Belt transmission device and steering device equipped with the belt transmission device

Abstract

To provide a belt transmission comprising a drive pulley whose external teeth are not deformed even if performance of an electric motor is measured while fitting a facility input shaft into a facility shaft hole of the drive pulley fixed to an output shaft of the electric motor.SOLUTION: A drive pulley 36 comprises: a first hole 36a which is formed over a predetermined first range Ar1 from an end at the side of a motor M in an axial direction of an output shaft 37 and to which the output shaft 37 is fitted so as to be integrally rotatable; and a second hole 36b which is formed over a predetermined second range Ar2 from an end at an opposite side of the side of the motor M. A plurality of convex shapes S are formed at equal intervals over a full circumference in a circumferential direction on an inner peripheral surface of the second hole 36b. First phases β1 which are phases of tops T of the convex shapes S in the circumferential direction of the second hole 36b and second phases β2 which are phases of bottoms of tooth grooves 36g in a circumferential direction on an outer peripheral surface are not matched at all or are matched only in one location.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a belt transmission device and a steering device equipped with the belt transmission device. [Background technology]

[0002] Conventionally, there is a belt transmission device that transmits the rotational driving force of an electric motor from an output shaft of the electric motor to another shaft via a drive pulley, a toothed belt, and a driven pulley. An example of a device to which a belt transmission device is applied is an electric power steering device. The electric power steering device transmits the rotational driving force of an electric motor to a ball screw device by the belt transmission device, and converts the force into axial thrust by the ball screw device to assist the operation of a rack shaft.

[0003] Usually, mainly during manufacturing of the belt transmission device, various performances related to the electric motor are measured by a performance measuring device with the drive pulley fixed to the output shaft of the electric motor. For this reason, the drive pulley is formed with an equipment shaft hole formed so that the axial cross section is, for example, an internal hexagonal shape on the side opposite to the side in the axial direction where the output shaft of the electric motor is fitted. When measuring the performance of the electric motor, the equipment input shaft of a performance measuring device formed, for example, as an external hexagon, is inserted into the equipment shaft hole to measure the performance such as the rotational drive torque of the electric motor.

[0004] At this time, there is a gap between the fitted equipment input shaft and the equipment shaft hole, so that when a performance measurement is performed in which a rotational torque is generated in the output shaft of the electric motor, the corners of the outer hexagon of the equipment input shaft come into contact with the inner hexagonal surface of the equipment shaft hole, generating a large stress, which may deform the external teeth of the drive pulley around and near the contact point of the inner hexagonal surface.

[0005] If the external teeth of the drive pulley are deformed, the stress generated in the toothed belt during operation of the belt transmission device becomes unbalanced in the rotation direction of the output shaft, which may cause operating noise. In addition, the deformation of the external teeth of the drive pulley may prevent the rotational driving force of the electric motor from being efficiently transmitted to the driven pulley.

[0006] In response to this, for example, Patent Document 1 discloses a belt transmission device that is applied to bicycles. In this belt transmission device, an inner transmission wheel 8 (corresponding to the equipment input shaft) that is connected to the rotating shaft of the pedal has external teeth formed by multiple projections and recesses on the entire circumference of its outer periphery. Some of the external teeth mesh with some of the internal teeth of a belt pulley 9 (corresponding to the drive pulley) that is formed by projections and recesses on the entire circumference of its inner periphery. This allows the external teeth of the inner transmission wheel and the internal teeth of the belt pulley to come into contact over a relatively large area, so that the stress generated at the contact position can be reduced compared to when the inner hexagonal hole and the outer hexagonal column come into contact at a point or line. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 6-147292 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when looking at the meshing state between the external teeth of the inner transmission wheel 8 and the internal teeth of the belt pulley 9 shown in Fig. 1, there are parts where the phase of the convex parts of the external teeth of the inner transmission wheel 8 in the circumferential direction (i.e., the phase of the concave parts of the internal teeth of the belt pulley 9) matches the phase of the concave parts (valleys) of the external teeth of the belt pulley 9 in the circumferential direction. The parts where the phases match are thinner and more likely to deform than other parts where they do not. For this reason, in the parts where the phases match, the convex parts of the external teeth of the inner transmission wheel 8 may deform the concave parts of the internal teeth of the belt pulley 9, and ultimately deform the external teeth of the belt pulley 9 that are in the same phase.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide a belt transmission device equipped with a drive pulley whose external teeth do not deform even when the equipment shaft hole of a performance measuring device is fitted into the equipment shaft hole of the drive pulley fixed to the output shaft of an electric motor to measure the performance of the electric motor, and a steering device equipped with a belt transmission device. [Means for solving the problem]

[0010] (1. Belt transmission device) The belt transmission device of the present invention comprises a housing, a motor having an output shaft fixed to the housing and at least its tip side housed inside the housing, a cylindrical drive pulley fixed to the tip end of the output shaft inside the housing and rotating integrally with the output shaft about an axis, a cylindrical driven pulley supported inside the housing so as to be rotatable about an axis, and a ring-shaped toothed belt wound around the drive pulley and the driven pulley so that its internal teeth mesh with the external teeth of the drive pulley and the external teeth of the driven pulley.

