Worm reducer

Abstract

To provide a worm reducer that can not only apply a proper preload to an engagement part between wheel teeth and worm teeth but also prevent or suppress noise from being generated on the basis of the fact that a tip part of a worm is displaced swiftly in a third reference direction, and also can be manufactured at low cost.SOLUTION: An energizing spring 6 which energizes a support bearing 5 elastically toward a worm wheel is constituted in one body on the whole, and has: a main body part 30; a first spring part 31 which is located in a first radius direction R1 as a direction of a component force F1, in a virtual plane orthogonal to a center axis of the worm 4, of engagement reaction force when the worm 4 rotates in a predetermined direction; a second spring part 32 which is located in a second radius direction R2 as a direction of a component force F2 in the virtual plane, of engagement reaction force when the worm 4 rotates in an opposite direction of the predetermined direction; and third spring parts 33a, 33b which are located at both ends in a third reference direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a worm reducer that can be incorporated into an electric power steering device or the like. [Background technology]

[0002] 2. Description of the Related Art In the field of steering devices, electric power steering devices that use an electric motor as an auxiliary power source to reduce the force required for a driver to operate a steering wheel have become widespread.

[0003] The electric power steering device includes a worm reducer for increasing the torque of the electric motor. The worm reducer includes a housing, a worm wheel, and a worm.

[0004] The housing has a wheel accommodating portion and a worm accommodating portion having a central axis that is twisted relative to the central axis of the wheel accommodating portion and an axially intermediate portion that opens into the wheel accommodating portion. The worm wheel has wheel teeth on its outer circumferential surface and is rotatably supported inside the wheel accommodating portion. The worm has worm teeth on its outer circumferential surface that mesh with the wheel teeth, is rotatably supported inside the worm accommodating portion, and has a base end connected to the output shaft of the electric motor.

[0005] The torque of the electric motor is amplified by being transmitted to the worm wheel via the worm, and then applied as auxiliary power to a steering force transmission member such as a steering shaft, a pinion shaft or a rack shaft of a steering gear unit, thereby reducing the force required by the driver to operate the steering wheel.

[0006] In a worm reducer, unavoidable backlash exists at the meshing portion between the wheel teeth and the worm teeth due to dimensional errors, assembly errors, etc. of the components that make up the worm reducer. Due to the existence of this backlash, an unpleasant rattle noise can occur at the meshing portion when changing the direction of rotation of the steering wheel.

[0007] JP 2012-086799 A describes a structure for biasing the tip of the worm toward the worm wheel to suppress rattle noise at the meshing portion between the wheel teeth and the worm teeth. The structure includes a support bearing for rotatably supporting the tip of the worm relative to the worm housing, and a biasing spring installed between the support bearing and the worm housing.

[0008] In the conventional structure described in JP 2012-086799 A, the biasing spring is integrally configured. The biasing spring includes a segmented annular main body fitted onto the support bearing and a pair of spring portions whose base ends are connected to opposite circumferential ends of the main body and project radially outward from the main body. The pair of spring portions are located at ends farther from the worm wheel in a portion between the outer circumferential surface of the support bearing and the inner circumferential surface of the worm accommodating portion in a first reference direction, which is the direction in which the biasing spring biases the tip end of the worm, and are in elastic contact with the inner circumferential surface of the worm accommodating portion. That is, the pair of spring portions are sandwiched between the outer circumferential surface of the support bearing and the inner circumferential surface of the worm accommodating portion in an elastically compressed state, and the pair of spring portions elastically restore their restoring force to bias the support bearing toward the worm wheel. This reduces backlash at the meshing portion between the wheel teeth and the worm teeth, thereby suppressing the generation of teeth rattle noise.

[0009] On the other hand, Japanese Patent Application Laid-Open No. 2006-008008 describes a structure in which a biasing spring that biases the tip of the worm toward the worm wheel is composed of a first spring piece and a second spring piece that are separate parts.

[0010] The first spring piece includes a first main body portion fitted onto a support bearing that rotatably supports the tip end of the worm, and a first spring portion whose base end is connected to one circumferential end of the first main body portion and which is provided so as to protrude radially outward beyond the first main body portion. The first spring portion is located in a circumferential location between the outer circumferential surface of the support bearing and the inner circumferential surface of the worm accommodating portion, in a first radial direction that is the direction of a component force in an imaginary plane perpendicular to the central axis of the worm of a meshing reaction force applied to the worm from the meshing portion between the wheel teeth and the worm teeth when the worm rotates in a predetermined direction, and is in elastic contact with the inner circumferential surface of the worm accommodating portion.

[0011] The second spring piece includes a second main body portion fitted onto the support bearing, and a second spring portion whose base end is connected to one circumferential end of the second main body portion and which is provided so as to protrude radially outward beyond the second main body portion. The second spring portion is disposed in a circumferential location between the outer circumferential surface of the support bearing and the inner circumferential surface of the worm accommodating portion, in a second radial direction that is the direction of a component force, within the imaginary plane, of a meshing reaction force applied to the worm from the meshing portion when the worm rotates in the direction opposite to the predetermined direction, and is in elastic contact with the inner circumferential surface of the worm accommodating portion.

[0012] In the conventional structure described in JP 2006-008008 A, regardless of the direction of rotation of the worm, the first spring portion or the second spring portion can provide resistance to the tip of the worm against the component force within the imaginary plane of the meshing reaction force applied to the worm from the meshing portion, thereby applying an appropriate preload to the meshing portion between the wheel teeth and the worm teeth. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-086799 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-008008 Summary of the Invention [Problem to be solved by the invention]

[0014] In the conventional structure described in JP 2012-086799 A, to allow the tip of the worm to move toward and away from the worm wheel, a gap is provided over almost the entire circumference between the outer peripheral surface of the support bearing that rotatably supports the tip of the worm and the inner peripheral surface of the worm housing. Therefore, based on the presence of this gap, the tip of the worm can also move in a third reference direction that is perpendicular to both the first reference direction, which is the biasing direction of the biasing spring, and the second reference direction, which is the axial direction of the worm housing.

