JP2018119583A - Belt transmission device and steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt transmission device having a toothed belt in which tension is not imbalanced even if a rotating shaft of a pulley is inclined by the tension of the belt, which is long in a life, and in which an operation sound is small, and a power steering device having the belt transmission device.SOLUTION: A belt transmission device 30 comprises: housings 31, 11b; a motor M; a first bearing part 32 and a second bearing part 33; a first rotating shaft 37; a drive pulley 36; a second rotating shaft 21; a driven pulley 34; and a toothed belt 35. The first rotating shaft is inclined to a reference axial line by the tension Pf of the toothed belt 35, and the drive pulley 36 fixed to the inclined rotating shaft is formed into a truncated cone shape. Pitches Pt of teeth 36b of the drive pulley are formed small as progressing toward a small-diameter side, and formed large as progressing toward a large-diameter side. Pitches Pt of teeth of the toothed belt 35 are formed constant over a width direction of the toothed belt 35.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a belt transmission device and a steering device using the belt transmission device.

  2. Description of the Related Art Conventionally, there is an electric power steering device that assists the operation of a rack shaft by converting the rotational driving force of an electric motor into an axial thrust by a ball screw device. As an example of this steering device, there is a type in which a rotating shaft of an electric motor and a rack shaft are arranged in parallel to an offset position (see, for example, Patent Document 1). In this case, the rotational driving force of the electric motor is transmitted to the ball screw device by the belt transmission device.

  The belt transmission device mainly includes an electric motor, a drive pulley provided on a rotating shaft of the electric motor, a driven pulley fixed to an outer periphery of a nut constituting a ball screw device between a rack shaft, and a predetermined tension. And a toothed belt stretched between the driving pulley and the driving pulley. Thereby, the rotational driving force of the electric motor is transmitted to the ball nut via the driven pulley, the ball nut is rotated around the axis, the ball screw device is operated, and the axial thrust is applied to the rack shaft.

  However, in the electric power steering apparatus described above, for example, the rotating shaft of the electric motor that is cantilevered may be tilted by a predetermined tension of the toothed belt. For this reason, in the toothed belt, the portion that engages with the drive pulley on the tip side of the rotating shaft where the amount of tilt of the rotating shaft increases, and the portion that engages with the drive pulley on the root side of the rotating shaft with relatively small tilt amount In this case, the tension is greatly different. In such a state, the stress generated in the toothed belt becomes unbalanced in the axial direction of the rotation shaft, which may cause the belt transmission to be misaligned and reduce the life of the toothed belt. Moreover, there is a possibility of generating an operating noise.

  On the other hand, although it is not an electric power steering device, for example, the image forming apparatus shown in Patent Document 2 includes a similar belt transmission device, and the side surface of the driven pulley is in accordance with the degree of tilting of the rotating shaft of the electric motor. It is formed to have an inclination. Thus, a metal belt (transmission belt) that is stretched between the driven pulley and the drive pulley with a predetermined tension and is engaged with each side surface of the pulley by the frictional force of the contact surface, and each pulley The belt tension is less likely to be unbalanced in the axial direction of the rotating shaft of the electric motor.

JP 2006-275282 A JP 2011-248303 A

  However, as described above, in the belt transmission device of Patent Document 2, the transmission belt and each pulley are engaged by friction. For this reason, as a result, it is the structure which accept | permits the relative slip between a transmission belt and each pulley. Thus, it cannot be applied to a belt transmission device of an electric power steering device that does not allow slippage (relative movement) between the belt and each pulley.

  The present invention has been made in view of the above circumstances, and includes a toothed belt having a long life and a low operating noise in which the tension does not become unbalanced even if the rotation shaft of the pulley is tilted by the tension of the belt. It is an object of the present invention to provide a power steering device including a transmission device and a belt transmission device.

(1. Belt transmission)
The belt transmission according to the present invention includes a housing, a motor provided in the housing, a first bearing portion and a second bearing portion provided in the housing, and one end side cantilevered on the first bearing portion. A first rotating shaft that is supported in a shape and outputs a rotational driving force generated by the motor, a driving pulley that is fixed to a free end side that is the other end side of the first rotating shaft, and that has external teeth; One end is supported in a cantilevered manner on the two bearing parts, and fixed to the second rotating shaft where the first rotating shaft and the reference axis are parallel to each other, and the free end that is the other end of the second rotating shaft And a driven pulley having external teeth and a span between the drive pulley and the driven pulley in a state having a predetermined tension, and internal teeth are the external teeth of the drive pulley and the external of the driven pulley. Extendable annular toothed belt arranged in mesh with teeth , Comprising a.

  Due to the tension of the toothed belt, at least one of the first rotating shaft and the second rotating shaft is tilted with respect to the reference axis, and the driving pulley is fixed to the tilting rotating shaft. And at least one of the driven pulleys is formed in a truncated cone shape having an outer diameter that gradually increases from a side on which the rotating shaft is supported toward a free end according to a tilting angle. The pitch of the teeth of the pulley formed in the shape is formed smaller as the smaller diameter side is formed, and as the larger diameter side is formed, the tooth pitch of the toothed belt is formed constant over the width direction of the toothed belt. Is done.

