JP6118603B2 - Gear preload structure and electric power steering device - Google Patents

Description

  The present invention relates to a gear preload structure and an electric power steering apparatus.

  In general, an electric power steering apparatus uses a structure in which the rotational force of a steering assist motor is transmitted to a steering system via a reduction gear mechanism, and a worm gear mechanism is frequently used as the reduction gear mechanism.

  11 and 12 show a conventional example of a worm gear mechanism used in an electric power steering apparatus. The worm gear mechanism 51 includes a worm wheel 101 that is attached to a steering shaft of an electric power steering device (not shown) and a worm 102 that is connected to a motor 103. The worm 102 has a shaft portion 102 a at one end supported by the housing 105 via a bearing 104, and a shaft portion 102 b at the other end supported by the housing 105 via a bearing 106. Reference numeral 111 denotes a stopper that is screwed to the housing 105 to position and fix the bearing 106 in the axial direction. The tip of the shaft portion 102 b that protrudes outward from the bearing 106 is connected to the output shaft 103 a of the motor 103 via the shaft joint 107.

  An example of the shaft coupling 107 is shown in FIG. The shaft coupling 107 includes a first coupling 108 that is pivotally attached to the shaft portion 102b, a second coupling 109 that is pivotally attached to the output shaft 103a, and an elastic bush 110 interposed between the couplings. Configured. A plurality (four in FIG. 13) of engaging claws 108 a are provided on one end face of the first coupling 108 so as to project toward the second coupling 109 side at equal intervals in the circumferential direction. The same number of engagement claws 109a (four in FIG. 13) as the engagement claws 108a are projected at equal intervals in the circumferential direction toward the first coupling 108 side. On the outer periphery of the elastic bushing 110, there are twice (eight in FIG. 13) claws of the engaging claws 108a so that the engaging claws 108a or the engaging space portions 110b with which the engaging claws 109a are engaged are formed. 110a are formed radially at equal intervals.

  The four engagement claws 108a of the first coupling 108 are engaged with the eight engagement space portions 110b of the elastic bush 110 every other one, and the four engagement claws 109a of the second coupling 109 are the remaining ones. Engage with the engagement space 110b. Accordingly, the elastic claw 110a is interposed between the engaging claw 108a and the engaging claw 109a, thereby preventing the hitting sound between the engaging claw 108a and the engaging claw 109a and the rattling in the rotation direction. The

  11 and 12, in order to suppress the meshing hitting sound between the worm 102 and the worm wheel 101, the shaft center O <b> 1 of the worm 102 and the worm wheel 101 are provided between the bearing 104 and the housing 105 as a preload structure. A first compression coil spring 112 is interposed to bias the shaft center distance X with the shaft center O2 in a direction to reduce the distance X. The first compression coil spring 112 is accommodated in a guide bush 114 fitted to the bearing 104. The guide bush 114 is held on the housing 105 via the mount collar 115. A flat spring seat 113 for seating one end of the first compression coil spring 112 is interposed between one end of the first compression coil spring 112 and the outer ring of the bearing 104. A flat stopper plate 116 on which the other end of the first compression coil spring 112 is seated is fastened and fixed to the mount collar 115 by screws 118 (FIG. 12).

  The mount collar 115 is positioned in the direction of the axial center O1 of the worm 3 by an O-ring 117 interposed between the mount collar 115 and the housing 105. Further, as shown in FIG. 11, the through hole 110c (FIG. 13) formed in the elastic bushing 110 has a shaft portion 102b of the worm 102 as shown in FIG. A second compression coil spring 119 is interposed between the end surface and the output shaft 103 a of the motor 103.

  According to the preload structure described above, the meshing hitting sound between the worm 102 and the worm wheel 101 is suppressed by the biasing force of the first compression coil spring 112. Further, the second compression coil spring 113 suppresses the swing of the worm 102 around the axis O1.

  Further, Patent Documents 1 and 2 describe techniques using a leaf spring as a biasing member that biases the shaft center between the worm shaft center and the worm wheel shaft center in a direction to reduce the distance between the shaft centers.