[0011] The drive pulley comprises a first hole formed over a predetermined first range from the end of the output shaft on the motor side in the axial direction, and into which the tip end of the output shaft is fitted so that the tip end can rotate integrally, and a second hole formed over a predetermined second range from the end of the output shaft opposite the motor side in the axial direction, and a plurality of convex shapes formed radially outward are formed at equal intervals around the entire circumferential direction on the inner surface of the second hole, and a first phase, which is the phase of the top of the convex shape in the circumferential direction of the inner surface of the second hole, and a second phase, which is the phase in the circumferential direction of the bottom of the tooth groove formed between adjacent external teeth on the outer circumferential surface of the drive pulley, do not coincide at all or coincide only at one point. The number of the convex shapes on the inner circumferential surface of the second hole and the number of the tooth grooves on the outer circumferential surface of the second hole are mutually prime.

[0012] In this way, the second hole of the drive pulley has a plurality of convex shapes formed radially outward on its inner peripheral surface at equal intervals around the entire circumference. Therefore, when the equipment input shaft, which is formed with an outer shape that can be fitted into the second hole by a clearance fit, is inserted into the second hole and fitted thereto, the equipment input shaft and the second hole of the drive pulley can contact each other over a large contact area. As a result, even if the motor is operated and the drive pulley applies a rotational force to the equipment input shaft during performance measurement, no large stress is generated between the equipment input shaft and the second hole of the drive pulley, and deformation of the contact area is effectively suppressed.

[0013] Furthermore, the first phase, which is the phase of the top of the convex shape, and the second phase, which is the phase of the bottom of the tooth groove, do not coincide at all or only coincide at one point. In other words, the state in which the thickness of the drive pulley is thinnest in the radial direction does not exist at all or exists at only one point. Therefore, even if deformation occurs at the convex shape position of the second hole, there is no tooth groove on the outer periphery of the drive pulley near the convex shape, or there is only one tooth groove, so a sufficient thickness is secured between the outer periphery and the deformation of the outer periphery, and the deformation of the outer periphery can be effectively suppressed. In this way, by devising the shape of the second hole and the convex shape and the arrangement position of the tooth groove, the deformation of the outer periphery of the drive pulley is effectively suppressed, and the operating noise during operation of the belt transmission device can be effectively suppressed. In addition, the rotational driving force of the motor M can be efficiently transmitted to the driven pulley side.

[0014] (2. Steering device) A steering device according to the present invention includes the above-mentioned belt transmission device, thereby providing a steering device with reduced operating noise. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing an electric power steering device according to the present invention; [Diagram 2] 2 is an enlarged cross-sectional view of a belt transmission device and a ball screw device portion of FIG. 1 according to the first embodiment. FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of the drive pulley shown in FIG. 2. [Figure 4]13 is a diagram showing the input shaft of a performance measuring device inserted into the second hole of the drive pulley. FIG. [Diagram 5] This is a view 1 from the P direction in Figure 3. [Figure 6] This is view 2 from the P direction in Figure 3. [Figure 7] FIG. 10 is a view illustrating a third modified example, and corresponds to FIG. [Figure 8] FIG. 10 is a view illustrating a fourth modified example, and corresponds to FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <1. First embodiment> A first embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram showing an entire electric power steering device, illustrating an example in which a belt transmission device according to the present invention is applied to an electric power steering device (corresponding to a steering device) of a vehicle.

[0017] An electric power steering device is a steering device that assists steering force with a steering assist force. The belt transmission device according to the present invention can be applied to various devices to which a 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.

[0018] (1-1. Steering device 10) The electric power steering device (hereinafter referred to as the steering device 10) is a device that changes the direction of steered wheels (not shown) of a vehicle by moving a steered shaft 20, which is connected to the steered wheels, back and forth in direction A (left and right direction in Figure 1) that coincides with the axial direction of the steered shaft 20.

[0019] 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 steered shaft 20 described above, a belt transmission device 30, and a ball screw device 40.

[0020] The housing 11 is a fixed member fixed to a vehicle. The housing 11 is formed in a cylindrical shape, and the steering shaft 20 (corresponding to a screw shaft) is inserted therethrough so as to be relatively movable in the direction A. The housing 11 includes a first housing 11a and a second housing 11b fixed to the other end side (left side in FIG. 1) of the first housing 11a in the direction A.

[0021] The steering wheel 12 is fixed to an end of a steering shaft 13, and is rotatably supported within the vehicle cabin. The steering shaft 13 transmits torque applied to the steering wheel 12 by the driver's operation to a steered shaft 20.

[0022] A pinion 13a constituting a rack and pinion mechanism is formed on the end of the steering shaft 13 on the steered shaft 20 side. A torque detector 14 detects the torque applied to the steering shaft 13 based on the amount of twist of the steering shaft 13.

[0023] The steered shaft 20 extends in the direction A. A rack 22 is formed on the steered shaft 20. The rack 22 meshes with the pinion 13a of the steering shaft 13, and together with the pinion 13a, forms a rack-and-pinion mechanism. For 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 application of the steering device 10.

[0024] Further, a ball screw portion 23 is formed on the steered shaft 20 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. Note that, although details will be described later, a steering assist force is transmitted to the ball screw device 40 by a belt transmission device 30. Both ends of the steered shaft 20 are connected to left and right steered wheels (not shown) via tie rods and knuckle arms (not shown), and the steered wheels are steered in the left and right directions by the axial movement of the steered shaft 20 in direction A.

