JP2008143434A - Electric power steering device - Google Patents

Abstract

A meshing state of a worm tooth 6a and a worm wheel 4 is made constant irrespective of the transmission direction of power. And the structure which the steering force which a driver | operator needs to apply to a steering wheel does not change with the rotation direction of this steering wheel is implement | achieved.
A rolling bearing 8a for rotatably supporting a distal end portion of a worm shaft 7a in a housing 3a can be displaced only on a virtual plane orthogonal to the central axis of the worm wheel 4. For this purpose, an outer ring 17a constituting the rolling bearing 8a is formed on an inner peripheral surface of the guide sleeve 20 held in the housing 3a, and is on a virtual plane that is parallel to each other and orthogonal to the central axis of the worm wheel 4. It is sandwiched between a pair of guide planes located at a distance. Further, the leaf spring 26 prevents the guide sleeve 20 from rattling in the housing 3a. With this configuration, the above problem is solved.
[Selection] Figure 1

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 and 2, it is considered that the worm is elastically pressed toward the worm wheel by an elastic member such as a spring as a structure capable of suppressing 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. 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 11 made of an elastic material is externally fitted to the bush 3, and the bush 11 is rotatably supported with respect to the housing 3 by the rolling bearing 8a. When the backlash is suppressed, the bush 11 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 may become inappropriate.

  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 11. 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.

JP 2000-43739 A JP 2004-306898 A

  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 was invented to realize an electric power steering device that does not change depending on the rotation direction of the steering wheel.

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 12 having the structure shown in FIG. 7 and the input shaft (pinion shaft) of the steering gear 13 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, A guide sleeve is provided. This guide sleeve is provided with a pair of guide planes parallel to each other on its inner peripheral surface. These two guide planes are arranged at an interval substantially coincident with the outer diameter of the distal end side bearing, and each is located on a virtual plane (a pair of parallel to each other) orthogonal to the central axis of the worm wheel. . And by pinching the said front end side bearing between these both guide planes, this front end side bearing can be displaced only on the virtual plane orthogonal to the central axis of the said worm wheel. Further, a second elastic member made of a metal plate having elasticity is provided between the outer peripheral surface of the guide sleeve and the inner peripheral surface of the housing.

  The state in which the distance between the two guide planes substantially coincides with the outer diameter of the tip end bearing means that the two positions opposite to each other in the diametrical direction of the outer peripheral surface of the tip end bearing are simultaneously applied to both guide planes. Further, it means a state in which the tip side bearing is displaced in a direction approaching the worm wheel by the elastic force of the elastic member. However, it is an object of the present invention that there is a gap of about several μm (less than 10 μm) that does not lead to a change in the meshing state between the outer peripheral surface of the front end side bearing and the both guide planes. It ’s okay. In other words, a state in which a gap of about several μm exists in the above-described portion is also a state in which the distance between the two guide planes substantially coincides with the outer diameter of the tip-end bearing.

  When the electric power steering apparatus of the present invention as described above is implemented, for example, as described in claim 2, the second elastic member is formed by bending a metal plate into a not-cylindrical shape, and this metal. At least one end portion in the circumferential direction of the plate is a leaf spring divided into a pair of elastic arm portions by a slit formed in the intermediate portion in the width direction and reaching the circumferential edge. Then, the outer peripheral surface of the guide sleeve is elastically inward in the radial direction by one elastic arm portion of both the elastic arm portions, and the inner peripheral surface of the housing is elastically outward in the radial direction by the other elastic arm portion. Press.

When the electric power steering apparatus according to the second aspect described above is implemented, preferably, as described in the third aspect, the second elastic member has a diameter from one end edge in the axial direction to the one end edge in the axial direction. At least one axial locking piece bent inward is provided. The second elastic member is prevented from shifting in the axial direction by sandwiching the axial locking piece between the axial end surface of the guide sleeve and the inner surface of the housing.
Alternatively, as described in claim 4, a guide sleeve having a cut at least at one place in the circumferential direction is used. Then, a circumferential locking piece bent radially inward from the tip edge of any one of the plurality of elastic arm portions provided on the second elastic member is engaged with the cut. This prevents the second elastic member from rotating around the guide sleeve.

