JP5509795B2 - 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 provides a sliding contact portion between the outer peripheral surface of the tip portion of the worm shaft constituting such an electric power steering device and the inner peripheral surface of a slide bearing for rotatably supporting the tip portion of the worm shaft. It was invented to realize a structure that can suppress the heat generation.

  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 recently become widespread. 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. The housing 3 is filled with a lubricant such as grease to lubricate the meshing portion between the worm wheel 4 and the worm tooth 5 and the rolling contact portions of the rolling bearings 9a and 9b. ing.

  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. 10) 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-short 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 base end side of the worm shaft 6. The same applies throughout the present specification. 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, when the backlash between the worm teeth 5 and the worm wheel 4 is suppressed and the rotation direction of the steering shaft 2 is changed, an unpleasant noise or vibration called a rattling noise is generated. Is preventing.

  In the case of the conventional structure as described above, the worm shaft 5 is supported in such a manner that the worm shaft 5 is elastically pressed toward the worm wheel 4 so that the worm shaft 6 can be moved in a perspective direction with respect to the worm wheel 4. 6 is supported by the elastic ring 14, the rolling bearing 9 a, the holder 13, the urging member 10, and the coil spring 11. In the case of such a structure, the number of parts is large, and as a result, the assembling work becomes troublesome and the manufacturing cost may increase.

  On the other hand, in Patent Document 2, the tip portion of the worm shaft is rotatably supported by a sliding bearing, and the tip portion of the worm shaft is directed to the worm wheel via the sliding bearing by an annular coil spring. An elastically pressing structure is described. Further, in Patent Document 3, the tip of the worm shaft is rotatably supported by a sliding bearing that is fitted and fixed inside the housing in an elastically deformed state (flexed), and the sliding bearing itself based on this bending is disclosed. A structure is described in which the tip of the worm shaft is elastically pressed toward the worm wheel by the elastic force.

  In the case of the structures of the inventions described in these Patent Documents 2 and 3, since the sliding bearing is used instead of the rolling bearing, the number of parts can be reduced, and the cost of the electric power steering apparatus can be reduced. . However, when the tip of the worm shaft is supported using a sliding bearing, the sliding contact portion between the inner peripheral surface (sliding surface) of the sliding bearing and the outer peripheral surface of the tip of the worm shaft becomes hot due to frictional heat. It becomes easy. That is, in the case of a general sliding bearing, since the sliding surface which is the inner peripheral surface is a single cylindrical surface, it is difficult to stably supply a sufficient amount of lubricant to the sliding contact portion. For this reason, an oil film breakage is likely to occur at the sliding contact portion, and the sliding contact portion is likely to become high temperature. And, since the sliding contact portion becomes high temperature in this way, the bearing life is likely to be shortened due to the occurrence of seizure or an increase in the amount of wear, and the rotational accuracy of the worm shaft is reduced (the shaft runout is increased). It may cause the above-mentioned problems. In particular, in the case of a structure in which the tip of the worm shaft is directly pressed by a sliding bearing as in the structures of the inventions described in Patent Documents 2 and 3, since the contact surface pressure at the sliding contact portion increases, The degree of heat generation becomes significant, and the problems as described above are more likely to occur.

  In addition, there exists invention described in patent document 4 as another prior art document relevant to this invention. Patent Document 4 describes an invention in which a pocket for holding a solid lubricant is formed on an inner peripheral surface of an aligning ring and an outer peripheral surface of an outer ring for a roller bearing with an aligning ring. However, the invention described in Patent Document 4 is an invention intended to prevent heat generation between the aligning ring and the outer ring which are relatively oscillating and displaced, and rotates relative to each other as in the present invention. It is not intended for heat generation at the sliding contact portion between the worm shaft and the sliding bearing.

JP 2004-306898 A Japanese Patent No. 3624309 Japanese Patent No. 3658682 JP 2006-214469 A

  In view of the circumstances as described above, the present invention is low cost by suppressing the number of parts, and can prevent generation of unpleasant noise and vibration such as rattling noise, and the tip of the worm shaft. The invention was invented to realize an electric power steering device capable of sufficiently suppressing heat generation at the sliding contact portion between the outer peripheral surface and the inner peripheral surface of the sliding bearing for rotatably supporting the tip of the worm shaft. .