[0025] The belt transmission device 30 is a mechanism that applies a steering assist force to the steered shaft 20 via a ball screw device 40, using an electric motor M (hereinafter referred to as motor M) constituting the belt transmission device 30 as a drive source. The rotation of the electric motor M is controlled by a control unit ECU. The control unit ECU determines the steering assist force based on an output signal from the torque detection device 14, and controls the output of the motor M. The output of the motor M is then transmitted via the belt transmission device 30 to the ball screw device 40, which will be described later. The belt transmission device 30 according to the present invention will be described in detail later.

[0026] (1-2. 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. A peripheral rolling groove 20a is formed in a spiral shape on the outer circumferential surface of the ball screw portion 23 of the steered shaft 20. The peripheral rolling groove 20a is formed by winding multiple times.

[0027] The ball nut 21 is formed in a cylindrical shape and is disposed coaxially with the ball screw portion 23 (the steered shaft 20) on the outer circumferential side of the ball screw portion 23. The other end side (the left side in FIG. 2) of the ball nut 21 is supported by the inner circumferential surface 11b1 of the second housing 11b via a ball bearing 33 so as to be rotatable relative to the second housing 11b.

[0028] At this time, the ball nut 21 is supported on the inner surface 11b1 of the second housing 11b (housing 11) via a ball bearing 33 so that its axis is coaxial with the axis L2 of the steering shaft 20, and is positioned parallel to the axis L1 of the output shaft 37 of the motor M.

[0029] The inner peripheral surface of the ball nut 21 is provided with an inner peripheral rolling groove 21a formed in a spiral shape. The inner peripheral rolling groove 21a is formed by winding multiple turns. 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 opposite to each other, and a rolling path R1 in which multiple rolling balls 24 roll is formed between the outer peripheral rolling groove 20a and the inner peripheral rolling groove 21a.

[0030] The multiple rolling balls 24 are arranged to be rollable in the rolling path R1. As a result, the outer circumferential rolling groove 20a of the ball screw portion 23 (steered shaft 20) and the inner circumferential rolling groove 21a of the ball nut 21 are screwed together via the multiple rolling balls 24. When the output shaft 37 of the motor M is rotationally driven and the ball nut 21 is rotationally driven via the belt transmission device 30, the steered shaft 20 (steered shaft) is moved axially via the multiple rolling balls 24.

[0031] The rolling balls 24 rolling in the rolling path R1 are circulated infinitely by a pair of deflectors (not shown) provided on the ball nut 21. However, since the technology for circulating the rolling balls 24 infinitely by using deflectors is well known, further detailed explanation will be omitted.

[0032] (1-3. Belt transmission device 30) As shown in Figures 1 and 2, the belt transmission device 30 includes a case 31 and the aforementioned second housing 11b (both are housings), a motor M, a control unit ECU that controls and drives the motor M, ball bearings 32, 32, a cylindrical driving pulley 36, a cylindrical driven pulley 34, and a circular toothed belt 35.

[0033] As shown in Fig. 2, the case 31 is fixed integrally to the first housing 11a of the housing 11. The case 31 is formed in a generally cylindrical shape. The case 31 accommodates 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 a steering assist force based on an output signal from the torque detection device 14 and controls the output of the motor M.

[0034] 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 peripheral surface of the stator St is fixed to the inner peripheral surface 31a of the case 31 by a predetermined means. At this time, any predetermined fixing means may be used. The rotor Rt is formed in a cylindrical shape. The outer peripheral surface of the rotor Rt faces the inner peripheral surface of the stator St with a certain gap therebetween, and the inner peripheral surface is fixed to the outer peripheral surface of the output shaft 37 by a predetermined means so as to be rotatable integrally with the output shaft 37. Any predetermined fixing means may be used.

[0035] Moreover, both axially outer portions of the rotor Rt of the output shaft 37 are supported by the inner circumferential surface 31a of the case 31 via ball bearings 32, 32 provided in the case 31. At this time, the output shaft 37 is disposed so that the axis L1 is parallel to the axis L2 of the steered shaft 20. Moreover, the axis L1 of the output shaft 37 is disposed so as to be coaxial with the axis of the stator St.

[0036] Thus, the output shaft 37 is formed in a cylindrical shape over the entire axial length, and one end (the right side in FIG. 2) is cantilever-supported by the ball bearings 32, 32 so as to be rotatable about the axis. The other end (tip side) of the output shaft 37 is housed inside the second housing 11b (housing) and outputs the rotational driving force generated by the motor M. Note that in FIG. 2, the ball bearings 32, 32 are illustrated as deep groove ball bearings. However, the ball bearings 32, 32 may be angular contact ball bearings or other ball bearings.

[0037] The drive pulley 36 is formed in a cylindrical shape, and is fixed to the other end (left side in FIG. 2) of the output shaft 37 at the tip end so as to be rotatable together with the output shaft 37 about the axis. The drive pulley 36 is formed by sintering or cutting a metal material such as an iron-based material. The drive pulley 36 has external helical teeth 36e formed on its outer circumferential surface. Details of the drive pulley 36 according to the present invention will be described later.

