JP5163626B2 - Electric power steering device - Google Patents

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 has been invented to realize a structure that can sufficiently suppress the temperature rise during operation with respect to a sliding bearing for rotatably supporting the tip of a worm shaft constituting such an electric power steering device. It is.

  Power steering devices are widely used as devices for reducing the force required for the driver to operate the steering wheel when giving a steering angle to the steered wheels (usually the front wheels except for special vehicles such as forklifts). It is used. In addition, an electric power steering apparatus that uses an electric motor as an auxiliary power source in such a power steering apparatus has begun to spread in recent years. Compared with a hydraulic power steering device, the electric power steering device is advantageous in that it can be made smaller and lighter, can easily control the magnitude (torque) of auxiliary power, and has less engine power loss.

  Various structures of the electric power steering apparatus are known. In any structure, the electric motor is mounted on the rotating shaft that is rotated by the operation of the steering wheel and gives a steering angle to the steered wheels in accordance with the rotation. The auxiliary power is applied through a reduction gear. 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.

  For example, Patent Document 1 discloses an electric power steering device as shown in FIGS. 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. Worm teeth 5 meshing with the worm wheel 4 are provided in the axial direction intermediate portion of the worm shaft 6, and both ends of the worm 8 driven to rotate by the electric motor 7 are paired with a pair of rolling bearings 9 a such as a deep groove ball bearing, 9b is rotatably supported in the housing 3.

  Further, in order to eliminate backlash at the meshing portion between the worm wheel 4 and the worm tooth 5, the tip end portion (the right end portion in FIG. 6) of the worm shaft 6 is elastically pressed toward the worm wheel 4. I have to. That is, the urging member 10 is externally fitted to a portion of the worm shaft 6 protruding from the distal end side rolling bearing 9a at the distal end, and a coil spring 11 or the like is interposed between the urging member 10 and the housing 3. An elastic member is provided.

Specifically, a holding recess 12 is provided in a portion of the housing 3 that faces the tip of the worm shaft 6, and a holder 13 is held in the holding recess 12. Further, a portion near the tip of the worm shaft 6 is formed on the holder 13 with an elastic ring 14 made of an elastic material such as an elastomer such as rubber, and the rolling bearing 9a held on the outer diameter side of the elastic ring 14. By this, it supports so that rotation and the far-and-near movement with respect to the said worm wheel 4 are possible. The urging member 10 has a portion that protrudes from the rolling bearing 9a at the tip of the worm shaft 6 so that it can rotate relative to the rolling bearing 9a (actually the worm shaft inside the urging member 10). 6 is freely fitted). The urging member 10 does not rotate, but can move in the direction of the worm wheel 4 so that the holder 13 can be moved in the axial direction (the outer side with respect to the axial direction is opposed to the tip side of the worm shaft 6. In the direction, “inner” refers to the proximal end side of the worm shaft 6. This is the same throughout the present specification and claims . Further, both end portions of the coil spring 11 are locked to the outer side surface of the holder 13 in the axial direction. In this state, the inner peripheral surface of the coil spring 11 is elastically in contact with the surface of the outer peripheral surface of the biasing member 10 opposite to the worm wheel 4. The worm teeth 5 are pressed against the worm wheel 4 by the coil spring 11 through the biasing member 10. With such a configuration, backlash between the worm teeth 5 and the worm wheel 4 is suppressed, and an unpleasant noise called a rattling noise is prevented from occurring when the rotation direction of the steering shaft 2 is changed. doing.

  On the other hand, Patent Documents 2 and 3 have a structure that can suppress the occurrence of rattling noise as described above, and a structure in which the tip portion of the worm shaft is rotatably supported by a sliding bearing instead of a rolling bearing. Is disclosed. Specifically, in Patent Document 2 described above, the guide member and the guide member are provided by a coil spring in a state in which the tip of the worm shaft is rotatably supported by a sliding bearing fitted and fixed inside the cylindrical guide member. A structure is described in which worm teeth are pressed against a worm wheel via a sliding bearing. Further, in Patent Document 3, the tip of the worm shaft is rotatably supported by a sliding bearing that is fitted and fixed in an elastically deformed (bent) state inside the housing, and a sliding bearing based on this bending. A structure that elastically presses the worm teeth toward the worm wheel by its own elastic force is described.