[0015] Meanwhile, a meshing reaction force acts on the worm from the meshing portion between the worm teeth and the wheel teeth. This meshing reaction force includes a third reference direction component. The direction of this third reference direction component reverses depending on the rotational direction of the worm. Furthermore, when a vehicle is in operation, the third reference direction component of vibrations input in reverse from the tire is transmitted to the worm. Therefore, if the tip of the worm is allowed to move in the third reference direction without resistance due to the presence of the gap, the third reference direction component of the meshing reaction force acting on the worm and the third reference direction component of vibrations input in reverse to the worm will cause the outer peripheral surface of the support bearing to collide with the inner peripheral surface of the worm housing portion in the third reference direction via the biasing spring, which is likely to generate unpleasant noises such as hammering sounds or rattles.

[0016] On the other hand, in the conventional structure described in JP 2006-008008 A, the first spring portion or the second spring portion can suppress the momentum of the worm tip portion moving in the third reference direction regardless of the direction of rotation of the worm. However, the first spring portion and the second spring portion are located in positions circumferentially offset from both ends in the third reference direction in the portion between the outer circumferential surface of the support bearing and the inner circumferential surface of the worm housing. For this reason, there is room for improvement in terms of more efficiently suppressing the momentum of the worm tip portion moving in the third reference direction using the biasing spring.

[0017] Furthermore, in the conventional structure described in JP 2006-008008 A, the biasing spring is composed of two parts, a first spring piece and a second spring piece, which increases the cost of managing the parts for the biasing spring and the labor cost of assembling the biasing spring to the worm reducer, which creates the problem of increasing the manufacturing cost of the worm reducer.

[0018] The present disclosure aims to provide a worm reducer that can not only apply an appropriate preload to the meshing portion between the wheel teeth and the worm teeth, but also can prevent or suppress the generation of abnormal noise by causing the tip of the worm to rapidly displace in a third reference direction that is perpendicular to both the first reference direction, which is the biasing direction of the tip, and the second reference direction, which is the axial direction of the worm accommodating section, and can be manufactured at low cost. [Means for solving the problem]

[0019] A worm reducer according to a first aspect of the present disclosure includes: a housing having a wheel accommodating portion and a worm accommodating portion having a central axis that is twisted relative to the central axis of the wheel accommodating portion and an axially intermediate portion that opens to the wheel accommodating portion; a worm wheel having wheel teeth on an outer peripheral surface and rotatably supported inside the wheel accommodating portion; a worm having worm teeth on an outer peripheral surface thereof that mesh with the wheel teeth and that is rotatably supported inside the worm accommodating portion; a support bearing fitted onto the tip end of the worm; a biasing spring that is disposed between the support bearing and a retaining portion that is a portion of the inner circumferential surface of the worm accommodating portion that is positioned around the support bearing, and that elastically biases the support bearing toward the worm wheel; Equipped with The biasing spring is The whole is composed as a whole, a main body portion having a circular or semicircular ring shape fitted onto the support bearing; a first spring portion disposed at a circumferential location in a first radial direction, which is the direction of a component force in an imaginary plane perpendicular to the central axis of the worm, of a meshing reaction force applied to the worm from the meshing portion between the wheel teeth and the worm teeth when the worm rotates in a predetermined direction, the first spring portion being provided so as to protrude radially outward from the main body portion and being in elastic contact with the retaining portion; a second spring portion disposed at a circumferential location in a second radial direction, which is a direction of a component force in the imaginary plane of a meshing reaction force applied to the worm from the meshing portion when the worm rotates in a direction opposite to the predetermined direction, and provided so as to protrude radially outward from the main body portion and in elastic contact with the retaining portion; a pair of third spring portions provided at circumferential locations located at both ends of a third reference direction perpendicular to both a first reference direction which is the biasing direction of the biasing spring and a second reference direction which is the axial direction of the worm accommodating portion, the third spring portions being provided so as to protrude radially outward from the main body portion and being in elastic contact with the retaining portion; It has.

[0020] A worm reducer according to a second aspect of the present disclosure is the worm reducer according to the first aspect of the present disclosure, The first spring portion and the second spring portion are disposed at different positions relative to the second reference direction.

[0021] A worm reducer of a third aspect of the present disclosure is the worm reducer of the second aspect of the present disclosure, The main body portion is configured in a segmented ring shape, the first spring portion has a base portion connected to a portion of the main body portion near one end in the circumferential direction, the second spring portion has a base portion connected to a portion of the main body portion near the other end in the circumferential direction, One side end portion, which is a portion of the main body portion located on one side in the circumferential direction of the portion to which the base portion of the first spring portion is connected, and the other side end portion, which is a portion of the main body portion located on the other side in the circumferential direction of the portion to which the base portion of the second spring portion is connected, are arranged at different positions from each other with respect to the second reference direction.

[0022] A worm reducer according to a fourth aspect of the present disclosure is the worm reducer according to any one of the first to third aspects of the present disclosure, The third spring portion of the pair of third spring portions that is arranged on one side of the third reference direction and the third spring portion of the pair of third spring portions that is arranged on the other side of the third reference direction are arranged at different positions from each other with respect to the second reference direction.