  Further, when the electric power steering apparatus of the present invention as described above is implemented, preferably, as described in claim 5, the guide sleeve is provided on the opposite side of the worm teeth from the both guide planes. Provide an extension that extends to the end. A pressing sleeve is externally fitted to a portion of the tip portion of the worm shaft that protrudes on the opposite side of the worm tooth from the tip side bearing. And the said elastic member for pressing a worm tooth toward a worm wheel between the outer peripheral surface of this press sleeve and the said extension part is provided.

In carrying out the invention described in claim 5, it is more preferable that the elastic member for pressing the worm teeth toward the worm wheel has elasticity as described in claim 6. The coil spring is formed by winding a metal wire, and includes a coil portion and a pair of locking portions protruding radially outward from the opposite side of the coil portion. Then, the coil portion is externally fitted to the pressing sleeve, and both the locking portions are locked to a pair of locking recesses formed in the extension portion of the guide sleeve.
Further, when the electric power steering apparatus of the present invention as described above is implemented, as described in claim 7, as the guide sleeve, the guide sleeve is separated by a virtual plane orthogonal to the central axis of the worm wheel. It is also preferable to use a divided structure. This virtual plane may be a plane including the center of the worm or a plane parallel to this plane.

  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 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 does not change depending on the rotation direction of the steering wheel.

  That is, in the case of the electric power steering apparatus of the present invention, the front end bearing that supports the front end portion of the worm shaft is guided by a pair of guide planes and is on a virtual plane orthogonal to the central axis of the worm wheel. It can be displaced only with. In other words, the tip side of the worm shaft supported by the tip side bearing is not displaced in the axial direction of the worm wheel. For this reason, as described above, the meshing state can be made constant regardless of the transmission direction of power, and the steering force can be prevented from changing depending on the rotation direction of the steering wheel.

Further, in the case of the electric power steering apparatus of the present invention, the second elastic member is stretched between the outer peripheral surface of the guide sleeve and the inner peripheral surface of the housing, so that a gap between these two peripheral surfaces is formed. It is substantially eliminated and the guide sleeve is prevented from being displaced (rattle) in the radial direction in the housing. For this reason, even if the relationship between the outer diameter of the guide sleeve and the inner diameter of the housing is not strictly regulated, the above-mentioned action and effect can be obtained. Further, since the second elastic member is made of a metal plate having elasticity, even when the electric power steering device is installed in the engine room where the temperature rises, the second elastic member Sufficient durability can be secured.
Furthermore, according to the second to seventh aspects of the present invention, an electric power steering apparatus with good operation feeling that can be realized with a structure that is easy to assemble and that has the above-described effects can be realized at low cost.

  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 14 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 is such that backlash at the meshing portion with the worm wheel 4 can be eliminated, and the meshing state of the meshing portion can be made constant regardless of the transmission direction of power in the worm speed reducer 14 portion. 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 15 is formed by providing worm teeth 6a at an 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 of the worm shaft 7a in the axial direction are formed by a pair of rolling bearings 8a and 8b, each of which is a single row deep groove type ball bearing. The housing 3a is rotatably supported. Among these rolling bearings 8a and 8b, the rolling bearing 8b for rotatably supporting the base end portion (right end portion in FIG. 1) of the worm shaft 7a with respect to the housing 3a includes the inner ring 16b and the worm shaft 7a. The outer ring 17b is fitted and fixed to the housing 3a by an interference fit. The rolling bearing 8b, which is a single row deep groove type ball bearing, has a low moment rigidity even when the internal clearance is zero. Therefore, the rolling bearing 8b causes the base end of the worm shaft 7a to move relative to the housing 3a. In a state in which the radial displacement is prevented, it is supported so as to allow a slight swing displacement. Since the amount of oscillating displacement of the worm shaft 7a required for eliminating the backlash of the meshing portion is very small, an unreasonable force is hardly applied to the rolling bearing 8b. In this way, the base end portion of the worm shaft 7a and the front end portion of the output shaft 18 of the electric motor 5 which are rotatably supported in the housing 3a are freely engaged in transmission of rotational force by the coupling 19. In combination, the worm shaft 7a can be driven to rotate in both directions.

  On the other hand, the tip of the worm shaft 7a is rotated with respect to the housing 3a through the rolling bearing 8a and the guide sleeve 20, and a slight movement relative to the worm wheel 4 (vertical direction in FIGS. 1 to 4). However, the worm wheel 4 is supported in a state in which displacement of the worm wheel 4 in the axial direction (front and back directions in FIGS. 1 and 2 and left and right directions in FIGS. 3 and 4) is prevented. For this purpose, the inner ring 16a of the rolling bearing 8a is fitted and fixed to the tip of the worm shaft 7a by an interference fit, and the outer ring 17a is arranged on the inner diameter side of the guide sleeve 20.