The electric power steering apparatus of the present invention is similar to the electric power steering apparatus having the conventional structure shown in FIGS. 9 to 10 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 are provided, and the housing is filled with a lubricant such as grease.
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. 9 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 urging member (for example, a coil spring or a leaf spring) is elastically abutted only on the surface of the urging member on the side opposite to the worm wheel, in the outer peripheral surface of the urging member. The worm teeth are pressed toward the worm wheel via the.

In particular, in the electric power steering apparatus according to the first aspect, at least the tip portion of the worm shaft is supported (from the electric motor) among the bearings that respectively support the axial end portions of the worm shaft. The bearing on the far side is a sliding bearing.
In addition, the sliding bearing has a minor axis in a direction parallel to the central axis of the worm wheel and a major axis in a direction perpendicular to the central axis of the worm wheel for rotatably supporting the tip of the worm shaft. A bearing main body portion having a through hole which is an oval oval arranged so as to face each other , and a cylindrical portion provided in a state of protruding in the axial direction from the axial side surface of the bearing main body portion. . Of these, the urging member and the elastic member are directly supported on the inner diameter side of the cylindrical portion, and the lubricant is applied to the inner peripheral surface (sliding surface) of the through hole. An oil retaining part that can be retained is formed.

Further, in the electric power steering apparatus according to the second aspect, at least the tip portion of the worm shaft is supported (from the electric motor) among the bearings respectively supporting the axial end portions of the worm shaft. The bearing on the far side is a sliding bearing.
In addition, the sliding bearing has a minor axis in a direction parallel to the central axis of the worm wheel and a major axis in a direction perpendicular to the central axis of the worm wheel for rotatably supporting the tip of the worm shaft. A bearing main body portion having a through hole which is an oval oval arranged so as to face each other , and a cylindrical portion provided in a state of protruding in the axial direction from the axial side surface of the bearing main body portion. . And it supports directly in the state which combined the said urging | biasing member and the said elastic member on the internal diameter side of the cylindrical part of these.
Further, an oil retaining portion capable of holding the lubricant is formed in a portion of the outer peripheral surface of the tip portion of the worm shaft that is in sliding contact with the inner peripheral surface (sliding surface) of the through hole during operation.

  Furthermore, when carrying out the invention described in claim 1 and claim 2 as described above, the oil retaining portion is a concave groove functioning as an oil groove, as in the invention described in claim 3, or The recess functions as an oil sump.

According to the electric power steering apparatus of the present invention having the above-described configuration, it is possible to prevent generation of unpleasant noise and vibration such as rattling noise, and sufficiently suppress heat generation at the sliding contact portion. Can be configured at a low cost with a reduced number of parts.
That is, in the case of the electric power steering device of the present invention, the worm shaft tip is supported by the sliding bearing, and the urging member and the elastic member for pressing the worm tooth toward the worm wheel are supported on the sliding bearing. And directly support. For this reason, in the case of this invention, the structure which can prevent generation | occurrence | production of unpleasant unusual noises and vibrations, such as a rattling sound, can be comprised at low cost, suppressing a number of parts small.

In the case of the present invention, the inner peripheral surface of the through hole provided in the sliding bearing (in the case of the invention described in claim 1) or the outer peripheral surface of the tip portion of the worm shaft (the invention described in claim 2) In this case, an oil retaining portion is formed that can hold the lubricant filled in the housing. Therefore, in the case of the present invention, the lubricant can be stably supplied from the oil retaining portion to the sliding contact portion. Accordingly, it is possible to prevent the oil film from being cut off at the sliding contact portion and to suppress heat generation at the sliding contact portion. In addition, in the case of the present invention, the contact surface pressure at the sliding contact portion is excessive because the tip portion of the worm shaft is pressed through the biasing member without being directly pressed by the sliding bearing. It is possible to prevent heat generation at this sliding contact portion from this surface. As a result, in the case of the present invention, the heat generation at the sliding contact portion during operation can be sufficiently suppressed, and the occurrence of seizure and the increase in the amount of wear can be prevented. Therefore, according to the present invention, the bearing life of the sliding bearing can be improved, and the rotational accuracy of the worm shaft can be improved (reduction in shaft runout).