  Thus, even if the rotation shaft of at least one of the driving pulley and the driven pulley is tilted by the tension of the toothed belt that is stretched, at least one of the driving pulley and the driven pulley provided on the tilted rotating shaft. Among the plurality of external teeth, the outer peripheral surface of the tooth tip at the substantially central portion in the circumferential direction in the portion meshing with the internal teeth of the toothed belt is substantially parallel to the reference axis that is the axis before the rotation axis is tilted. Become.

  For this reason, the outer teeth of the substantially central portion in the circumferential direction of at least one of the pulleys and the inner teeth of the toothed belt can be meshed substantially uniformly over the entire length in the axial direction. At this time, the circumference is different between the small-diameter side and the large-diameter side of the pulley formed in a truncated cone shape, and thus the pitch of the teeth (external teeth) is different, but since the toothed belt can be extended, the external teeth Can be reliably engaged with the internal teeth of the toothed belt from the small diameter side to the large diameter side. Therefore, as in the prior art, the tension of the toothed belt becomes unbalanced in the axial direction of the rotating shaft, and the alignment of the belt transmission device is largely prevented from being greatly lost. As a result, the stress generated in the toothed belt is stabilized and the toothed belt has a long life, and as a result, the belt transmission device has a long life. In addition, the operating noise is suppressed well.

(2. Steering device)
A steering device according to the present invention includes the belt transmission device. As a result, a steering device with a long life and reduced operating noise can be obtained.

1 is a schematic view showing an electric power steering apparatus according to the present invention. It is an expanded sectional view of the belt transmission device and ball screw device portion of FIG. 1 according to the first embodiment. FIG. 3 is an enlarged view of the drive pulley shown in FIG. 2. FIG. 4 is a P view of FIG. 3. However, it includes a toothed belt hung over a drive pulley. FIG. 3 is a diagram showing a state in which the toothed belt is stretched between the driving pulley and the driven pulley with tension between FIG. 2 and FIG. It is a figure explaining the belt power transmission apparatus which concerns on 2nd embodiment.

<1. First embodiment>
Hereinafter, a first embodiment according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an entire electric power steering apparatus exemplifying an aspect in which a belt transmission device according to the present invention is applied to an electric power steering apparatus (corresponding to a steering apparatus) of a vehicle.

  The electric power steering device is a steering device that assists the steering force by the steering assist force. The belt transmission device according to the present invention can be applied to various devices to which the belt transmission device can be applied, such as a four-wheel steering device, a rear wheel steering device, and a steer-by-wire device, in addition to the electric power steering device.

(1-1. Configuration of Steering Device 10)
The electric power steering device 10 (hereinafter referred to as the steering device 10) includes a steered shaft 20 connected to a steered wheel (not shown) of a vehicle in an A direction (left and right in FIG. 1) coinciding with the axial direction of the steered shaft 20. It is a device that changes the direction of the steered wheels by reciprocating in the direction).

  As shown in FIG. 1, the steering device 10 includes a housing 11, a steering wheel 12, a steering shaft 13, a torque detection device 14, the aforementioned steering shaft 20, a belt transmission device 30, and a ball screw device 40. And comprising.

  The housing 11 is a fixing member that is fixed to the vehicle. The housing 11 is formed in a cylindrical shape, and passes through the steered shaft 20 (corresponding to a screw shaft) so as to be relatively movable in the A direction. The housing 11 includes a first housing 11a and a second housing 11b fixed to the other end side in the A direction (left side in FIG. 1) of the first housing 11a.

  The steering wheel 12 is fixed to the end of the steering shaft 13 and is rotatably supported in the vehicle interior. The steering shaft 13 transmits torque applied to the steering wheel 12 by the driver's operation to the steered shaft 20.

  A pinion 13a constituting a rack and pinion mechanism is formed at the end of the steering shaft 13 on the steered shaft 20 side. The torque detection device 14 detects the torque applied to the steering shaft 13 based on the amount of twist of the steering shaft 13.

  The steered shaft 20 extends in the A direction. A rack 22 is formed on the steered shaft 20. The rack 22 meshes with the pinion 13a of the steering shaft 13, and constitutes a rack and pinion mechanism together with the pinion 13a. In the rack and pinion mechanism, the maximum axial force that can be transmitted between the steering shaft 13 and the steered shaft 20 is set based on the use of the steering device 10 or the like.

  Further, the steered shaft 20 is formed with a ball screw portion 23 at a position different from the rack 22. The ball screw portion 23 constitutes a ball screw device 40 together with a ball nut 21 described later. Although details will be described later, the ball screw device 40 is transmitted with a steering assist force by the belt transmission device 30. Both ends of the steered shaft 20 are connected to left and right steered wheels (not shown) via unillustrated tie rods, knuckle arms, etc., and the steered wheels are moved in the left-right direction by the axial movement of the steered shaft 20 in the A direction. Steered to.

  The belt transmission device 30 is a mechanism that applies a steering assist force to the steered shaft 20 via the ball screw device 40 using an electric motor M (hereinafter referred to as a motor M) constituting the belt transmission device 30 as a drive source. The rotation of the electric motor M is controlled by the control unit ECU. The control unit ECU determines the steering assist force based on the output signal of the torque detection device 14 and controls the output of the motor M. The output of the motor M is transmitted to a ball screw device 40 described later via the belt transmission device 30. The belt transmission device 30 according to the present invention will be described in detail later.