The guide sleeve 20 is made of a slippery synthetic resin having oil resistance and is formed into an annular shape as a whole, and a pair of guide planes 21 and 21 parallel to each other at two positions on the radially opposite side of the inner peripheral surface (FIG. 3). Both the guide planes 21 and 21 are located on virtual planes (planes parallel to the planes shown in FIGS. 1 and 2) orthogonal to the central axis of the worm wheel 4. Further, the distance D ₂₁ between the two guide planes 21 and 21, coincides with the outer diameter D ₁₇ of the outer ring 17a of the rolling bearing 8a is the tip side bearing. On the other hand, the inner diameter R ₂₀ of the guide sleeve 20 with respect to the direction of movement is larger than the outer diameter D ₁₇ of the outer ring 17a (D ₂₁ = D ₁₇ <R ₂₀ ).

Above for the two guide planes 21, 21 spacing D ₂₁ between the present embodiment in order to match to the outer diameter D ₁₇ of the outer ring 17a is the guide sleeve 20, as shown in FIG. 5, each half It is configured by combining a pair of sleeve elements 22a and 22b each having an arc shape. These sleeve elements 22a and 22b are mirror-symmetrical to each other, each outer peripheral surface is a semi-cylindrical surface, and each inner peripheral surface is a stepped substantially semi-cylindrical surface. Both the guide planes 21 and 21 are formed in the middle portion in the circumferential direction of the large diameter portion 23 of the inner peripheral surface. Locking recesses 25 and 25 are formed in the center portion in the circumferential direction of the small diameter portion 24 on the inner peripheral surface. The sleeve elements 22a and 22b, each having such a configuration, are combined into a state in which their circumferential end faces face each other to form the guide sleeve 20.

  A leaf spring 26 as a second elastic member as shown in FIG. 6 is externally fitted to such a guide sleeve 20. The plate spring 26 is formed by bending a metal plate having elasticity, such as a stainless steel plate, into a cylindrical shape. Further, a total of four elastic arm portions 28a, 28b, each paired by a pair of slits 27a, 27b that are formed at the intermediate portion in the width direction and reach the circumferential edge, are formed at both ends in the circumferential direction of the metal plate. It is divided into. Among these elastic arm portions 28a and 28b, a pair of elastic arm portions 28a and 28a located on one side in the width direction (front side in FIG. 6) at both ends in the circumferential direction are radially outward in a free state. The elasticity which is suitable for is given. On the other hand, a pair of elastic arm portions 28b and 28b located on the other side in the width direction (the back side in FIG. 6) at both ends in the circumferential direction are given elastic force directed radially inward in a free state. ing.

  In addition, axial locking pieces 29 and 29 that are bent radially inward from the one end edge are formed at a plurality of positions (two positions on the opposite side in the diametrical direction in the illustrated example) at one end edge in the axial direction of the leaf spring 26. is doing. Further, of the elastic arms 28b, 28b, which are given a radially inwardly elastic force in a free state, the distal edge of one elastic arm 28b is connected to the distal edge of the elastic arm 28b. A circumferential locking piece 30 bent inward in the radial direction is formed.

  The guide sleeve 20 and the leaf spring 26 as described above are assembled around the outer ring 17a while holding the outer ring 17a from the opposite side in the radial direction by the guide planes 21 and 21 of the guide sleeve elements 22a and 22b. Next, in the guide sleeve 20, a coil spring 32, which is an elastic member, is provided between the extended portion 31 protruding from the outer ring 17a toward the distal end side and the distal end portion of the worm shaft 7a. The coil spring 32 is formed by winding one 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 outward from substantially the opposite side with respect to the radial direction of the coil portion 33. However, in the free state of the coil spring 32, the positions of the locking portions 34, 34 are slightly biased to one side in the circumferential direction (the side far from the worm wheel 4).