[0023] A worm reducer of a fifth aspect of the present disclosure is the worm reducer of any one of the first to fourth aspects of the present disclosure, the retaining portion has a first recessed portion provided to be recessed radially outward at a circumferential location located in the first radial direction, a second recessed portion provided to be recessed radially outward at a circumferential location located in the second radial direction, and a pair of third recessed portions provided to be recessed radially outward at circumferential locations located at both end portions in the third reference direction, the first spring portion is disposed inside the first recess and is in elastic contact with a bottom surface of the first recess, the second spring portion is disposed inside the second recess and is in elastic contact with a bottom surface of the second recess, one of the pair of third spring portions that is disposed on one side in the third reference direction is disposed inside one of the pair of third recesses that is disposed on one side in the third reference direction, and is in elastic contact with a bottom surface of the third recess; The third spring portion of the pair of third spring portions that is arranged on the other side of the third reference direction is arranged inside the third recess of the pair of third recesses that is arranged on the other side of the third reference direction, and is in elastic contact with the bottom surface of the third recess.

[0024] A worm reducer of a sixth aspect of the present disclosure is the worm reducer of any one of the first to fifth aspects of the present disclosure, At least one of the first spring portion, the second spring portion, and the pair of third spring portions is composed of a plurality of spring pieces arranged at different positions with respect to the second reference direction.

[0025] A worm reducer according to a seventh aspect of the present disclosure is the worm reducer according to any one of the first to sixth aspects of the present disclosure, The biasing spring is arranged at a circumferential location located at the end farther from the worm wheel in relation to the first reference direction, and has a fourth spring portion that protrudes radially outward from the main body portion and elastically contacts the retaining portion.

[0026] A worm reducer of an eighth aspect of the present disclosure is the worm reducer of the seventh aspect of the present disclosure, the retaining portion has a fourth recessed portion provided to recess radially outward at a circumferential location located at an end portion farther from the worm wheel in relation to the first reference direction, The fourth spring portion is disposed inside the fourth recess and is in elastic contact with the bottom surface of the fourth recess.

[0027] A worm reducer of a ninth aspect of the present disclosure is the worm reducer of the seventh or eighth aspect of the present disclosure, The fourth spring portion is made up of a plurality of spring pieces.

[0028] A worm reducer of a tenth aspect of the present disclosure is the worm reducer of the ninth aspect of the present disclosure, The plurality of spring pieces that form the fourth spring portion are arranged at different positions relative to the second reference direction.

[0029] A worm reducer of an eleventh aspect of the present disclosure is the worm reducer of any one of the seventh to tenth aspects of the present disclosure, The radial height of the fourth spring portion is smaller than the radial height of the first spring portion and is also smaller than the radial height of the second spring portion. [Effects of the Invention]

[0030] According to one embodiment of the worm reducer of the present disclosure, not only can an appropriate preload be applied to the meshing portion between the wheel teeth and the worm teeth, but the tip of the worm is forcefully displaced in a third reference direction that is perpendicular to both the first reference direction, which is the biasing direction of the tip, and the second reference direction, which is the axial direction of the worm accommodating section, thereby preventing or suppressing the generation of abnormal noise, and the device can be manufactured at low cost. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram illustrating an electric power steering device incorporating a worm reduction gear according to a first example of an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 3 is an enlarged view of part B in FIG. [Figure 4] FIG. 4 is an exploded perspective view of the portion shown in FIG. [Figure 5] FIG. 5 is a view of the part shown in FIG. 3 from the right side with the cover and retaining ring removed. [Figure 6] 6(a) is a view of the worm accommodating section as seen from the right side of FIG. 3, FIG. 6(b) is a cross-sectional view taken along CC in FIG. 6(a), and FIG. 6(c) is a cross-sectional view taken along DD in FIG. 6(a). [Figure 7] 7(a) is a view of the biasing spring from the right side of FIG. 3, FIG. 7(b) is a view of the biasing spring from the left side of FIG. 7(a), and FIG. 7(c) is a view of the biasing spring from the right side of FIG. 7(a). [Figure 8] FIG. 8 is a diagram corresponding to FIG. 5 and relating to a second example of an embodiment of the present disclosure. [Figure 9] FIG. 9 is a perspective view of the portion of the worm housing of the second example shown in FIG. [Figure 10] FIG. 10 is a perspective view of a second example of a biasing spring. [Figure 11] Figure 11 is a view corresponding to Figure 7(a) for the second example of the biasing spring, Figure 11(b) is a view from the left side of Figure 11(a), and Figure 11(c) is a view from the right side of Figure 11(a). [Figure 12] FIG. 12(a) is a diagram corresponding to FIG. 5 and illustrating a third example of an embodiment of the present disclosure. [Figure 13] FIG. 13 is a perspective view of a biasing spring according to a third example. [Figure 14] FIG. 14 is a perspective view of a biasing spring according to a fourth example embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0032] [Example 1] A worm reducer according to a first example of an embodiment of the present disclosure will be described with reference to FIGS. 1 to 7(c).

[0033] <Worm reducer> The worm reducer of the present disclosure can be applied to worm reducers incorporated into parts of various mechanical devices, but in this example, we will explain the case where the worm reducer of the present disclosure is applied to a worm reducer incorporated into part of an electric power steering device for an automobile.

[0034] As shown in FIGS. 2 to 5, the worm reducer 1 of this example includes a housing 2, a worm wheel 3, a worm 4, a support bearing 5, and a biasing spring 6.

[0035] The housing (2) has a wheel accommodating portion (7) and a worm accommodating portion (8) having a central axis that is twisted relative to the central axis of the wheel accommodating portion (7) and an axially intermediate portion that opens into the wheel accommodating portion (7).