(1-2. Configuration of ball screw device)
As shown in FIG. 2, the ball screw device 40 is mainly accommodated in the second housing 11b. The ball screw device 40 includes a ball screw portion 23 of the steered shaft 20, a ball nut 21, and a plurality of rolling balls 24. The ball screw portion 23 of the steered shaft 20 is formed with an outer peripheral rolling groove 20a formed in a spiral shape on the outer peripheral surface. The outer peripheral rolling groove 20a is formed by being wound a plurality of times.

  The ball nut 21 is formed in a cylindrical shape and is arranged coaxially with the ball screw portion 23 (steering shaft 20) on the outer peripheral side of the ball screw portion 23. The ball nut 21 is supported on the inner peripheral surface 11b1 of the second housing 11b via the ball bearing 33 on the other end side (left side in FIG. 2) so as to be rotatable relative to the second housing 11b. As will be described in detail later, the second housing 11b is also a housing for the belt transmission device 30. The ball bearing 33 is also a second bearing portion of the belt transmission device 30. Further, the ball nut 21 is also a second rotating shaft of the belt transmission device 30.

  The inner peripheral surface of the ball nut 21 includes an inner peripheral rolling groove 21a formed in a spiral shape. The inner peripheral rolling groove 21a is formed by winding a plurality of turns. Then, the outer peripheral rolling groove 20a of the ball screw portion 23 and the inner peripheral rolling groove 21a of the ball nut 21 are arranged to face each other, and a plurality of rolling is provided between the outer peripheral rolling groove 20a and the inner peripheral rolling groove 21a. A rolling path R1 in which the moving ball 24 rolls is formed.

  The plurality of rolling balls 24 are arranged in the rolling path R1 so as to be able to roll. Thereby, the outer peripheral rolling groove 20 a of the ball screw portion 23 (steering shaft 20) and the inner peripheral rolling groove 21 a of the ball nut 21 are screwed together via the plurality of rolling balls 24. When the motor M is rotationally driven and the ball nut 21 is rotationally driven via the belt transmission device 30, the turning shaft 20 (steering shaft) is moved in the axial direction via the plurality of rolling balls 24. The

  The plurality of rolling balls 24 rolling on the rolling path R1 are infinitely circulated by a pair of unillustrated deflectors (not illustrated) provided on the ball nut 21. However, since a technique for infinite circulation of the rolling ball 24 by the deflector is known, further detailed description is omitted.

(1-3. Belt transmission device 30)
As shown in FIG. 2, the belt transmission 30 includes a case 31 and the second housing 11b (both correspond to the housing), a motor M, and a control unit ECU that controls and drives the motor M (see FIG. 1). The ball bearings 32 and 32 (corresponding to the first bearing portion), the above-described ball bearing 33 (corresponding to the second bearing portion), the shaft 37 (corresponding to the first rotating shaft), the drive pulley 36, and the aforementioned The ball nut 21 (corresponding to the second rotating shaft), the driven pulley 34, and the toothed belt 35 are provided. In FIG. 2, the toothed belt 35 is not attached to the belt transmission device 30. A state where the toothed belt 35 is stretched between the driving pulley 36 and the driven pulley 34 is shown in FIG.

  As shown in FIG. 2, the case 31 (housing) is integrally fixed to the first housing 11 a of the housing 11. The case 31 is formed in a substantially cylindrical shape. The case 31 houses the motor M and a control unit ECU (see FIG. 1) that controls and drives the motor M inside the cylinder. The control unit ECU is a control unit that determines the steering assist force based on the output signal of the torque detection device 14 and controls the output of the motor M.

  As shown in FIG. 2, the motor M includes a stator St and a rotor Rt. The stator St is formed in a cylindrical shape. The outer surface of the stator St is fixed to the inner peripheral surface 31a of the case 31 by a predetermined means. Any predetermined fixing means may be used. The rotor Rt is formed in a cylindrical shape. The outer surface of the rotor Rt faces the inner surface of the stator St with a certain gap (gap), and the inner surface of the rotor Rt is the shaft 37 (first rotating shaft) so that it can rotate integrally with the shaft 37. It is fixed to the outer peripheral surface by a predetermined means. Any predetermined fixing means may be used.

  In addition, the shaft 37 is supported on the inner peripheral surface 31a of the case 31 via ball bearings 32 and 32 (corresponding to the first bearing portion) provided on the case 31 (housing) at both axially outer portions of the rotor Rt. The At this time, the shaft 37 is arranged such that the axis is parallel to the axis of the steered shaft 20. The axis of the shaft 37 is arranged so as to be coaxial with the axis of the stator St. The axis of the shaft 37 (first rotation axis) in this arrangement state is referred to as “reference axis L1”.

  As described above, the shaft 37 is supported by the ball bearings 32 and 32 at one end side (right side in FIG. 2) in a cantilevered manner, and outputs the rotational driving force generated by the motor M. In FIG. 2, the ball bearings 32 and 32 are deep groove ball bearings. However, the ball bearings 32 may be angular ball bearings or other ball bearings. However, the ball bearing to be selected is when a predetermined load is applied to the other end side of the shaft 37 in a direction perpendicular to the axis while the shaft 37 is supported by the ball bearings 32 and 32 in a cantilevered manner. The shaft 37 is a ball bearing having a structure in which the shaft 37 is tilted with respect to the “reference axis L1” by a tilt angle θ1 ° (corresponding to an angle) with a tilt according to a given load applied. The tilt angle θ1 ° will be described in detail later.

