JP2010095006A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a structure without generating an unpleasant abnormal sound and vibration, without changing steering force by the rotational direction of a steering wheel, by setting a meshing state of a worm tooth and a worm wheel substantially constant regardless of the transmission direction of motive power. <P>SOLUTION: An elastic holding member 21 is arranged between an outer peripheral surface of an outer ring 20 and an inner peripheral surface of a holding cylindrical part 24 for constituting a rolling bearing 8a for supporting a cip part of a worm shaft 7a. This elastic holding member 21 includes a semicylindrical part 22 and a pair of elastic arm parts extending to the worm wheel 4 side from both end parts in the circumferential direction of this semicylindrical part 22. An opposite side half part of the worm wheel 4 of the outer ring 20 is held by the semicylindrical part 22, and a chip part of both elastic arm parts is elastically allowed to abut on the inner peripheral surface of the holding cylindrical part 24. With this constitution, the chip part of the worm shaft 7a is less likely to be displaced in the axial direction of a worm wheel 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 can suppress the generation of an unpleasant noise called a rattling noise in the worm type reduction gear portion constituting such an electric power steering apparatus, and can improve the operational feeling of the steering wheel. Invented with the intention of realizing the 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. 7 to 10 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. Both ends of the worm shaft 7 that meshes with the worm wheel 4 and is rotationally driven by the electric motor 5 are provided at the intermediate portion in the axial direction by a pair of rolling bearings 8a and 8b such as deep groove ball bearings. The housing 3 is rotatably supported. Further, a pressing piece 9 is externally fitted to a portion protruding from the rolling bearing 8 a at the tip of the worm shaft 7, and a coil spring 10 as an elastic member is provided between the pressing piece 9 and the housing 3. ing. Specifically, a holder 11 for holding the rolling bearing 8 a is fitted and fixed in the housing 3, and a pair of locking portions 12, 12 protruding from the side surface of the holder 11 are connected to the coil. The bent portions 13 and 13 provided at both ends of the spring 10 are locked. The coil spring 10 presses the worm teeth 6 toward the worm wheel 4 through the pressing piece 9. 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.

  However, in the case of the conventional structure described in Patent Document 2 as described above, the direction in which the tip of the worm shaft 7 moves toward and away from the worm wheel 4 inside the housing 3 (FIGS. 8 to 10). The worm wheel 4 is supported not only in the vertical direction but also in the axial direction of the worm wheel 4 (front and back directions in FIGS. 8 to 9 and left and right direction in FIG. 10). That is, in the case of the conventional structure, as shown at the right end of FIG. 9, the tip of the worm shaft 7 is supported in order to support the tip of the worm shaft 7 so that the worm wheel 4 can move in the distance direction. A bush 14 made of an elastic material is externally fitted to the housing 3, and the bush 14 is rotatably supported with respect to the housing 3 by the rolling bearing 8a. When the backlash is suppressed, the bush 14 is elastically deformed. In the case of such a conventional structure, the tip portion of the worm shaft 7 needs to be displaced in order to eliminate the backlash. It is possible to displace in the axial direction as well. Based on this axial displacement, the meshing state between the worm teeth 6 and the worm wheel 4 becomes inappropriate, or the rattling noise is generated at the meshing portion between the worm teeth 6 and the worm wheel 4. Such an unpleasant noise or vibration may occur.

  For example, in a state where the central axis of the worm shaft 7 exists on a virtual plane (on the surface shown in FIGS. 8 to 9) orthogonal to the central axis of the worm wheel 4, the worm wheel 4 and the worm When the meshing state with the teeth 6 is appropriate, the meshing state becomes inappropriate when the tip of the worm shaft 7 is displaced in the axial direction of the worm wheel 4 by the elastic deformation of the bush 14. The displacement of this elastic deformation is slight, and the degree to which the meshing state becomes inappropriate is slight. However, the frictional loss at the meshing portion between the worm wheel 4 and the worm tooth 6 is caused by improperness. growing. As the friction loss increases, the magnitude (torque) of auxiliary power applied from the electric motor 5 to the steering shaft 2 changes (reduces). Further, the degree of change becomes more significant as the degree of inappropriateness of the meshing state increases.