  Furthermore, in the case of the present invention, the sliding bearing, the biasing member, and the elastic member can be integrally handled as an assembly (subassembly), so that 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.

The figure equivalent to the AA expanded cross section of FIG. 9 which shows the 1st example of embodiment of this invention. The B section enlarged view of FIG. 1 similarly. Sectional drawing which shows four examples of the slide bearing which can be similarly used for this example. The figure which took out the sliding bearing similarly and was seen from the left side of FIG. The disassembled perspective view which similarly takes out and shows a sliding bearing, a biasing member, and a coil spring. FIG. 3 is a view taken in the direction of arrow C in FIG. The figure equivalent to FIG. 2 which shows the 2nd example of embodiment of this invention. The figure which shows three examples of the front-end | tip part of the worm shaft which can be similarly used for this example. The partially cut side view which shows an example of a conventional structure. Similarly AA expanded sectional drawing of FIG.

[First example of embodiment]
1 to 6 show a first example of an embodiment of the present invention corresponding to claims 1 and 3. The electric power steering apparatus according to the present embodiment is characterized in that the sliding between the outer peripheral surface of the tip of the worm shaft 6 and the inner peripheral surface of the sliding bearing 17 for rotatably supporting the tip of the worm shaft 6. In order to suppress the heat generation at the contact portion, the structure of the sliding bearing 17 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. 9 to 10 described above, the illustration and description of the equivalent parts are omitted or simplified. The description will focus on the characteristic part.

  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. Also in this example, the meshing portion between the worm wheel 4 and the worm tooth 5, the rolling contact portion of the rolling bearing 9b, the sliding contact portion between the sliding bearing 17 and the worm shaft 6, etc. In order to lubricate, the housing 3a is filled with grease. 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 fitted and fixed in a holding recess 12a formed in a portion facing the tip of the worm shaft 6 inside the housing 3a. The tip end portion (the portion closer to the base end than the portion where the biasing member 10a is externally fitted) is rotatably supported. In the case of this example, the holding recess 12a is a recess having a cylindrical surface shape with a bottom that opens inside the housing 3a and does not change in diameter in the axial direction (constant inner diameter). On the other hand, the sliding bearing 17 is a slippery (low sliding resistance) synthetic resin such as polyamide resin or polytetrafluoroethylene resin, or a self-lubricating material such as copper or a copper-based alloy. The bearing main body 18, the cylindrical portion 19, and the pair of guide wall portions 20 are integrally made of a single member such as a soft metal (relative to an aluminum alloy or the like constituting the housing 3 a). , 20.

  Of these, the bearing body portion 18 is a portion that exhibits the original function of the sliding bearing, has a circular outer peripheral surface, and a through hole for rotatably supporting the tip of the worm shaft 6 at the center. 21. The cylindrical portion 19 has an outer peripheral surface that is continuous with the outer peripheral surface of the bearing main body portion 18 (having the same outer diameter). The bearing main body portion 18 is provided integrally with the bearing main body portion 18 so as to protrude in the direction. The guide wall portions 20 and 20 are integrally formed with the bearing body 18 in a state of projecting outward from the axially outer side surface of the bearing body 18 toward the inner diameter side of the cylindrical portion 19. Is provided. The inner side surfaces of both the guide wall portions 20, 20 are planes parallel to each other.

  In particular, in this example, as shown in FIG. 3A, the grease filled in the housing 3a is held on a sliding surface which is the inner peripheral surface of the through hole 21. A plurality of concave grooves 22 and 22 corresponding to the oil retaining portion described in the claims are formed. Each of these concave grooves 22, 22 functions as an oil groove, and is recessed in the radially outward direction from the inner peripheral surface of the through hole 21 in the axial direction of the sliding bearing 17 (parallel to the axial direction). To be formed. The concave grooves 22 and 22 are arranged on the inner peripheral surface of the through hole 21 in the circumferential direction at equal intervals. The cross-sectional shape of each of the concave grooves 22 and 22 is not particularly limited as long as it is a shape capable of holding grease, such as an arc shape, a rectangular shape, a trapezoidal shape, a V shape, or a U shape. Further, the sliding bearing 17 having such concave grooves 22 and 22 can be manufactured by one injection molding using, for example, a split mold, and the inner peripheral surface of the through hole 21 is a single cylindrical surface. It can also be made by forming the concave grooves 22 and 22 by cutting or the like after processing into a shape.