JP 2001-146169 A Japanese Patent Laid-Open No. 2004-203154

  However, the preload structure of the worm gear mechanism 51 has a problem in that it takes time and effort to assemble because the number of parts increases. Moreover, the guide bush 114 is comprised from the resin member so that a metal contact sound may not be produced between the 1st compression coil springs 112. However, if the guide bush 114 is made of a resin member, the linear expansion coefficient is larger than that of the bearing 104, which is a metal part, so that the dimensional change due to temperature increases. There is a possibility that the stroke characteristics of meshing between the worm wheel 101 and the worm wheel 101 are narrowed, and conversely, when the temperature is high, the fitting clearance with the bearing 104 is expanded and the swaying of the worm 102 is increased.

  In addition, the technique of interposing a metal leaf spring between the bearing and the housing described in the cited documents 1 and 2 has the advantage of reducing the number of components, but when the worm swings. In addition, there is a problem that metal contact noise is generated between the leaf spring and the housing.

  The present invention has been made to solve the above-described problems, and provides a gear preload structure capable of solving the problem of metal contact noise with a small number of components and an electric power steering apparatus including the gear preload structure. With the goal.

In order to solve the above problems, the present invention provides a worm, a worm wheel meshing with the worm, a first bearing that pivotally supports a shaft portion at one end of the worm, and a second bearing that pivotally supports a shaft portion of the other end. And a biasing means for biasing the worm to the worm wheel via the first bearing, and a housing for supporting the first bearing, wherein the biasing means comprises: The cylinder is formed of an elastic support member made of a rubber material that elastically supports the first bearing with respect to the housing, and the elastic support member is formed with a fitting hole for fitting an outer periphery of the first bearing. And a plurality of protrusions radially projecting from the cylindrical body part over the entire circumference of the cylindrical body part, the tip of which is pressed against the housing. The height of at least one protrusion of Law is formed to be different from that of the other projection, wherein said that the plurality of projections are housed in all the said housing deformed by compression in the radial direction of the first bearing.

  According to the present invention, the first bearing is elastically supported by the housing by the elastic support member, that is, in a floating state, and the worm swing is suppressed. Since the elastic support member is made of a rubber material, when a leaf spring made of a metal material is interposed between the bearing and the housing as in the prior art, the leaf spring and the housing are caused by the swirling of the worm. This also eliminates the problem of metal contact noise between the two. Moreover, it becomes a simple component structure only of an elastic support member, and it becomes a gear preload structure with a simple assembly process.

  According to the present invention, both the simplification of the shape of the elastic support member and the improvement of the floating support function can be achieved.

  According to the present invention, the distribution in the circumferential direction of the elastic restoring force can be made non-uniform with a simple configuration in which the heights of the protrusions are made different.

  According to the present invention, the elastic support member elastically supports the first bearing with respect to the housing in the axial direction of the first bearing, thereby allowing the worm to move through the first bearing. The bearing is biased toward the bearing side.

  According to the present invention, the elastic support member biases the worm to the second bearing side through the first bearing as a thrust load, and the worm swinging is further suppressed.

  Further, the present invention is an electric power steering device having a gear preload structure in which a motor is connected to the worm and the worm wheel is pivotally attached to a pinion shaft.

  According to the present invention, an electric power steering device that can suppress the worm swing and reduce the metal contact noise is provided.

  According to the present invention, in the gear preload structure and the electric power steering apparatus, it is possible to suppress worm swinging, reduce metal contact noise, and simplify the components.

It is a schematic block diagram of an electric power steering device. It is sectional drawing of the gear preload structure which concerns on 1st Embodiment. It is AA sectional drawing in FIG. It is explanatory drawing of the elastic support member which concerns on 1st Embodiment, (a) is a front view, (b) is BB sectional drawing in (a). It is explanatory drawing of the elastic support member which concerns on 2nd Embodiment, (a) is a front view, (b) is CC sectional drawing in (a). It is sectional drawing of the gear preload structure which concerns on 2nd Embodiment. It is explanatory drawing of the elastic support member which concerns on 3rd Embodiment, (a) is a front view, (b) is DD sectional drawing in (a). It is sectional drawing of the gear preload structure which concerns on 3rd Embodiment. It is explanatory drawing of the elastic support member which concerns on 4th Embodiment, (a) is a front view, (b) is EE sectional drawing in (a). It is sectional drawing of the gear preload structure which concerns on 4th Embodiment. It is sectional drawing of the conventional gear preload structure. It is FF sectional drawing in FIG. It is a disassembled perspective view of a shaft coupling.