  The drive pulley 36 is fixed to the free end side which is the other end side (left side in FIG. 2) of the shaft 37 (first rotation shaft) so as to be integrally rotatable with the shaft 37. The drive pulley 36 is made of, for example, an iron metal. As shown in the enlarged views of FIGS. 2 and 3, in this embodiment, the drive pulley 36 gradually has an outer diameter from the side (one end side) on which the shaft 37 is supported toward the free end side (the other end side). It is formed in a truncated cone shape that increases φD.

  At this time, the magnitude of the inclination of the outer peripheral surface in the axial direction of the truncated cone is suspended between the driving pulley 36 and the driven pulley 34 in a state where the toothed belt 35 described later has a predetermined tension Pf. When this is done, the shaft 37 is set according to the tilt angle θ1 ° tilted with respect to the “reference axis” by the predetermined tension Pf. In the present embodiment, the tilt angle θ2 °, which is the magnitude of the tilt of the frustoconical shape of the drive pulley 36 in the axial direction, is equal to the tilt angle θ1 ° of the shaft 37 (θ1 ° = θ2 °).

  Note that the tilt angle θ1 ° and the tilt angle θ2 ° are actually very small values, for example, about 0.1 to 0.5 deg. However, in FIG. 2 and FIG. 3, it is added that the tilt angle θ1 ° and the tilt angle θ2 ° are described with a larger tilt than actual so as to be easily understood visually.

(1-3-1. Description of the external tooth shape of the drive pulley 36)
As shown in FIGS. 3 and 4, the drive pulley 36 has a plurality of external teeth 36 b formed on the outer peripheral surface formed at an inclination angle θ2 ° in the axial direction. That is, the outer peripheral surface 36a of the outer periphery is equal to the tooth tip surface 36b1 of the plurality of external teeth 36b. In the present embodiment, the external teeth 36b are helical teeth (not shown). The tooth profile of the external teeth 36b is basically formed based on JIS B 1856 (toothed pulley). Further, terms such as pitch Pt described below are also based on JIS B 1856 (toothed pulley) unless otherwise specified.

  The pitch Pt (see FIG. 4) of the external teeth 36b of the drive pulley 36 is formed smaller as the truncated cone has a smaller diameter side, and is formed larger as the truncated cone shape has a larger diameter side. As shown in FIG. 4, the pitch Pt is the arc length between the center lines c and c of the adjacent external teeth 36b on the PCD (Pitch Circle Diameter) (based on JIS B 1856). Since PCD is publicly known, detailed description thereof is omitted.

  Further, as shown in FIG. 3, the root diameter φd changes so that the bottom surface 36b2 of the external tooth 36b is parallel to the tip surface 36b1. That is, in the present embodiment, the tooth depth k is constant in the extending direction of the external teeth 36b. The width W of the external teeth 36b of the drive pulley 36 is constant from the small diameter side to the large diameter side of the truncated cone shape. A tooth gap is a space between adjacent teeth defined in JIS B 0102. Further, the tooth thickness t of the external teeth 36b is variable in order to make the width W of the tooth gap constant. That is, the tooth thickness t is formed to be smaller as the truncated cone has a smaller diameter, and the tooth thickness t is formed to be larger as the truncated cone has a larger diameter.

  As shown in FIG. 4, an identification mark m for identifying the direction of inclination of the truncated cone shape is provided on the end surface of the drive pulley 36 formed in the truncated cone shape. Specifically, in the drive pulley 36, for example, a circular recess is engraved on a part of the end surface on the large diameter side having a large outer diameter φD. The identification mark m may have any shape and depth as long as it is stamped with a force that does not affect the shape of the drive pulley 36.

  In addition, the identification mark is not limited to the depressed recess, and a coloring material may be applied. Any other method may be used as long as it can be identified. Further, the identification mark m may be provided on the end surface of the drive pulley 36 on the small diameter side where the outer diameter φD of the outer peripheral surface is small. The identification mark m may be provided on both the large diameter end surface and the small diameter end surface. In this case, it goes without saying that the identification marks m at both ends can be identified.

  The second rotating shaft is the ball nut 21 constituting the ball screw device 40. As shown in FIG. 2, the ball nut 21 (second rotating shaft) is cantilevered at the other end (left side in FIG. 2) to a ball bearing 33 (corresponding to the second bearing portion) provided in the second housing 11b. It is supported in the form. Thereby, the ball nut 21 (second rotating shaft) is supported by the inner peripheral surface 11b1 of the second housing 11b (housing 11) via the ball bearing 33. The axis L2 of the ball nut 21 at this time is referred to as “reference axis L2”.

  The “reference axis L2” refers to the axis of the ball nut 21 in a state where a force in a direction orthogonal to the axis L2 is not applied to one end of the ball nut 21. The ball nut 21 is arranged such that the reference axis L2 and the reference axis L1 of the shaft 37 (first rotation axis) are parallel to each other.