  In any case, in the case of this example, the inner diameter of the through hole 21 having the concave grooves 22 and 22 as described above is inserted into the through hole 21 in the tip portion of the worm shaft 6. It is larger than the outer diameter of the part. As a result, the worm shaft 6 is allowed to displace (in the radial direction) within the through hole 21. More specifically, as shown in FIG. 4, the through hole 21 has an oval oval shape, and the short diameter of the through hole 21 is set in a state in which the sliding bearing 17 is fitted in the holding recess 12a. The worm wheel 4 is arranged in a direction parallel to the central axis of the worm wheel 4 so that the long diameter of the through hole 21 faces in a direction perpendicular to the central axis of the worm wheel 4. Therefore, in this example, the tip of the worm shaft 6 has a displacement tolerance in a direction perpendicular to the central axis of the worm wheel 4 as compared to a displacement tolerance in a direction parallel to the central axis of the worm wheel 4. growing.

  As shown in detail in FIG. 4, at least one pair of locking projections 23 is provided on the outer peripheral surface of the bearing main body 18 constituting the sliding bearing 17 so as to protrude radially outward from the outer peripheral surface. , 23 are provided. At the same time, on the inner surface of the holding recess 12a, the sliding bearing 17 is fitted in the holding recess 12a and is aligned with the locking projections 23, 23 to be radially outward from the inner surface. A locking groove 24 that is recessed in the direction is provided over the entire circumference. Then, in a state in which the sliding bearing 17 is fitted in the holding recess 12a, the locking protrusions 23 and 23 and the locking groove 24 are engaged with each other.

In the case of this example, the sliding bearing 17 is elastically deformed, and is fitted in the holding recess 12a without looseness (by an interference fit). Therefore, the outer diameter of the bearing body 18 in a free state (for example, as shown in FIG. 4, the outer diameter of the bearing body 18 is D ₁₈ and the height of the locking projection 23 is h. In this case, the outer diameter D = D ₁₈ + h including the height h of the locking projection 23 is defined as the inner diameter of the holding recess 12a (for example, as shown in FIG. 2, the inner diameter of the holding recess 12a is d _12. When the depth of the locking groove 24 is f, the inner diameter d = d ₁₂ + f) including the depth f of the locking groove 24 is slightly larger (D> d). . At the same time, on the inner side surface in the axial direction of the bearing body 18, an elastic deformation allowing recess is recessed into the inner diameter side portion of each locking projection 23, 23 from the inner side surface in the axial direction. 25 is provided.

  In the case of this example, in a state in which the sliding bearing 17 is fitted in the holding recess 12a, a part of the sliding bearing 17, that is, the peripheral portion of the elastic deformation allowing recess 25 is the bearing main body portion 18. It is elastically deformed radially inward. Then, based on the elastic force of the sliding bearing 17 itself based on the elastic deformation, the locking projections 23 and 23 are pressed toward the bottom of the locking groove 24, and the sliding bearing 17 is held by the holding. The recess 12a is fitted (held) without rattling. In the case of this example, since the sliding bearing 17 can be easily elastically deformed in a predetermined direction by the elastic deformation allowing recess 25, the sliding bearing 17 is incorporated into the holding recess 12a in an elastically deformed state. Can be easily performed (improvement of built-in workability). Further, the displacement of the sliding bearing 17 in the axial direction is prevented based on the concave-convex engagement between the locking projections 23, 23 and the locking groove 24. Instead of the pair of locking projections 23, 23, as shown in FIG. 6, a locking projection 23a can be provided on the outer peripheral surface of the bearing body 18 over the entire circumference. As described above, the inner side surfaces (side surfaces facing each other) of the guide wall portions 20 and 20 are respectively connected to the central axis of the worm wheel 4 in a state where the sliding bearing 17 is fitted in the holding recess 12a. It is arranged in a direction perpendicular to it.