[0036] The wheel accommodating portion 7 is configured in a cylindrical shape. In Fig. 2, the central axis of the wheel accommodating portion 7 extends in the front-to-rear direction.

[0037] The worm accommodating portion 8 is cylindrical. In FIG. 2 , the central axis of the worm accommodating portion 8 extends in the left-right direction. An opening on one axial side of the worm accommodating portion 8 is closed by a cover 9. An opening on the other axial side of the worm accommodating portion 8 is closed by an electric motor 10 fixedly coupled to the housing 2.

[0038] With respect to the worm housing portion 8 and the members housed in the worm housing portion 8, one axial side is the right side in FIG. 2, and the other axial side is the left side in FIG.

[0039] The worm wheel 3 has helical gear-shaped wheel teeth 11 on its outer circumferential surface, and is rotatably supported inside the wheel accommodating portion 7. In this example, the worm wheel 3 is fitted and fixed to the outside of a portion in the axial direction of the rotation shaft rotatably supported inside the wheel accommodating portion 7 (the front portion of the steering shaft 38 in the longitudinal direction of the vehicle).

[0040] The worm 4 has threaded worm teeth 12 on the outer peripheral surface of an axially intermediate portion thereof, which mesh with the wheel teeth 11 of the worm wheel 3, and is rotatably supported inside the worm accommodating portion 8. In this example, the twist direction of the worm teeth 12 is a right-hand thread direction. However, the twist direction may also be a left-hand thread direction.

[0041] A portion of the worm 4 near the base end (a portion near the left end in FIG. 2 ) is rotatably supported by a ball bearing 13 relative to the worm housing 8. In this example, the outer ring 52 of the ball bearing 13 is fitted internally into the worm housing 8 with a radial gap therebetween, and the inner ring 53 of the ball bearing 13 is fitted externally to the portion of the worm 4 near the base end with a radial gap therebetween. This allows the portion of the worm 4 near the base end to be supported relative to the worm housing 8 so as to be rotatable and swingable. Note that the structure for supporting the portion of the worm 4 near the base end with respect to the worm housing 8 so as to be rotatable and swingable relative to the worm housing 8 is not limited to the structure in this example, and various other structures can be employed. In this example, the inner ring 53 of the ball bearing 13 is fitted externally to the portion of the worm 4 near the base end with a radial gap therebetween, so the worm 4 is supported relative to the inner ring 53 so as to be axially displaceable.

[0042] The worm reducer 1 of this example further includes two worm dampers 54, which are arranged on both axial sides of the inner ring 53 of the ball bearing 13 and elastically support the worm 4 in the axial direction relative to the inner ring 53. The worm dampers 54 are elastically deformed, allowing the worm 4 to be displaced in the axial direction relative to the inner ring 53. This makes it possible to provide resistance to the axial component of the meshing reaction force applied to the worm 4 from the meshing portion between the wheel teeth 11 and the worm teeth 12 when the rotation direction of the worm 4 is changed. Therefore, when the rotation direction of the worm 4 is changed, the force of collision between the tooth surfaces of the wheel teeth 11 and the worm teeth 12 is alleviated, thereby suppressing the generation of rattle noise at the meshing portion between the wheel teeth 11 and the worm teeth 12.

[0043] The base end of the worm 4 is connected to the tip end of the output shaft 14 of the electric motor 10 using a coupling 15 to enable torque transmission, axial displacement, and swing displacement. Note that the base end of the worm 4 can also be connected to the tip end of the output shaft 14 of the electric motor 10 by spline engagement or the like to enable torque transmission, axial displacement, and swing displacement.

[0044] The support bearing 5 is fitted onto the tip end (the right end in FIG. 2) of the worm 4. The tip end of the worm 4 is supported by the support bearing 5 with respect to the worm housing portion 8 so as to be rotatable.

[0045] In this example, the support bearing 5 is a ball bearing. That is, as shown in Fig. 3, the support bearing 5 includes an inner ring 16 having an inner ring raceway on its outer peripheral surface, an outer ring 17 having an outer ring raceway on its inner peripheral surface, and a plurality of balls 18 arranged between the inner ring raceway and the outer ring raceway. The inner ring 16 is fitted and fixed to the tip end of the worm 4. Note that when implementing the worm reducer of the present disclosure, the support bearing can also be formed from other types of bearings, such as roller bearings.

[0046] The biasing spring 6 is disposed between the support bearing 5 and a retaining portion 19 located around the support bearing 5 on the inner circumferential surface of the worm accommodating portion 8, and elastically biases the support bearing 5 toward the worm wheel 3. This suppresses backlash between the wheel teeth 11 and the worm teeth 12, thereby suppressing the occurrence of teeth rattle noise.

[0047] The inner peripheral surface of the worm accommodating portion 8 has a cylindrical large-diameter portion 20 configured to have a larger diameter than the retaining portion 19 at one axial end, specifically at a portion adjacent to one axial side of the retaining portion 19. The retaining portion 19 and the large-diameter portion 20 are connected by a stepped surface 21 facing one axial side. The large-diameter portion 20 has an engagement groove 22 around its entire circumference at the other axial end.

[0048] A retaining ring 23 is engaged in the engaging groove 22. The radially inner end of the retaining ring 23 faces the biasing spring 6 in the axial direction. The retaining ring 23 prevents the biasing spring 6 from falling out from between the retaining portion 19 and the support bearing 5 to one side in the axial direction. A portion of the lid 9 near the outer periphery is press-fitted into one end of the large-diameter portion 20 in the axial direction.