  An embodiment in which the gear preload structure according to the present invention is applied to an electric power steering apparatus will be described below. First, a schematic configuration of the electric power steering apparatus will be described with reference to FIG. The electric power steering device 80 includes a steering handle 81 operated by a driver, a steering shaft 82 integrally connected to the steering handle 81, and an upper connecting shaft connected to the steering shaft 82 via a universal joint 83. 84, a lower connection shaft 86 connected to the upper connection shaft 84 via a universal joint 85, a pinion shaft 88 connected to the lower connection shaft 86 via a torsion bar 87, and a pinion 88a formed at the lower part, Rack teeth 89a meshing with the pinion 88a are formed, and rack shafts 89 to which the left and right front wheels 91 are coupled via tie rods 90 are provided at both ends.

  In addition, the electric power steering device 80 includes a gear box 92 that covers the lower part of the lower connecting shaft 86 and the upper part of the pinion shaft 88. The gear box 92 includes a housing 2 as a housing fixed to a vehicle frame (not shown). The lower connecting shaft 86 and the pinion shaft 88 are rotatably supported by the housing 2 via a bearing (not shown). The housing 2 houses a torque sensor (not shown) that detects the torque of the steering handle 81 based on the relative angle between the lower connecting shaft 86 and the pinion shaft 88, and a worm that is rotated by the motor 8 (FIG. 2). 3 and the worm wheel 4 that is attached to the pinion shaft 88 and meshes with the worm 3 are housed.

  In the electric power steering apparatus 80 configured as described above, the torque applied to the steering handle 81 is detected by the torque sensor, and the motor 8 (FIG. 2) is operated by a control device (not shown) according to the detected torque. Drive controlled. The generated torque of the motor 8 is transmitted to the pinion shaft 88 through the worm 3 and the worm wheel 4 as an auxiliary force for the driver's operating force applied to the steering handle 81.

“First Embodiment”
A first embodiment of a gear preload structure 1 according to the present invention will be described with reference to FIGS. 2 and 3, the gear preload structure 1 includes a worm 3, a worm wheel 4 that meshes with the worm 3, a first bearing 5 that supports a shaft portion 3 a at one end of the worm 3, and the other end of the worm 3. The second bearing 6 that pivotally supports the shaft portion 3b and the housing 2 that incorporates the above components are provided. In addition, the gear preload structure 1 elastically supports the first bearing 5 with respect to the housing 2 over its entire circumference, and elastically recovers in the radial direction passing through the axis of the first bearing 5 when assembled to the housing 2. An elastic support member 7 made of a rubber material having a non-uniform circumferential distribution of force is provided. The elastic support member 7 constitutes a biasing means 31 that biases the worm 3 toward the worm wheel 4.

  The housing 2 has a shape including a worm housing portion 9 in which the worm 3 is housed and a worm wheel housing portion 10 in which the worm wheel 4 is housed. The worm accommodating portion 9 is formed as a substantially cylindrical portion that extends along the axis O1 of the worm 3 and has openings at both ends. The worm wheel housing portion 10 is formed as a substantially cylindrical portion along the axis O <b> 2 of the worm wheel 4. The inner wall surface of the worm housing portion 9 has, in order from one end side, a worm housing hole 9a formed so as to surround substantially the entire length of the worm 3 except for a part of the shaft portion 3b, and a diameter larger than that of the worm housing hole 9a. The second bearing fitting hole 9b, the female screw 9c having a larger diameter than the second bearing fitting hole 9b, and the motor fitting hole 9d having a larger diameter than the female screw 9c are formed. The opening on one end side of the worm accommodating portion 9 is closed by a cover plate 2 a as a part of the housing 2.