  In the case of this example, the urging member 10a and the coil spring 11a for elastically pressing the worm tooth 5 against the worm wheel 4 against the sliding bearing 17 are combined with each other. It is assembled. Specifically, the urging member 10a is clamped between the inner side surfaces of the guide wall portions 20 and 20 on the inner diameter side of the cylindrical portion 19, and around the urging member 10a. In a state where the coil spring 11a is disposed, the bent portions 26 and 26 provided at both ends of the coil spring 11a are locked to the locking portions 27 and 27 formed on the both guide wall portions 20 and 20, respectively.

Here, since the inner side surfaces of the both guide wall portions 20, 20 are arranged in a direction perpendicular to the central axis of the worm wheel 4 in the assembled state of the sliding bearing 17, the both guide wall portions 20, The urging member 10a sandwiched between the inner side surfaces of the 20 enables displacement along the inner side surfaces of the guide wall portions 20 and 20 and is displaced in the direction of the central axis of the worm wheel 4. It is supported in a state that suppresses. Therefore, the worm shaft 6 in which such a biasing member 10a is externally fitted (freely fitted) to the tip portion thereof is attached to the worm wheel 4 by the guide wall portions 20 and 20 via the biasing member 10a. Guided only for perspective movement. Further, with the biasing member 10a and the coil spring 11a supported by the sliding bearing 17, the inner peripheral surface of the coil spring 11a is the same as the worm wheel 4 among the outer peripheral surfaces of the biasing member 10a. Is elastically in contact with only the opposite surface. Therefore, also in this example, the worm teeth 5 are pressed toward the worm wheel 4 by the coil spring 11a via the biasing member 10a.

In the case of this example having the above-described configuration, it is possible to prevent unpleasant noises and vibrations such as rattling noises from occurring and to sufficiently suppress the heat generation at the sliding contact portion. It can be configured with low cost and low cost.
That is, in the case of this example, the tip of the worm shaft 6 is supported by the sliding bearing 17 and the above-mentioned attachment for pressing the worm teeth 5 against the worm wheel 4 against the sliding bearing 17. The urging member 10a and the coil spring 11a are directly supported in a combined state. For this reason, in the case of this example, the number of parts can be reduced by using a slide bearing having a simpler structure than a rolling bearing, and the biasing member 10a and the coil spring 11a can be supported. The number of parts can be reduced by omitting the dedicated member (holder 13 as shown in FIG. 10). Therefore, in the case of this example, a structure capable of preventing the generation of unpleasant noises and vibrations such as rattling noise can be configured at a low cost with a reduced number of parts.

  Particularly in the case of this example, since a plurality of concave grooves 22 and 22 are formed on the inner peripheral surface (sliding surface) of the through hole 21 constituting the sliding bearing 17, the inside of each of the concave grooves 22 and 22 is formed. In addition, (a part of) the grease filled in the housing 3a can be held. Therefore, during operation, a sufficient amount of grease can be stably supplied to the sliding contact portion between the outer peripheral surface of the tip portion of the worm shaft 6 and the inner peripheral surface of the through hole 21 through the concave grooves 22 and 22. In the case of this example, since each of the concave grooves 22 and 22 has a long shape in the axial direction, it is easy to supply grease over the entire axial width of the sliding contact portion. Therefore, in the case of this example, it is possible to effectively prevent the oil film from being cut off at the sliding contact portion and to suppress the heat generation at the sliding contact portion. Further, in the case of this example, as in the case of the structure of the invention described in Patent Documents 2 and 3 described above, the urging member 10a is not directly pressed by the sliding bearing on the tip of the worm shaft 6. Therefore, the contact surface pressure at the sliding contact portion can be prevented from becoming excessive, and the heat generation at the sliding contact portion can also be suppressed from this surface. In addition, in the case of this example, the frictional heat generated at the sliding contact portion can also be radiated from each of the concave grooves 22 and 22 (via a lubricant entering and exiting each of the concave grooves 22 and 22). . As a result, in the case of this example, the heat generation at the sliding contact portion during operation can be sufficiently suppressed, and the occurrence of seizure and the increase in the amount of wear can be prevented. Accordingly, the bearing life of the sliding bearing 17 can be improved, and the rotational accuracy of the worm shaft 6 can be improved (reduction in shaft runout).