[0049] The inner peripheral surface of the worm accommodating portion 8 has a cylindrical small diameter portion 24 that is smaller in diameter than the retaining portion 19, in a portion adjacent to the other axial side of the retaining portion 19. The small diameter portion 24 and the retaining portion 19 are connected by a step surface 25 facing one axial side.

[0050] In the following description, the direction in which the biasing spring 6 biases the support bearing 5, which is perpendicular to both the central axis of the worm accommodating section 8 and the central axis of the wheel accommodating section 7 (the direction in which the tip of the worm 4 approaches or approaches the worm wheel 3, the up-and-down direction in Figures 2, 3, and 5) is referred to as the "first reference direction," the axial direction of the worm accommodating section 8 (the left-right direction in Figures 2 and 3, the front-to-back direction in Figure 5) is referred to as the "second reference direction," and the direction perpendicular to both the first reference direction and the second reference direction (the front-to-back direction in Figures 2 and 3, the left-to-right direction in Figure 5) is referred to as the "third reference direction."

[0051] Furthermore, 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 wheel teeth 11 and the worm teeth 12. The meshing reaction force has a first reference direction component, a second reference direction component, and a third reference direction component.

[0052] The axial component of the meshing reaction force applied from the meshing portion to the worm 4 is the second reference direction component. Of the meshing reaction force applied from the meshing portion to the worm 4, the component in an imaginary plane perpendicular to the central axis of the worm 4, i.e., the radial component of the meshing reaction force, is the sum of the first reference direction component and the third reference direction component.

[0053] The direction of the first reference direction component of the radial component of the meshing reaction force applied from the meshing portion to the worm 4 is always opposite to the worm wheel 3 (upward in FIG. 5 ), regardless of the rotational direction of the worm 4. In contrast, the direction of the third reference direction component of the radial component of the meshing reaction force applied from the meshing portion to the worm 4 is opposite when the worm 4 rotates in a predetermined direction and when the worm 4 rotates in a direction opposite to the predetermined direction. Furthermore, the ratio between the first reference direction component and the third reference direction component constituting the radial component of the meshing reaction force applied from the meshing portion to the worm 4 differs between when the worm 4 rotates in a predetermined direction and when it rotates in the opposite direction.

[0054] 5, a radial component F1 of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in a predetermined direction and a radial component F2 of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in the direction opposite to the predetermined direction are inclined in opposite directions with respect to the first reference direction. Furthermore, the inclination angle θ1 of the radial component F1 with respect to the first reference direction is different from the inclination angle θ2 of the radial component F2 with respect to the first reference direction (θ1 ≠ θ2). While this example illustrates an example in which the twist direction of the worm teeth 12 is a right-hand thread direction, if the twist direction of the worm teeth 12 is a left-hand thread direction, the directions of the radial components F1 and F2 of the meshing reaction force in FIG. 5 will be reversed with respect to the third reference direction.

[0055] In this example, as shown in Figures 5 and 6(a) to 6(c), the holding portion 19 includes a main holding portion 26, a first recess 27, a second recess 28, and two third recesses 29a, 29b.

[0056] The main retaining portion 26 is configured with a cylindrical surface that is larger than the outer peripheral surface of the outer ring 17, which is the outer peripheral surface of the support bearing 5. In this example, since the main retaining portion 26 is configured with a cylindrical surface, it is easier to form the main retaining portion 26 and to manage the tolerance of the dimensions of the main retaining portion 26, compared to when the main retaining portion is configured with an oval shape that extends in the first reference direction when viewed from the second reference direction.

[0057] The first recess 27 is configured to recess radially outward from the main holding portion 26 at a circumferential location of the holding portion 19, which is located in the first radial direction R1, which is the direction of a component force (radial component force F1) in the virtual plane of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in a predetermined direction.

[0058] Specifically, the circumferential range in which the first recess 27 exists includes the same circumferential position as the straight line representing the first radial direction R1 when viewed from the second reference direction. In other words, when viewed from the second reference direction, the straight line representing the first radial direction R1 intersects with the first recess 27.

[0059] The radially inner end of the first recess 27 opens to the main holding portion 26, and the end on one axial side of the first recess 27 opens to the step surface 21. The first recess 27 is provided only on one axial side portion of the entire axial range of the holding portion 19. However, when implementing the present disclosure, a configuration in which the first recess is provided over the entire axial range of the holding portion can also be adopted.

[0060] The first recess 27 has a pair of inner surfaces 27A facing each other in the circumferential direction and a bottom surface 27B connecting the radially outer ends of the pair of inner surfaces 27A. The bottom surface 27B is formed by a partial cylindrical surface centered on the central axis of the main holding portion 26.

[0061] The second recess 28 is configured to recess radially outward from the main holding portion 26 at a circumferential location of the holding portion 19 located in the second radial direction R2, which is the direction of a component (radial component force F2) in the virtual plane of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in the direction opposite to the specified direction.

[0062] Specifically, the circumferential range in which the second recesses 28 exist includes the same circumferential position as the line representing the second radial direction R2 when viewed from the second reference direction. That is, when viewed from the second reference direction, the line representing the second radial direction R2 intersects with the second recesses 28.

[0063] The radially inner end of the second recess 28 opens to the main holding portion 26, and the end on one axial side of the second recess 28 opens to the step surface 21. The second recess 28 is provided over the entire axial range of the holding portion 19.

[0064] The second recess 28 has a pair of inner surfaces 28A that face each other in the circumferential direction and a bottom surface 28B that connects the radially outer ends of the pair of inner surfaces 28 A. The bottom surface 28B is formed by a partial cylindrical surface that is centered on the central axis of the main holding portion 26.