  The second bearing 6 is fitted into the second bearing fitting hole 9b, one end of the outer ring abuts on the step surface 9e between the worm accommodation hole 9a and the second bearing fitting hole 9b, and the other end of the outer ring is connected to the female screw 9c. Positioning in the axial direction is achieved by contacting the cylindrical stopper 11 to be screwed. The motor fitting hole 9d is fitted around the tip of the motor 8, and the tip of the shaft portion 3b protruding outward from the second bearing 6 is connected to the output shaft 8a of the motor 8 via the shaft coupling 12. Yes. The structure of the shaft coupling 12 is, for example, the same as that of the shaft coupling 107 shown in FIG. 13, and the detailed description of the shaft coupling 12 is omitted because it is out of the spirit of the present invention.

"Elastic support member 7 (biasing means 31)"
When the elastic support member 7 is assembled to the housing 2, the circumferential distribution of the radial elastic restoring force passing through the axis of the first bearing 5 (the axis O1 of the worm 3) becomes non-uniform, The first bearing 5 is urged in a direction to reduce the distance X between the shaft centers of the worm 3 and the worm wheel 4.

  FIG. 4 is an explanatory view of the elastic support member 7 in a state before being assembled to the housing 2 (FIG. 2). In FIG. 4, the elastic support member 7 is formed with a fitting body 13 in which the outer periphery of the first bearing 5 (FIG. 2) is fitted, and a cylindrical body part 14 having a constant radial thickness t, and a cylindrical body part. A plurality of (eight in the present embodiment) projections 15a to 15h that are radially projected from the circumferential direction at 14 at an equal interval and each tip is pressed against the worm accommodation hole 9a (FIG. 3) of the housing 2. It consists of the shape which has. The fitting hole 13 is recessed in the one end surface 14a of the cylindrical body part 14 without penetrating to the other end surface 14b side. The bottom surface of the fitting hole 13 is formed in a stepped manner because its outer edge bottom surface 13a is positioned shallower than the center bottom surface 13b, that is, on the one end surface 14a side. As shown in FIG. 2, the first bearing 5 is positioned with respect to the elastic member 7 in the direction of the axis O <b> 1 by the side surface of the outer ring being abutted against the outer edge bottom surface 13 a. The uneven space formed by the outer edge bottom surface 13 a and the center bottom surface 13 b functions as a clearance space for the inner ring of the first bearing 5.

Each of the protrusions 15a to 15h has a length dimension l along the axis O1, and extends from the root to the tip, and has the same dimension as the body length of the tube body part 14 (distance between the one end surface 14a and the other end surface 14b). Is formed. Each of the protrusions 15a to 15h is formed so as to exhibit a substantially trapezoidal cross section in which the width dimension w when viewed from the direction along the axis O1 becomes narrower toward the radially outward direction. On the other hand, with respect to the height dimension h from the base to the tip, only the protrusion 15a is formed highest among the eight protrusions 15a to 15h, and the adjacent protrusions 15b and 15h are the same height. The remaining protrusions 15c to 15g are formed at the same height and lower than the protrusions 15b and 15h.
In addition, a flat columnar projecting portion 16 centering on the axis O <b> 1 projects from the center of the other end surface 14 b of the cylindrical body portion 14.

The elastic support member 7 described above is accommodated in the worm accommodation hole 9a as shown in FIG. 3 by compressing and deforming the protrusions 15a to 15b. The projection 15a having the highest height in the state before assembly is accommodated so that the mesh portion of the worm 3 and the worm wheel 4 is positioned 180 degrees opposite to the shaft center O1.
That is, the elastic support member 7 is formed such that the height dimension of at least one of the plurality of protrusions 15 a to 15 h is different from that of the other protrusions, and the protrusions formed higher than the worm wheel 4 The protrusion which is arrange | positioned in the remote side or formed low is arrange | positioned at the worm wheel 4 side. In other words, the elastic support member 7 is disposed on the side farthest from the worm wheel 4 in the virtual outer shape connecting the tips of the plurality of protrusions 15a to 15h, or the axis O1. The place where the distance from is the shortest is arranged on the worm wheel 4 side.
Further, after the elastic support member 7 is accommodated, when the cover plate 2a is assembled to the housing 2, the protrusion 16 is pressed against the cover plate 2a, so that the protrusion 16 is compressed and deformed in the direction along the axis O1. It is supposed to be.