  In the case of this example, the urging member 10a is guided by the guide wall portions 20 and 20 provided integrally with the sliding bearing 17, so that the worm shaft 6 is displaced via the urging member 10a. Can be strictly regulated in a predetermined direction (direction in which the worm teeth 5 are pressed against the worm wheel 4). For this reason, it is possible to effectively 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. Compared to the case, the force for pressing the worm teeth 5 toward the worm wheel 4 can be set more finely, and the generation of unpleasant noises and vibrations such as rattling noises can be prevented more effectively. it can.

  Further, in the case of this example, the sliding bearing 17, the biasing member 10a, and the coil spring 11a can be integrally handled as an assembly (subassembly), so that the assembly work of the electric power steering device is facilitated. Can be planned. In addition, the number of parts can be reduced, and parts production and parts management can be reduced.

In the case of this example, as described above, the concave grooves 22 and 22 as shown in FIG. 3A are formed on the inner peripheral surface of the through hole 21 constituting the slide bearing 17. As described above, it is possible to form the concave grooves 22a and 22b as shown in FIGS. 5B and 5C, or the concave portions 28 and 28 as shown in FIG.
First, in the case of the structure shown in FIG. 5B, annular concave grooves 22a and 22a are formed at a plurality of axial locations (three locations in the illustrated example) on the inner peripheral surface of the through hole 21. Yes. When such a configuration is adopted, it becomes easy to spread the grease over the entire circumference between the inner peripheral surface of the through hole 21 and the outer peripheral surface of the tip portion of the worm shaft 6. Further, it is advantageous from the viewpoint of suppressing the rotational resistance of the worm shaft 6.
In the case of the structure shown in FIG. 3C, spiral grooves (inclined with respect to the circumferential direction) 22b and 22b are formed on the inner peripheral surface of the through hole 21. When such a configuration is adopted, as the worm shaft 6 rotates, an axial direction and a circumferential direction are formed between the outer peripheral surface of the tip portion of the worm shaft 6 and the inner peripheral surface of the through hole 21. This makes it easier to supply grease.
Further, in the case of the structure shown in FIG. 4D, a plurality of recesses 28 and 28 functioning as oil reservoirs are formed on the inner peripheral surface of the through hole 21. When such a configuration is adopted, the number, size, shape, depth, and the like of each of the recesses 28, 28 are appropriately changed according to the circumferential direction and the axial position of the through hole 21. The amount of grease supplied to the sliding contact portion can be easily and finely set.
Further, in the case of this example, the case where the through hole 21 is an oval oval has been described. However, the through hole 21 is inserted into the through hole 21 in the tip portion of the worm shaft 6. It is good also as a circle which has an internal diameter larger than the outer diameter of the part to carry out. When such a configuration is adopted, the workability of the through hole 21 can be improved, which is advantageous from the viewpoint of reducing the processing cost.

[Second Example of Embodiment]
7 to 8 show a second example of an embodiment of the present invention corresponding to claims 2 and 3. In the first example of the above-described embodiment, the concave grooves 22 and 22 (the concave grooves 22a and 22b and the concave portion 28) capable of holding the grease are formed on the inner peripheral surface of the through hole 21 constituting the sliding bearing 17. I explained about the case. On the other hand, in the case of this example, the concave grooves 22 and 22 are not formed on the inner peripheral surface of the through hole 21a constituting the sliding bearing 17a, and the outer peripheral surface of the tip portion of the worm shaft 6a. In addition, concave grooves 29 and 29 that can hold the grease are formed. The structure of the sliding bearing 17a of this example is the same as that of the sliding bearing 17 of the first example except for the shape of the inner peripheral surface of the through hole 21a (the presence or absence of the concave grooves 22, 22a, 22b, and the concave part 28). It is.