  On the other hand, the force that displaces the tip of the worm shaft 7 in the axial direction of the worm wheel 4 is applied as a reaction force accompanying the transmission of the auxiliary power from the meshing portion. Therefore, the direction in which the tip of the worm shaft 7 is displaced in the axial direction is reversed when the transmission direction of the auxiliary power, that is, the rotation direction of the steering shaft 2 is reversed. If the magnitude of the power loss when the steering shaft 2 rotates in a predetermined direction is different from the magnitude of the power loss when the steering shaft 2 rotates in the opposite direction, the force required to operate the steering wheel 1 ( There is a possibility that different states may occur depending on the rotation direction of the steering wheel 1. Such a state is not preferable because it gives an uncomfortable feeling to the driver who operates the steering wheel 1.

  Further, when the transmission of auxiliary power or the reverse rotation of the steering shaft 2 is suddenly performed, and the tip of the worm shaft 7 is suddenly displaced in the axial direction of the worm wheel 4, the teeth Unpleasant noises and vibrations such as beating sounds occur. Patent Documents 1 and 3 describe an electric power steering device having a structure different from that shown in FIGS. 8 to 9, but the above-described problem occurs in the same manner.

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

  In view of the circumstances as described above, the present invention can make the meshing state of the worm teeth and the worm wheel constant regardless of the transmission direction of the power, and the steering force that the driver needs to apply to the steering wheel is The present invention has been invented to realize an electric power steering device that does not change depending on the rotation direction of the steering wheel and does not generate unpleasant noises and vibrations such as rattling noises.

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 in accordance with the rotation. As such a rotating shaft, for example, the steering shaft 2 or the intermediate shaft 15 having the structure shown in FIG. 7 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.
The worm teeth are pressed toward the worm wheel by an elastic member provided between the tip of the worm shaft and the inner surface of the housing.

In particular, in the electric power steering device of the present invention, between the outer peripheral surface of the tip side bearing for rotatably supporting the tip of the worm shaft relative to the housing, and the inner surface of the housing, An elastic holding member is provided.
The elastic holding member is made of an elastic plate, and includes a semi-cylindrical portion and a pair of elastic arm portions extending from both circumferential ends of the semi-cylindrical portion toward the worm wheel.
In such an elastic holding member, the semi-cylindrical part holds the half part opposite to the worm wheel in the outer peripheral surface of the tip side bearing, and the tip parts of the both elastic arm parts are attached to the inner surface of the housing. It is provided between the two peripheral surfaces in a state of elastic contact.

When implementing the electric power steering apparatus of the present invention as described above, for example, as described in claim 2, the tip side bearing is provided on the inner ring raceway provided on the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring. A radial ball bearing provided with a plurality of balls between the provided outer ring raceway.
Moreover, let the part which installed the said front end side bearing among the said housing be a holding | maintenance cylindrical part which has a cylindrical internal peripheral surface.
And the abutting part formed by holding the half part opposite to the worm wheel in the outer peripheral surface of the outer ring by the semi-cylindrical part and bending the tip part of the pair of elastic arm parts toward each other Is brought into contact with the inner peripheral surface of the holding cylindrical portion.

Further, when the electric power steering device of the present invention as described above is implemented, preferably, as described in claim 3, the axial direction of the worm shaft is within the both end edges of the semi-cylindrical portion. A retaining tongue piece bent inward in the radial direction is formed at one or a plurality of positions on the edge opposite to the worm tooth. In addition, guide tongue pieces that are bent by less than 90 degrees radially outward are formed at a plurality of positions on the worm tooth side edge among the both end edges.
The type of the elastic plate constituting the elastic holding member is not particularly limited, such as stainless spring steel, galvanized spring steel, etc. Preferably, as described in claim 4, the elastic holding member is made of copper. Or made of a copper-based alloy such as phosphor bronze.