"Action"
The shaft portion 3 a at one end of the worm 3 is supported by the housing 2 via the elastic support member 7 when the first bearing 5 is fitted into the fitting hole 13. The projections 15A～15 h of the elastic support member 7 is accommodated by compression deformation in the radial direction with respect to the worm receiving bore 9a of the perfect circle cross section. Of course, all the protrusions 15a to 15h are accommodated in a state where they can still be compressed and deformed in the radial direction without reaching the elastic deformation limit. Accordingly, the first bearing 5 is elastically supported around the entire circumference, that is, in a floating state, and is supported by the housing 2, and the swing of the worm 3 around the axis O <b> 1 is suppressed. Since the elastic support member 7 is made of a rubber material, when a leaf spring made of a metal material is interposed between the bearing and the housing as in the prior art, the leaf spring The problem that metal contact noise is generated between the housing and the housing is also eliminated.

The amount of compressive deformation of the projections 15A～15 h when housed in the housing 2, most large protrusion 15a of the tallest, followed protrusions 15b, 15h is large, the remaining projections 15c~15g The amount of deformation is small. In other words, the circumferential distribution of the elastic restoring force in the radial direction of the elastic support member 7 is non-uniform with the protrusion 15a being the largest. In FIG. 4, the code | symbol 17 has shown the image of the circumferential direction distribution of elastic restoring force, and represents that elastic restoring force is so large that there is distance from the axial center O1. Due to the circumferential distribution of the elastic restoring force described above, the elastic support member 7 biases the first bearing 5 in the direction in which the distance X between the axial centers of the worm 3 and the worm wheel 4 is reduced. The hitting sound and rattling (backlash) of the engagement with the wheel 4 are suppressed. Since the elastic restoring force also exists in the protrusions 15d to 15f, the urging force in the direction of reducing the distance X between the shaft centers is not excessively applied to the first bearing 5.

  Further, the elastic restoring force of the protrusions 15b and 15h both urges the first bearing 5 in the direction of reducing the distance X between the centroids of the worm 3 and the worm wheel 4, and sandwiches the axis O1 with the same force. From both sides (from the left-right direction in FIG. 3), the first bearing 5 acts to push the shaft center O1. As a result, the swing of the worm 3 around the axis O1 is further suppressed.

Furthermore, the protrusion 16 is elastically deformed by being pressed by the cover plate 2a. That is, the elastic support member 7 elastically supports the first bearing 5 in the direction of the axis O1 with respect to the cover plate 2a that is a part of the housing 2. As a result, the elastic support member 7 biases the worm 3 to the second bearing 6 side through the first bearing 5 as a thrust load, and the worm 3 swings around the axis O1 is further suppressed.
Moreover, a metal contact sound can be effectively suppressed by using the elastic support member 7 from which the protruding portion 16 protrudes.

“Second Embodiment”
A second embodiment will be described with reference to FIGS. 5 and 6. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the second embodiment, the front shape of the elastic support member 7 viewed from the direction of the axis O1 is a substantially equilateral triangle. The elastic support member 7 is pressed into contact with the worm accommodation hole 9a of the housing 2 at the three corners 17a, 17b, and 17c. The axial center (axial center O1) of the fitting hole 13 is eccentric toward the corner 17c by a distance s from the center O3 of the equilateral triangle. In FIG. 5 (a), the phantom line shows the outer shape of the elastic support member 7 after deformation accommodated in the worm accommodating hole 9a, and the respective compression deformation amounts u1 and u2 of the corner portions 17a and 17b are the same as those of the corner portion 17c. It is larger than the amount of compressive deformation u3.

  Also in this embodiment, the first bearing 5 is supported by the housing 2 via the elastic support member 7 by being fitted into the fitting hole 13. Accordingly, the first bearing 5 is elastically supported around the entire circumference, that is, in a floating state, and is supported by the housing 2, and the worm swinging around the axis O1 is suppressed. Since the elastic support member 7 is made of a rubber material, the problem that a metal contact sound is generated between the elastic support member 7 and the housing 2 is also solved as in the first embodiment.

