Worm reducer

Abstract

An elastic biasing means (6) and an elastic clamping means (7) are provided. The elastic biasing means (6) biases the inner diameter-side member (5) toward the worm wheel (3). The elastic clamping unit (7) has a pair of clamping plate springs (41) disposed on both sides of the inner diameter-side member (5) in the third direction in a portion between the outer peripheral surface of the inner diameter-side member (5) and the inner peripheral surface of the outer diameter-side member (9). Each clamping plate spring (41) exhibits a non-linear spring characteristic such that the spring constant increases as the amount of deflection in the direction including the component in the third direction increases.

Description

Technical Field

[0001] The present invention relates to a worm reducer that can be assembled in an electric power steering device or the like.

[0002] In the field of steering devices, electric power steering devices that use electric motors as auxiliary power sources to reduce the force required for a driver to operate a steering wheel are becoming popular.

[0003] The electric power steering device is provided with a worm reducer for increasing the torque of the electric motor. The worm reducer includes a housing, a worm wheel and a worm. The housing has: a worm wheel housing; a worm housing having a center axis in a torsion position relative to the center axis of the worm wheel housing, and an axial middle portion opening to the worm wheel housing. The worm wheel has gear teeth on the outer peripheral surface, and is rotatably supported on the inner side of the worm wheel housing. The worm has worm teeth meshing with the gear teeth on the outer peripheral surface, and is rotatably supported on the inner side of the worm housing. The torque of the electric motor is increased by transmitting to the worm wheel via the worm, and then applied as auxiliary power to the steering force transmission components such as the steering shaft, the pinion shaft or the rack shaft of the steering gear unit. As a result, the force required for the driver to operate the steering wheel is reduced.

[0004] In a worm reducer, there is inevitable backlash at the meshing portion between the gear teeth and the worm teeth due to dimensional errors and assembly errors of the components constituting the worm reducer. Due to the existence of this backlash, a harsh sound of teeth clattering sometimes occurs at the meshing portion when the steering wheel's rotation direction is changed.

[0005] The following structure is described in Japanese Patent Gazette No. 2020-128803: In order to suppress the occurrence of tooth-clicking sound at the meshing portion between the gear teeth and the worm teeth, force is applied to the distal end of the worm toward the worm wheel. The structure comprises: an externally embedded component, which is externally embedded in a support bearing that supports the distal end of the worm so that it can rotate freely, and is configured to be able to move far or near relative to the worm wheel; and a force spring (elastic force unit) that is disposed between the externally embedded component and the worm housing portion. The force spring elastically deforms, and the externally embedded component is forced toward the worm wheel by the elastic restoring force of the force spring. As a result, the backlash at the meshing portion between the gear teeth and the worm teeth is suppressed, and the occurrence of tooth-clicking sound is suppressed.

[0006] In the structure described in Japanese Patent Publication No. 2020-128803, in order to enable the tip of the worm to move forward or backward relative to the worm wheel, a gap is provided over the entire circumference between the outer peripheral surface of the externally embedded component in the support bearing that supports the tip of the worm to rotate freely and the inner peripheral surface of the worm housing. Therefore, based on the existence of the gap, the tip of the worm can move in a third direction that is orthogonal to both the first direction of the force application direction of the force application spring and the second direction of the axial direction of the worm housing.

[0007] On the other hand, the meshing reaction force acts on the worm from the meshing portion between the worm teeth and the gear teeth. The meshing reaction force includes a force of a third directional component. The direction of the third directional component is reversed according to the rotation direction of the worm. In addition, when the car is driven, the third directional component of the vibration input from the tire is transmitted to the worm. Therefore, when the tip of the worm is allowed to move in the third direction without resistance based on the existence of the gap, due to the third directional component of the meshing reaction force acting on the worm and the third directional component of the vibration input in the opposite direction to the worm, the outer peripheral surface of the externally embedded component collides violently with the inner peripheral surface of the worm housing in the third direction, which is likely to produce harsh impact sounds, rattling sounds and other abnormal noises.

[0008] Therefore, in order to suppress the generation of such abnormal noise, the structure described in Japanese Patent Publication No. 2020-128803 includes a pair of clamping leaf springs that clamp the external fitting component from both sides in the third direction. Moreover, the momentum of the tip of the worm gear moving in the third direction is suppressed by the pair of clamping leaf springs, thereby suppressing the generation of the abnormal noise mentioned above.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Publication No. 2020-128803 Summary of the invention

[0012] Problems to be solved by the invention

[0013] The conventional structure described in Japanese Patent Application Laid-Open No. 2020-128803 has room for improvement from the following aspects.

[0014] That is, in the existing structure described in Japanese Patent Application Publication No. 2020-128803, in order to make the force application action of the force application spring on the terminal end of the worm smooth, that is, in order to make the movement of the terminal end of the worm in the first direction smooth, the spring constant of the pair of clamping leaf springs is required to be low. On the other hand, in order to fully suppress the third direction component of the meshing reaction force acting on the worm and the third direction component of the vibration reversely input to the worm, which causes the outer peripheral surface of the external fitting part to collide violently with the inner peripheral surface of the worm housing portion in the third direction, the spring constant of the pair of clamping leaf springs is required to be large.

[0015] However, in the conventional structure described in Japanese Patent Application Laid-Open No. 2020-128803, the spring constant of the pair of clamping leaf springs is constant, and therefore it is difficult to satisfy the above two requirements that are in a contradictory relationship with each other.

[0016] An object of the present invention is to provide a worm reducer which can make the urging operation of the elastic urging means on the tip of the worm smooth and easily suppress the collision force between components in the third direction around the tip of the worm.

[0017] Means for solving problems

[0018] A worm reducer according to one embodiment of the present invention includes a housing, a worm wheel, a worm, a support bearing, an elastic urging unit, and an elastic clamping unit.

[0019] The housing has a worm wheel housing portion and a worm housing portion having a center axis in a twisted position relative to a center axis of the worm wheel housing portion, and an axial intermediate portion opening toward the worm wheel housing portion.

[0020] The worm wheel has gear teeth on an outer peripheral surface and is rotatably supported inside the worm wheel housing portion.

[0021] The worm has worm teeth meshing with the gear teeth on an outer peripheral surface, and is rotatably supported inside the worm housing portion.

[0022] The support bearing is externally fitted on the distal end of the worm.

[0023] The elastic urging means urges an inner diameter side member toward the worm wheel side, and the inner diameter side member is the support bearing or an externally fitted member externally fitted on the support bearing.

[0024] The elastic clamping unit has a pair of clamping leaf springs in the portion between the outer circumferential surface of the inner diameter side component and the inner circumferential surface of the outer diameter side component. The outer diameter side component is the worm housing portion or an embedded component embedded in the worm housing portion. The pair of clamping leaf springs are arranged on both sides of the inner diameter side component in a third direction that is orthogonal to the force application direction of the elastic force application unit, i.e., the first direction, and the axial direction of the worm housing portion, i.e., the second direction.

[0025] In a worm reducer of one embodiment of the present invention, each of the clamping leaf springs constituting the pair of clamping leaf springs exhibits a nonlinear spring characteristic in which the spring constant increases as the deflection in the direction including the component in the third direction increases. Here, the increase in the spring constant accompanying the increase in the deflection in the direction including the component in the third direction may be a stepwise increase or a continuous increase.

[0026] In a worm reducer of one embodiment of the present invention, each clamping leaf spring constituting a pair of the clamping leaf springs makes the circumferential middle portion contact the inner peripheral surface of the outer diameter side component, and makes the circumferential side portions contact the outer peripheral surface of the inner diameter side component respectively, and as the deflection amount in the direction including the component of the third direction increases, the distance between the contact portions of the circumferential side portions relative to the outer peripheral surface of the inner diameter side component decreases, thereby increasing the spring constant.

[0027] In the worm reducer of one embodiment of the present invention, when viewed from the second direction, the circumferential intermediate portion of each of the pair of clamp leaf springs intersects with a third direction straight line Lx passing through the center of the worm and extending in the third direction.

[0028] In the worm reducer according to one aspect of the present invention, a portion of the inner peripheral surface of the outer diameter side member that contacts a circumferential intermediate portion of each of the pair of clamp leaf springs is formed of a flat surface portion extending in the first direction.

[0029] In a worm reducer of one embodiment of the present invention, when viewed from the second direction, the circumferential middle portion of one clamping leaf spring constituting a pair of the clamping leaf springs intersects with a radial straight line L1, which includes a vector of an engagement reaction force F1 applied to the worm from the meshing portion between the worm teeth and the wheel teeth when the worm rotates in a specified direction, and when viewed from the second direction, the circumferential middle portion of the other clamping leaf spring constituting a pair of the clamping leaf springs intersects with a radial straight line L2, which includes a vector of an engagement reaction force F2 applied to the worm from the meshing portion when the worm rotates in a direction opposite to the specified direction.

[0030] In a worm reducer of one embodiment of the present invention, in the object clamping leaf spring of at least one of the pair of clamping leaf springs, the circumferential middle portion is composed of a first portion having a partial cylindrical shape bent along the outer peripheral surface of the inner diameter side component. The circumferential side portions are respectively composed of second portions having a partial cylindrical shape bent along the outer peripheral surface of the inner diameter side component and smoothly continuous with respect to the first portion. The radius of curvature of the radially inner side surface of the first portion in a free state is smaller than the radius of curvature of the outer peripheral surface of the inner diameter side component. The radius of curvature of the radially inner side surface of the second portion in a free state is greater than the radius of curvature of the radially inner side surface of the first portion in a free state. Here, the radius of curvature of the radially inner side surface of the second portion in a free state can be constant over the entire circumferential length, and can also be changed in stages or continuously in the circumferential direction.