  According to the present invention having the above-described configuration, the meshing state of the worm teeth and the worm wheel constituting the worm type reduction gear for transmitting the rotational force of the electric motor to the rotation shaft such as the steering shaft is determined by the power. It can be made constant or almost constant regardless of the transmission direction. In addition, it is possible to realize an electric power steering apparatus in which the steering force that the driver needs to apply to the steering wheel hardly or hardly changes depending on the rotation direction of the steering wheel. In addition, when the transmission of auxiliary power is started or the rotation direction of the steering shaft is reversed suddenly, the tip of the worm shaft tends to be suddenly displaced in the axial direction of the worm wheel. Such an unpleasant noise and vibration can be prevented.

  That is, in the case of the electric power steering apparatus of the present invention, the front end side bearing that supports the front end portion of the worm shaft is held by the semi-cylindrical portion of the elastic holding member. Further, in order for the semi-cylindrical portion to be displaced in the axial direction of the worm wheel, the elasticity of the elastic arm portion existing in the direction to be displaced among the pair of elastic arm portions constituting the elastic holding member. You must overcome it. Therefore, the front end bearing can be easily displaced on a virtual plane orthogonal to the central axis of the worm wheel, but a relatively large resistance is applied to displacement in the axial direction of the worm wheel. Of course, the same applies to the tip of the worm shaft supported by the tip bearing. The magnitude of the resistance can be adjusted based on the elasticity of the elastic plate constituting the elastic holding member, and if this elasticity is increased, the tip of the worm shaft is hardly displaced in the axial direction of the worm wheel. I can do it. For this reason, as described above, the meshing state can be made constant regardless of the transmission direction of the power by increasing the elasticity of the elastic plate within a range in which the work of incorporating the elastic holding member into the housing is not troublesome. Thus, the steering force can be prevented from changing depending on the rotation direction of the steering wheel. At the same time, it is possible to prevent the abnormal noise and vibration from occurring.

According to a third aspect of the present invention, when a retaining tongue piece or a guide tongue piece is provided on the semi-cylindrical portion of the elastic holding member, the work for assembling the tip end bearing on the inner diameter side of the elastic holding member In addition, it is possible to prevent the elastic holding member from falling out of a predetermined position after the elastic holding member and the front end side bearing are assembled in the housing.
Furthermore, as described in claim 4, if the elastic holding member is made of a copper-based alloy such as phosphor bronze which is softer than spring steel or the like, the elastic holding member can be easily processed. It is possible to prevent abnormal noise and vibration from occurring due to the collision between the elastic holding member and the counterpart member (housing and front end side bearing).

  1 to 6 show an example of an embodiment of the present invention corresponding to all claims. The electric power steering device of this example is characterized by the worm teeth 6a constituting the worm speed reducer 17 for transmitting the rotational force of the electric motor 5 to a rotating shaft such as the steering shaft 2 (see FIG. 7). The structure that can eliminate the backlash of the meshing portion with the worm wheel 4, and the meshing state of the meshing portion is made constant regardless of the transmission direction of the power in the worm speed reducer 17 portion. The structure can more effectively prevent the generation of abnormal noise and noise. 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.

  The worm 18 is formed by providing the worm teeth 6a at the intermediate portion in the axial direction of the worm shaft 7a. Then, in a state where the worm teeth 6a are engaged with the worm wheel 4, both ends in the axial direction of the worm shaft 7a are paired with a pair of rolling bearings 8a and 8b (base bearings), each of which is a single row deep groove type ball bearing. The rolling bearing 8b on the end side is rotatably supported with respect to the housing 3a by referring to FIGS. Of these two rolling bearings 8a and 8b, the rolling bearing 8b on the base end side has the worm shaft 7a slightly connected to the housing 3a in the same manner as the conventional structure described in Patent Documents 1 to 3 described above. Supports oscillating displacement. Since the angle of this oscillating displacement is small, it can be easily absorbed by the low moment rigidity of the single row deep groove ball bearing. Since this point is the same as in the case of the conventional structure, illustration and detailed description are omitted.