  In the case of the structures of the inventions described in Patent Documents 2 and 3 as described above, the number of parts is reduced compared to the case where the tip end portion of the worm shaft is supported using a rolling bearing. The overall cost can be reduced. However, when a slide bearing is used to rotatably support the tip of the worm shaft, the following problems may occur. That is, the sliding bearing for supporting the tip of the worm shaft generates heat by frictional heat generated at the sliding contact portion between the sliding surface provided on the inner peripheral surface and the outer peripheral surface of the tip of the worm shaft during operation. It is not only easy to use, but is also exposed to frictional heat generated at the meshing portion between the worm teeth and the worm wheel, and is used in a high temperature environment. For this reason, a sliding bearing for rotatably supporting the tip of the worm shaft tends to be particularly hot, resulting in a decrease in bearing life due to increased wear and seizure, and dimensional deformation accompanying thermal expansion. As a result, the rotational accuracy of the worm shaft may be reduced. Furthermore, when a synthetic resin sliding bearing is used, the sliding surface melts due to frictional heat when a high load is continuously applied to the sliding surface from the outer peripheral surface of the worm shaft. May occur.

  Here, when the inventions described in Patent Documents 2 and 3 are examined more specifically, in the case of the structure of the invention described in Patent Document 2 out of these, the outer peripheral surface of the slide bearing is arranged inside the guide member. Since it is in contact with the peripheral surface, heat can be released to a certain extent from the slide bearing to the guide member by heat conduction. However, since this guide member has a small volume and its heat capacity is limited, it is difficult to sufficiently reduce the temperature of the slide bearing. In addition, in the case of the structure of the invention described in Patent Document 3, the radial bearing needs to be elastically deformed (bent), so that the thickness in the radial direction is thick and the volume is increased. For this reason, the frictional heat generated at the sliding contact portion is not easily dissipated (is easily accumulated inside), and the sliding bearing is also likely to become high temperature. As described above, in any of the structures of the inventions described in Patent Documents 2 and 3, it is not possible to sufficiently prevent the sliding bearing from reaching a high temperature. May cause problems.

JP 2004-306898 A Japanese Patent No. 3998519 Japanese Patent No. 3658682

  In view of the above-described circumstances, the electric power steering device of the present invention is an invention for realizing a structure capable of preventing the sliding bearing for rotatably supporting the tip of the worm shaft from becoming hot during operation. It is a thing.

The electric power steering apparatus of the present invention is similar to the electric power steering apparatus having the conventional structure shown in FIGS. 5 to 6 described above, and includes a housing, a rotating shaft, a worm wheel, a worm, an electric motor, and an urging force. A member and an elastic member.
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. 5 described above, or the input shaft (pinion shaft) of the steering gear unit 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.
In the electric motor, the base end portion of the worm shaft and the tip end portion of the output shaft are engaged with each other so as to freely transmit a rotational force, so that the worm shaft can be driven to rotate in both directions.
Further, the urging member is provided so as to be able to move to and away from the worm wheel in a state where the tip of the worm shaft is rotatably supported.
Further, the elastic member (for example, a coil spring or a leaf spring) presses the worm teeth toward the worm wheel via the biasing member.

In particular, in the electric power steering apparatus according to the present invention, at least the tip of the worm shaft is supported among the bearings that respectively support both axial ends of the worm shaft (on the side far from the electric motor). ) The bearing is a sliding bearing.
Further, this sliding bearing is formed by integrally forming a thin cylindrical bearing main body having an inner peripheral surface as a sliding surface and a housing for assembling the urging member and the elastic member.
Further, the sliding bearing has an outer surface shape that matches the inner surface shape of the holding recess provided in the portion facing the tip end portion of the worm shaft inside the housing.
Then, such a sliding bearing is substantially connected to the outer peripheral surface and the axial outer side surface of the bearing main body portion and the outer peripheral surface and the axial outer side surface of the housing portion on the inner peripheral surface and the axial inner side surface of the holding recess. It is fitted and supported inside the housing in a close contact state with no gap.

Further , when the invention described in claim 1 as described above is carried out, the slide bearing is preferably fitted and supported inside the housing, as in the invention described in claim 2 , for example. The outer surface of the part is formed into an uneven shape for increasing the surface area.