[0065] The two third recesses 29a, 29b are provided at circumferential locations on both ends of the retaining portion 19 in the third reference direction, so as to recess radially outward from the main retaining portion 26. The radially inner ends of the two third recesses 29a, 29b open to the main retaining portion 26, and the ends on one axial side of the two third recesses 29a, 29b open to the step surface 21.

[0066] Of the two third recesses 29a, 29b, the third recess 29a, which is located on one side of the third reference direction (the left side in Figures 5 and 6(a)), is provided over the entire axial range of the retaining portion 19.

[0067] The third recess 29a has a pair of inner surfaces 29aA that face each other in the circumferential direction and a bottom surface 29aB that connects the radially outer ends of the pair of inner surfaces 29aA. The bottom surface 29aB is formed by a partial cylindrical surface that is centered on the central axis of the main holder 26.

[0068] Of the two third recesses 29a, 29b, the other third recess 29b, which is located on the other side in the third reference direction (the right side in FIGS. 5 and 6(a)), is provided only on one axial side of the entire axial range of the holding portion 19. However, when implementing the present disclosure, a configuration can also be adopted in which the other third recess is provided over the entire axial range of the holding portion.

[0069] The other third recess 29b has a pair of inner surfaces 29bA facing each other in the circumferential direction and a bottom surface 29bB connecting the radially outer ends of the pair of inner surfaces 29bA. The bottom surface 29bB is formed by a partial cylindrical surface centered on the central axis of the main holder 26.

[0070] In this example, the radial depth of the first recess 27 and the radial depth of the second recess 28 are equal to each other. Furthermore, the radial depth of one third recess 29a and the radial depth of the other third recess 29b are equal to each other. Furthermore, the radial depth of each of the two third recesses 29a, 29b is smaller than the radial depth of the first recess 27 and the radial depth of the second recess 28. However, when implementing the present disclosure, the magnitude relationship between the radial depths of the first recess, the second recess, and the two third recesses can be set arbitrarily and can also be different from this example.

[0071] The biasing spring 6 is configured as a single unit. In other words, the biasing spring 6 is configured from a single part. The biasing spring 6 has a main body portion 30, a first spring portion 31, a second spring portion 32, and two third spring portions 33a and 33b.

[0072] In this example, the biasing spring 6 is made of a metal leaf spring having a partially cut circular (C-shaped) shape. The biasing spring 6 is made by pressing a band-shaped metal flat plate material.

[0073] The main body 30 is configured in a segmented annular shape, specifically, in a segmented cylindrical shape. However, when implementing the present disclosure, the main body may also be configured in a segmented annular shape, such as a cylindrical shape with a continuous periphery.

[0074] The main body portion 30 is fitted onto the support bearing 5 with one discontinuous portion in the circumferential direction positioned at the end farther from the worm wheel 3 in the first reference direction. The outer diameter of the main body portion 30 when fitted onto the support bearing 5 is smaller than the inner diameter of the main holder 26, and a radial gap exists over the entire circumference between the outer peripheral surface of the main body portion 30 and the inner peripheral surface of the main holder 26. This allows the support bearing 5 to be displaced inside the main holder 26 in the radial direction including the first reference direction, which is the biasing direction of the biasing spring 6.

[0075] 5, the inner diameter of the main holder 26 is larger than the outer diameter of the main body 30 when fitted onto the support bearing 5 by about twice the plate thickness of the main body 30. However, the difference between the inner diameter of the main holder 26 and the outer diameter of the main body 30 when fitted onto the support bearing 5 can also be made smaller or larger than in the illustrated example, as long as it does not interfere with the operation of the worm reducer 1 of this example.

[0076] The first spring portion 31 is connected to the main body portion 30 and is arranged to protrude radially outward from the main body portion 30 at a circumferential location located in a first radial direction R1, which is the direction of a component (radial component force F1) in the virtual plane of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in a predetermined direction, and is in elastic contact with the retaining portion 19.

[0077] Specifically, the circumferential range in which the first spring portions 31 exist includes the same circumferential position as the straight line representing the first radial direction R1 when viewed from the second reference direction. That is, when viewed from the second reference direction, the straight line representing the first radial direction R1 intersects with the first spring portions 31. The elastic restoring force of the first spring portions 31 includes a component in a direction that elastically biases the support bearing 5 toward the worm wheel 3 with respect to the first reference direction.

[0078] The second spring portion 32 is connected to the main body portion 30 and is arranged to protrude radially outward from the main body portion 30 at a circumferential location located in the second radial direction R2, which is the direction of a component (radial component force F2) in the virtual plane of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in the direction opposite to the specified direction, and is in elastic contact with the retaining portion 19.

[0079] Specifically, the circumferential range in which the second spring portion 32 exists includes the same circumferential position as the straight line representing the second radial direction R2 when viewed from the second reference direction. That is, when viewed from the second reference direction, the straight line representing the second radial direction R2 intersects with the second spring portion 32. The elastic restoring force of the second spring portion 32 includes a component in a direction that elastically biases the support bearing 5 toward the worm wheel 3 with respect to the first reference direction.

[0080] The two third spring portions 33a, 33b are connected to the main body portion 30, and are provided so as to protrude radially outward from the main body portion 30 at circumferential locations located at both ends in the third reference direction, and are in elastic contact with the retaining portion 19. Therefore, when the meshing reaction force applied to the worm 4 is zero, it is possible to prevent the support bearing 5 from rattling inside the retaining portion 19 in the third reference direction.

[0081] In this example, the first spring portion 31 and the second spring portion 32 are disposed at different positions in the second reference direction. That is, the first spring portion 31 and the second spring portion 32 are disposed at positions where they do not overlap in the second reference direction.