[0031] In a worm reducer of one embodiment of the present invention, in the object clamping leaf spring of at least one of the pair of clamping leaf springs, the circumferential middle portion is composed of a first portion having a partial cylindrical shape bent along the outer peripheral surface of the inner diameter side component. The circumferential side portions are respectively composed of second portions having a partial cylindrical shape bent along the outer peripheral surface of the inner diameter side component and smoothly continuous with respect to the first portion. The radius of curvature of the radial inner surface of each of the first portion and the second portion in a free state is equal to each other and is smaller than the radius of curvature of the outer peripheral surface of the inner diameter side component. The second portion has a low-rigidity leaf spring portion at the circumferential end portion on the first portion side, and the rigidity of the low-rigidity leaf spring portion is lower than the rigidity of the remaining circumferential portion and the first portion.

[0032] In this case, in a worm reducer of one embodiment of the present invention, each clamping leaf spring constituting a pair of the clamping leaf springs is the object clamping leaf spring, and the elastic clamping unit has a circumferential connecting portion that circumferentially connects the circumferential end portions of the pair of the clamping leaf springs on the side close to the worm wheel to each other, and the circumferential connecting portion has a partial cylindrical shape bent along the outer circumferential surface of the inner diameter side component, and is smoothly continuous relative to the pair of the clamping leaf springs, and the curvature radius of the radial inner surface of the circumferential connecting portion in the free state is equal to the curvature radius of the radial inner surface of each of the first part and the second part in the free state.

[0033] In the worm reducer according to one aspect of the present invention, the elastic clamping unit has a circumferential connection portion that connects circumferential end portions of the pair of clamping leaf springs on a side close to the worm wheel to each other in the circumferential direction.

[0034] In the worm reducer according to one aspect of the present invention, the circumferential connection portion has a low-rigidity connection portion having lower rigidity than the pair of clamp leaf springs in at least a portion in the circumferential direction.

[0035] In the worm reducer according to the aspect of the present invention, each of the clamp leaf springs constituting the pair of clamp leaf springs is given residual stress in a portion contacting the inner peripheral surface of the outer diameter side member.

[0036] In the worm reducer according to one aspect of the present invention, the elastic clamping means includes a circumferential positioning piece that engages with the inner diameter side member or the outer diameter side member in the circumferential direction.

[0037] In the worm reducer according to one aspect of the present invention, the elastic clamping means includes an axial positioning piece that is engaged with the inner diameter side member or the outer diameter side member in the axial direction.

[0038] In the worm reducer of one embodiment of the present invention, when the horizontal axis is the deflection in the third direction and the vertical axis is the load, the nonlinear spring characteristic is represented by a graph that is convex downward and whose slope increases as the deflection in the third direction increases.

[0039] The present invention can be implemented by appropriately combining the above-mentioned various aspects within a range where no contradiction occurs.

[0040] Effects of the Invention

[0041] According to the worm reducer of one aspect of the present invention, the urging operation of the elastic urging means on the tip of the worm can be smoothed, and the collision force between components in the third direction can be easily suppressed around the tip of the worm. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a diagram showing an electric power steering system incorporating a worm speed reducer according to a first example of an embodiment of the present invention.

[0043] Figure 2 yes Figure 1 AA section view.

[0044] Figure 3 yes Figure 2 Magnified image of the upper right portion.

[0045] Figure 4 yes Figure 3 Exploded perspective view of the parts shown.

[0046] Figure 5 is from Figure 3 Remove the cover and retaining ring from the part shown. Figure 3 Observation diagram on the right.

[0047] Figure 6 yes Figure 5 Enlarged view of part B.

[0048] Figure 7 yes Figure 5 Enlarged view of part C.

[0049] Figure 8 In the first case, Figure 3 Figure 2. Observation of the housing on the right side.

[0050] Fig. 9 This is a perspective view showing the support bearing, the elastic urging unit, and the elastic clamping unit removed from the first example.

[0051] Fig.10 Yes Fig. 9 The components shown are separated from the figure.

[0052] Fig.11 (a) is a side view of the elastic force applying unit in the first example, Fig.11 (b) is from Fig.11 (a) is a diagram viewed from the upper side. Fig.11 (c) is from Fig.11 (a) is a diagram viewed from the bottom. Fig.11 (d) is from Fig.11 The left side of (a) is observed. Fig.11 (e) is from Fig.11 The figure observed on the right side of (a).

[0053] Fig.12 (a) is a side view of the elastic clamping unit in the first example, Fig.12 (b) is from Fig.12 (a) is a diagram viewed from the upper side. Fig.12 (c) is from Fig.12 (a) is a diagram viewed from the bottom. Fig.12 (d) is from Fig.12 The left side of (a) is observed. Fig.12 (e) is from Fig.12 The figure observed on the right side of (a).

[0054] Fig.13 (a)~ Fig.13 (d) is a diagram schematically showing a state in which the deflection amount in the first direction of the elastic urging means in the first example increases.

[0055] Fig.14 It is a line diagram (conceptual diagram) showing the spring characteristics of the elastic urging means in the first example.

[0056] Fig.15 (a)~ Fig.15 (c) is a diagram schematically showing a state in which the deflection amount in the third direction of the elastic clamping unit (clamping leaf spring) in the first example increases.

[0057] Fig.16 It is a line diagram (conceptual diagram) showing the spring characteristics of the elastic clamping unit (clamping leaf spring) in the first example.

[0058] Fig.17 (a)~ Fig.17 (c) is a diagram schematically showing a situation in which the deflection amount of the elastic clamping unit (clamping leaf spring) in the third direction does not change with the movement in the first direction in the first example.

[0059] Fig.18 (a) is a side view of the elastic clamping unit in the second example of the embodiment of the present invention, Fig.18 (b) is a stereoscopic view of the elastic clamping unit.

[0060] Fig.19 (a)~ Fig.19 (c) is a diagram schematically showing a state in which the deflection amount in the third direction of the elastic clamping unit (clamping leaf spring) in the second example increases.

[0061] Fig. 20 This is a diagram showing, in an exaggerated and schematic manner, a state in which the elastic clamping unit (clamping leaf spring) in the second example is bent in the third direction.

[0062] Fig.21 The third example of the embodiment of the present invention is equivalent to Figure 5 Part of the diagram. DETAILED DESCRIPTION

[0063] [First example]

[0064] use Figure 1 to Figure 17 A first example of an embodiment of the present invention will be described.

[0065] (1) Worm reducer

[0066] The worm reducer of the present invention can be applied to a worm reducer incorporated in a part of various mechanical devices, but in this example, a case where the present invention is applied to a worm reducer incorporated in a part of an electric power steering device for an automobile will be described.

[0067] like Figure 1 to Figure 5 As shown, the worm speed reducer 1 of this example includes a housing 2 , a worm wheel 3 , a worm 4 , a support bearing 5 , an elastic urging unit 6 , and an elastic clamping unit 7 .

[0068] The housing 2 includes a worm wheel accommodation portion 8 and a worm accommodation portion 9 having a center axis in a twisted position relative to the center axis of the worm wheel accommodation portion 8 and an axially intermediate portion opening toward the worm wheel accommodation portion 8 .

[0069] The worm wheel housing portion 8 is configured in a cylindrical shape. Figure 2 In the figure, the central axis of the worm wheel housing portion 8 extends in the front-back direction.

[0070] The worm housing portion 9 is configured in a cylindrical shape and has openings at both ends in the axial direction. Figure 2 The central axis of the worm housing portion 9 extends in the left-right direction. The opening on one axial side of the worm housing portion 9 is closed by a cover 10 mounted on the opening using a retaining ring 47. The opening on the other axial side of the worm housing portion 9 is closed by an electric motor 11 fixedly coupled to the housing 2.

[0071] In addition, regarding the worm housing portion 9 and the components housed in the worm housing portion 9, one side in the axial direction is Figure 2The right side of the axis is Figure 2 on the left side of the .

[0072] The worm wheel 3 has helical gear-shaped gear teeth 12 on the outer peripheral surface and is rotatably supported inside the worm wheel housing portion 8. In this example, the worm wheel 3 is externally fixed to an axial portion of a rotating shaft rotatably supported inside the worm wheel housing portion 8 (in this example, the front side portion of the steering shaft 50 in the front-rear direction of the vehicle).

[0073] The worm 4 has a threaded worm tooth 13 meshing with the gear teeth 12 of the worm wheel 3 on the outer peripheral surface of the axial middle portion, and is rotatably supported inside the worm housing portion 9. In this example, the twisting direction of the worm tooth 13 is right-handed. However, the twisting direction may also be left-handed.

[0074] The base end portion of the worm 4 ( Figure 2 The left end portion of the worm 4 is supported by a ball bearing 14 so as to be rotatable relative to the worm housing portion 9. In this example, the outer ring of the ball bearing 14 is embedded in the worm housing portion 9 with a radial gap, and the inner ring of the ball bearing 14 is embedded in the portion of the worm 4 near the base end with a radial gap. As a result, the portion of the worm 4 near the base end is supported so as to be rotatable and swingable relative to the worm housing portion 9. In addition, the outer ring of the ball bearing 14 can also be embedded in the worm housing portion 9 in an interference fit manner. In addition, the structure for supporting the portion of the worm 4 near the base end so as to be rotatable and swingable relative to the worm housing portion 9 is not limited to the structure of this example, and various structures can be adopted.

[0075] The base end of the worm 4 is connected to the terminal end of the output shaft 15 of the electric motor 11 using a coupling 16 so as to enable torque transmission and swing displacement. In addition, the base end of the worm 4 can also be connected to the terminal end of the output shaft 15 of the electric motor 11 by spline engagement so as to enable torque transmission and swing displacement.