According to the electric power steering device of the present invention having the above-described configuration, it is possible to sufficiently suppress the temperature rise of the sliding bearing for rotatably supporting the tip end portion of the worm shaft. Can be prevented.
That is, in the case of the present invention, among the above-mentioned sliding bearings, the bearing main body portion, which is likely to become high temperature during operation, is configured to be thin, so that heat hardly accumulates in this bearing main body portion. Heat can be quickly released to the housing. In addition, in the case of the present invention, the outer peripheral surface of the bearing main body, which constitutes the outer surface of the sliding bearing by matching the outer surface shape of the sliding bearing with the inner surface shape of the holding recess formed inside the housing, and the axially outer side and housing part outer peripheral surface and the axially outer sides of, because it has substantially brought into close contact without a gap on the inner peripheral surface and axially inner surface constituting the inner surface of the holding recess, the sliding bearing and the A wide contact area with the housing can be secured, and heat can be efficiently released from the slide bearing to the housing. In particular, the housing has a sufficiently large volume and a large heat capacity as well as a large surface area (heat dissipating area) compared to the sliding bearing, so that the temperature of the sliding bearing can be sufficiently lowered.
As a result, in the case of the present invention, the temperature rise of the sliding bearing can be sufficiently suppressed, and the sliding bearing can be prevented from becoming high temperature.

In the case of the present invention , since the bearing main body part and the accommodating part for assembling the biasing member and the elastic member are integrated, the slide bearing, the biasing member, and the elastic member are assembled (subassembly). Can be handled as one. For this reason, the assembly work of the electric power steering apparatus can be facilitated. In addition, the number of parts can be reduced, and parts production and parts management can be reduced.
Furthermore, in the case of the invention described in claim 2 , since the surface area (heat dissipating area) of the housing, in particular, the portion where the sliding bearing is installed can be increased, the heat dissipating efficiency of the housing can be improved. For this reason, the temperature of this housing can be reduced more efficiently, and the temperature rise of the sliding bearing fitted and supported by this housing can be suppressed more effectively.

Moreover, when implementing this invention, a 1 thru | or several groove | channel (or recessed part) can also be formed in the internal peripheral surface (sliding surface) of the bearing main-body part which comprises the said sliding bearing. If such a configuration is adopted, grease can be held in the groove (can function as a grease reservoir) and a heat radiation effect can be expected.
Furthermore, when carrying out the present invention, the bearing main body constituting the sliding bearing is not limited to a cylindrical shape, but may be a non-cylindrical shape (for example, a polygonal cylindrical shape). It can also be circular). If the bearing body is configured in a non-cylindrical shape, the sliding bearing can be prevented from rotating relative to the housing, and the bearing body and the housing are integrally provided as in the present invention . In this case, it is possible to prevent the moving direction of the urging member from changing without providing a separate anti-rotation mechanism.

The figure equivalent to the AA expanded cross section of FIG. 5 which shows the 1st example of embodiment of this invention. The B section enlarged view of FIG. 1 similarly. Similarly, a slide bearing, an urging member, and an elastic member are taken out and shown in cross-sectional views (a) and (a) as viewed from the left (b), and as viewed from the right (a) (c). The figure similar to FIG. 1 which shows the 2nd example of embodiment of this invention. The partially cut side view which shows an example of a conventional structure. The AA expanded sectional view of FIG. 5 similarly.

[First example of embodiment]
1 to 3 show a first example of an embodiment of the present invention corresponding to claim 1 . The feature of the electric power steering device of this example includes the structure of the sliding bearing 17 in order to prevent the sliding bearing 17 for rotatably supporting the tip of the worm shaft 6 from being heated. The structure of the portion that supports the tip of the worm shaft 6 is devised. Since the structure, operation, and effect of the other parts are almost the same as those of the conventional structure shown in FIGS. 5 to 6 described above, the illustration and description of the equivalent parts are omitted or simplified. The description will focus on the characteristic part. 6 and FIG. 1 and FIG. 4 to be described later differ in the mounting direction of the electric motor 7 with respect to the housings 3, 3a (3b). This point is appropriately designed according to the vehicle to be installed. It is to be changed and has nothing to do with the features of the present invention.

  Also in this example, the worm 8 is formed by providing the worm teeth 5 at the intermediate portion in the axial direction of the worm shaft 6. In the state where the worm teeth 5 are engaged with the worm wheel 4, the base end portion on the side closer to the electric motor 7 among the axial end portions of the worm shaft 6 is a single row deep groove type ball bearing. Similarly, the rolling bearing 9b supports the distal end portion on the side far from the electric motor 7 by the sliding bearing 17 so as to be rotatable with respect to the housing 3a. The rolling bearing 9b supports the worm shaft 6 with respect to the housing 3a so as to be able to be slightly swung.

