 2004-306898 A JP-T-2006-513906 JP 2004-122852 A

  In view of the circumstances as described above, the present invention ensures a certain amount of backlash of the spline engaging portion between the spline shaft portion and the spline hole so that the assembling work can be easily performed. The present invention has been invented to realize an electric power steering apparatus that can suppress rattling noise generated at the moment when the rotation direction of the motor is changed.

The electric power steering apparatus according to the present invention includes a housing, a rotating shaft, a worm wheel, a worm, and an electric motor, similarly to the above-described conventionally known electric power steering apparatus.
Of these, the housing is supported by a fixed part such as a vehicle body and does not rotate during steering.
The rotating shaft is rotatably provided with respect to the housing, and is rotated by an operation of a steering wheel, and gives a steering angle to the steered wheels as it rotates. As such a rotation shaft, any shaft that moves in synchronization with the steering wheel and the steering wheel can be employed. For example, the steering shaft 2 or the intermediate shaft 15 in the structure shown in FIG. 8 and the input shaft (pinion shaft) of the steering gear 16 can be employed.
Further, the worm wheel is concentric with a part of the rotating shaft inside the housing, concentric with the rotating shaft (a state in which relative rotation is prevented by an external fitting fixing by an interference fit, a key engagement, a spline engagement, etc. Supported) and rotate with this axis of rotation.
The worm is provided with worm teeth at an intermediate portion in the axial direction of the worm shaft. Then, in a state where the worm teeth are engaged with the worm wheel, both end portions in the axial direction of the worm shaft are rotatably supported with respect to the housing by bearings.
Further, the electric motor is configured such that the worm shaft can be driven to rotate in both directions by engaging the proximal end portion of the worm shaft and the distal end portion of the output shaft so as to be able to freely transmit the rotational force.
And the spline shaft formed in the tip end part of the spline hole which formed the output shaft of the electric motor, and the worm shaft in the state where it opened to the base end face of this worm shaft in the base end part of this worm shaft The transmission of rotational force is freely coupled by spline engagement with the part.

In particular, the electric power steering apparatus of the present invention includes a preload applying member made of an elastic material. The preload applying member is made of an elastic material, and is sandwiched between the inner peripheral surface of the spline hole and the outer peripheral surface of the spline shaft, and in the circumferential direction of the spline engaging portion between the spline hole and the spline shaft. Reduce rattling.
The preload imparting member includes a base and at least one tongue piece.
Of these, the base is annular, and is formed over the entire circumference of the circumferential surface at the axially intermediate portion of at least one of the outer circumferential surface of the spline shaft portion and the inner circumferential surface of the spline hole. It is fitted and supported in the formed locking groove.
The tongue piece protrudes in the axial direction from at least one axial side surface of the base, and the circumferential side surface of at least one female spline tooth existing on the inner circumferential surface of the spline hole and the spline shaft. It is clamped in an elastically compressed state between the circumferential side surfaces of at least one male spline tooth existing on the outer peripheral surface.

According to the electric power steering apparatus of the present invention having the above-described configuration, a certain amount of backlash of the spline engaging portion between the spline shaft portion and the spline hole is secured, and the rotation direction of the electric motor is converted. The rattling noise that occurs at the moment of being played is suppressed.
For this reason, securing the backlash to some extent facilitates the insertion of the spline shaft portion into the spline hole, improves the assembly workability, and suppresses the manufacturing cost of the electric power steering apparatus. In addition, since the problem of torque increase due to twisting is less likely to occur without increasing the assembly accuracy of the output shaft provided with the spline shaft portion and the worm shaft provided with the spline hole, the electric power steering is also used. The manufacturing cost of the apparatus can be suppressed.

  1 to 7 show an example of an embodiment of the present invention. The electric power steering device of this example is characterized by a spline shaft portion 14 provided at the distal end portion (left end portion in FIG. 1) of the output shaft 12 of the electric motor 7 and a proximal end portion (FIG. 1). In the structure of the connecting portion with the spline hole 13 provided in the right end portion of the head. In addition, since the structure and operation of the entire electric power steering apparatus are the same as those of the conventional structure described in the above-mentioned Patent Document 2, illustrations and explanations relating to parts equivalent to the conventional structure are omitted or simplified. Hereinafter, the characteristic part of this example will be mainly described. 8 to 9 and FIG. 1 are different in the mounting direction of the electric motor 7 with respect to the housing 3, but this point is appropriately changed in design according to the automobile to be installed. It has nothing to do with the features of the invention.