  The driven pulley 34 is formed in a substantially cylindrical shape. External teeth 34 a of helical teeth are formed on the outer peripheral surface of the driven pulley 34. The driven pulley 34 is made of, for example, an iron metal. The driven pulley 34 is fixed to the outer peripheral surface on the free end side which is one end side (the right side in FIG. 2) of the ball nut 21 (second rotating shaft).

  In the present embodiment, a toothed belt 35 is stretched between the driven pulley 34 and the driving pulley 36, and a predetermined tension of the toothed belt 35 is provided at one end of the ball nut 21 (second rotating shaft). The description will be made assuming that even if Pf is applied, the ball nut 21 (second rotating shaft) is firmly supported by the ball bearing 33 (second bearing portion) and does not tilt.

  Also, at both ends of the driven pulley 34 in the axial direction, a toothed belt 35 that prevents the toothed belt 35 from moving from the driven pulley 34 in the axial direction after the toothed belt 35 is stretched over the driven pulley 34. Ring members 38, 38 are fixed. However, the flanged ring members 38, 38 may not be provided.

  The toothed belt 35 shown in FIGS. 4 and 5 is formed in an annular shape by a material (material) such as rubber that can be extended. As shown in FIG. 4, the toothed belt 35 includes inner teeth 35 a formed of helical teeth on an annular inner peripheral surface. The internal teeth 35 a are formed with a constant tooth pitch over the width direction of the toothed belt 35. The shape and terms (pitch, etc.) of the internal teeth 35a are based on JIS B 6372 (general toothed belt). The inner teeth 35 a are formed so as to be able to mesh well with the outer teeth 36 b of the driving pulley 36 and the outer teeth 34 a of the driven pulley 34.

  The toothed belt 35 is formed of, for example, a back rubber (such as chloroprene rubber), a tooth rubber (such as chloroprene rubber), a core wire (glass fiber, aramid, etc.), and a tooth cloth (such as nylon canvas). However, the present invention is not limited to this mode, and the toothed belt 35 may be formed using any material as long as it can be extended.

  As shown in FIG. 5, the toothed belt 35 is driven with the drive pulley 36 in a state where the inner teeth 35a mesh with the outer teeth 36b, 34a of the drive pulley 36 and the driven pulley 34 and have a predetermined tension Pf. It is spanned between the pulley 34. As a result, the axis of the shaft 37 (first rotation axis) and the axis L3 in a state of being tilted by a predetermined tilt angle (angle) θ1 ° with respect to the “reference axis L1” of the shaft 37 (first rotation axis). Become. At this time, the shaft 37 is tilted by a backlash between the outer ring and the inner ring of the ball bearings 32 and 32 that support the shaft 37.

  As described above, in the present embodiment, the outer peripheral surface 36a of the drive pulley 36 formed in a truncated cone shape such that the axis L3 is equal to the tilt angle θ1 ° tilted with respect to the “reference axis L1”. An inclination angle θ2 ° in the axial direction is set. In the present embodiment, as described above, the ball nut 21 (second rotating shaft) to which the driven pulley 34 is fixed is not tilted by the predetermined tension Pf by the toothed belt 35, and the axis L2 (reference axis) ) Is maintained parallel to the axis L1 (reference axis).

(1-4. Action)
As described above, in the belt transmission 30, when the toothed belt 35 is stretched between the drive pulley 36 and the driven pulley 34 with the predetermined tension Pf, as shown in FIG. The shaft 37 (first rotation axis) of the pulley 36 is tilted by a predetermined tilt angle θ1 °. However, the drive pulley 36 is formed in a truncated cone shape whose outer diameter gradually increases from the side (one end side) on which the shaft 37 (first rotating shaft) is supported toward the free end side (the other end side). Yes. At this time, the inclination angle of the outer peripheral surface of the frustoconical drive pulley 36 is formed at θ2 ° which is equal to a predetermined inclination angle θ1 °.

  Therefore, when the cross section of the drive pulley 36 is viewed from a direction orthogonal to the plane including the reference axis L1 of the drive pulley 36 and the reference axis L2 of the driven pulley 34, that is, the cross section of the drive pulley 36 in FIG. In this case, among the outlines representing the outer peripheral surface 36a, the outline L4 at the lower end in FIG. 5 is parallel to the reference axis L1.

  As shown in FIG. 4, the outline L4 is located at a substantially central portion in the circumferential direction in a range Ar1 where the external teeth 36b of the drive pulley 36 and the internal teeth of the toothed belt mesh. The inner teeth 35a of the toothed belt 35 and the outer teeth 36b of the drive pulley 36 mesh with each other in the extending direction of the outer line L4 along the reference axis L1. As a result, the toothed belt 35 substantially uniformly applies the tension Pf to the drive pulley 36 in the width direction of the toothed belt 35 at the meshing point.

  For this reason, as in the prior art, the tension Pf of the toothed belt 35 and the stress generated in the toothed belt 35 (particularly the inner teeth 35a) in the direction along the outline L4, that is, the “reference axis L1” are unenhanced. It becomes a balance, and the alignment of the belt transmission device 30 is greatly suppressed from being greatly lost. As a result, the toothed belt 35 has a long life, and the operating noise generated by the imbalance of the alignment is also satisfactorily suppressed.