  Such a coil spring 32 elastically presses the tip portion toward the worm wheel 4 between the extension portion 31 of the guide sleeve 20 and the tip portion of the worm shaft 7 a via the pressing sleeve 35. It is handed over in the state. Therefore, in a state where the coil portion 33 of the coil spring 32 is externally fitted to the pressing sleeve 35, the pressing sleeve 35 is externally attached to a portion located on the inner diameter side of the extension portion 31 at the distal end portion of the worm shaft 7a. At the same time, the locking portions 34 and 34 are locked to the locking recesses 25 and 25 provided at two positions opposite to the extending portion 31 in the radial direction (see FIG. 4). At this time, as shown by arrows α and α in FIG. 5, both the locking portions 34 and 34 are locked to the both locking recesses 25 and 25 while being elastically deformed in a direction approaching the worm wheel 4. . As a result, the distal end portion of the worm shaft 7a is applied with elasticity in the direction approaching the worm wheel 4 on the inner diameter side of the extension portion 31, and the direction in which the worm shaft 7a moves toward and away from the worm wheel 4 ( Only the displacement in the vertical direction of FIGS. 1 to 4 is supported. In other words, the tip portion of the worm shaft 7a is prevented from being displaced toward the inner diameter side of the extension portion 31 in the axial direction of the worm wheel 4 (front and back directions in FIGS. 1 and 2 and left and right directions in FIGS. 3 and 4). Supported in state.

  As described above, when the members 7a, 35, 32, 20, 26 are combined, the members 7a, 35, 32, 20, 26 are provided on a part of the housing 3a. Of the members 7a, 35, 32, 20, and 26, the elastic arm portions 28a and 28b constituting the leaf spring 26 are pushed into the cylindrical holding cylinder portion 36 while being elastically deformed. That is, a pair of elastic arm portions 28a, 28a located on one side in the width direction of each of the elastic arm portions 28a, 28b is paired with a pair of elastic arm portions 28b located on the other side in the width direction. The leaf spring 26 is pushed into the holding cylindrical portion 36 together with the guide sleeve 20 while elastically deforming 28b radially outward. In a state after completion of pushing, the pair of elastic arm portions 28a, 28a located on one side in the width direction is a pair of elastic arm portions located on the radially outer side of the inner peripheral surface of the housing and on the other side in the width direction. 28b and 28b elastically press the outer peripheral surface of the guide sleeve radially inward. As a result, a tension force in the directions of arrows β and β in FIG. 4 is applied between the inner peripheral surface of the holding cylindrical portion 36 and the outer peripheral surface of the guide sleeve 20. The magnitude of this tension force is larger than the elasticity of the coil spring 32. Based on this tension force, the guide sleeve 20 is held and fixed in the holding cylindrical portion 36 without rattling. That is, regardless of the elasticity of the coil spring 32, the guide sleeve 20 is not displaced in the radial direction of the guide sleeve 20 and the holding cylindrical portion 36 in the holding cylindrical portion 36.

  Further, the pair of guide planes 21, 21 provided on the inner peripheral surface of the guide sleeve 20 is positioned on a virtual plane orthogonal to the central axis of the worm wheel 4 after the pushing-in is completed. . Then, the outer ring 17a of the rolling bearing 8a that supports the tip of the worm shaft 7a is elastically moved toward the worm wheel 4 along the both guide planes 21 and 21 based on the elasticity of the coil spring 32. The state is pressed. Further, the axial locking pieces 29 and 29 are clamped between one axial end surface of the guide sleeve 20 and the inner surface of the holding cylindrical portion 36. Then, the leaf spring 26 is prevented from moving in the axial direction. Further, by engaging the circumferential locking piece 30 with a discontinuous portion (cut) between the sleeve elements 22a and 22b constituting the guide sleeve 20, the leaf spring 26 is moved to the guide sleeve. Rotation around 20 is prevented (see FIG. 4).

  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 14 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 constant irrespective 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.

  That is, in the case of the electric power steering apparatus of this example, the outer ring 17a of the rolling bearing 8a that supports the tip of the worm shaft 7a is guided by the both guide planes 21 and 21, so that the worm wheel 4 It can be displaced only on a virtual plane orthogonal to the central axis of. In other words, the tip side of the worm shaft 7a supported by the rolling bearing 8a is not displaced in the axial direction of the worm wheel 4. For this reason, as described above, the meshing state can be made constant regardless of the transmission direction of power, and the steering force can be prevented from changing depending on the rotation direction of the steering wheel 1.