  On the other hand, the rolling bearing 8a that supports the tip of the worm shaft 7a is rotated and slightly moved in the housing 3a with respect to the worm wheel 4 (see FIGS. 1-2). (Displacement in the vertical direction) is possible, however, the worm wheel 4 is supported in a state in which the displacement in the axial direction (front and back direction in FIG. 1, left and right direction in FIGS. 2 and 4) is limited. For this purpose, the inner ring 19 of the rolling bearing 8a is externally fixed to the tip of the worm shaft 7a by an interference fit, and the outer ring 20 is held by the semi-cylindrical portion 22 of the elastic holding member 21.

  The elastic holding member 21 is formed by bending an elastic plate such as a phosphor bronze plate. Of the semi-cylindrical portion 22 and both circumferential edges of the semi-cylindrical portion 22, the worm A pair of elastic arm portions 23, 23 extending from the half portion on the tooth 6 a side to the worm wheel 4 side is provided. The inner diameter of the semi-cylindrical portion 22 in the free state is the same as or slightly smaller than the outer diameter of the outer ring 20. The outer diameter of the semi-cylindrical portion 22 in the free state is such that the small-diameter portion 36 of the holding cylindrical portion 24 provided in a part of the housing 3a in order to rotatably support the tip portion of the worm shaft 7a. It is the same as or slightly larger than the inner diameter. The elastic arm portions 23 and 23 are substantially parallel to each other in the assembled state in the holding cylindrical portion 24, and abut each other by bending each tip portion slightly (less than 90 degrees) in a direction approaching each other. Portions 25 and 25 are formed. In the example shown in the drawing, both the abutting portions 25 and 25 each have a convex arc shape. In addition, with respect to the axial direction of the worm shaft 7a, the two ends of the semi-cylindrical portion 22 are perpendicular to the radially inward at a plurality of locations (three locations in the illustrated example) opposite to the worm teeth 6a. The tongue pieces 26, 26 for retaining are bent. Further, the guide tongue pieces 27, 27 bent slightly outward (less than 90 degrees) radially outwardly at a plurality of locations (three locations in the illustrated example) on the worm teeth 6a side among the both end edges. Is forming.

  As shown in FIGS. 1 and 2, the elastic holding member 21 having such a shape includes an outer peripheral surface of the outer ring 20 and an inner peripheral surface of the holding cylindrical portion 24 that constitute the rolling bearing 8 a that is a front end side bearing. Assemble between. That is, the semi-cylindrical portion 22 constituting the elastic holding member 21 holds the half portion on the opposite side to the worm wheel 4 in the outer peripheral surface of the outer ring 20. First, the outer ring 20 constituting the rolling bearing 8a is attached to the semi-cylindrical portion 22 from the side where the guide tongue pieces 27, 27 are provided, and the axial end face of the outer ring 20 and the above-mentioned retaining members. This is done by pushing the tongues 26, 26 until they abut against the inner surface. In a state after the pushing-in is completed, the both elastic arm portions 23, 23 project from the outer peripheral surface of the outer ring 20 radially outward, so that both the elastic arm portions 23, 23 are connected to the outer ring 20. The elastic holding member 21 is pushed into the large diameter portion 37 of the holding cylindrical portion 24 while being elastically deformed in a direction approaching the outer peripheral surface of the holding cylindrical portion 24. In the pushed state, the both abutting portions 25, 25 provided at the distal end portions of the both elastic arm portions 23, 23 are elastically applied to the inner peripheral surface of the large-diameter portion 37 of the holding cylindrical portion 24. Make contact. The semi-cylindrical portion 22 of the elastic holding member 21 is loosely fitted into the small diameter portion 36 of the holding cylindrical portion 24.