On the other hand, the sliding bearing 17 is internally fitted and supported (indentation fitting) by press-fitting into a holding recess 12a formed in a portion facing the tip of the worm shaft 6 inside the housing 3a. The tip of the worm shaft 6 is rotatably supported inside. Particularly in the case of this example, by matching the inner surface shape of the holding recess 12a with the outer surface shape of the sliding bearing 17, the outer peripheral surface and shaft of the bearing body 18 constituting the outer surface of the sliding bearing 17 are formed. The outer side surface in the direction, the outer peripheral surface of the accommodating portion 19 and the outer side surface in the axial direction are brought into close contact with the inner peripheral surface and the inner side surface in the axial direction constituting the inner surface of the holding recess 12a substantially without any gap.

  In the case of this example, the housing 3a is made of a metal such as an aluminum alloy, and the inner peripheral surface shape of the holding recess 12a is a stepped cylindrical surface shape. In contrast, the sliding bearing 17 is a synthetic resin having a low friction coefficient (low sliding resistance) such as polyamide resin, polytetrafluoroethylene resin, polyacetal resin, polyphenylene sulfide resin, polyurethane resin, or the like. A synthetic resin in which a lubricating oil is dispersed and contained in the above resin is injection-molded, and the whole is formed in a stepped cylindrical shape with a crank-shaped cross section. Specifically, the sliding bearing 17 is formed in a thin, small-diameter cylindrical bearing main body 18 that does not change in thickness in the circumferential direction, and a larger-diameter and thicker accommodating section 19 than the bearing main body 18. And consists of

  Of these, the bearing main body 18 is a portion that exhibits the original function of a sliding bearing that rotatably supports the tip of the worm shaft 6 with respect to the housing 3a. The sliding surface 20 is as follows. The inner diameter of the sliding surface 20 is slightly larger than the outer diameter of the outer peripheral surface of the tip portion of the worm shaft 6, and a gap is provided between the sliding surface 20 and the outer peripheral surface of the tip portion of the worm shaft 6. Yes.

  On the other hand, the accommodating portion 19 is a portion that accommodates (assembles) the urging member 10a and the coil spring 11a for pressing the tip end portion of the worm shaft 6 toward the worm wheel 4, and a portion closer to the outer diameter thereof. The housing groove 21 is provided so as to open inward in the axial direction. Further, as shown in FIG. 3C, a pair of guides in an axially inward projecting state on the inner diameter side of the housing groove 21 in the inner side surface of the housing portion 19 in the axial direction. Wall portions 22 and 22 are provided. Both the guide wall portions 22 and 22 are separated from each other in the axial direction of the worm wheel 4 (front and back direction in FIG. 1, left and right direction in FIG. 3C). The inner side surfaces 23, 23 of the guide wall portions 22, 22 are planes parallel to each other, and are attached to the central axis of the worm wheel 4 with the sliding bearing 17 fitted and supported in the holding recess 12a. It is arranged in a direction perpendicular to it. The distance between the inner side surfaces 23, 23 is slightly larger than the width dimension of the urging member 10a. Further, locking recesses 24, 24 that are recessed inward in the radial direction are provided on the outer surfaces of the guide wall portions 22, 22.

  In the case of this example, the biasing member 10a and the coil spring 11a are assembled in the following manner in the housing part 19 having such a configuration. That is, the inner side surfaces 23 of the guide wall portions 22 and 22 in a state where the urging member 10a is externally fitted to a portion near the tip of the worm shaft 6 (the worm shaft 6 can be freely rotated on the inner side). , 23 is inserted between each other. Thereby, the movable direction of the urging member 10 a is limited to the perspective movement with respect to the worm wheel 4 along the inner side surfaces 23, 23. The coil spring 11a is housed in the housing groove 21, and a pair of locking portions 26 formed by bending both ends of the wire constituting the coil spring 11a inward in the radial direction of the coil portion 25. , 26 are locked to locking recesses 24, 24 formed on the outer surfaces of the guide wall portions 22, 22.

  In this state, the inner peripheral surface of the coil spring 11a is in a state of elastically contacting the surface of the outer peripheral surface of the biasing member 10a opposite to the worm wheel 4. The worm teeth 5 are pressed against the worm wheel 4 by the coil spring 11a via the biasing member 10a. Here, since there is a gap between the outer peripheral surface of the tip of the worm shaft 6 and the sliding surface 20, the tip of the worm shaft 6 is displaced toward the worm wheel 4 based on this gap. Is acceptable. As a result, also in the case of this example, backlash between the worm teeth 5 and the worm wheel 4 is suppressed, and generation of rattling noise is prevented. When power is transmitted between the worm teeth 5 and the worm wheel 4, the worm 8 is oscillated and displaced in the direction away from the worm wheel 4 around the rolling bearing 9b as a reaction of the power transmission. In this state, the outer peripheral surface of the tip portion of the worm shaft 6 and the sliding surface 20 are in sliding contact with the side opposite to the worm wheel 4, and the worm 8 is rotatable while supporting the reaction force accompanying the power transmission. To support.