  As described above, in the external teeth 36b of the drive pulley 36, the width W of the tooth gap is constant in the extending direction of the external teeth 36b, but the pitch Pt and the tooth thickness t are changed from the small diameter side to the large diameter side. It is formed so that it gradually becomes larger. However, the inner teeth 35a of the toothed belt 35 formed at a constant pitch Pt in the width direction are formed to be extensible with rubber. For this reason, even if the pitch Pt and the tooth thickness t of the external teeth 36b of the drive pulley 36 are slightly changed in the extending direction of the external teeth 36b, the internal teeth 35a of the toothed belt 35 that can be extended can be driven. The outer teeth 36b of the pulley 36 can sufficiently mesh with each other when the toothed belt 35 extends. As a result, the above-described effect of extending the life of the toothed belt 35 and reducing the operating noise can be obtained, and the relative rotation of the drive pulley 36 with respect to the toothed belt 35 is reliably controlled, and the rotational driving force of the motor M Is transmitted efficiently.

<2. Second embodiment>
Next, the belt transmission device 130 of the second embodiment will be described with reference to FIG. In the belt transmission device 30 of the first embodiment, only the shaft 37 (first rotation shaft) of the drive pulley 36 among the drive pulley 36 and the driven pulley 34 constituting the belt transmission device 30 is the tension Pf of the toothed belt 35. To tilt. However, it is not limited to this aspect.

  As the belt transmission device 130 of the second embodiment, not only the shaft 37 of the driving pulley 36 but also the ball nut 21 (corresponding to the second rotating shaft) to which the driven pulley 134 is fixed may be tilted simultaneously. Although belt transmission device 130 has the same configuration as belt transmission device 30, only a part of belt transmission device 130 is taken out and described in FIG. 6.

  In the belt transmission device 130, the axis of the ball nut 21 described above is tilted with respect to the “reference axis L2” by the tilt angle θ3 ° to become the axis L5 by the tension Pf of the toothed belt 35. The driven pulley 134 is gradually moved from the side (other end side) on which the ball nut 21 is supported toward the free end side (one end side) according to the tilt angle (angle) θ3 ° at which the ball nut 21 tilts. It is formed in a truncated cone shape with an increased outer diameter. At this time, the inclination of the outer peripheral surface 134b of the driven pulley 134 formed in a truncated cone shape is formed at an inclination angle θ4 ° corresponding to the inclination angle (angle) θ3 °. At this time, the tilt angle θ3 ° = the tilt angle θ4 °.

  Further, the pitch Pt of the external teeth (teeth) 134a of the driven pulley 134 is formed smaller as the small diameter side and larger as the large diameter side, like the external teeth 36b of the drive pulley 36. Other portions (tooth thickness, tooth gap, etc.) of the external teeth (teeth) 134a are also formed in the same manner as the external teeth 36b of the drive pulley 36 in the first embodiment. For this reason, the driven pulley 134 can obtain the same effect as that of the driving pulley 36. Therefore, the tension Pf of the toothed belt 35 and the stress generated in the toothed belt 35 are unbalanced in the width direction of the toothed belt 35, and the belt It is greatly suppressed that the alignment of the transmission device 130 is largely lost.

  In the belt transmission device 130 of the second embodiment, when the toothed belt 35 is passed between the driving pulley 36 and the driven pulley 34, the large diameter side of the driving pulley 36 and the small diameter side of the driven pulley 34 are opposed to each other. Thus, the small diameter side of the drive pulley 36 and the large diameter side of the driven pulley 34 are paired. That is, the long side and the short side of the portion where the toothed belt 35 abuts are paired. For this reason, when viewed from the overall length of the toothed belt 35, the tension imbalance of the toothed belt 35 between the large diameter side and the small diameter side of the drive pulley 36 is smaller than that of the belt transmission device 30 of the first embodiment.

  The internal teeth 35a of the extendable toothed belt 35 and the external teeth (teeth) 134a of the driven pulley 134 can be sufficiently meshed with each other when the toothed belt 35 extends. As a result, the above-described effect of extending the life of the toothed belt 35 and reducing the operating noise can be obtained, and the relative rotation of the driven pulley 134 with respect to the toothed belt 35 is reliably restricted, and the rotational driving force of the motor M Is transmitted efficiently.

<3. Other>
In the first and second embodiments, the external teeth 36b, 34a, and 134a included in the drive pulley 36 and the driven pulleys 34 and 134, respectively, are helical teeth. However, it is not limited to this aspect. The external teeth 36b, 34a, 134a may be spur teeth whose tooth lines are parallel to the reference axes L1, L2 of the pulleys, respectively. This also provides the same effect.

  Further, in the first (second) embodiment, strictly speaking, the toothed belt is different from the large-diameter side and the small-diameter side of the driving pulley 36 (driven pulley 134) formed in a truncated cone shape by the difference in diameter. The circumferential lengths (peripheral lengths) of the portions where the inner teeth 35a of the 35 abut and mesh are different. Therefore, the inclination angle θ2 ° (θ4 °) of the outer peripheral surface of the drive pulley 36 (driven pulley 134) is adjusted with the difference in tension Pf in the “reference axis L1” direction caused by the difference in length (peripheral length). You may make it relax.