[0076] The support bearing 5 is externally fitted to the distal end of the worm 4. Figure 2 as well as Figure 3 The left and right directions Figure 5 In the "second direction", the tip of the worm 4 is the tip on one side of the axial direction ( Figure 2 right end of the ).

[0077] In this example, the support bearing 5 is composed of a ball bearing. Figure 3As shown, the support bearing 5 includes an inner ring 17, an outer ring 18, and a plurality of balls 19, and the plurality of balls 19 are arranged between an inner ring raceway provided on the outer circumferential surface of the inner ring 17 and an outer ring raceway provided on the inner circumferential surface of the outer ring 18. The inner ring 17 is externally fitted and fixed to the distal end of the worm 4. In addition, when implementing the present invention, the support bearing can also be composed of other types of bearings such as roller bearings.

[0078] In this example, the inner peripheral surface of the worm housing portion 9 has a small-diameter cylindrical surface portion 20 having a smaller diameter than the outer peripheral surface of the support bearing 5, that is, the outer peripheral surface of the outer ring 18, at a portion of the end portion close to the axial side, and has a retaining portion 21 having a larger diameter than the small-diameter cylindrical surface portion 20 at a portion adjacent to the axial side of the small-diameter cylindrical surface portion 20. The small-diameter cylindrical surface portion 20 and the retaining portion 21 are connected by a step surface 22 facing the axial side. In this example, the support bearing 5 is arranged inside the retaining portion 21 so as to be movable in the radial direction.

[0079] It should be noted that in the following description, the force direction of the elastic force applying unit 6, that is, the direction in which the worm 4 moves relative to the worm wheel 3 ( Figure 2 , Figure 3 and Figure 5 The vertical direction of the worm housing portion 9 is set as the “first direction”, and the axial direction ( Figure 2 and Figure 3 The left and right directions, Figure 5 The front and back direction of the first direction is set as the “second direction”, and the direction orthogonal to both the first direction and the second direction ( Figure 2 and Figure 3 The table and back direction, Figure 5 direction) as the “third direction”.

[0080] like Figure 5 as well as Figure 8 As shown in FIG. 1 , the holding portion 21 of the worm housing portion 9 includes a main holding portion 23, a secondary holding portion 24, and a locking portion 25. The main holding portion 23 is arranged substantially coaxially with the small-diameter cylindrical surface portion 20, and has a substantially cylindrical shape that is one circle larger than the outer peripheral surface of the support bearing 5. The secondary holding portion 24 is formed from a side (ie, the side) of the main holding portion 23 that is away from the worm wheel 3 in the first direction. Figure 5 and Figure 8 The locking portion 25 protrudes radially outward from the end of the main retaining portion 23 that is close to the worm wheel 3 in the first direction.

[0081] The main holding portion 23 is a portion in which the support bearing 5 is arranged to be movable in the radial direction. The ends of the main holding portion 23 on both sides in the third direction are formed by a pair of flat surfaces 26 (see FIG. 2 ) extending in the first direction. Figure 7) is composed. The pair of flat portions 26 are the portions that are in contact with the circumferential middle portions of the pair of clamping leaf springs 41 that constitute the elastic clamping unit 7. The spacing between the pair of flat portions 26 in the third direction is larger than the diameter of the outer circumferential surface of the support bearing 5. The length of the pair of flat portions 26 in the first direction is ensured to be larger than the stroke amount that the elastic clamping unit 7 can move in the first direction together with the terminal end of the worm 4 and the support bearing 5 during operation. Therefore, no matter how the elastic clamping unit 7 moves in the first direction, the pair of clamping leaf springs 41 that constitute the elastic clamping unit 7 are maintained in contact with the pair of flat portions 26.

[0082] The portion of the main retaining portion 23 that is circumferentially offset from the pair of flat portions 26 is formed by a cylindrical surface portion 27 having a larger diameter than the outer peripheral surface of the support bearing 5. In the embodiment of the present invention, the pair of flat portions of the main retaining portion may be omitted and the main retaining portion may be formed only by the cylindrical surface portion.

[0083] In the worm reducer 1 of this example, when torque is transmitted from the worm 4 to the worm wheel 3, a meshing reaction force is applied to the worm 4 from the meshing portion between the gear teeth 12 and the worm teeth 13. This meshing reaction force includes not only a first direction component but also a third direction component. When the worm 4 rotates in a prescribed direction and when the worm 4 rotates in a direction opposite to the prescribed direction, the directions of the third direction component in the meshing reaction force are opposite to each other. In addition, when the worm 4 rotates in a prescribed direction and when it rotates in the opposite direction, the ratio of the first direction component to the third direction component contained in the meshing reaction force is different. That is, when torque is transmitted between the worm 4 and the worm wheel 3, according to the rotation direction of the worm 4, a first direction component is applied to the distal end of the worm 4 as follows: Figure 5 The meshing reaction force F1 or F2 shown. The meshing reaction forces F1 and F2 are directed in directions that are asymmetric to each other in the third direction. This example is an example in which the torsion direction of the worm gear 13 is the right-hand direction, but when the torsion direction of the worm gear 13 is the left-hand direction, Figure 5 The directions of the meshing reaction forces F1 and F2 in the embodiment are respectively reversed relative to the third direction. Figure 5 The structure of the part shown is reversed in the third direction, i.e. Figure 5 Reverse left and right.

[0084] like Figure 5 As shown, when viewed from the second direction, the circumferential range of the cylindrical surface 27 of the main retaining portion 23 includes the same circumferential position as the vectors of the meshing reaction forces F1 and F2. That is, the radial lines L1 and L2 including the vectors of the meshing reaction forces F1 and F2 intersect a part of the circumferential direction of the cylindrical surface 27 of the main retaining portion 23.

[0085] The auxiliary holding portion 24 is a portion on the inner side of which the elastic urging unit 6 is arranged. The auxiliary holding portion 24 is on one side of the third direction ( Figure 5 and Figure 8 The auxiliary holding portion 24 has a large recess 28 that is recessed toward one side of the third direction. Figure 5 and Figure 8 The left side of the auxiliary holding portion 24 has a small recess 29 that is recessed toward the side away from the worm wheel 3 in the first direction. The auxiliary holding portion 24 has a first inclined surface portion 30 and a second inclined surface portion 31 in order from the side of the large recess 28 between the large recess 28 and the small recess 29. The first inclined surface portion 30 and the second inclined surface portion 31 are respectively composed of planes that are inclined toward the direction of the side away from the worm wheel 3 in the first direction as they move toward the other side in the third direction. Figure 6 As shown, the inclination angle θ2 of the second inclined surface portion 31 relative to the third direction is greater than the inclination angle θ1 of the first inclined surface portion 30 relative to the third direction (θ2>θ1). In this example, when viewed from the second direction, the length of the second inclined surface portion 31 is longer than the length of the first inclined surface portion 30. The large recess 28 is connected to the first inclined surface portion 30 via the first corner portion 32. The first inclined surface portion 30 and the second inclined surface portion 31 are connected via the second corner portion 33. The second inclined surface portion 31 and the small recess 29 are connected via the third corner portion 34. That is, the first corner portion 32, the second corner portion 33, and the third corner portion 34 are oriented in the third direction in a direction away from the pin 36 disposed in the large recess 28 ( Figure 5 , Figure 6 as well as Figure 8 The first corner portion 32, the second corner portion 33 and the third corner portion 34 are arranged in the order of the first corner portion 32, the second corner portion 33 and the third corner portion 34, and the first direction is toward the direction away from the worm wheel 3 ( Figure 5 , Figure 6 as well as Figure 8 The first corner portion 32, the second corner portion 33 and the third corner portion 34 are arranged in this order. The first corner portion 32, the second corner portion 33 and the third corner portion 34 are portions that the elastic urging unit 6 contacts during operation.

[0086] like Figure 5 and Figure 8 As shown, the locking portion 25 is a portion for locking a part of the elastic clamping unit 7 in the circumferential direction. In the example shown in the figure, the locking portion 25 is composed of a semi-cylindrical concave surface.

[0087] In this example, the worm housing portion 9 has a partially open recess 35 located inside the large recess 28 in the stepped surface 22. The other axial end of a cylindrical pin 36 extending in the second direction is press-fitted and supported in the recess 35. The pin 36 is a member for holding the elastic urging unit 6.

[0088] The elastic force applying means 6 applies force to the support bearing 5 corresponding to the inner diameter side member toward the worm wheel 3. Thus, the generation of the tooth rattling sound is suppressed by suppressing the backlash between the gear teeth 12 and the worm teeth 13. It should be noted that, when implementing the present invention, an externally embedded member externally embedded in the support bearing 5 may be used as the inner diameter side member. That is, the externally embedded member may be applied toward the worm wheel by the elastic force applying means.

[0089] In this example, the elastic urging means 6 exhibits nonlinear spring characteristics in which the spring constant increases as the deflection amount in the first direction increases when the elastic urging means 6 is installed in the use site.

[0090] Therefore, in this example, as the elastic force applying unit 6, a Fig.11 (a)~ Fig.11 The structure shown in (e) and as Figure 5 A metal biasing plate spring 37 is provided as shown.

[0091] like Fig.11 (a)~ Fig.11 As shown in (e), the urging plate spring 37 includes: a strip plate portion 38 having a rectangular flat plate shape with a large aspect ratio; a proximal end side ( Fig.11 The end edge of (a) on the right side) is oriented to one side in the thickness direction ( Fig.11 (a) of the lower side) bent into an obtuse angle formed by the substrate portion 39; from the end side of the length direction of the strip plate portion 38 ( Fig.11 The folded-back plate portion 40 has an end edge portion (left side of (a)) folded back 180 degrees to one side in the thickness direction and its terminal side portion overlaps with the terminal side portion of the strip plate portion 38.