[0038] The driven pulley 34 is supported inside the second housing 11b (housing) so as to be rotatable about the axis L2. In detail, the driven pulley 34 is formed in a substantially cylindrical shape, and is disposed on the outer periphery of the free end side, which is one end side (the right side in FIG. 2) of the above-mentioned ball nut 21 so as to be rotatable integrally with the ball nut 21. Helical external teeth 34a are formed on the outer periphery of the driven pulley 34. The driven pulley 34 is formed of, for example, an iron-based metal.

[0039] A circular toothed belt 35 is wound between the external teeth 34a of the driven pulley 34 and the external teeth 36e of the drive pulley 36. In addition, flanged circular members 38, 38 are fixed to both axial ends of the driven pulley 34 to prevent the toothed belt 35 from moving axially and falling off the driven pulley 34 after the toothed belt 35 is wound around the driven pulley 34. However, the flanged circular members 38, 38 may be omitted.

[0040] The toothed belt 35 shown in Figs. 4 and 5 is formed in a ring shape from an extensible material such as rubber. As shown in Fig. 4, the toothed belt 35 has internal teeth 35a formed of helical teeth on the inner peripheral surface of the ring shape. The internal teeth 35a are formed with a constant tooth pitch across the width direction of the toothed belt 35. The shape of the internal teeth 35a is formed based on JIS B 6372 (general-purpose toothed belt). The internal teeth 35a are formed so as to be able to mesh well with the external teeth 36e of the driving pulley 36 and the external teeth 34a of the driven pulley 34.

[0041] The toothed belt 35 is formed, for example, from a back rubber (chloroprene rubber, etc.), a tooth rubber (chloroprene rubber, etc.), a core wire (glass fiber, aramid, etc.), and a tooth cloth (nylon canvas, etc.). However, the toothed belt 35 is not limited to this embodiment, and may be formed from any material as long as it is stretchable.

[0042] (1-4. Drive pulley 36) Next, the shape of the drive pulley 36 according to the present invention will be described in detail. As shown in the cross-sectional views of Figures 2 and 3, in this embodiment, the drive pulley 36 has a first hole 36a and a second hole 36b in the axial direction of the output shaft 37.

[0043] (1-4-1. First hole 36a) 3, the first hole 36a is formed in a cylindrical shape over a predetermined first range Ar1 from the end face (end) on the motor M side in the axial direction of the output shaft 37. The tip end of the output shaft 37 is press-fitted into the first hole 36a so that the output shaft 37 and the drive pulley 36 can rotate together.

[0044] (1-4-2.Second hole 36b) The second hole 36b is formed over a predetermined second range Ar2 from the end face (end face) of the output shaft 37 on the side opposite to the motor M in the axial direction. The axial length of the second range Ar2 is shorter than the axial length of the first range Ar1. In detail, the first range Ar1 occupies most of the overall length of the drive pulley 36 in the axial direction, and the length of the second range Ar2 is, for example, 2 mm or less, and preferably about 1.5 mm. However, this is not limiting, and the length of the second range Ar2 may exceed 2 mm.

[0045] The second hole 36b is a hole for measuring the performance of the motor M by inserting and fitting the equipment input shaft Z1 of the performance measuring device Z shown in Fig. 4 so as to be coaxial with the drive pulley 36, in a state in which the tip end of the output shaft 37 is press-fitted into the first hole 36a and the drive pulley 36 is fixed to the tip end of the output shaft 37 of the motor M. The type of performance of the motor M measured by the performance measuring device Z is not limited, but for example, the rotational torque of the electric motor M is measured.

[0046] 5 and 6, which are views taken from the perspective of P in FIG. 3, in this embodiment, the inner peripheral surface of the second hole 36b has 16 (corresponding to a plurality) convex shapes S formed radially outward and spaced at equal intervals all around the circumference. That is, on the inner peripheral surface of the second hole 36b, the convex shapes S are recesses on the inner peripheral surface of the second hole 36b, and the convex shapes S form tooth grooves 36c. In this embodiment, the tooth grooves 36c formed along the axis are formed parallel to the axis.

[0047] The convex shape S (tooth grooves 36c) is formed by an involute spline formed by an involute curve based on JIS B1603 (see Figs. 5 and 6). The involute spline formed on the inner peripheral surface of the second hole 36b is also referred to as the internal teeth 36b1 hereinafter. Therefore, the internal teeth 36b1 are formed by tooth grooves 36c consisting of 16 convex shapes S formed at equal intervals all around the circumference, and tooth traces 36d which are teeth formed between adjacent convex shapes S (tooth grooves 36c). The tooth traces 36d are also formed parallel to the axis, like the tooth grooves 36c.

[0048] In the above description, the number of the convex shapes S in the internal teeth 36b1 of the second hole 36b is 16, but this is merely an example. The number of the convex shapes S may be other than 16 as long as it satisfies a certain condition in relation to the number of teeth in the external teeth 36e formed on the outer circumferential surface of the drive pulley 36, which will be described later. The certain condition will be described later.