According to the electric power steering apparatus of this example having the above-described configuration, the temperature rise of the sliding bearing 17 for rotatably supporting the tip of the worm shaft 6 can be sufficiently suppressed. It can prevent that 17 becomes high temperature.
That is, in the case of this example, a configuration in which the worm teeth 5 are pressed against the worm wheel 4 by the biasing member 10a and the coil spring 11a is employed, which is described in Patent Document 3 described above. Unlike the structure of the invention, it is not necessary to give elasticity to the slide bearing itself, and it is not necessary to make the slide bearing thick. Therefore, in the case of this example, among the sliding bearings 17, the bearing body 18 that is likely to become hot during operation is configured to be thin (for example, 3 mm or less, more preferably 2 mm or less). In the case of this example, heat hardly accumulates in the bearing body 18 and heat can be released (transmitted) from the bearing body 18 to the housing 3a at an early stage. Therefore, the temperature rise of the sliding bearing 17 (bearing body 18) can be suppressed. Note that the minimum value of the thickness of the bearing body 18 is restricted in terms of strength and rigidity durability required for the bearing body 18. That is, from the viewpoint of temperature rise suppression, the thinner the thickness, the better. However, considering these performances, 1.0 mm or more is necessary.

In addition, in the case of this example, the outer surface shape of the sliding bearing 17 and the inner surface shape of the holding recess 12a formed on the inner side of the housing 3a are matched, and the outer surface of the sliding bearing 17 (the outer periphery of the bearing main body portion 18). The surface and the axially outer surface, and the outer peripheral surface and the axially outer surface of the accommodating portion 19 are in close contact with the inner surface (the inner peripheral surface and the axially inner surface ) of the holding recess 12a with substantially no gap. For this reason, a sufficiently large contact area between the sliding bearing 17 and the housing 3a can be secured, and heat can be efficiently released from the sliding bearing 17 to the housing 3a. In particular, since the housing 3a has a sufficiently large volume and a large heat capacity as compared with the sliding bearing 17, the temperature of the sliding bearing 17 can be sufficiently lowered because of a large surface area.

  As a result, in the case of this example, the temperature rise of the sliding bearing 17 can be sufficiently suppressed, and the sliding bearing 17 can be prevented from becoming high temperature during operation. Therefore, it is possible to prevent the sliding bearing 17 (sliding surface 20) from increasing in wear and seizure, and to suppress a decrease in bearing life of the sliding bearing 17. Further, since the amount of thermal expansion of the sliding bearing 17 can be suppressed, a decrease in the rotational accuracy of the worm shaft 6 can be suppressed. Further, even when a high load is continuously applied to the sliding surface 20 from the outer peripheral surface of the worm shaft 6, the problem that the sliding surface 20 is melted by frictional heat is prevented from occurring. it can. In the case of this example, since the outer surface of the sliding bearing 17 is brought into close contact with the inner surface of the holding recess 12a substantially without any gap, the sliding bearing 17 is made of synthetic resin as in this example, In addition, even when the bearing body 18 is thin, the bearing body 18 can be sufficiently rigid.

  In the case of this example, since the biasing member 10a is guided by the guide wall portions 22 and 22 provided integrally with the sliding bearing 17, the displacement of the worm shaft 6 is predetermined via the biasing member 10a. (Direction in which the worm teeth 5 are pressed against the worm wheel 4) can be strictly regulated. For this reason, it is possible to reliably prevent the auxiliary force applied from the electric motor 7 from becoming unstable (the auxiliary torque is likely to fluctuate) due to the worm shaft 6 being displaced in a direction other than the predetermined direction. Further, since the coil spring 11a is provided between the sliding bearing 17 and the biasing member 10a, an elastic member is provided between the housing and the housing as in the conventional structure shown in FIG. As compared with the case, the force for pressing the worm teeth 5 toward the worm wheel 4 can be set more finely, and unpleasant noises and vibrations such as rattling noises can be prevented more reliably. .