  In the case of this example, as shown in FIG. 7, the worm shaft is placed on a portion of the outer peripheral surface of the worm shaft 6 a that is in sliding contact with the inner peripheral surface (sliding surface) of the through hole 21 a during operation. A plurality of concave grooves 29, 29 are formed in the axial direction 6a (in parallel with the axial direction). Further, the concave grooves 29 and 29 are arranged on the outer peripheral surface of the tip portion of the worm shaft 6a at equal intervals in the circumferential direction. Further, the cross-sectional shape of each of the concave grooves 29 and 29 is not particularly limited as long as it is a shape capable of holding grease, such as an arc shape, a rectangular shape, a trapezoidal shape, a V shape, and a U shape.

  Also in this example having such a configuration, the grease filled in the housing 3a can be held in each of the concave grooves 29, 29. Therefore, a sufficient amount of grease can be stably supplied to the sliding contact portion between the outer peripheral surface of the tip portion of the worm shaft 6a and the inner peripheral surface of the through hole 21a through the concave grooves 29, 29. In particular, in the case of this example in which each of the concave grooves 29, 29 is formed on the outer peripheral surface of the tip portion of the worm shaft 6a, the grease held in each of the concave grooves 29, 29 is utilized by utilizing centrifugal force. It can be efficiently supplied to the sliding contact portion. Further, in the case of this example, since each of the concave grooves 29 and 29 has a shape that is long in the axial direction, it is easy to supply grease over the entire axial width of the sliding contact portion. Therefore, in the case of this example, it is possible to effectively prevent the oil film from being cut off at the sliding contact portion and to suppress the heat generation at the sliding contact portion. Further, also in the case of this example, as in the case of the structure of the invention described in Patent Documents 2 and 3 described above, the biasing member 10a is not directly pressed by the sliding bearing on the tip of the worm shaft 6a. Therefore, the contact surface pressure at the sliding contact portion can be prevented from becoming excessive, and the heat generation at the sliding contact portion can also be suppressed from this surface. Moreover, the frictional heat generated at the sliding contact portion can be radiated from the concave grooves 29 and 29. As a result, also in this example, the heat generation at the sliding contact portion during operation can be sufficiently suppressed, and the occurrence of seizure and the increase in the amount of wear can be prevented. Accordingly, the bearing life of the sliding bearing 17a can be improved, and the rotational accuracy of the worm shaft 6a can be improved (reduction in shaft runout).

In the case of this example, as described above, the case where the concave grooves 29 and 29 as shown in FIG. 7 are formed on the outer peripheral surface of the tip of the worm shaft 6a has been described. ) And (B), or concave portions 30 and 30 as shown in FIG. 5C can be formed.
First, in the case of the structure shown in FIG. 5A, annular concave grooves 29a and 29a are formed at a plurality of axial locations (three locations in the illustrated example) on the outer peripheral surface of the tip of the worm shaft 6a. ing. When such a configuration is adopted, it becomes easy to spread the grease over the entire circumference between the inner peripheral surface of the through hole 21a and the outer peripheral surface of the tip portion of the worm shaft 6a. Further, it is advantageous from the viewpoint of suppressing the rotational resistance of the worm shaft 6a.
In the case of the structure shown in FIG. 5B, spiral grooves (inclined with respect to the circumferential direction) 29b and 29b are formed on the outer peripheral surface of the tip portion of the worm shaft 6a. . When such a configuration is adopted, along with the rotation of the worm shaft 6a, an axial direction and a circumferential direction are provided between the outer peripheral surface of the tip portion of the worm shaft 6a and the inner peripheral surface of the through hole 21a. This makes it easier to supply grease.
Furthermore, in the case of the structure shown in FIG. 5C, a large number of recesses 30 and 30 functioning as oil sumps are formed on the outer peripheral surface of the tip of the worm shaft 6a. When such a configuration is adopted, the number, size, shape and depth of each of the recesses 30 and 30 are appropriately changed according to the axial position of the worm shaft 6a, so that the sliding contact portion is formed. The amount of grease to be supplied can be easily set finely (finely in the axial direction).
About another structure, an effect | action, and an effect, it is the same as that of the case of the 1st example of embodiment mentioned above.