[0049] As described above, the external teeth Z2 on the outer circumferential surface of the equipment input shaft Z1 are formed by an involute spline (not shown) and can be fitted with the internal teeth 36b1 by clearance fit. That is, the outer circumferential surface of the end of the equipment input shaft Z1 of the performance measuring device Z is fitted with a depth within the range of the second range Ar2 into the second hole 36b. The external teeth Z2 of the equipment input shaft Z1 and the internal teeth 36b1 of the second hole 36b are fitted with "tooth surface alignment" (JIS B1603) in which the tooth surfaces of the involute splines come into contact with each other. As a result, the external teeth Z2 of the equipment input shaft Z1 and the internal teeth 36b1 can come into contact with each other over a sufficient area when fitted.

[0050] (1-4-3. Outer teeth) Next, a description will be given of the external teeth 36e formed on the outer peripheral surface of the drive pulley 36. As shown in Figures 5 and 6, tooth traces 36f, which are the teeth of the external teeth 36e, are formed by a plurality of protrusions W protruding radially outward over the entire circumferential circumference of the outer peripheral surface of the drive pulley 36. At this time, a plurality of tooth grooves 36g are formed between the tooth traces 36f adjacent to each other in the circumferential direction.

[0051] As described above, the external teeth 36e are helical teeth, and the multiple tooth traces 36f are formed at a predetermined angle (not shown) with respect to the axis of the drive pulley 36. The shape of the tooth profile of the external teeth 36e is basically formed based on JIS B1856 (standard for toothed pulleys).

[0052] That is, the outer teeth 36e have tooth surfaces that mesh with the inner teeth 35a of the annular toothed belt 35, which are formed by a plurality of tooth traces 36f and a plurality of tooth grooves 36g that are formed between the tooth traces 36f that are adjacent in the circumferential direction. In this embodiment, 37 (corresponding to a plurality) of tooth traces 36f and tooth grooves 36g are formed all around the circumference in the circumferential direction. In this case, the number (16) of the convex shapes S of the inner teeth 36b1 of the second hole 36b and the number (37) of the tooth grooves 36g are in a "prime relationship" having no common divisor other than 1.

[0053] (1-4-4. Relationship between the inner teeth 36b1 and the outer teeth 36e) In this way, the number of convex shapes S of the internal teeth 36b1 and the number of tooth grooves 36g of the external teeth 36e only need to have a "primary relationship," and the condition is that this relationship be satisfied. Therefore, any combination of the number of convex shapes S of the internal teeth 36b1 and the number of tooth grooves 36g of the external teeth 36e may be used as long as this relationship is satisfied.

[0054] Furthermore, in this embodiment, a condition is that the first phase β1, which is the phase of the top T of the convex shape S in the circumferential direction of the inner peripheral surface of the second hole 36b, and the second phase β2, which is the phase of the bottom Q of the tooth groove 36g in the circumferential direction of the outer peripheral surface of the drive pulley 36, do not coincide at all. Note that the first phase β1 of the top T of the convex shape S is the phase at the apex of the convex shape S.

[0055] However, this is not limiting, and the first phase β1 of the apex T may have a predetermined width in the circumferential direction. In this case, the phase of the apex T has a width of a° to b°. In this case, the first phase β1 and the second phase β2 "do not match" may be defined as a state in which the predetermined width of the phases do not overlap at all. Also, even if some of the predetermined widths of the phases overlap, a state in which all widths do not completely overlap may be defined as a "mismatch" state. In this way, the predetermined width may be set by each individual.

[0056] Specifically, when designing the drive pulley 36, a position where the first phase β1 of the convex shape S in the circumferential direction of the inner peripheral surface of the second hole 36b and the second phase β2 of the tooth grooves 36g on the outer peripheral surface of the drive pulley 36 do not coincide at all in the circumferential direction is searched for, and the phase (position) of the convex shape S in the circumferential direction of the inner peripheral surface of the second hole 36b with respect to the phase (position) of the tooth grooves 36g on the outer peripheral surface is set, as shown in Figures 5 and 6. In this embodiment, the number (37) of the convex shapes S and the number (16) of the tooth grooves 36g of the external teeth 36e have a "prime relationship" with no common divisor other than 1, and therefore such a positional relationship can be easily searched for.

[0057] By setting it in this manner, it is possible to easily avoid a state in which the first phase β1 of the convex shape S and the second phase β2 of the tooth groove 36g, which is the thinnest part of the thickness between the inner and outer surfaces of the drive pulley 36, coincide.

[0058] (1-5. Effect) As described above, in the belt transmission device 30, when the performance of the motor M is measured by the performance measuring device Z, the equipment input shaft Z1 of the performance measuring device Z, whose outer periphery is formed by an involute spline, is fitted with a clearance fit into the second hole 36b of the drive pulley 36 formed by an involute spline. Then, the output shaft 37 of the motor M is rotated to rotate the drive pulley 36 fixed to the end of the output shaft 37 about its axis. At this time, the tooth surfaces of the external teeth Z2 of the equipment input shaft Z1 and the convex shape S of the internal teeth 36b1 come into contact with each other over a sufficiently large area as described above.