  As described above, the outer ring 20 approaches the worm wheel 4 in the state where the elastic holding member 21 and the rolling bearing 8a are assembled in the holding cylindrical portion 24 as shown in FIGS. Can be displaced relatively easily (below -2), but is less likely to be displaced in the axial direction of the worm wheel 4 (the front-back direction in FIG. 1, the left-right direction in FIG. 2). That is, in order to displace the worm wheel 4 in the axial direction, it is necessary to elastically deform the elastic arm portion 23 existing on the side of the elastic arm portions 23, 23 to be displaced. Accordingly, the tip portion of the worm shaft 7a that is rotatably supported by the rolling bearing 8a can also be displaced relatively easily in the direction approaching the worm wheel 4, but in the axial direction of the worm wheel 4, It becomes difficult to displace.

  As described above, the rolling is performed at the tip of the worm shaft 7a that is supported inside the holding cylindrical portion 24 so as to be rotatable and displaceable in a predetermined direction (direction approaching the worm wheel 4). A pressing sleeve 28 and a coil spring 10a, which is an elastic member, are provided between the outer peripheral surface of the portion protruding from the inner ring 19 constituting the bearing 8a and the inner peripheral surface of the rear portion of the holding cylindrical portion 24. Of these, the pressing sleeve 28 is formed by injection molding a synthetic resin such as polyamide, polyphenylene sulfide, polyacetal, etc., and includes a disk part 29 and a central cylindrical part 30 provided at the center part of the disk part 29, A pair of receiving portions 31, 31 provided at two positions on the opposite side in the radial direction around the central cylindrical portion 30 and a central hole 32 are provided. The center hole 32 has an inner diameter that allows the end portion of the worm shaft 7a to protrude from the inner ring 19 without being rattled and can be inserted rotatably. The both receiving portions 31, 31 are directed to the opposite side of the worm wheel 4.

  The coil spring 10a is formed by winding a single metal wire having elasticity such as spring steel, and includes a coil portion 33 and a pair of locking portions 34 and 34. Both the locking portions 34, 34 protrude radially inward from the substantially opposite side with respect to the radial direction of the coil portion 33. However, in the free state of the coil spring 10a, the positions of the locking portions 34, 34 are slightly biased to one side in the circumferential direction (worm wheel 4 side). Such a coil spring 10a is provided between the distal end of the holding cylindrical portion 24 and a portion protruding from the inner ring 19 at the distal end portion of the worm shaft 7a via the pressing sleeve 28. The portion is provided in a state where it is elastically pressed toward the worm wheel 4. For this purpose, both the locking portions 34, 34 are locked to the receiving portions 31, 31 with the coil portion 33 of the coil spring 10 a being disposed around the central cylindrical portion 30 of the pressing sleeve 28. Yes. In a state where both the locking portions 34 and 34 are locked to the receiving portions 31 and 31 and no external force is applied, a part of the coil portion 33 is a disk of the pressing sleeve 28 as shown in FIG. It protrudes larger on the side opposite to the worm wheel 4 than the outer peripheral edge of the portion 29.

  The pressing sleeve 28 and the coil spring 10a as described above are assembled in the holding cylindrical portion 24 before the elastic holding member 21 and the rolling bearing 8a are assembled in the holding cylindrical portion 24. Alternatively, it is assembled to a portion protruding from the inner ring 19 at the tip of the worm shaft 7a. In the former case, due to the elasticity of the coil spring 10a, the outer peripheral surface of the arc wall portion 35 provided at the outer peripheral edge portion of the pressing sleeve 28 is pressed against the inner peripheral surface of the holding cylindrical portion 24, and the pressing sleeve 28 is pressed. Is temporarily fixed in the holding cylindrical portion 24 in the vicinity of the position after the assembly is completed. From this state, the pressing sleeve 28 is slightly displaced in the direction away from the worm wheel 4 against the elasticity of the coil spring 10a, and the tip of the worm shaft 7a is inserted into the center hole 32, The elastic holding member 21 and the rolling bearing 8 a are assembled in the holding cylindrical portion 24.