[0092] The entirety of the force plate spring 37 is disposed inside the worm housing portion 9. Figure 5 As shown, the urging plate spring 37 is arranged on the side away from the worm wheel 3 in the first direction in the portion between the outer peripheral surface of the support bearing 5 and the retaining portion 21 provided on the inner peripheral surface of the worm housing portion 9 corresponding to the outer diameter side component. More specifically, the urging plate spring 37 is arranged on the inner side of the auxiliary retaining portion 24 constituting the retaining portion 21. In addition, when implementing the present invention, an embedded component embedded in the worm housing portion can also be used as the outer diameter side component. That is, the retaining portion 21 can also be provided on the inner peripheral surface of the embedded component.

[0093] In this example, the force applying plate spring 37 is provided at the use position, and in the unloaded state of the worm reducer 1, that is, when the torque transmitted from the worm 4 to the worm wheel 3 is zero and the meshing reaction forces F1 and F2 applied to the distal end of the worm 4 are zero, the force applying plate spring 37 is configured as follows relative to the surrounding parts.

[0094] The base end of the base plate portion 39 elastically contacts the bottom of the large recessed portion 28 constituting the auxiliary holding portion 24. The side surface (ie, the side surface on the concave side) of the connecting portion between the strip plate portion 38 and the base plate portion 39 in the thickness direction Figure 5 The lower side surface of the strip plate portion 38 is in elastic contact with the outer peripheral surface of the pin 36. The other side surface ( Figure 5 The upper side surface of the folded-back plate portion 40 is in elastic contact with the first corner portion 32 constituting the auxiliary holding portion 24. The surface ( Figure 5 The lower side surface of the support bearing 5 is elastically in contact with the end of the outer peripheral surface of the support bearing 5 on the side away from the worm wheel 3 in the first direction. It should be noted that the strip plate portion 38 does not contact the second corner portion 33 and the third corner portion 34, and there is a gap between the strip plate portion 38 and the second corner portion 33 and the third corner portion 34.

[0095] In this state, the urging plate spring 37 elastically urges the support bearing 5 toward the worm wheel 3 in such a manner that the contact portion with the first corner portion 32 becomes a fulcrum S and the contact portion with the outer peripheral surface of the support bearing 5 becomes a load point P (see Fig.13 (a)). It should be noted that, in this example, the force plate spring 37 is held in the use position by the friction force acting on the contact portion with the worm housing portion 9 and the pin 36. In addition, the load point P is arranged at a position substantially the same as the third corner portion 34 of the auxiliary retaining portion 24 in the third direction.

[0096] In this example, when the meshing reaction force F1 or F2 applied to the distal end of the worm 4 increases due to an increase in the torque transmitted from the worm 4 to the worm wheel 3, the pressing force applied from the support bearing 5 to the load point P of the force leaf spring 37 increases, and the deflection of the force leaf spring 37 (with the plate portion 38) in the first direction increases. Fig.13 (a)~ Fig.13 (d) is a diagram schematically showing the case where the deflection amount increases. In this example, when the deflection amount of the urging plate spring 37 in the first direction increases, the elastic contact position of the urging plate spring 37 relative to the auxiliary retaining portion 24 is as follows: Fig.13 (a)~ Fig.13 That is, the position of the fulcrum S of the urging plate spring 37 changes stepwise toward the direction approaching the load point P. As a result, the spring constant of the urging plate spring 37 is as follows: Fig.14 (Conceptual diagram) and increases in stages.

[0097] More specifically, in this example, when the deflection amount of the urging plate spring 37 in the first direction increases, the elastic contact position of the urging plate spring 37 with respect to the auxiliary holding portion 24 changes from Fig.13 The first corner 32 (one place) shown in (a) is changed to Fig.13The first corner 32 and the second corner 33 (two places) shown in (b) are then changed to Fig.13 The second corner 33 (one place) shown in (c) is then changed to Fig.13 The second corner 33 and the third corner 34 (two locations) shown in (d).

[0098] like Fig.13 As shown in (a), when the urging plate spring 37 is in elastic contact with only the first corner portion 32 (at one location), the fulcrum S of the urging plate spring 37 becomes the contact portion with the first corner portion 32. Fig.14 In this state (first stage), the spring constant of the urging plate spring 37 is relatively small. In addition, in this example, during normal operation without a large meshing reaction force acting on the worm, the deflection amount of the urging plate spring 37 in the first direction is suppressed to be small, and the urging plate spring 37 always contacts the first corner 32.

[0099] like Fig.13 As shown in (b), in the state where the force plate spring 37 is in elastic contact with the first corner portion 32 and the second corner portion 33 (two locations), and as shown in Fig.13 As shown in (c), when the urging plate spring 37 is in elastic contact with only the second corner portion 33 (at one location), the fulcrum S of the urging plate spring 37 becomes the contact portion with the second corner portion 33. Fig.14 As shown, the spring constant of the biasing plate spring 37 in this state (second stage) is relatively large, specifically, larger than that in the first stage.

[0100] like Fig.13 As shown in (d), when the urging plate spring 37 elastically contacts the second corner portion 33 and the third corner portion 34 (at two locations), the urging plate spring 37 cannot further increase the deflection amount in the first direction, and is in a so-called bottoming state.

[0101] That is, in this example, the spring constant of the urging plate spring 37 changes in two stages according to the deflection amount in the first direction of the urging plate spring 37. Specifically, as the deflection amount in the first direction of the urging plate spring 37 increases, the spring constant of the urging plate spring 37 increases from a relatively small value (first stage) to a relatively large value (second stage).

[0102] Therefore, the torque transmitted from the worm 4 to the worm wheel 3 increases, thereby increasing the deflection amount of the biasing plate spring 37 in the first direction. Fig.13 As shown in (d), the spring constant of the urging plate spring 37 can be made relatively large (second stage) just before the urging plate spring 37 collides with the third corner portion 34. Therefore, the momentum of the collision can be effectively suppressed by utilizing the large elastic force of the urging plate spring 37. Thus, the generation of the collision sound can be effectively suppressed.

[0103] Furthermore, by Fig.13The state shown in (d) of FIG. 1 reverses the rotation direction of the worm 4, thereby reducing the deflection amount of the urging plate spring 37 in the first direction to Fig.13 Before the state shown in (a), the spring constant of the urging plate spring 37 becomes a relatively small value (first stage). Therefore, by reducing the urging force of the urging plate spring 37, the collision momentum between the gear teeth 12 and the worm teeth 13 caused by the reversal of the rotation direction of the worm 4 can be effectively suppressed. As a result, the occurrence of the tooth-striking sound between the gear teeth 12 and the worm teeth 13 can be effectively suppressed.

[0104] It should be noted that, in this example, the corners that become the fulcrum S of the force leaf spring 37 are set to the first corner 32 and the second corner 33. However, in the case of implementing the present invention, by increasing the number of the corners compared to this example, the spring constant of the force leaf spring 37 can also be changed in three or more stages. In addition, the portion of the auxiliary retaining portion 24 with which the force leaf spring 37 elastically contacts, such as the portion between the first corner 32 and the second corner 33, and the portion between the second corner 33 and the third corner 34, can also be set as a convex surface. If such a structure is adopted, as the deflection amount of the force leaf spring 37 in the first direction increases, the force leaf spring 37 bends along the convex surface. Therefore, the position of the fulcrum S of the force leaf spring 37 can be continuously changed in the direction close to the load point P, and the spring constant of the force leaf spring 37 can be continuously increased.

[0105] In the case of implementing the present invention, the spring characteristic of the elastic force applying unit may be non-linear or linear. In the case of implementing the present invention, when a leaf spring is used as the elastic force applying unit, the shape of the leaf spring may be different from that of this example. In the case of implementing the present invention, various springs other than leaf springs such as coil springs or rubbers may be used as the elastic force applying unit.

[0106] The elastic clamping unit 7 has a pair of clamping leaf springs 41 disposed on both sides of the support bearing 5 in the third direction, in a portion between the outer peripheral surface of the support bearing 5 corresponding to the inner diameter side member and the retaining portion 21 provided on the inner peripheral surface of the worm housing portion 9 corresponding to the outer diameter side member. Each clamping leaf spring 41 constituting the pair of clamping leaf springs 41 exhibits a nonlinear spring characteristic in which the spring constant increases as the deflection amount in the direction including the component of the third direction (in this example, the deflection amount in the third direction) increases.

[0107] In this example, if Fig.12 (a)~ Fig.12As shown in (e), the elastic clamping unit 7 is composed of a metal leaf spring having a cylindrical shape (C-shaped) as a whole. A pair of clamping leaf springs 41 constitute the circumferential side portions of the elastic clamping unit 7. The elastic clamping unit 7 has a circumferential connecting portion 42, which connects the circumferential ends of the pair of clamping leaf springs 41 on the side close to the worm wheel 3 to each other in the circumferential direction. Fig.12 In (a), the dotted line α represents the boundary line between the pair of clamping leaf springs 41 and the circumferential connecting portion 42 .

[0108] In this example, each of the pair of clamping leaf springs 41 has a first portion 43 constituting a circumferential middle portion and a second portion 44 constituting both circumferential side portions. Fig.12 In (a), the dotted line β represents the boundary line between the first portion 43 and the second portion 44 .

[0109] The first portion 43 has a partial cylindrical shape bent along the outer peripheral surface of the support bearing 5. The second portion 44 has a partial cylindrical shape bent along the outer peripheral surface of the support bearing 5, and is smoothly continuous with the first portion 43. That is, when viewed from the axial direction of the worm 4, the circumferential ends of the radially inner side surfaces of the first portion 43 and the second portion 44 are connected to each other in a manner having a common tangent line, and the circumferential ends of the radially outer side surfaces of the first portion 43 and the second portion 44 are connected to each other in a manner having a common tangent line.