[0059] This suppresses the contact surface pressure at the contact portion between the external teeth Z2 and the internal teeth 36b1 of the equipment input shaft Z1, and reduces the stress that the second hole 36b receives from the equipment input shaft Z1. Therefore, there is no risk that the contact portion between the second hole 36b and the equipment input shaft Z1 will be deformed due to the stress from the equipment input shaft Z1, and further that the outer circumferential surface of the drive pulley 36 near the deformed contact portion will be deformed, and it is possible to suppress the risk of operating noise being generated when the belt transmission device 30 is operated.

[0060] As described above, the tooth surfaces of the external teeth Z2 of the equipment input shaft Z1 and the convex shape S of the internal teeth 36b1 contact each other over a sufficiently large area, thereby reducing the surface pressure at the contact portion. Therefore, the depth to which the equipment input shaft Z1 is inserted and fitted into the second hole 36b can be shortened compared to the conventional case. This allows the overall length of the drive pulley 36 to be shortened, improving mountability and reducing weight.

[0061] In addition to the above, the first phase β1 of the convex shape S in the circumferential direction on the inner peripheral surface of the second hole 36b and the second phase β2 of the tooth groove 36g on the outer peripheral surface of the drive pulley 36 are set so as not to coincide at all in the circumferential direction. Note that the position on the drive pulley 36 where the first phase β1 and the second phase β2 coincide is the position where the thickness of the drive pulley 36 in the radial direction is the thinnest.

[0062] In order to achieve the above, in this embodiment, the number (16) of convex shapes on the inner peripheral surface of the second hole 36b and the number (37) of tooth grooves 36g of the external teeth 36e are in a "natural relationship." This makes it easy to avoid a state in which the first phase β1 and the second phase β2, where the thickness is the thinnest, coincide with each other, and makes it possible to more effectively suppress deformation of the outer peripheral surface of the drive pulley 36.

[0063] Therefore, even if the belt transmission device 30 operates in response to the operation of the steering device 10, the stress generated in the toothed belt 35 does not become unbalanced in the rotational direction of the output shaft 37, and there is no risk of the meshing state between the external teeth of the drive pulley 36 and the toothed belt 35 becoming unstable and generating operating noise. Also, the rotational driving force of the motor M can be efficiently transmitted to the driven pulley side.

[0064] <2. Other embodiments> (2-1. Variation 1) In the above first embodiment, the first phase β1 and the second phase β2 are set so that they do not coincide with each other at any point in the entire circumferential direction, but the present invention is not limited to this. As a first modified example (not shown), the first phase β1 and the second phase β2 may be set so that they coincide with each other at only one point in the entire circumferential direction. In this case, the number of the convex shapes S of the second hole 36b (e.g., 16) and the number of the tooth grooves 36g of the external teeth 36e (e.g., 37) are in a "prime relationship."

[0065] Therefore, even if the phases are matched at only one point, the other phases do not match at all. However, only at the position where the first phase β1 and the second phase β2 are matched, the thickness of the drive pulley 36 in the radial direction becomes thin, and there is a risk of slight deformation of the external teeth 36e. However, the deformation occurs only at one point on the outer periphery of the drive pulley 36. Therefore, even if the stress generated in the toothed belt 35 fluctuates at one point in the rotational direction of the output shaft 37 during operation of the belt transmission device 30, a mode in which the toothed belt 35 vibrates resonantly due to multiple deformations does not occur, and the generation of operating noise can be sufficiently suppressed.

[0066] (2-2. Variation 2) In the first embodiment, the number of the convex shapes S on the inner peripheral surface of the second hole 36b and the number of the tooth grooves 36g of the external teeth 36e are in a "primary relationship". However, this is not limited to this embodiment. As a second modified example (not shown), the number of the convex shapes S and the number of the tooth grooves 36g of the external teeth 36e may be the same. In this case, if the first phase β1 and the second phase β2 coincide at even one point in the circumferential direction, all the phases will coincide. However, if one point is shifted, all the phases will not coincide. In this way, it is easy to set all the phases to be shifted. As a result, the same effect as the above embodiment can be expected.

[0067] (2-3. Variations 3 and 4) In the above first embodiment, the convex shape S of the inner peripheral surface of the second hole 36b of the drive pulley 36 is described as being formed by an involute spline, but this is not limited to the above. As shown in FIG. 7, as a modified example 3, the convex shape S may be formed in a knurled shape that is a simple rectangular uneven shape in the circumferential direction. Also, as shown in FIG. 8, as a modified example 4, the convex shape S may be a simple triangular shape. With these, the area of ​​contact between the second hole 36b and the equipment input shaft Z1 can be increased compared to the conventional technology in which the outer peripheral surface of the equipment input shaft is formed in a hexagonal shape, so that the surface pressure of the contact portion can be reduced and the deformation of the outer peripheral surface of the drive pulley 36 can be appropriately suppressed.

[0068] (2-4. Variation 5) In the above first embodiment, the first hole 36a of the drive pulley 36 is formed in a cylindrical shape over a predetermined first range Ar1 from the end face on the motor M side in the axial direction of the output shaft 37, and the end portion on the tip side of the output shaft 37 is press-fitted into the first hole 36a. However, this is not limited to the above. As a sixth modification, convex shapes similar to the convex shapes S formed on the inner peripheral surface of the second hole 36b may be formed at equal intervals over the predetermined first range Ar1 on the entire circumferential circumference of the inner peripheral surface of the first hole 36a of the drive pulley 36.