  In order to make the distance between the pair of guide planes exactly the same as the outer diameter of the tip bearing, the guide sleeve does not necessarily have to be made by combining a pair of sleeve elements. For example, the entire guide sleeve is formed in a substantially cylindrical shape, and a slit is formed over the entire length in the axial direction at one circumferential direction so that the inner diameter of the guide sleeve (the interval between a pair of guide planes) can be adjusted. You can also do it. Since this adjustment amount is very small, the parallelism of the two guide planes is not substantially impaired based on this adjustment. In addition, when such a substantially cylindrical (not-cylindrical) guide sleeve provided with a slit at one circumferential position is used, the circumference of the axial end edge of the leaf spring combined with the guide sleeve is used. Axial locking pieces can be provided at three positions at equal intervals in the direction.

The principal part cutaway view which shows an example of embodiment of this invention. The A section enlarged view of FIG. BB sectional drawing of FIG. CC sectional drawing of FIG. The disassembled perspective view of the rotation support part of the worm shaft front-end | tip part shown in FIGS. The perspective view of the leaf | plate spring which is a 2nd elastic member. The partially cut side view which shows an example of a conventional structure. The expanded DD sectional view of FIG. The lower right enlarged view of FIG. EE 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 Coil spring 11 Bush 12 Intermediate shaft 13 Steering gear 14 Worm speed reducer 15 Worm 16a, 16b Inner ring 17a, 17b Outer ring 18 Output shaft 19 Coupling 20 Guide sleeve 21 Guide plane 22a, 22b Sleeve element 23 Large diameter part 24 Small diameter part 25 Locking recess 26 Leaf spring 27a, 27b Slit 28a, 28b Elastic arm part 29 Axial locking piece 30 Circumferential locking piece 31 Extension part 32 Coil spring 33 Coil part 34 Locking part 35 Pressing sleeve 36 Holding cylinder part

Claims (7)

  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 Between the inner surface of the housing, a pair is arranged in parallel with each other and at a distance substantially coincident with the outer diameter of the front end bearing, and each is located on a virtual plane perpendicular to the central axis of the worm wheel. By providing a guide sleeve having a guide plane on the inner peripheral surface, and sandwiching the tip-end bearing between the two guide planes, the tip-side bearing is perpendicular to the central axis of the worm wheel. A second elastic member made of a metal plate having elasticity is provided between the outer peripheral surface of the guide sleeve and the inner peripheral surface of the housing. Electric power steering apparatus characterized.   The second elastic member is formed by bending the metal plate into a not-cylindrical shape, and at least one end portion in the circumferential direction of the metal plate is formed in the intermediate portion in the width direction and reaches a circumferential edge. A leaf spring divided into a pair of elastic arm portions, one elastic arm portion of these elastic arm portions being radially inward of the outer peripheral surface of the guide sleeve, and the other elastic arm portion being an inner portion of the housing. The electric power steering apparatus according to claim 1, wherein the peripheral surface is elastically pressed outward in the radial direction.   By sandwiching at least one axial locking piece bent radially inward from one axial end edge of the second elastic member between the axial end surface of the guide sleeve and the inner surface of the housing, The electric power steering apparatus according to claim 2, wherein the second elastic member is prevented from moving in an axial direction.   The guide sleeve has a cut in at least one circumferential direction, and is radially inward from the tip edge of one of the plurality of elastic arm portions provided on the second elastic member. 4. The second elastic member is prevented from rotating around the guide sleeve by engaging a circumferential locking piece bent in the direction with the cut. 5. The electric power steering apparatus described in any one of the items.   The guide sleeve is provided with an extension that extends to the opposite side of the worm tooth from the pair of guide planes, and protrudes to the opposite side of the worm tooth from the tip side bearing of the tip part of the worm shaft. A pressing sleeve is externally fitted to the portion, and an elastic member for pressing the worm teeth toward the worm wheel is provided between the outer peripheral surface of the pressing sleeve and the extension. The electric power steering apparatus described in any one of the above.   An elastic member for pressing the worm teeth toward the worm wheel is made by winding a metal wire having elasticity, and protrudes radially outward from the coil portion and the opposite side of the coil portion. A coil spring having a pair of locking portions, and the coil portion is externally fitted to the pressing sleeve, and the both locking portions are locked to a pair of locking recesses formed in the extension portion of the guide sleeve. The electric power steering apparatus according to claim 5.   The electric power steering apparatus according to any one of claims 1 to 6, wherein the guide sleeve is divided into two with a virtual plane orthogonal to the central axis of the worm wheel as a boundary.

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