[0110] The curvature radius R1 of the radially inner side surface of the first portion 43 in the free state is larger than the curvature radius Rs of the outer peripheral surface of the support bearing 5 (see Figure 5 ) is smaller (R1<Rs). The curvature radius R2 of the radially inner side surface of the second portion 44 in the free state is larger than the curvature radius R1 of the radially inner side surface of the first portion 43 in the free state (R2>R1). In this example, the curvature radius R2 is made equal to the curvature radius Rs of the outer peripheral surface of the support bearing 5 (R2=Rs). However, when implementing the present invention, the curvature radius R2 may be slightly larger or smaller than the curvature radius Rs.

[0111] In this example, each of the pair of clamping leaf springs 41 applies residual stress to the first portion 43 corresponding to the portion in contact with the retaining portion 21 provided on the inner circumferential surface of the worm housing portion 9. This makes it easy to ensure the durability of the first portion 43, which tends to have a larger elastic deformation amount during operation than other portions. In the case of implementing the present invention, the application of the residual stress may be omitted.

[0112] The circumferential connecting portion 42 has a partial cylindrical shape that is bent along the outer circumferential surface of the support bearing 5, and is smoothly continuous with respect to each clamping leaf spring 41 constituting the pair of clamping leaf springs 41. That is, when viewed from the axial direction of the worm 4, the circumferential ends of the radial inner side surfaces of the clamping leaf spring 41 and the circumferential connecting portion 42 are connected to each other in a manner having a common tangent line, and the circumferential ends of the radial outer side surfaces are connected to each other in a manner having a common tangent line. In this example, the radius of curvature Rj of the radial inner side surface of the circumferential connecting portion 42 in the free state is made equal to the radius of curvature R2 of the radial inner side surface of the second portion 44 in the free state (Rj=R2). In addition, when implementing the present invention, the circumferential connecting portion can also be omitted, that is, the pair of clamping leaf springs 41 can be separated from each other.

[0113] In this example, the elastic clamping unit 7 has a circumferential positioning piece 45 that engages with the worm housing portion 9 in the circumferential direction.

[0114] In this example, two circumferential positioning pieces 45 are provided in a circumferentially separated manner in the circumferential middle portion of the circumferential connecting portion 42. The two circumferential positioning pieces 45 are provided in a manner of protruding radially outward from the circumferential middle portion of the circumferential connecting portion 42. More specifically, the two circumferential positioning pieces 45 are formed by bending a pair of tongue pieces radially outward, and the pair of tongue pieces are provided by forming an H-shaped through hole in the circumferential middle portion of the circumferential connecting portion 42. The circumferential positioning piece 45 is a portion for positioning and stopping the elastic clamping unit 7 in the circumferential direction by engaging with the stopper 25 of the retaining portion 21 in the circumferential direction.

[0115] In addition, when implementing the present invention, when circumferential positioning pieces are provided, the shape, number and circumferential position of the circumferential positioning pieces may also be different from those in this example. In addition, the circumferential positioning pieces may also be provided to engage circumferentially with an inner diameter side component formed by a support bearing or an externally embedded component externally embedded in the support bearing.

[0116] In this example, the circumferential connecting portion 42 has a low-rigidity connecting portion 60 in the circumferential middle portion, specifically, in the portion between the two circumferential positioning pieces 45, and the rigidity of the low-rigidity connecting portion 60 is lower than the rigidity of the circumferential side portions of the circumferential connecting portion 42 and the pair of clamping leaf springs 41, which are other circumferential portions. In this example, in order to reduce the rigidity of the low-rigidity connecting portion 60, a rectangular through hole 61 is formed in the circumferential portion where the low-rigidity connecting portion 60 is located, thereby reducing the cross-sectional modulus of the circumferential portion. The low-rigidity connecting portion 60 is provided to reduce the interaction between the pair of clamping leaf springs 41 by reducing the flexural resistance of the low-rigidity connecting portion 60. In the case of implementing the present invention, a low-rigidity portion may be provided in at least a portion of the circumference of the circumferential connecting portion. The provision of the low-rigidity portion in the circumferential connecting portion may also be omitted.

[0117] Furthermore, when the present invention is implemented, as a means for reducing the rigidity of the low rigidity portion, a means different from the present example, such as reducing the plate thickness of the low rigidity portion, can be adopted.

[0118] In this example, the elastic clamping unit 7 has an axial positioning piece 46 that engages with the support bearing 5 in the axial direction.

[0119] In this example, two axial positioning pieces 46 are provided circumferentially spaced apart from each other in each of the pair of clamping leaf springs 41. More specifically, the axial positioning pieces 46 are bent radially inward from the axial end of each circumferential middle portion of the second portion 44.

[0120] In addition, when implementing the present invention, when an axial positioning piece is provided, the shape, number, circumferential position and axial position of the axial positioning piece may also be different from those in this example. In addition, the axial positioning piece may also be provided to engage axially with an inner diameter side component formed by a worm housing portion or an embedded component embedded in the worm housing portion.

[0121] like Figure 5 As shown, the elastic clamping unit 7 is arranged between the outer peripheral surface of the support bearing 5 and the holding portion 21 provided on the inner peripheral surface of the worm housing portion 9. Specifically, the elastic clamping unit 7 is externally fitted to the support bearing 5 and arranged inside the main holding portion 23 constituting the holding portion 21.

[0122] In this state, the two circumferential positioning pieces 45 of the elastic clamping unit 7 are arranged on the inner side of the stopper 25 constituting the holding portion 21, so as to engage with the stopper 25 in the circumferential direction. Thus, the elastic clamping unit 7 is positioned in the circumferential direction, so that the pair of clamping leaf springs 41 constituting the elastic clamping unit 7 are arranged on both sides of the third direction in the portion between the outer peripheral surface of the support bearing 5 and the main holding portion 23. In this example, a gap in the first direction and a gap in the third direction are provided between the two circumferential positioning pieces 45 and the stopper 25. Thus, a small displacement of the two circumferential positioning pieces 45 relative to the stopper 25 in the first direction and the third direction required during operation can be allowed. In this example, the first direction dimensions of the two circumferential positioning pieces 45 are set as follows: during operation, no matter how the elastic clamping unit 7 moves in the first direction together with the terminal end of the worm 4 and the support bearing 5, the intrusion amount of the two circumferential positioning pieces 45 relative to the stopper 25 in the first direction is always fully ensured.

[0123] The axial positioning pieces 46 of the elastic clamping unit 7 abut against the axial side surface of the outer ring 18 of the support bearing 5, and are axially engaged with the outer ring 18. Thus, the elastic clamping unit 7 is positioned relative to the support bearing 5 in the axial direction.

[0124] In this example, when viewed from the second direction, the circumferential middle portion of each clamping leaf spring 41 constituting a pair of clamping leaf springs 41, namely the first portion 43 (more specifically, the circumferential center portion of the first portion 43) intersects with a straight line passing through the center O4 of the worm 4 and extending along the third direction, namely the third direction straight line Lx.

[0125] More specifically, each of the clamping leaf springs 41 constituting the pair of clamping leaf springs 41 is arranged as follows with respect to the surrounding portion in a state where the meshing reaction forces F1 and F2 are zero.

[0126] The circumferential center of the radially outer side surface of the first portion 43 is Fig.15 The point Q1 shown in (a) of FIG. 1 is in contact with the flat surface portion 26 constituting the main retaining portion 23. The circumferentially outer end of the radially inner side surface of each second portion 44, that is, the end of the second portion 44 on the side away from the first portion 43 in the circumferential direction is Fig.15 The first portion 43 contacts the outer peripheral surface of the support bearing 5 at point Q2 shown in (a). The radially inner side surface of the first portion 43 does not contact the outer peripheral surface of the support bearing 5, and there is a gap between the radially inner side surface of the first portion 43 and the outer peripheral surface of the support bearing 5. The radially outer side surfaces of the second portions 44 do not contact the main retaining portion 23, and there is a gap between the radially outer side surfaces of the second portions 44 and the main retaining portion 23. That is, the clamping leaf spring 41 is only in one place ( Fig.15 The outer peripheral surface of the support bearing 5 is in contact with the point Q1 shown in (a), and is only in contact with the outer peripheral surface of the support bearing 5 at two locations ( Fig.15 2 ). When the meshing reaction forces F1 and F2 are zero, each of the clamping leaf springs 41 constituting the pair of clamping leaf springs 41 generates initial deflection in the third direction. Thus, even when the meshing reaction forces F1 and F2 are zero, the support bearing 5 can be suppressed from shaking in the third direction on the inner side of the main retaining portion 23. However, from the viewpoint of suppressing the friction force of the pair of clamping leaf springs 41 relative to the flat surface portion 26 when the meshing reaction forces F1 and F2 are zero, it is preferable to set the initial deflection in the third direction to be extremely small.

[0127] When viewed from the second direction, one of the pair of clamping leaf springs 41 is located on the other side in the third direction ( Figure 5 The second portion 44 of the clamping leaf spring 41 on the side away from the worm wheel 3 (left side) intersects the radial straight line L1 containing the vector of the meshing reaction force F1. Figure 5 A second portion 44 of the other clamping leaf spring 41 on the right side of the meshing plate ( FIG. 4 ) which is away from the worm wheel 3 intersects with a radial straight line L2 including a vector of the meshing reaction force F2.