[0069] In other words, the cross-sectional shape of the convex shape cut along a plane perpendicular to the axis of the first hole 36a and the second hole 36b may be the same. The convex shape may be an involute spline, a knurled shape, or a triangular shape. In this case, it is preferable that the convex shape of the first hole 36a and the convex shape S of the second hole 36b are continuously connected over the entire length of the drive pulley 36 in the axial direction.

[0070] The tip end of the output shaft 37 is fitted into the first hole 36a by clearance fit. At this time, a predetermined fixing means may be provided to prevent the drive pulley 36 from moving in the axial direction relative to the output shaft 37. This makes it possible to easily fix the drive pulley 36 to the output shaft 37. The output shaft 37 may be fitted into the first hole 36a by press fitting.

[0071] (2-5. Variation 6) In the first embodiment, the tooth grooves 36c formed by the convex shape S in the second hole 36b of the drive pulley 36 are formed so that their angles with respect to the axis are parallel, but this is not limited to the above. As a sixth modified example (not shown), the angle of the tooth grooves 36c in the second hole 36b with respect to the axis may be parallel to the tooth traces 36f of the external teeth 36e of the drive pulley 36, which are helical teeth. By doing so, for example, when the extension length of the tooth grooves 36c formed by the convex shape S in the second hole 36b is set to be relatively long, it is possible to prevent the first phase β1 of the tooth grooves 36c formed by the convex shape S from intersecting and coinciding with the second phase β2 of the tooth grooves 36g on the outer circumferential surface, which have a different angle with respect to the axis, from intersecting and coinciding.

[0072] Furthermore, according to the above embodiment, the steering device 10 includes the belt transmission device 30 of the above embodiment. This provides a steering device with reduced operating noise.

[0073] (3. Effects of the First Embodiment) According to the above first embodiment, the drive pulley of the belt transmission device 30 is provided with a first hole 36a formed over a predetermined first range from the end on the motor side in the axial direction of the output shaft 37, into which the tip end of the output shaft 37 is fitted so as to rotate integrally, and a second hole 36b formed over a predetermined second range Ar2 from the end (end face) opposite the motor M side in the axial direction of the output shaft 37, and a plurality (16) of convex shapes S formed radially outward are formed at equal intervals around the entire circumferential direction on the inner surface of the second hole 36b, and a first phase β1, which is the phase of the top T of the convex shape S in the circumferential direction of the inner surface of the second hole 36b, and a second phase β2, which is the phase in the circumferential direction of the bottom of the tooth groove 36g formed between adjacent tooth traces 36f on the outer circumferential surface of the drive pulley 36, do not coincide at all or coincide only at one point.

[0074] In this way, the second hole 36b of the drive pulley 36 has a plurality of convex shapes S formed radially outward on the inner peripheral surface at equal intervals around the entire circumference. Therefore, when the equipment input shaft Z1 formed to be able to be fitted into the second hole 36b by clearance fit is inserted and fitted into the second hole 36b, the equipment input shaft Z1 and the second hole 36b of the drive pulley 36 can contact with each other over a large contact area. As a result, even if the motor M is operated and the drive pulley 36 applies a rotational force to the equipment input shaft Z1 during performance measurement, no large stress is generated between the equipment input shaft Z1 and the second hole 36b of the drive pulley 36, and deformation of the contact portion is effectively suppressed.

[0075] Furthermore, the first phase β1, which is the phase of the top T of the convex shape S, and the second phase β2, which is the phase of the bottom of the tooth groove 36g, do not coincide at all or coincide only at one point. In other words, there is no state where the thickness of the drive pulley 36 in the radial direction is the thinnest, or there is only one state. Therefore, even if deformation occurs at the convex shape position of the second hole 36b, there is no tooth groove 36g on the outer periphery of the drive pulley 36 in the vicinity of the convex shape S, or there is only one tooth groove 36g, so that a sufficient thickness is secured between the outer periphery and the outer periphery, and deformation of the outer periphery can be effectively suppressed. Note that, if there is a tooth groove 36g in the vicinity of only one point, there is a risk that deformation will occur on the outer periphery, but this is not a problem because it is known that there is a low risk that the operating noise during operation of the belt transmission device 30 will increase due to deformation occurring only at one point in the circumferential direction. In this way, by innovating the shape of the second hole 36b and the positioning of the convex shape S and the tooth groove 36g, deformation of the outer periphery of the drive pulley 36 is effectively suppressed, and the operating noise when the belt transmission device 30 is in operation is effectively suppressed.

[0076] In the first embodiment, the number of the convex shapes S of the second hole 36b over the entire circumferential direction and the number of the tooth grooves 36g between the tooth traces 36f on the outer circumferential surface of the drive pulley 36 are prime to each other. This makes it possible to easily avoid a state in which the first phase β1 and the second phase β2, at which the thickness is the thinnest, coincide with each other, and thus makes it possible to more effectively suppress deformation of the outer circumferential surface of the drive pulley 36.