  The spline hole 13 is formed concentrically with the worm shaft 6 in a state where the spline hole 13 is opened at the base end surface of the worm shaft 6. Further, the spline shaft portion 14 is formed concentrically with the output shaft 12 at the distal end portion of the output shaft 12. The spline shaft portion 14 and the spline hole 13 are spline-engaged so that the output shaft 12 and the worm shaft 6 are freely coupled to transmit rotational force. The pitch circle diameter of the female spline teeth 17 and 17 formed on the inner peripheral surface of the spline hole 13 is slightly larger than the pitch circle diameter of the male spline teeth 18 and 18 formed on the outer peripheral surface of the spline shaft portion 14. Thus, the spline shaft portion 14 can be loosely inserted into the spline hole 13. Therefore, the spline engaging portion 19 between the spline shaft portion 14 and the spline hole 13 has a tip end portion (see FIG. 5) of the spline shaft portion 14 in order to eliminate backlash of the meshing portion between the worm tooth 5 and the worm wheel 4. There is sufficient backlash to displace the left end of 1) towards the worm wheel 4. In other words, there is no inconvenience such as galling in the spline engaging portion 19 when the backlash of the meshing portion between the worm tooth 5 and the worm wheel 4 is eliminated.

  As described above, the preload applying member 20 made of an elastic material is provided between the inner peripheral surface of the spline hole 13 and the outer peripheral surface of the spline shaft portion 14 which are loosely spline-engaged. The preload applying member 20 is made of an elastic material such as an elastomer such as rubber, and has a base 21 and at least one tongue piece 22, 22 (in the example shown, the same number as the female and male spline teeth 17, 18). With. Further, in order to make it possible to assemble such a preload applying member 20, a locking groove 23 is formed over the entire circumference in the axially intermediate portion of the outer peripheral surface of the spline shaft portion 14. The groove bottom diameter of the locking groove 23 is smaller than the groove bottom diameter of the spline shaft portion 14 (groove bottom diameter of the male spline teeth 18, 18).

  Among the preload imparting members 20, the base 21 is a rectangle having a cross-sectional shape having a larger axial width dimension (rounded corners) than a radial thickness dimension, and the whole is annular. Such a base portion 21 is supported and fixed to the intermediate portion in the axial direction of the spline shaft portion 14 by fitting and supporting the locking recess groove 23. In addition, each of the tongue pieces 22, 22 is formed in a state where both end portions in the length direction are integrally coupled to the outer diameter side end portion of the base portion 21 at the intermediate portion in the length direction. Is protruded in the axial direction from both side surfaces of the base portion 21 in the axial direction. In the case of this example, the tongue pieces 22, 22 are formed in the same number as the spline teeth 17, 18 at the same pitch as the female spline teeth 17, 17 and the male spline teeth 18, 18. is doing. Further, the tongue pieces 22 and 22 are inclined with respect to the base portion 21 in accordance with the portions of the spline teeth 17 and 18 in the circumferential direction where the tongue pieces 22 and 22 are to be sandwiched. ing.

The longitudinal ends of the tongue pieces 22 and 22 are connected to the circumferential side surfaces of the female spline teeth 17 and 17 as the spline hole 13 and the spline shaft portion 14 are spline-engaged. These are held in an elastically compressed state between the male spline teeth 18, 18 and the side surfaces in the circumferential direction. This operation is performed by pushing the spline shaft portion 14 that has been fitted and supported in advance with the preload applying member 20 into the spline hole 13 while elastically reducing the thickness of the tongue pieces 22 and 22. In the case of this example, in order to facilitate this pushing operation, the lengthwise ends of the tongue pieces 22 and 22 are inclined so that the thickness dimension becomes smaller toward the edge. It has a wedge shape. Preferably, a solid lubricant such as PTFE or MoS ₂ or a lubricant such as grease is applied or coated on at least the surfaces of the tongue pieces 22 and 22 (in practice, the entire surface of the preload applying member 20). Keep it.