  Furthermore, in the case of this example, the bearing main body 18 that exhibits the original function of the sliding bearing and the accommodating portion 19 that accommodates the biasing member 10a and the coil spring 11a are integrally formed. The slide bearing 17, the biasing member 10a, and the coil spring 11a can be integrally handled as an assembly (subassembly) assembled with each other. For this reason, the operation | work which attaches these members 17, 10a, 11a to the said housing 3a and the said worm shaft 6 can be performed easily. Further, unlike the conventional structure shown in FIG. 6, it is not necessary to provide a separate holder for assembling the urging member and the elastic member, so that the number of parts can be reduced, and the production of parts and the management of parts can be reduced. I can plan.

[Second Example of Embodiment]
FIG. 4 shows a second example of an embodiment of the invention corresponding to all claims. The feature of this example is that the outer surface of the portion of the housing 3b where the sliding bearing 17 is fitted and supported on the inner side is formed into a concavo-convex shape 27. Specifically, in the case of this example, a plurality of slits 28 and 28 that are parallel to each other are formed on the outer surface of the wall portion that forms the bottom of the holding recess 12a in the housing 3b, and these slits 28 and 28 are formed. Radiating fins 29 and 29 are provided between the two. The slits 28 and the heat radiating fins 29 constitute the concavo-convex shape 27.

In the case of this example, it is possible to increase the surface area (heat radiation area) of the portion of the housing 3b where the sliding bearing 17 is installed, and to improve the heat radiation efficiency of the housing 3b. it can. For this reason, this housing 3b can be cooled early compared with the case where the said uneven | corrugated shape 27 is not provided. As a result, the temperature rise of the sliding bearing 17 that is fitted and supported in the housing 3b can be more effectively suppressed.
The configurations, functions, and effects of other parts including the configuration of the sliding bearing 17 and the holding recess 12a are the same as those in the first example of the above-described embodiment.

As a material constituting the slide bearing , in addition to the synthetic resin as described above, a metal having self-lubricating properties such as copper or a copper-based alloy can be used. Furthermore, instead of such a single material structure of metal or synthetic resin, a multilayer structure of synthetic resin and metal may be used. The housing is not limited to the aluminum alloy as described above, and a metal having excellent heat dissipation can be used as appropriate. Also, a film having excellent heat dissipation (for example, a heat radiation film having an emissivity of 0.50 or more) can be formed on the outer surface of the housing (and also the outer surface of the sliding bearing). Further, the uneven shape formed on the outer surface of the housing is not limited to the structure including the slit and the heat radiating fin as shown in the figure, and may be any shape that can increase the surface area of the housing, such as a cross-sectional sawtooth shape or a cross-sectional wave shape.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3, 3a, 3b Housing 4 Worm wheel 5 Worm tooth 6 Worm shaft 7 Electric motor 8 Worm 9a, 9b Rolling bearing 10, 10a Energizing member 11, 11a Coil spring 12, 12a Holding recessed part 13 Holder 14 Elastic ring 15 Intermediate shaft 16 Steering gear unit 17 Sliding bearing 18 Bearing body portion 19 Housing portion 20 Sliding surface 21 Housing groove 22 Guide wall portion 23 Inner side surface 24 Locking recess 25 Coil portion 26 Locking portion 27 Uneven shape 28 Slit 29 Heat dissipation fin

Claims (2)

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 meshing with the worm wheel, both end portions of the worm shaft in the axial direction are rotatably supported with respect to the housing by bearings, the base end portion of the worm shaft and the tip end of the output shaft An electric motor that freely engages the transmission of rotational force with the worm wheel, and a worm wheel with the tip of the worm shaft rotatably supported. A biasing member provided perspective rotatably in that, at the worm teeth through the urging member to the electric power steering apparatus provided with an elastic member for pressing toward the worm wheel,
Of the bearings that respectively support both axial ends of the worm shaft, at least the bearing that supports the tip of the worm shaft is a sliding bearing,
This sliding bearing is formed by integrally forming a thin cylindrical bearing main body portion having an inner peripheral surface as a sliding surface and a housing portion for assembling the urging member and the elastic member. The outer surface has a shape matching the inner surface of the holding recess provided in the portion facing the tip of the worm shaft, and the outer peripheral surface and the axially outer surface of the bearing main body, the outer peripheral surface of the housing portion, and electric power steering apparatus of the axially outer side, characterized in that it is fitted and supported on the inside of the housing in a state of substantially brought into close contact without a gap with the inner circumferential surface and axially inner surface of the holding recess. The electric power steering apparatus according to claim 1 , wherein an outer surface of a portion of the housing, on which the sliding bearing is fitted and supported, has an uneven shape.

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