  Specifically, since the circumference of the portion with which the toothed belt 35 abuts is larger on the large diameter side of the drive pulley 36 (driven pulley 134) than on the small diameter side, the inclination angle θ2 ° (θ4 ° of the drive pulley 36). ) Is slightly reduced to reduce the difference in the circumferential length between the large diameter side and the small diameter side. As a result, the tension Pf of the toothed belt 35 in the “reference axis L1” direction approaches a more uniform state.

  In the above embodiment, only the driving pulley 36 or the driving pulley 36 and the driven pulley 134 are formed in a truncated cone shape. However, the present invention is not limited to this, and only the driven pulley 134 may have a truncated cone shape. That is, only the ball nut 21 (second rotation shaft) that is the rotation shaft of the driven pulley 134 may be tilted by the tension Pf of the toothed belt 35. This also provides a reasonable effect.

<4. Effects according to the embodiment>
According to the above-described embodiment, the belt transmission devices 30 and 130 include the case 31 and the second housing 11 b (housing), the motor M provided in the case 31, and the ball bearings 32 and 32 ( The first bearing portion) and the ball bearing 33 (second bearing portion) provided in the second housing 11b and the ball bearings 32, 32 are supported in a cantilevered manner at one end, and the rotational driving force generated by the motor M is generated. The shaft 37 (first rotating shaft) for output, the drive pulley 36 having external teeth 36b fixed to the free end side which is the other end side of the shaft 37, and one end side supported by the ball bearing 33 in a cantilevered manner. The ball nut 21 (second rotary shaft) in which the shaft 37 (first rotary shaft) and the reference axis lines L1 and L2 are parallel to each other are fixed to the free end side which is the other end side of the second rotary shaft. The driven pulleys 34 and 134 having the external teeth 34 a and the drive pulley 36 and the driven pulleys 34 and 134 with a predetermined tension Pf are spanned, and the internal teeth 35 a are external teeth of the drive pulley 36. 36b and an annular toothed belt 35 disposed in mesh with the external teeth 34a and 134a of the driven pulleys 34 and 134.

  Due to the tension Pf of the toothed belt 35, at least one of the rotation shafts of the shaft 37 (first rotation shaft) and the ball nut 21 (second rotation shaft) is tilted with respect to the reference axis (L1, L2). At least one of the drive pulley 36 and the driven pulley 134 fixed to the rotating shaft (the shaft 37, the ball nut 21) is rotated according to the tilting angle (θ1 °, θ2 °). The nut 21) is formed in a truncated cone shape whose outer diameter gradually increases from the side on which the nut 21) is supported toward the free end side. At this time, the pitch Pt of the external teeth (teeth) 36b and 134a of the pulleys (the drive pulley 36 and the driven pulley 134) is formed smaller as the small diameter side and larger as the large diameter side. Further, the tooth pitch Pt of the toothed belt 35 is formed constant over the width direction of the toothed belt 35.

  Thus, even if the rotation shaft (the shaft 37 and the ball nut 21) of at least one of the driving pulley 36 and the driven pulley 134 is tilted by the tension Pf of the toothed belt 35 that is stretched, the rotation is provided on the tilted rotation shaft. Of the plurality of external teeth (36b, 134a) of at least one of the driven pulley 36 and the driven pulley 134, the tooth tip of the substantially central portion in the circumferential direction in the range Ar1 meshing with the internal tooth 35a of the toothed belt 35 The outer peripheral surfaces (36a, 134b) are substantially parallel to reference axes (L1, L2) that are axes before the rotation shaft (shaft 37, ball nut 21) tilts.

  For this reason, the external teeth (36b, 134a) of the substantially central portion in the circumferential direction of at least one pulley (36, 134) and the internal teeth 35a of the toothed belt 35 extend over the entire length in the reference axis L1, L2 direction. Can be engaged evenly. Therefore, as in the prior art, the tension of the toothed belt becomes unbalanced in the axial direction of the rotating shaft, and the alignment of the belt transmission device is largely prevented from being greatly lost. Accordingly, the stress generated in the inner teeth 35a of the toothed belt 35 is stabilized, so that the toothed belt 35 has a long life, and the belt transmission device 30 has a long life. In addition, the operating noise is suppressed well.

  Further, according to the belt transmission device 130 of the second embodiment, the shaft 37 (first rotating shaft) is tilted with respect to the reference axis L1 by the tension Pf of the toothed belt 35, and the drive pulley 36 is A cone whose outer diameter gradually increases from the side on which the shaft 37 (first rotation shaft) is supported toward the free end according to the tilt angle (angle) θ1 ° at which the shaft 37 (first rotation shaft) tilts. It is formed in a trapezoidal shape, and the pitch Pt of the external teeth 36b (teeth) of the drive pulley 36 is formed smaller as the smaller diameter side and larger as the larger diameter side.

  Also, the ball nut 21 (second rotation shaft) tilts with respect to the reference axis L2 by the tension Pf of the toothed belt 35, and the driven pulley 134 tilts so that the ball nut 21 (second rotation shaft) tilts. Depending on the angle (angle) θ3 °, the outer diameter of the driven pulley 134 is formed so that the outer diameter gradually increases from the side on which the ball nut 21 (second rotating shaft) is supported toward the free end. The pitch Pt of the teeth 134a (teeth) is formed smaller as the smaller diameter side and larger as the larger diameter side.