[0082] Specifically, in this example, the base 31A of the first spring portion 31 is connected to one axial side portion of the main body portion 30 near the end portion on one circumferential side (clockwise side in Figures 5 and 7(a)).

[0083] Specifically, the first spring portion 31 has a semi-cylindrical base portion 31A bent radially outward from one axial side portion of the main body portion 30 near one circumferential end portion, a partially cylindrical pressing portion 31B extending from the radially outer end portion of the base portion 31A toward the other circumferential side (counterclockwise side in FIGS. 5 and 7(a)), and a turned-back portion 31C bent radially inward from the other circumferential end portion of the pressing portion 31B. The radius of curvature of the radially outer surface of the pressing portion 31B is smaller than the radius of curvature of the bottom surface 27B of the first recess 27.

[0084] In this example, the base portion 32A of the second spring portion 32 is connected to the other axial side portion of the main body portion 30 near the other circumferential end portion.

[0085] Specifically, the second spring portion 32 has a semi-cylindrical base portion 32A bent radially outward from a portion of the main body portion 30 near the other circumferential end portion thereof, a partially cylindrical pressing portion 32B extending from the radially outer end portion of the base portion 32A to one circumferential side, and a turned-back portion 32C bent radially inward from the circumferentially one end portion of the pressing portion 32B. The radius of curvature of the radially outer surface of the pressing portion 32B is smaller than the radius of curvature of the bottom surface 28B of the second recess 28.

[0086] In this example, the first spring portion 31 is disposed inside the first recess 27 and is in elastic contact with the bottom surface 27B of the first recess 27. Specifically, of the first spring portion 31, a circumferentially intermediate portion of the radially outer surface of the pressing portion 31B is in elastic contact with a circumferentially intermediate portion of the bottom surface 27B of the first recess 27. In this example, the circumferentially intermediate portion of the radially outer surface of the pressing portion 31B is in elastic contact with the circumferentially intermediate portion of the bottom surface 27B at a circumferential location located in the first radial direction R1.

[0087] In this example, the side surface on one circumferential side of the base portion 31A of the first spring portion 31 is brought into contact with the inner surface 27A on one circumferential side of the first recess 27, thereby positioning the first spring portion 31 in the circumferential direction with respect to the retaining portion 19 and preventing the biasing spring 6 from rotating in one circumferential direction with respect to the retaining portion 19. In this example, a circumferential gap is provided between the side surface on the other circumferential side of the return portion 31C of the first spring portion 31 and the inner surface 27A on the other circumferential side of the first recess 27. This prevents the pair of inner surfaces 27A from interfering with the elastic crushing action of the first spring portion 31 by the radial component force F1 of the meshing reaction force. In this example, the edge portion of the first spring portion 31 on the other axial side is positioned at the end portion on the other axial side of the first recess 27 and is in contact with or closely opposed to the wall surface 27C facing one axial side, thereby preventing the biasing spring 6 from falling off from between the retaining portion 19 and the support bearing 5 to the other axial side.

[0088] In this example, the second spring portion 32 is disposed inside the second recess 28 and is in elastic contact with the bottom surface 28B of the second recess 28. Specifically, of the second spring portion 32, a circumferentially intermediate portion of the radially outer surface of the pressing portion 32B is in elastic contact with a circumferentially intermediate portion of the bottom surface 28B of the second recess 28. In this example, the circumferentially intermediate portion of the radially outer surface of the pressing portion 32B is in elastic contact with the circumferentially intermediate portion of the bottom surface 28B at a circumferential location located in the second radial direction R2.

[0089] In this example, the side surface on the other circumferential side of the base portion 32A of the second spring portion 32 is brought into contact with the inner surface 28A on the other circumferential side of the second recess 28, thereby positioning the second spring portion 32 in the circumferential direction with respect to the retaining portion 19 and preventing the biasing spring 6 from rotating in the other circumferential direction with respect to the retaining portion 19. In this example, a circumferential gap is provided between the side surface on one circumferential side of the return portion 32C of the second spring portion 32 and the inner surface 28A on one circumferential side of the second recess 28. This prevents the pair of inner surfaces 28A from interfering with the elastic crushing action of the second spring portion 32 by the radial component force F2 of the meshing reaction force.

[0090] In this example, one third spring portion 33a arranged on one side in the third reference direction and the other third spring portion 33b arranged on the other side in the third reference direction are arranged at different positions in the second reference direction. That is, one third spring portion 33a and the other third spring portion 33b are arranged at positions that do not overlap in the second reference direction.

[0091] Specifically, in this example, the base portion 33aA of one third spring portion 33a is connected to the other axial side portion of the end portion of the main body portion 30 on one side in the third reference direction.

[0092] Specifically, one third spring portion 33a has a semi-cylindrical base portion 33aA bent radially outward from the other axial side portion of one end portion of the main body portion 30 in the third reference direction, a partially cylindrical pressing portion 33aB extending to one circumferential side from the radially outer end portion of the base portion 33aA, and a turned-back portion 33aC bent radially inward from the one circumferential end portion of the pressing portion 33aB. The radius of curvature of the radially outer surface of the pressing portion 33aB is smaller than the radius of curvature of the bottom surface 29aB of one third recess portion 29a.

[0093] In this example, the base portion 33bA of the other third spring portion 33b is connected to one axial side portion of the end portion of the main body portion 30 on the other side in the third reference direction.

[0094] Specifically, the other third spring portion 33b has a semi-cylindrical base portion 33bA bent radially outward from one axial side portion of the end portion on the other side in the third reference direction of the main body portion 30, a partially cylindrical pressing portion 33bB extending to the other circumferential side from the radially outer end portion of the base portion 33bA, and a turned-back portion 33bC bent radially inward from the other circumferential end portion of the pressing portion 33bB. The radius of curvature of the radially outer surface of the pressing portion 33bB is smaller than the radius of curvature of the bottom surface 29bB of the other third recess portion 29b.