  In any case, when the spline hole 13 and the spline shaft portion 14 are spline-engaged via the tongue pieces 22 and 22, the circumferential splines of the female spline teeth 17 and 17 are provided. Between the side surface and one circumferential side surface of each male spline tooth 18, 18, each tongue piece 22, 22 is elastic between one circumferential direction side surface of each spline tooth 17, 18. Exists in a compressed state. On the other hand, the other circumferential side surface of each female spline tooth 17, 17 and the other circumferential side surface of each male spline tooth 18, 18 are elastic based on the elasticity of each tongue piece 22, 22. Will be in contact with each other.

  Therefore, as described above, the spline engagement portion 19 has a circumferential backlash in spite of the presence of sufficient backlash in the spline engagement portion 19 between the spline shaft portion 14 and the spline hole 13. You can suppress the date. And the rattling sound produced at the moment when the rotation direction of the electric motor 7 is converted can be suppressed. For this reason, the assembly workability is improved and the manufacturing cost of the electric power steering apparatus can be suppressed. Further, even if the assembly accuracy (concentricity) between the output shaft 12 of the electric motor 7 provided with the spline shaft portion 14 and the worm shaft 6 provided with the spline hole 13 is not increased, the torque caused by the twisting Since the problem of the rise is less likely to occur, the manufacturing cost of the electric power steering apparatus can be reduced.

  In the illustrated example, the case where only one preload applying member 20 is provided on the outer peripheral surface side of the spline shaft portion 14 is shown. On the other hand, the preload member can be provided on the inner peripheral surface side of the spline hole. Furthermore, a plurality of preload imparting members can be provided at a plurality of locations separated in the axial direction. In this case, one of the preload applying members can be provided on the outer peripheral surface side of the spline shaft, and the other preload applying member can be provided on the inner peripheral surface side of the spline hole.

The figure equivalent to the AA cross section of FIG. 8 which shows an example of embodiment of this invention. The B section enlarged view of FIG. 1 which abbreviate | omits and shows a part. CC sectional drawing of FIG. 2 which abbreviate | omits and shows a part. The D section enlarged view of FIG. The figure which took out the front-end | tip application member and the front-end | tip part of an output shaft, and was seen from the same direction as FIG. EE sectional drawing of FIG. The partial expansion perspective view of a preload provision member. The partially cut side view which shows an example of a conventional structure. The expanded AA sectional view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Housing 4 Worm wheel 5 Worm tooth 6 Worm shaft 7 Electric motor 8 Worm 9a, 9b Rolling bearing 10 Pressing drive 11 Coil spring 12 Output shaft 13 Spline hole 14 Spline shaft part 15 Intermediate shaft 16 Steering gear 17 Female spline teeth 18 Male spline teeth 19 Spline engaging portion 20 Preloading member 21 Base portion 22 Tongue piece 23 Locking groove

Claims (1)

  A housing that is supported by a fixed portion and does not rotate; a rotating shaft 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 rotary shaft inside the housing and rotates together with the rotary shaft, and a worm tooth is provided at an axially intermediate portion of the worm shaft. In a state where the worm teeth are engaged with the worm wheel, the worm shaft is rotatably supported at both ends in the axial direction with respect to the housing by a bearing, and an electric motor for rotationally driving the worm. The output shaft of the electric motor and the worm shaft are formed in the base end portion of the worm shaft so as to open to the base end surface of the worm shaft. In the electric power steering apparatus in which transmission of rotational force is freely coupled by spline engagement between the spline hole and the spline shaft portion formed at the tip end portion of the output shaft, A preload imparting member made of an elastic material, which is sandwiched between the peripheral surface and the outer peripheral surface of the spline shaft and suppresses rattling in the circumferential direction of the spline engagement portion between the spline hole and the spline shaft, The preload imparting member is a latch formed over the entire circumference of the peripheral surface at an axially intermediate portion of at least one of the outer peripheral surface of the spline shaft portion and the inner peripheral surface of the spline hole. An annular base portion fitted and supported in the concave groove, and a circumferential direction of at least one female spline tooth projecting axially from at least one axial side surface of the base portion and existing on the inner peripheral surface of the spline hole Side and And at least one tongue piece that is sandwiched in an elastically compressed state between at least one male spline tooth circumferential side surface existing on the outer peripheral surface of the spline shaft This is an electric power steering device.

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