  On the other hand, in the latter case, after the elastic holding member 21 and the rolling bearing 8a are assembled to the tip of the worm shaft 7a, the pressing sleeve 28 and the coil spring 10a are assembled, and then the holding is performed. These members 28, 10 a, 21, 8 a are sequentially assembled in the cylindrical portion 24. That is, the coil portion 33 of the coil spring 10a is elastically deformed in the direction approaching the worm wheel 4 with respect to the central axis of the worm shaft 7a, and the tip end portion of the worm shaft 7a is moved to the holding cylindrical portion. The coil part 33 is pushed into the holding cylindrical part 24 by being inserted into the holding cylindrical part 24. Then, the elastic holding member 21 and the rolling bearing 8a are assembled in the holding cylindrical portion 24 by continuing the insertion operation of the worm shaft 7a as it is.

  In any case, in the state after the assembly of each of the members 28, 10a, 21, 8a, the tip of the worm shaft 7a has elasticity in the direction approaching the worm wheel 4 in the holding cylindrical portion 24. Supported in the applied state. In this state, the worm shaft 7a can be displaced relatively freely in the direction of moving in the direction of the worm wheel 4 (the vertical direction in FIGS. 1, 2, and 4), but the axial direction of the worm wheel 4 (see FIG. 1 is subjected to a large resistance when attempting to move in the front and back direction of FIG.

  According to the electric power steering apparatus of this example having the above-described configuration, the worm teeth 6a constituting the worm-type speed reducer 17 for transmitting the rotational force of the electric motor 5 to the steering shaft 2 and the above-mentioned The meshing state with the worm wheel 4 can be made almost constant regardless of the transmission direction of power. And it can suppress that the steering force which a driver | operator needs to apply to the steering wheel 1 (refer FIG. 7) at the time of course change changes with the rotation direction of this steering wheel 1. FIG. Further, the start of transmission of auxiliary power accompanying the start-up of the electric motor 5 and the change of the rotation direction of the steering shaft 2 based on the change of the rotation direction of the electric motor 5 are abruptly performed, and the tip of the worm shaft 7a. Even when there is a tendency to suddenly displace in the axial direction of the worm wheel 4, it is possible to prevent generation of unpleasant noises and vibrations such as rattling noises.

  That is, in the case of the electric power steering apparatus of this example, the outer ring 20 of the rolling bearing 8a that supports the tip of the worm shaft 7a is the elastic arm portions 23, 23 constituting the elastic holding member 21. It is guided to. The outer ring 20 can be displaced with a small force on a virtual plane orthogonal to the central axis of the worm wheel 4. On the other hand, in order to displace the front end side of the worm shaft 7a supported by the rolling bearing 8a in the axial direction of the worm wheel 4, the elastic arm portions 23, 23 of the both elastic arm portions 23, 23 are to be displaced. It is necessary to elastically deform the elastic arm portion 23 existing on the side to be operated. For this reason, the tip of the worm shaft 7a, which includes the outer ring 20 and is rotatably supported by the rolling bearing 8a, is easy on a virtual plane orthogonal to the central axis of the worm wheel 4. Although it can be displaced, a relatively large resistance is applied to the displacement of the worm wheel 4 in the axial direction.