[0128] In the above state, the elastic clamping unit 7 clamps the support bearing 5 from both sides in the third direction by means of the pair of clamping leaf springs 41. Thus, the momentum of the distal end of the worm 4 when moving in the third direction is suppressed, thereby suppressing the generation of abnormal noise.

[0129] That is, in the structure of this example, in order to enable the tip of the worm 4 to move forward or backward relative to the worm wheel 3 in the first direction, the main retaining portion 23 disposed around the support bearing 5 is formed to be larger than the outer peripheral surface of the support bearing 5. Therefore, the tip of the worm 4 can also move in the third direction.

[0130] On the other hand, the meshing reaction forces F1 and F2 acting on the worm 4 include not only the components in the first direction, but also the forces in the third direction. The direction of the third direction component is reversed according to the rotation direction of the worm 4. In addition, when the mechanical device (in this example, the automobile) assembled with the worm reducer 1 of this example is in operation, when vibration is reversely input to the worm reducer 1 from the part located on the downstream side of the worm reducer 1 in the power transmission direction (in this example, the tire), the third direction component of the vibration is transmitted to the worm 4. Therefore, if the distal end of the worm 4 is allowed to move in the third direction without resistance, the outer peripheral surface of the support bearing 5 collides violently with the main retaining portion 23 in the third direction due to the third direction components of the meshing reaction forces F1 and F2 acting on the worm 4 and the third direction components of the vibration reversely input to the worm 4, which is likely to produce abnormal noises such as harsh impact sounds and rattling sounds.

[0131] Therefore, in the structure of this example, in order to suppress the generation of such abnormal noise, the support bearing 5 is clamped from both sides of the third direction by a pair of clamping leaf springs 41 constituting the elastic clamping unit 7. Thus, the momentum of the distal end of the worm 4 moving in the third direction is suppressed, thereby suppressing the generation of abnormal noise.

[0132] In this example, if the torque transmitted from the worm 4 to the worm wheel 3 increases, and the meshing reaction force F1 or F2 applied to the distal end of the worm 4 increases, the support bearing 5 acts on one side ( Figure 5 left side) or the other side ( Figure 5 The pressing force of the clamping leaf spring 41 in the third direction (on the right side) increases. As a result, the deflection amount of the clamping leaf spring 41 in the third direction increases. Fig.15 (a)~ Fig.15 (c) is a diagram schematically showing a situation where the deflection amount increases.

[0133] In this example, as the deflection amount of the clamping leaf spring 41 in the third direction increases, the distance W in the first direction between the radial inner side surfaces of the two second portions 44 and the contact portion (point Q2) of the outer peripheral surface of the support bearing 5 is increased as follows: Fig.15 (a)~ Fig.15In addition, as shown in the order of (c), Fig.15 As shown in (c), if the first portion 43 of the clamping leaf spring 41 is clamped between the flat portion 26 of the main retaining portion 23 and the outer peripheral surface of the support bearing 5, the clamping leaf spring 41 cannot further increase the deflection amount in the third direction, and reaches the so-called bottoming state. That is, in this example, during the period before reaching the bottoming state, as the deflection amount of the clamping leaf spring 41 in the third direction increases, the distance W continuously decreases, so that the spring constant of the clamping leaf spring 41 is as follows: Fig.16 That is, as described above, the clamping leaf spring 41 exhibits a nonlinear spring characteristic in which the spring constant increases as the deflection amount in the third direction increases. Fig.16 In the example, when the horizontal axis is the deflection in the third direction and the vertical axis is the load, the graph showing the nonlinear spring characteristic is convex downward, and the slope increases as the deflection in the third direction increases. Fig.16 In the example of FIG. 1 , any nonlinear characteristic can be applied. For example, a spring characteristic can be represented by a curve graph that is convex upward and whose slope decreases as the deflection amount in the third direction increases. In addition, a spring characteristic can be represented by a curve graph composed of a plurality of curves and / or straight lines.

[0134] Therefore, in the structure of this example, the urging operation of the urging plate spring 37 on the distal end of the worm 4 and the support bearing 5 can be smoothed, and the collision force between the components around the distal end of the worm 4 in the third direction can be easily suppressed.

[0135] That is, the spring constant of the clamping leaf spring 41 becomes smaller in the stage (low load region) where the deflection amount in the third direction is small, so in this stage, the friction force acting between the clamping leaf spring 41 and the flat surface 26 of the main holding portion 23, and the friction force acting between the clamping leaf spring 41 and the outer peripheral surface of the support bearing 5 become smaller. Therefore, the movement of the tip of the worm 4 and the support bearing 5 in the first direction can be smoothed. Therefore, the urging action of the urging leaf spring 37 on the tip of the worm 4 and the support bearing 5 can be smoothed accordingly.

[0136] On the other hand, the spring constant of the clamping leaf spring 41 increases in the stage where the deflection amount in the third direction increases (high load region), so the large elastic force of the clamping leaf spring 41 can effectively suppress the Fig.15 The momentum of the movement of the support bearing 5 in the third direction before the bottoming state shown in (c) is reduced. Thus, the occurrence of the collision sound when the bottoming is reached can be effectively suppressed.

[0137] Furthermore, by Fig.15The state shown in (c) reverses the rotation direction of the worm 4, which can reduce the deflection amount of the clamping leaf spring 41 in the third direction to Fig.15 The spring constant of the clamping leaf spring 41 before the state shown in (a) is reduced. Therefore, by reducing the force of the clamping leaf spring 41, the momentum of the collision between the gear teeth 12 and the worm teeth 13 accompanying the reversal of the rotation direction of the worm 4 can be effectively suppressed. As a result, the occurrence of the tooth-striking sound between the gear teeth 12 and the worm teeth 13 can be effectively suppressed.

[0138] In addition, in this example, the curvature radius of the radial inner surface of the second part 44 constituting the circumferential side portions of the clamping leaf spring 41 is set to a constant size, but when implementing the present invention, the curvature radius of the radial inner surface of the second part can also be changed in stages or continuously in the circumferential direction.

[0139] In this example, the portion of the main holding portion 23 that elastically contacts each of the pair of clamping leaf springs 41 is formed by the flat surface portion 26 extending in the first direction. Fig.17 (a)~ Fig.17 As shown in (c), even when the elastic clamping unit 7 moves in the first direction, the deflection amount of the pair of clamping leaf springs 41 in the third direction, that is, the distance W, does not change, and the spring constant of each clamping leaf spring 41 constituting the pair of clamping leaf springs 41 can be kept constant. Therefore, with respect to the elastic force applying unit 6 and the elastic clamping unit 7, stable spring characteristics can be ensured. In addition, when the present invention is implemented, the length of the pair of plane portions 26 in the first direction can be made smaller than the stroke amount by which the elastic clamping unit 7 can move in the first direction together with the terminal end of the worm 4 and the support bearing 5 during operation, that is, when a large meshing reaction force is applied to the worm 4, etc., the elastic contact portion of the clamping leaf spring 41 relative to the main retaining portion 23 can be made to pass over the cylindrical surface portion 27 from the plane portion 26. In this case, it is also possible to keep the spring constant of the clamping leaf spring 41 constant while the contact portion exists on the plane portion 26.

[0140] In this example, when viewed from the second direction, radial lines L1 and L2 including the vectors of the meshing reaction forces F1 and F2 intersect a portion of the circumferential direction of the cylindrical surface portion 27 of the main retaining portion 23. Figure 5 The second portion 44 of the clamping leaf spring 41 on the left side of the pair of clamping leaf springs 41 away from the worm wheel 3 intersects the radial straight line L1 including the vector of the meshing reaction force F1. Figure 5The second portion 44 of the clamping leaf spring 41 on the right side of the meshing reaction force F2, which is away from the worm wheel 3, intersects with the radial straight line L2 including the vector of the meshing reaction force F2.

[0141] Therefore, during operation, even if the support bearing 5 tends to move in the direction of the meshing reaction force F1, the momentum of the movement can be suppressed by the elastic force of the second portion 44 of the clamping leaf spring 41 located on one side in the third direction and away from the worm wheel 3. Furthermore, the meshing reaction force F1 can be supported by the cylindrical surface portion 27 of the main retaining portion 23.

[0142] During operation, even if the support bearing 5 tends to move in the direction of the meshing reaction force F2, the momentum of the movement can be suppressed by the elastic force of the second portion 44 of the clamping leaf spring 41 located on the other side in the third direction and away from the worm wheel 3. Furthermore, the meshing reaction force F2 can be supported by the cylindrical surface portion 27 of the main retaining portion 23.

[0143] In addition, in this case, Figure 5 As shown, the circumferential range of the cylindrical surface portion 27 of the main retaining portion 23 is limited to intersecting the radial lines L1 and L2 containing the vectors of the meshing reaction forces F1 and F2, but the inclination angle of the radial line L2 with respect to the third direction is smaller than the inclination angle of the radial line L1 with respect to the third direction, so that the cylindrical surface portion 27 on the radial line L2 side in the third direction ( Figure 5 The circumferential end edge E2 is arranged on the side of the radial straight line L1 ( Figure 5 The circumferential end edge E1 of the worm wheel 3 is located on the left side of the worm wheel 3 in the first direction. Figure 5 Therefore, in this example, the main holding portion 23 is moved away from the worm wheel 3 on the first direction ( Figure 5 and Figure 8 The portion of the auxiliary retaining portion 24 where the pin 36 is arranged, i.e., the large recess 28, which is arranged on the radial straight line L2 side ( Figure 5 Thus, the large recess 28 is arranged on the radial line L1 side in the third direction ( Figure 5 Compared with the case of the left side of the main holding portion 23, the large recess 28 can be arranged in the first direction at a position close to the worm wheel 3. That is, by adopting such an arrangement, the width dimension of the entire holding portion 21 including the main holding portion 23 and the auxiliary holding portion 24 in the first direction can be minimized.