  The amount of compressive deformation of each corner 17a to 17c when accommodated in the housing 2 is small only at the corner 17c. Therefore, the circumferential distribution of the elastic restoring force in the radial direction of the elastic support member 7 is small near the corner portion 17c, and the elastic support member 7 sets the distance between the axial centers of the worm and the worm wheel to the first bearing 5. Energize in the shrinking direction. Thereby, the hitting sound and rattling (backlash) of the meshing between the worm and the worm wheel are suppressed.

  In the present embodiment, the elastic support member 7 has a substantially regular triangular shape, but may have a regular rectangular shape or a regular polygonal shape higher than that. If the elastic support member 7 has a regular polygonal shape when viewed from the direction of the axis O1 and the fitting hole 13 is eccentric from the center of the regular polygon, the circumferential distribution of the elastic restoring force in the radial direction is not uniform. Therefore, the structural design of the elastic support member 7 becomes easy.

“Third Embodiment”
A third embodiment will be described with reference to FIGS. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the third embodiment, the front shape of the elastic support member 7 viewed from the direction of the axis O1 is an elliptical shape. The elastic support member 7 is pressed against the worm accommodation hole 9a of the housing 2 at the longitudinal end portions 18a and 18b. The axial center (axial center O1) of the fitting hole 13 is eccentric toward the longitudinal end 18b by a distance s from the elliptical center O3. In FIG. 7A, the phantom line indicates the outer shape of the elastic support member 7 after deformation accommodated in the worm accommodation hole 9a, and the amount of compressive deformation u1 of the longitudinal end 18a is longer in the longitudinal end 18b. Is greater than the amount of compressive deformation u2.

  Also in this embodiment, the first bearing 5 is supported by the housing 2 via the elastic support member 7 by being fitted into the fitting hole 13. Accordingly, the first bearing 5 is elastically supported around the entire circumference, that is, in a floating state, and is supported by the housing 2, and the worm swinging around the axis O1 is suppressed. Since the elastic support member 7 is made of a rubber material, the problem that a metal contact sound is generated between the elastic support member 7 and the housing 2 is also solved as in the first embodiment.

  The amount of compressive deformation of the longitudinal end portions 18a and 18b when accommodated in the housing 2 is smaller in the longitudinal end portion 18b. Therefore, the circumferential distribution of the elastic restoring force in the radial direction of the elastic support member 7 is small near the end 18b in the longitudinal direction, and the elastic support member 7 moves the first bearing 5 between the shaft centers of the worm and the worm wheel. Energize in the direction to reduce the distance. Thereby, the hitting sound and rattling (backlash) of the meshing between the worm and the worm wheel are suppressed.

  In this embodiment, the elastic support member 7 has an elliptical shape, but may have a perfect circular shape. If the elastic support member 7 is formed into an elliptical shape or a perfect circular shape when viewed from the direction of the axis O1, and the fitting hole 13 is eccentric from the center of the circle, the circumferential direction of the elastic restoring force in the radial direction The structural design of the elastic support member 7 in making the distribution non-uniform becomes easy.

“Fourth Embodiment”
A fourth embodiment will be described with reference to FIGS. 9 and 10. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the fourth embodiment, the shaft center O6 of the first bearing housing hole (worm housing hole 9a) of the housing 2 that supports the first bearing 5 connects the shaft center O1 of the worm 3 and the shaft center O2 of the worm wheel 4. With respect to the direction along the shortest line 20, the shaft center of the second bearing receiving hole 9b of the housing 2 supporting the second bearing 6, that is, the shaft center O1 of the worm 3 is shifted by a distance y closer to the worm wheel 4. Yes.

  For example, as shown in FIG. 9, the elastic support member 7 is provided with a cylindrical body portion 14 in which a fitting hole 13 is formed, and radially protruding from the cylindrical body portion 14 at equal intervals in the circumferential direction. And a plurality of (eight in the present embodiment) protrusions 19 that are in pressure contact with the two worm accommodation holes 9a (FIG. 10). Unlike the protrusions 15a to 15h of the elastic support member 7 of the first embodiment, the protrusions 19 are all formed with the same height.