  The magnitude of this resistance can be adjusted based on the elasticity of the elastic plate constituting the elastic holding member 21. If this elasticity is increased, the tip of the worm shaft 7a is moved in the axial direction of the worm wheel 4. Almost no displacement is possible. For this reason, if the elasticity of the elastic plate is increased within the range in which the work of incorporating the elastic holding member 21 into the holding cylindrical portion 24 of the housing 3a is not troublesome, as described above, the meshing state is changed to the power. The steering force can be kept constant regardless of the transmission direction, and the steering force can be prevented from changing depending on the rotation direction of the steering wheel 1. At the same time, it is possible to prevent the abnormal noise and vibration from occurring.

The principal part cutaway view which shows an example of embodiment of this invention. AA sectional drawing of FIG. The perspective view of an elastic holding member. BB sectional drawing of FIG. The exploded perspective view of a press sleeve and a coil spring. The figure seen from the same direction as FIG. 4 in the state before assembling between the front-end | tip part of a worm shaft, and a holding | maintenance cylindrical part, after combining a press sleeve and a coil spring. The partially cut side view which shows an example of a conventional structure. The expanded CC sectional view of FIG. The lower right enlarged view of FIG. DD sectional drawing of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3, 3a Housing 4 Worm wheel 5 Electric motor 6, 6a Worm tooth 7, 7a Worm shaft 8a, 8b Rolling bearing 9 Pressing piece 10, 10a Coil spring 11 Holder 12 Locking part 13 Bending part 14 Bush DESCRIPTION OF SYMBOLS 15 Intermediate shaft 16 Steering gear 17 Worm speed reducer 18 Worm 19 Inner ring 20 Outer ring 21 Elastic holding member 22 Semi-cylindrical part 23 Elastic arm part 24 Holding cylindrical part 25 Butting part 26 Retaining tongue piece 27 Guide tongue piece 28 Pressing sleeve 29 Disc part 30 Central cylindrical part 31 Receiving part 32 Center hole 33 Coil part 34 Locking part 35 Arc wall part 36 Small diameter part 37 Large diameter part

Claims (4)

  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. With the worm teeth meshed with the worm wheel, both end portions of the worm shaft in the axial direction are rotatably supported by the housing by bearings, the worm shaft proximal end portion, and the output shaft distal end And an electric motor that freely engages transmission of rotational force, and is provided between the tip of the worm shaft and the inner surface of the housing. Thus, in the electric power steering apparatus in which the worm teeth are pressed toward the worm wheel, the outer peripheral surface of the tip side bearing for rotatably supporting the tip of the worm shaft with respect to the housing, and An elastic holding member provided between the inner surface of the housing and made of an elastic plate and provided with a semi-cylindrical portion and a pair of elastic arm portions extending from both circumferential ends of the semi-cylindrical portion toward the worm wheel. The semi-cylindrical part holds the half part opposite to the worm wheel in the outer peripheral surface of the tip side bearing, and the tip parts of both elastic arm parts are elastically brought into contact with the inner surface of the housing. An electric power steering device characterized by being provided in a state.   The tip side bearing is a radial ball bearing in which a plurality of balls are provided between an inner ring raceway provided on the outer peripheral surface of the inner ring and an outer ring raceway provided on the inner peripheral surface of the outer ring. Is a holding cylindrical part having a cylindrical inner peripheral surface, and the semi-cylindrical part is holding the half part opposite to the worm wheel in the outer peripheral surface of the outer ring. 2. The electric power steering apparatus according to claim 1, wherein an abutting portion formed by bending the distal end portion of the arm portion in a direction approaching each other is brought into contact with the inner peripheral surface of the holding cylindrical portion.   With respect to the axial direction of the worm shaft, a retaining tongue piece bent inward in the radial direction is formed at one or a plurality of positions on the edge opposite to the worm tooth among both end edges of the semi-cylindrical portion. The guide tongue piece bent by less than 90 degrees radially outward is formed at a plurality of positions on the worm tooth side edge among the edges, according to any one of claims 1 and 2. The described electric power steering device.   The electric power steering apparatus according to any one of claims 1 to 3, wherein an elastic plate constituting the elastic holding member is made of copper or a copper-based alloy.

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