[0144] (2) Electric power steering

[0145] like Figure 1As shown, the electric power steering device 48 of this example includes a steering wheel 49 , a steering shaft 50 , a steering column 51 , a pair of universal joints 52 a and 52 b , an intermediate shaft 53 , a steering gear unit 54 , the worm speed reducer 1 of this example, and an electric motor 11 .

[0146] The steering wheel 49 is supported and fixed to the rear end of the steering shaft 50. The steering shaft 50 is rotatably supported on the inner side of a steering column 51 supported by the vehicle body. The front end of the steering shaft 50 is connected to the pinion shaft 55 of the steering gear unit 54 via a universal joint 52a on the rear side, an intermediate shaft 53, and a universal joint 52b on the front side. Therefore, when the driver rotates the steering wheel 49, the rotation of the steering wheel 49 is transmitted to the pinion shaft 55 via the steering shaft 50, a pair of universal joints 52a, 52b, and the intermediate shaft 53. The rotation of the pinion shaft 55 is converted into a linear motion of a rack shaft (not shown) of the steering gear unit 54 meshing with the pinion shaft 55. As a result, a pair of steering tie rods 56 are pushed and pulled, thereby giving a steering angle corresponding to the rotation operation amount of the steering wheel 49 to the left and right steering wheels.

[0147] The electric power steering system 48 of this example is configured to reduce the force required for the driver to operate the steering wheel 49 by increasing the auxiliary power of the electric motor 11 through the worm speed reducer 1 and applying the increased auxiliary power to the front end of the steering shaft 50 .

[0148] When the present invention is implemented, the worm speed reducer 1 and the electric motor 11 can be arranged at a position where auxiliary power is applied to the pinion shaft or the rack shaft of the steering gear unit.

[0149] [Second example]

[0150] use Figure 18 to Figure 20 A second example of the embodiment of the present invention will be described.

[0151] In this example, the specific structure of the elastic clamping unit 7a is different from that of the first example.

[0152] Specifically, the elastic clamping unit 7a of this example is in a free state, such as Fig.18 (a) and Fig.18 As shown in (b), it has a cylindrical shape having a discontinuous portion (slit) 57 at one point in the circumferential direction, and the radius of curvature of the inner circumferential surface is constant over the entire circumference.

[0153] More specifically, regarding each of the clamping leaf springs 41a constituting the pair of clamping leaf springs 41a, the radial inner side surface of the first portion 43a located in the circumferential middle portion and the radial inner side surface of the second portion 44a located in the circumferential side portions are smoothly continuous, and the radius of curvature R1 of the radial inner side surface of the first portion 43a and the radius of curvature R2 of the radial inner side surface of the second portion 44a are equal to each other (R1=R2). In addition, the radial inner side surface of each of the clamping leaf springs 41a constituting the pair of clamping leaf springs 41a are smoothly continuous with the radial inner side surface of the circumferential connecting portion 42a, and the radius of curvature R1 and R2 of the radial inner side surface of the clamping leaf spring 41a and the radius of curvature Rj of the radial inner side surface of the circumferential connecting portion 42a are equal to each other (R1=R2=Rj). In addition, the circumferential ends of the pair of clamping leaf springs 41a on the side opposite to the circumferential connecting portion 42a are butted against each other, and the butted portion becomes a discontinuous portion 57. However, when implementing the present invention, the discontinuous portion 57 may be partially set as a gap portion where the circumferential ends of a pair of clamping leaf springs 41a on the side opposite to the circumferential connecting portion 42a are separated in the circumferential direction, or an overlapping portion where the circumferential ends of a pair of clamping leaf springs 41a on the side opposite to the circumferential connecting portion 42a overlap in the radial direction.

[0154] In this example, in the free state of the elastic clamping unit 7a, the curvature radii R1, R2, and Rj of the radial inner side surfaces of the first portion 43a, the second portion 44a, and the circumferential connecting portion 42a are larger than the curvature radius Rs of the outer peripheral surface of the support bearing 5 (refer to Figure 5 ) is small (R1=R2=Rj<Rs).

[0155] In this example, the second portion 44a has a low-rigidity leaf spring portion 58 having lower rigidity than the remaining portion and the first portion 43a in the circumferential direction at the circumferential end portion on the first portion 43a side. In this example, in order to reduce the rigidity of the low-rigidity leaf spring portion 58, a rectangular through hole 59 is formed in the circumferential portion where the low-rigidity leaf spring portion 58 is located, thereby reducing the section modulus of the circumferential portion.

[0156] Furthermore, when the present invention is implemented, as a means for reducing the rigidity of the low rigidity portion, a means different from the present example, such as reducing the plate thickness of the low rigidity portion, can be adopted.

[0157] The elastic clamping unit 7a is fitted on the support bearing 5 (see Figure 5 ), and is arranged in the main holding portion 23 constituting the holding portion 21 (refer to Figure 5 ) In this state, a pair of clamping leaf springs 41a constituting the elastic clamping unit 7a are arranged on both sides of the third direction in the portion between the outer peripheral surface of the support bearing 5 and the main retaining portion 23.

[0158] In this example, each clamping leaf spring 41a constituting a pair of clamping leaf springs 41a is in a state where the meshing reaction forces F1 and F2 are zero, relative to the surrounding parts, such as Fig.19 (a) is schematically shown in FIG. 4 . That is, the circumferential center portion of the radially outer side surface of the first portion 43a contacts the flat surface portion 26 constituting the main retaining portion 23 at point Q1. The circumferentially outer end portion of each of the second portions 44a, that is, the end portion of the second portion 44a on the side away from the first portion 43a in the circumferential direction, contacts the outer peripheral surface of the support bearing 5 at point Q2. The radially inner side surfaces of each of the first portion 43a and the second portion 44a do not contact the outer peripheral surface of the support bearing 5, and there is a gap between the radially inner side surfaces of each of the first portion 43a and the second portion 44a and the outer peripheral surface of the support bearing 5. The radially outer side surfaces of each of the second portions 44a do not contact the main retaining portion 23, and there is a gap between the radially outer side surfaces of each of the second portions 44a and the main retaining portion 23. That is, the clamping leaf spring 41a contacts the main retaining portion 23 only at one point (point Q1), and contacts the outer peripheral surface of the support bearing 5 only at two points (point Q2).

[0159] In this example, when the meshing reaction force F1 or F2 increases, the pressing force in the third direction acting on the clamping leaf spring 41a located on one side or the other side in the third direction from the support bearing 5 increases. As a result, the deflection amount of the clamping leaf spring 41a in the third direction increases. Fig.19 (a)~ Fig.19 (c) is a diagram schematically showing a situation where the deflection amount increases.

[0160] In this example, as the deflection amount of the clamping leaf spring 41a in the third direction increases, the distance W in the first direction between the contact portions where the two second portions 44a contact the outer peripheral surface of the support bearing 5 is changed as follows: Fig.19 (a)~ Fig.19 The amount is reduced in stages as shown in the order of (c).

[0161] That is, in the stage where the deflection in the third direction is small (low load region), Fig.19 (a) and Fig.19 As shown in (b), the distance W hardly changes. In contrast, when the deflection in the third direction reaches a certain level (high load region), as shown in Fig.19 As shown in (c), the two second portions 44a are in contact with the outer peripheral surface of the support bearing 5 not only at the circumferential outer end but also at the circumferential inner end, i.e., the low-rigidity leaf spring portion 58, at point Q3. The reason for this is that Fig. 20 As shown in an exaggerated manner, the low-rigidity leaf spring portion 58 is bent more greatly than other portions and is close to the outer peripheral surface of the support bearing 5. Fig.19In the state shown in (c), the distance between the contact portions of the low-rigidity leaf spring portions 58 of the two second portions 44a with respect to the outer peripheral surface of the support bearing 5 becomes the distance W, which is equal to Fig.19 (a) and Fig.19 Compared with the state shown in (b), the distance W suddenly decreases. And, accompanying this, the spring constant of the clamping leaf spring 41a suddenly increases. In other words, in this example, the clamping leaf spring 41a exhibits a nonlinear spring characteristic in which the spring constant changes in two stages as the deflection amount in the third direction increases.

[0162] In this example, the elastic clamping unit 7a has a simple shape in which the curvature radius of the inner peripheral surface is constant over the entire circumference in the free state, so the manufacturing cost of the elastic clamping unit 7a can be suppressed. The other structures and effects of the second example are the same as those of the first example.

[0163] [Third example]

[0164] use Fig.21 A third example of the embodiment of the present invention will be described.

[0165] In this example, the pair of clamping leaf springs 41 constituting the elastic clamping unit 7b are arranged on the side farther from the worm wheel 3 in the first direction than in the first example. Specifically, in this example, when viewed from the second direction, one of the pair of clamping leaf springs 41 located on the other side in the third direction ( Fig.21 The circumferential middle portion of one clamping leaf spring 41 (the left side of the pair of clamping leaf springs 41) (more specifically, the circumferential center portion of the first portion 43) intersects with the radial straight line L1 including the vector of the meshing reaction force F1. In addition, when viewed from the second direction, one of the pair of clamping leaf springs 41 located on one side ( Fig.21 The circumferential middle portion of the other clamping leaf spring 41 (on the right side), namely the first portion 43 (more specifically, the circumferential center portion of the first portion 43) intersects with the radial straight line L2 containing the vector of the meshing reaction force F2.