"Action"
The shaft center O6 of the first bearing housing hole (worm housing hole 9a) that supports the first bearing 5 is the shaft center of the second bearing housing hole 9b of the housing 2 that supports the second bearing 6, that is, the shaft center of the worm 3. When the elastic support member 7 is assembled in the worm accommodating hole 9a by being shifted by the distance y closer to the worm wheel 4 than O1, the protrusion 19 is located above the protrusion 19 positioned above in FIG. It will be compressed and deformed more greatly than the protrusion 19 located on the lower side. As a result, the elastic support member 7 has a non-uniform distribution in the circumferential direction of the elastic restoring force in the radial direction of the elastic support member 7, and reduces the distance X between the axial centers of the worm 3 and the worm wheel 4 in the first bearing 5. Energize in the direction. Thereby, the hitting sound and rattling (backlash) of the meshing between the worm 3 and the worm wheel 4 are suppressed.

  Of course, also according to the present embodiment, the first bearing 5 is elastically supported by the elastic support member 7 over the entire circumference, that is, in a floating state, and is supported by the housing 2, so that the swing of the worm 3 around the axis O <b> 1 is suppressed. The Since the elastic support member 7 is made of a rubber material, the problem that a metal contact sound is generated between the elastic support member 7 and the housing 2 is also solved as in the first embodiment.

According to the present embodiment, the shaft center O6 of the first bearing housing hole (worm housing hole 9a) that supports the first bearing 5 is shifted and positioned closer to the worm wheel 4, for example, as shown in FIG. Even when the elastic support member 7 has a uniform shape in the circumferential direction before assembly, when the elastic support member 7 is assembled to the housing 2, the circumferential distribution of the elastic restoring force in the radial direction of the elastic support member 7. And the worm 3 and the worm wheel 4 can be urged in a direction to reduce the distance X between the centers of the axes.
Moreover, in this embodiment, although the elastic support member 7 in which all the protrusions 19 were formed in the same height dimension was used, the shape of the elastic support member 7 is not specifically limited. For example, the shape of the elastic support member 7 in the first embodiment, the second embodiment, or the third embodiment can be applied.

  The preferred embodiment of the present invention has been described above. Although not shown in the drawing, as the circumferential positioning of the elastic support member 7 with respect to the housing 2, for example, the worm accommodation hole 9 a of the housing 2 and the elastic support member 7 can be positioned by engaging with each other. In addition, the design of the present invention can be changed without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Gear preload structure 2 Housing 3 Worm 4 Worm wheel 5 1st bearing 6 2nd bearing 7 Elastic support member 8 Motor 13 Fitting hole 14 Cylindrical part 15a-15h Projecting part 16 Protruding part 31 Energizing means O1 Shaft center O2 Worm wheel shaft center X Distance between shaft centers

Claims (3)

A worm, a worm wheel that meshes with the worm, a first bearing that pivotally supports a shaft portion at one end of the worm, a second bearing that pivotally supports a shaft portion at the other end, and the worm via the first bearing A gear preload structure comprising a biasing means for biasing the worm wheel and a housing supporting the first bearing,
The biasing means is
An elastic support member made of a rubber material that elastically supports the first bearing with respect to the housing ;
The elastic support member is
A cylindrical body portion in which a fitting hole for fitting the outer periphery of the first bearing is formed;
A plurality of protrusions radially projecting from the cylindrical body part over the entire circumference of the cylindrical body part, the tip of which is pressed against the housing;
A shape having
A height dimension of at least one of the plurality of protrusions is different from that of the other protrusions;
The gear preload structure, wherein the plurality of protrusions are all compressed and deformed in the radial direction of the first bearing and are accommodated in the housing . The elastic support member urges the worm toward the second bearing via the first bearing by elastically supporting the first bearing with respect to the housing in the axial direction of the first bearing. The gear preload structure according to claim 1 . The electric power steering apparatus provided with the gear preload structure according to claim 1 or 2 , wherein a motor is connected to the worm, and the worm wheel is pivotally attached to a pinion shaft.

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