  In the first example of the above-described embodiment, the example in which the concave grooves 22 and 22 are arranged on the inner peripheral surface of the through hole 21 in the circumferential direction at equal intervals has been described. However, the present invention is limited to such a structure. Instead, the concave grooves 22 and 22 may be arranged at unequal intervals on the inner peripheral surface of the through hole 21. That is, in the inner peripheral surface of the through-hole 21, there are a number of portions that are easily in sliding contact with the outer peripheral surface of the tip portion of the worm shaft 6, or portions that are easily pressed against the outer peripheral surface of the worm shaft 6. The concave grooves 22 and 22 are formed, and the concave grooves 22 and 22 are not formed in other portions, or the number of the concave grooves 22 and 22 to be formed can be reduced. From the same viewpoint, the groove depths of the concave grooves 22 and 22 can be appropriately changed according to the formation position. As described above, the number of grooves and the depth of the grooves can be appropriately changed according to the position of formation, and can be applied to the grooves 22a and 22b shown in FIGS. The same applies to the recesses 28 and 28 as shown in FIG.

  Further, on the inner peripheral surface of the through hole 21, concave grooves 22, 22a, 22b as shown in FIGS. 3A to 3C and concave portions 28, 28 as shown in FIG. They can also be formed in appropriate combinations. Similarly, the groove 29 as shown in FIG. 7 and the grooves 29a and 29b and the recess 30 as shown in FIG. 8 can be appropriately combined on the outer peripheral surface of the tip portion of the worm shaft 6a. . Further, if necessary, an oil retaining portion capable of holding grease may be formed on both the inner peripheral surface of the through hole 21 (21a) and the outer peripheral surface of the tip end portion of the worm shaft 6 (6a). .

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3, 3a 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 DESCRIPTION OF SYMBOLS 15 Intermediate shaft 16 Steering gear unit 17, 17a Sliding bearing 18 Bearing main-body part 19 Cylindrical part 20 Guide wall part 21, 21a Through-hole 22 Groove 23, 23a Locking convex part 24 Locking concave groove 25 Elastic deformation allowable recessed part 26 Bending Part 27 Locking part 28 Concave part 29 Concave groove 30 Concave part

Claims (3)

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. That a perspective dynamic possible to provided a biasing member, while this is a worm wheel elastically contact with only the surface on the opposite side of the outer circumferential surface of the biasing member through the urging member In the electric power steering apparatus comprising an elastic member that presses the worm teeth toward the worm wheel, and the housing is filled with a lubricant,
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 has a minor axis in a direction parallel to the central axis of the worm wheel and a major axis in a direction perpendicular to the central axis of the worm wheel for rotatably supporting the tip of the worm shaft. A bearing body portion having a through hole and a cylindrical portion provided in a state of protruding in the axial direction from the side surface in the axial direction of the bearing body portion. The urging member and the elastic member are directly supported on the inner diameter side of the cylindrical portion, and an oil retaining portion capable of holding the lubricant is formed on the inner peripheral surface of the through hole. Electric power steering device characterized by being. 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. That a perspective dynamic possible to provided a biasing member, while this is a worm wheel elastically contact with only the surface on the opposite side of the outer circumferential surface of the biasing member through the urging member In the electric power steering apparatus comprising an elastic member that presses the worm teeth toward the worm wheel, and the housing is filled with a lubricant,
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 has a minor axis in a direction parallel to the central axis of the worm wheel and a major axis in a direction perpendicular to the central axis of the worm wheel for rotatably supporting the tip of the worm shaft. A bearing body portion having a through hole and a cylindrical portion provided in a state of protruding in the axial direction from the side surface in the axial direction of the bearing body portion. It is directly supported on the inner diameter side of the cylindrical portion in a state where the biasing member and the elastic member are combined,
An electric power characterized in that an oil retaining portion capable of holding the lubricant is formed on a portion of the outer peripheral surface of the tip portion of the worm shaft that is in sliding contact with the inner peripheral surface of the through hole during operation. Steering device. The electric power steering apparatus according to any one of claims 1 and 2, wherein the oil retaining portion is a concave groove or a concave portion.

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