[0166] In this example, one clamping leaf spring 41 exhibits a nonlinear spring characteristic in which the spring constant increases as the deflection amount in the direction of the component including the third direction (specifically, the deflection amount in the direction of the meshing reaction force F1) increases. The other clamping leaf spring 41 exhibits a nonlinear spring characteristic in which the spring constant increases as the deflection amount in the direction of the component including the third direction (specifically, the deflection amount in the direction of the meshing reaction force F2) increases.

[0167] Therefore, in this example, when the support bearing 5 tends to move in the direction of the meshing reaction force F1, the momentum of the movement can be efficiently suppressed by the elastic force of one clamping leaf spring 41. In addition, when the support bearing 5 tends to move in the direction of the meshing reaction force F2, the momentum of the movement can be suppressed with good efficiency by the elastic force of the other clamping leaf spring 41.

[0168] In this example, the main holding portion 23 constituting the holding portion 21 does not have a pair of flat surfaces extending in the first direction at both ends in the third direction, and the entire circumferential direction is constituted by the cylindrical surface portion 27. The other structures and effects of the third example are the same as those of the first example.

[0169] The present invention can be implemented by appropriately combining the configurations of the above-described embodiments within a range where no contradiction occurs.

[0170] In addition, this application is based on the Japanese patent application (Japanese Patent Application No. 2022-123209) filed on August 2, 2022, and the contents thereof are incorporated herein by reference.

[0171] Description of Reference Numerals

[0172] 1 Worm reducer

[0173] 2 Housing

[0174] 3 Worm gear

[0175] 4 Worm

[0176] 5 Support bearing

[0177] 6 Elastic force unit

[0178] 7, 7a, 7b elastic clamping unit

[0179] 8 Worm gear housing

[0180] 9 Worm housing

[0181] 10 Cover

[0182] 11 Electric Motor

[0183] 12 teeth

[0184] 13 Worm teeth

[0185] 14 Ball bearings

[0186] 15 Output shaft

[0187] 16 Coupling

[0188] 17 Inner Circle

[0189] 18 Outer ring

[0190] 19 Ball

[0191] 20 Small diameter cylindrical surface

[0192] 21. Maintaining part

[0193] 22 Step surface

[0194] 23 Main holding part

[0195] 24. Secondary holding unit

[0196] 25 Stopper

[0197] 26 Flat surface

[0198] 27 Cylindrical face

[0199] 28 large recesses

[0200] 29 small recesses

[0201] 30 First inclined face

[0202] 31 Second inclined face

[0203] 32 First corner

[0204] 33 Second corner

[0205] 34 Third corner

[0206] 35 recess

[0207] 36 Pins

[0208] 37 Force leaf spring

[0209] 38 Strip plate

[0210] 39 Substrate Department

[0211] 40 Fold back plate

[0212] 41, 41a Clamping leaf spring

[0213] 42, 42a Circumferential connection portion

[0214] 43, 43a Part I

[0215] 44, 44a Part 2

[0216] 45 Circumferential positioning piece

[0217] 46 Axial positioning piece

[0218] 47 Retaining ring

[0219] 48 Electric power steering

[0220] 49 Steering Wheel

[0221] 50 Steering shaft

[0222] 51 Steering column

[0223] 52a, 52b universal joint

[0224] 53 Intermediate shaft

[0225] 54 Steering gear unit

[0226] 55 Pinion shaft

[0227] 56 Steering tie rod

[0228] 57 Discontinuity

[0229] 58 Low rigidity leaf spring part

[0230] 59 Through Hole

[0231] 60 Low rigidity connection

[0232] 61 Through Holes

Claims

1. A worm reducer, characterized in that: have: a housing having a worm wheel housing portion and a worm housing portion, the worm housing portion having a central axis in a twisted position relative to a central axis of the worm wheel housing portion, and an axial middle portion of the worm housing portion opening toward the worm wheel housing portion; a worm wheel having gear teeth on an outer peripheral surface and rotatably supported inside the worm wheel housing portion; a worm having worm teeth meshing with the gear teeth on an outer peripheral surface and rotatably supported inside the worm housing portion; A support bearing, the support bearing is externally embedded in the distal end of the worm; an elastic force applying unit, the elastic force applying unit applying force to the inner diameter side component toward the worm wheel side, the inner diameter side component being the support bearing or an externally embedded component externally embedded in the support bearing; as well as An elastic clamping unit, wherein the elastic clamping unit has a pair of clamping leaf springs in a portion between the outer circumferential surface of the inner diameter side component and the inner circumferential surface of the outer diameter side component, the outer diameter side component is the worm housing portion or an embedded component embedded in the worm housing portion, and the pair of clamping leaf springs are arranged on both sides of the inner diameter side component in a third direction that is orthogonal to both the first direction, the force application direction of the elastic force application unit, and the second direction, the axial direction of the worm housing portion. Each of the clamping leaf springs constituting the pair of clamping leaf springs exhibits a nonlinear spring characteristic in which a spring constant increases as the amount of deflection in a direction including a component in the third direction increases.

2. The worm reducer according to claim 1, characterized in that: Each clamping leaf spring constituting a pair of the clamping leaf springs makes the circumferential middle portion contact the inner peripheral surface of the outer diameter side component, and makes the circumferential side portions contact the outer peripheral surface of the inner diameter side component respectively, and as the deflection amount in the direction including the component of the third direction increases, the distance between the contact portions of the circumferential side portions relative to the outer peripheral surface of the inner diameter side component decreases, thereby increasing the spring constant.

3. The worm reducer according to claim 2, characterized in that: When viewed from the second direction, a circumferential intermediate portion of each of the pair of clamp leaf springs intersects a third direction straight line (Lx) that passes through the center of the worm and extends in the third direction.

4. The worm reducer according to claim 3, characterized in that: A portion of the inner peripheral surface of the outer diameter side member that contacts the circumferential middle portion of each of the pair of clamp leaf springs is formed of a flat surface portion extending in the first direction.

5. The worm reducer according to claim 2, characterized in that: When viewed from the second direction, a circumferential middle portion of one of the pair of clamping leaf springs intersects a radial straight line (L1), the radial straight line (L1) including a vector of a meshing reaction force (F1) applied to the worm from a meshing portion between the worm teeth and the gear teeth when the worm rotates in a predetermined direction, When viewed from the second direction, the circumferential middle portion of the other clamping leaf spring constituting a pair of the clamping leaf springs intersects with a radial straight line (L2), which contains a vector of the meshing reaction force (F2) applied to the worm from the meshing portion when the worm rotates in a direction opposite to the specified direction.

6. The worm reducer according to claim 2, characterized in that: In the counterpart clamping leaf spring as at least one of the pair of clamping leaf springs, The circumferential middle portion is composed of a first portion having a partially cylindrical shape curved along the outer peripheral surface of the inner diameter side member. The two circumferential side portions are respectively composed of a second portion having a partially cylindrical shape curved along the outer circumferential surface of the inner diameter side member and smoothly continuing with respect to the first portion. The radius of curvature of the radially inner side surface of the first portion in a free state is smaller than the radius of curvature of the outer peripheral surface of the inner diameter side component. A radius of curvature of a radially inner side surface of the second portion in a free state is greater than a radius of curvature of a radially inner side surface of the first portion in a free state.

7. The worm reducer according to claim 2, characterized in that: In the counterpart clamping leaf spring as at least one of the pair of clamping leaf springs, The circumferential middle portion is composed of a first portion having a partially cylindrical shape curved along the outer peripheral surface of the inner diameter side member. The two circumferential side portions are respectively composed of a second portion having a partially cylindrical shape curved along the outer circumferential surface of the inner diameter side member and smoothly continuing with respect to the first portion. The curvature radii of the radially inner side surfaces of the first portion and the second portion in a free state are equal to each other and smaller than the curvature radius of the outer peripheral surface of the inner diameter side member. The second portion includes a low-rigidity leaf spring portion at a circumferential end portion on the first portion side, wherein the low-rigidity leaf spring portion has a lower rigidity than the remaining portion in the circumferential direction and the first portion.

8. The worm reducer according to claim 7, characterized in that: Each of the clamping leaf springs constituting the pair of the clamping leaf springs is the target clamping leaf spring, The elastic clamping unit has a circumferential connecting portion that connects the circumferential ends of the pair of clamping leaf springs on the side close to the worm wheel to each other in the circumferential direction. The circumferential connecting portion has a partial cylindrical shape bent along the outer peripheral surface of the inner diameter side member and is smoothly continuous with respect to the pair of clamping leaf springs. The radius of curvature of the radially inner side surface of the circumferential connecting portion in a free state is equal to the radius of curvature of the radially inner side surfaces of the first portion and the second portion in a free state.

9. The worm reducer according to claim 1, characterized in that: The elastic clamping unit has a circumferential connecting portion that connects circumferential ends of a pair of the clamping leaf springs on a side close to the worm wheel to each other in the circumferential direction.

10. The worm reducer according to claim 9, characterized in that: The circumferential connection portion has a low-rigidity connection portion having lower rigidity than the pair of clamp leaf springs in at least a portion in the circumferential direction.

11. The worm reducer according to claim 1, characterized in that: Residual stress is applied to each of the clamp leaf springs constituting the pair of clamp leaf springs at a portion in contact with the inner peripheral surface of the outer diameter side member.

12. The worm reducer according to claim 1, characterized in that: The elastic clamping unit includes a circumferential positioning piece engaged with the inner diameter side component or the outer diameter side component in the circumferential direction.

13. The worm reducer according to claim 1, characterized in that: The elastic clamping unit includes an axial positioning piece that is engaged with the inner diameter side component or the outer diameter side component in the axial direction.

14. The worm reducer according to claim 1, characterized in that: When the horizontal axis represents the deflection in the third direction and the vertical axis represents the load, the nonlinear spring characteristic is represented by a graph that is convex downward and whose slope increases as the deflection in the third direction increases.

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