[0077] In the first embodiment, the convex shape S of the second hole 36b is formed by an involute spline. The second hole 36b is a hole for measuring the performance of the motor M by inserting and fitting the equipment input shaft Z1 of the performance measuring device Z shown in FIG. 4 so as to be coaxial with the drive pulley 36 in a state in which the tip of the output shaft 37 is press-fitted into the first hole 36a and the drive pulley 36 is fixed to the tip of the output shaft 37 of the motor M. Therefore, if the outer peripheral surface shape of the equipment input shaft Z1 is formed so as to be able to fit with the convex shape S of the second hole 36b formed by the involute spline by clearance fit, the equipment input shaft Z1 and the second hole 36b can be fitted well with a large contact area. As a result, even if the motor M is operated and the drive pulley 36 applies a rotational force to the equipment input shaft Z1 during performance measurement of the motor M, no large stress is generated between the equipment input shaft Z1 and the second hole 36b of the drive pulley 36, and deformation of the contact portion is effectively suppressed.

[0078] In the first embodiment, the external teeth 36e of the drive pulley 36, the external teeth 34a of the driven pulley 34, and the internal teeth 35a of the toothed belt 35 are all formed with helical teeth so that they can mesh with each other. However, this is not limited to the above embodiment. The external teeth 36e, the external teeth 34a, and the internal teeth 35a may be formed with teeth parallel to the respective rotation axes. This also provides the same effects as the above embodiment.

[0079] In the first embodiment, the first hole 36a of the drive pulley 36 is a cylindrical hole, and the output shaft 37 of the motor M is press-fitted into the first hole 36a. This allows the drive pulley 36 and the output shaft 37 to be manufactured at low cost. [Explanation of symbols]

[0080] 10;steering device; 11;housing; 11a;first housing; 11b;second housing; 21;ball nut; 30;belt transmission device; 31;case; 31a;inner surface; 35;toothed belt; 35a;internal teeth; 36;drive pulley; 36a;first hole; 36b;second hole; 36b1;internal teeth; 36c;tooth space; 36e;external teeth; 36g;tooth space; 37;output shaft; Ar1;first region; Ar2;second region; L1;axis; L2;axis; M;electric motor (motor); Q;bottom; S;convex shape; T;top; W;convex portion; Z;performance measuring device; Z1;equipment input shaft; Z2;external teeth; β1;first phase; β2;second phase.

Claims

1. Housing and a motor including an output shaft fixed to the housing and at least a tip side of which is accommodated inside the housing; a cylindrical drive pulley that is fixed to the tip end of the output shaft inside the housing and rotates integrally with the output shaft about an axis line; a cylindrical driven pulley supported inside the housing so as to be rotatable about an axis; a circular toothed belt that is wound around the drive pulley and the driven pulley such that the internal teeth of the belt mesh with the external teeth of the drive pulley and the external teeth of the driven pulley; Equipped with The drive pulley is a first hole formed over a first predetermined range from the end of the output shaft on the motor side in the axial direction of the output shaft, into which the end of the tip side of the output shaft is fitted so as to be rotatable integrally with the output shaft; a second hole formed over a second predetermined range from an end of the output shaft opposite to the motor side in the axial direction, A plurality of convex shapes are formed on an inner peripheral surface of the second hole at equal intervals around the entire circumferential direction, the convex shapes being formed radially outwardly, a first phase, which is a phase of a top of the convex shape in the circumferential direction of the inner peripheral surface of the second hole, and a second phase, which is a phase of a bottom of a tooth groove formed between tooth traces of adjacent external teeth on the outer peripheral surface of the drive pulley, do not match at all or match at only one point; A belt transmission device, wherein the number of the convex shapes on the inner circumferential surface of the second hole and the number of the tooth grooves on the outer circumferential surface of the second hole are in a prime relationship with each other.

2. The belt transmission device according to claim 1 , wherein the convex shape of the second hole is formed by an involute spline.

3. 3. The belt transmission device according to claim 1, wherein the first hole of the drive pulley is a cylindrical hole, and the output shaft of the motor is press-fitted into the first hole.

4. A plurality of convex shapes are formed on an inner peripheral surface of the first hole at equal intervals around the entire circumferential direction, the convex shapes being formed radially outward, The belt transmission device according to claim 1 or 2, wherein a convex portion is formed around the entire circumferential circumference of the output shaft that is fitted into the first hole so as to fit into the convex shape formed in the first hole.

5. 5. The belt transmission device according to claim 4, wherein the cross-sectional shape of the convex shape formed in the first hole when cut along a plane perpendicular to the axis of the output shaft is the same as the convex shape formed in the second hole, and is formed so as to be continuously connected to the convex shape of the second hole in the axial direction of the drive pulley.

6. When the external teeth of the drive pulley are helical teeth, and the tooth trace of the helical teeth is formed at a predetermined angle with respect to the axis line of the output shaft, A belt transmission device as described in any one of claims 1 to 5, wherein the convex shape is formed in the second hole of the drive pulley so that the angle of the tooth groove formed by the convex shape relative to the axis is the same as the angle of the tooth trace of the external teeth of the drive pulley or is parallel to the axis.

7. an input shaft of a performance measuring device is inserted and fitted into the second hole of the drive pulley with a gap between the input shaft and the inner peripheral surface of the second hole; 7. The belt transmission device according to claim 1, wherein the performance of the motor is measured by the performance measuring device in a state in which the equipment input shaft is inserted into the second hole.

8. A steering device comprising the belt transmission device according to any one of claims 1 to 7.

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