  For this reason, even if both the rotation shafts of the shaft 37 (first rotation shaft) and the ball nut 21 (second rotation shaft) are tilted by the tension Pf of the toothed belt 35, the belt is driven by the same principle as in the first embodiment. It is greatly suppressed that the alignment of the transmission device 130 is largely lost. As a result, the toothed belt 35 has a long life, and the operating noise generated by the imbalance of the alignment is also satisfactorily suppressed.

  Further, according to the belt transmission devices 30 and 130 of the first and second embodiments, the external teeth 36b, 34a, 134a and the internal teeth 35a included in the drive pulley 36, the driven pulleys 34 and 134, and the toothed belt 35, respectively. Is a tooth. Thereby, even if the driving pulley 36 and the driven pulleys 34 and 134 are formed in a truncated cone shape, the driving pulley 36 and the driven pulleys 34 and 134 first mesh with the toothed belt 35 on the small diameter side, Then, since it meshes toward the large diameter side, it is easy to mesh by absorbing a slight change in the shape of the tooth profile. In addition, due to the characteristics of the helical gear, abnormal noise is hardly generated when meshing.

  Moreover, according to the belt transmission devices 30 and 130 of the first and second embodiments, at least one of the driving pulley 36 and the driven pulley 134 formed in a truncated cone shape among the driving pulley 36 and the driven pulley 134. The end face is provided with an identification mark for identifying the direction of the truncated cone shape. By such a simple method, erroneous assembly of the drive pulley 36 and the driven pulley 134 can be avoided at low cost.

  Moreover, according to the said embodiment, the steering apparatus 10 is provided with the belt transmission apparatuses 30 and 130 of the said embodiment. As a result, a steering device with a long life and reduced operating noise can be obtained.

DESCRIPTION OF SYMBOLS 10; Steering device (electric power steering device), 11b; Housing (second housing), 20; Steering shaft, 21; Second rotating shaft (ball nut), 30, 130; Belt transmission device, 31; ), 32; first bearing part (ball bearing), 33; second bearing part (ball bearing), 34, 134; driven pulley, 34a, 36b, 134a; tooth (external tooth), 35; toothed belt, 35a ; Internal teeth, 36; drive pulley, 37; first rotating shaft (shaft), L1, L2; reference axis, M: electric motor (motor), Pf; tension, Pt; pitch, θ1, θ3; angle (tilt) angle).

Claims (6)

A housing;
A motor provided in the housing;
A first bearing portion and a second bearing portion provided in the housing;
A first rotating shaft that is supported by the first bearing portion in a cantilevered manner and that outputs a rotational driving force generated by the motor;
A driving pulley fixed on the free end side which is the other end side of the first rotating shaft and having external teeth;
A second rotating shaft supported at one end on the second bearing portion in a cantilevered manner, wherein the first rotating shaft and a reference axis are parallel to each other;
A driven pulley fixed to the free end side which is the other end side of the second rotating shaft and having external teeth;
Extending between the drive pulley and the driven pulley in a state having a predetermined tension, and having an internal tooth arranged in mesh with the external tooth of the drive pulley and the external tooth of the driven pulley A possible annular toothed belt,
A belt transmission device comprising:
Due to the tension of the toothed belt, at least one of the first rotating shaft and the second rotating shaft is tilted with respect to the reference axis,
At least one of the driving pulley and the driven pulley fixed to the rotating shaft that tilts has an outer diameter that gradually increases from the side on which the rotating shaft is supported toward the free end depending on the tilting angle. Formed in a truncated cone shape,
The pitch of the teeth of the pulley formed in the shape of the truncated cone is formed smaller as the smaller diameter side, and larger as the larger diameter side,
A belt transmission device in which the tooth pitch of the toothed belt is formed constant over the width direction of the toothed belt. Due to the tension of the toothed belt, the first rotation shaft tilts with respect to the reference axis,
The drive pulley is formed in the truncated cone shape whose outer diameter gradually increases from the side on which the first rotation shaft is supported toward the free end according to the angle at which the first rotation shaft tilts,
The pitch of the teeth of the drive pulley is formed smaller on the smaller diameter side and larger on the larger diameter side,
Due to the tension of the toothed belt, the second rotating shaft tilts with respect to the reference axis,
The driven pulley is formed in the truncated cone shape whose outer diameter gradually increases from the side on which the second rotation shaft is supported toward the free end according to the angle at which the second rotation shaft tilts,
The belt transmission device according to claim 1, wherein a pitch of teeth of the driven pulley is formed to be smaller toward a smaller diameter side and larger toward a larger diameter side.   3. The belt transmission device according to claim 1, wherein the outer teeth and the inner teeth included in the driving pulley, the driven pulley, and the toothed belt are helical teeth. 4.   The inclination angle of the outer peripheral surface of the pulley formed in the truncated cone shape is set equal to the angle at which the rotation shaft to which the pulley formed in the truncated cone shape is attached is tilted with respect to the reference axis. The belt transmission device according to any one of claims 1 to 3, wherein the belt transmission device is provided.   The identification mark for identifying the direction of inclination of the truncated cone shape is provided on at least one end surface of the pulley formed in the truncated cone shape among the driving pulley and the driven pulley. The belt transmission device according to any one of claims.   A steering device comprising the belt transmission device according to any one of claims 1 to 5.

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