[0095] In this example, one third spring portion 33a is disposed inside one third recessed portion 29a and is in elastic contact with a bottom surface 29aB of one third recessed portion 29a. Specifically, of one third spring portion 33a, a circumferentially intermediate portion of a radially outer surface of a pressing portion 33aB is in elastic contact with a circumferentially intermediate portion of the bottom surface 29aB of one third recessed portion 29a.

[0096] In this example, the side surface on one circumferential side of the base 33aA of one third spring portion 33a and the side surface on the other circumferential side of the return portion 33aC are brought into contact with a pair of inner surfaces 29aA of one third recess 29a, thereby preventing the biasing spring 6 from rotating in both circumferential directions relative to the retaining portion 19.

[0097] In this example, the other third spring portion 33b is disposed inside the other third recessed portion 29b and is in elastic contact with the bottom surface 29bB of the other third recessed portion 29b. Specifically, of the other third spring portion 33b, a circumferentially intermediate portion of the radially outer surface of the pressing portion 33bB is in elastic contact with a circumferentially intermediate portion of the bottom surface 29bB of the other third recessed portion 29b.

[0098] In this example, the side surface on the other circumferential side of the base portion 33bA of the other third spring portion 33b and the side surface on one circumferential side of the return portion 33bC are brought into contact with a pair of inner surfaces 29bA of the other third recessed portion 29b, thereby preventing the biasing spring 6 from rotating in both circumferential directions relative to the retaining portion 19. Also, in this example, the edge portion on the other axial direction side of the other third spring portion 33b is positioned at the end portion on the other axial side of the other third recessed portion 29b and is brought into contact with or closely opposed to a wall surface 29bC facing one axial side, thereby preventing the biasing spring 6 from falling off from between the retaining portion 19 and the support bearing 5 to the other axial side.

[0099] In this example, when the meshing reaction force acting on the worm 4 is zero, the following dimensional relationships are established: The radial height of the first spring portion 31 is equal to the radial height of the second spring portion 32. The radial height of one third spring portion 33a is equal to the radial height of the other third spring portion 33b. Furthermore, the radial height of each of the two third spring portions 33a, 33b is smaller than the radial height of each of the first spring portion 31 and the second spring portion 32. However, when implementing the present disclosure, the radial heights of the first spring portion, the second spring portion, and the two third spring portions can be set arbitrarily and can differ from those in this example.

[0100] In this example, the main body portion 30 has a one-side end portion 34, which is a portion located on one circumferential side of the portion to which the first spring portion 31 is connected, and a other-side end portion 35, which is a portion located on the other circumferential side of the portion to which the second spring portion 32 is connected. The one-side end portion 34 and the other-side end portion 35 are arranged at different positions with respect to the second reference direction. Specifically, in this example, the one-side end portion 34 is arranged on the other axial side portion of the main body portion 30, and the other-side end portion 35 is arranged on one axial side portion of the main body portion 30.

[0101] According to the worm reducer 1 of this embodiment, an appropriate preload can be applied to the meshing portion between the wheel teeth 11 and the worm teeth 12.

[0102] That is, in the worm reducer 1 of this example, the biasing spring 6 that elastically biases the support bearing 5 toward the worm wheel 3 has a first spring portion 31 and a second spring portion 32. The first spring portion 31 is provided at a circumferential location located in a first radial direction R1, which is the direction of a component force (radial component force F1) in an imaginary plane perpendicular to the central axis of the worm 4, of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in a predetermined direction, and is in elastic contact with the retaining portion 19. The elastic restoring force of the first spring portion 31 includes a component in a direction that elastically biases the support bearing 5 toward the worm wheel 3 with respect to the first reference direction. The second spring portion 32 is provided at a circumferential location located in a second radial direction R2, which is the direction of a component (radial component F2) in the imaginary plane of the meshing reaction force applied to the worm 4 from the meshing portion when the worm 4 rotates in the direction opposite to the predetermined direction, and is in elastic contact with the retaining portion 19. The elastic restoring force of the second spring portion 32 includes a component in a direction that elastically biases the support bearing 5 toward the worm wheel 3 with respect to the first reference direction.

[0103] Therefore, in the worm reducer 1 of this embodiment, an appropriate preload can be applied to the meshing portion between the wheel teeth 11 and the worm teeth 12.

[0104] Furthermore, when the worm 4 rotates in a predetermined direction, the first spring portion 31 is elastically crushed in the first radial direction R1 by the radial component force F1 of the meshing reaction force, and as a result, the elastic restoring force of the first spring portion 31 can urge the tip end of the worm 4 in the direction opposite to the radial component force F1 of the meshing reaction force. Therefore, even when the worm 4 rotates in a predetermined direction, movement of the tip end of the worm 4 in the first radial direction R1 can be suppressed, and the preload at the meshing portion between the wheel teeth 11 and the worm teeth 12 can be maintained at an appropriate magnitude.

[0105] When the worm 4 rotates in the direction opposite to the predetermined direction, the second spring portion 32 is elastically crushed in the second radial direction R2 by the radial component force F2 of the meshing reaction force, and as a result, the elastic restoring force of the second spring portion 32 can urge the tip end of the worm 4 in the direction opposite to the radial component force F2 of the meshing reaction force. Therefore, when the worm 4 starts to rotate in the direction opposite to the predetermined direction, movement of the tip end of the worm 4 in the second radial direction R2 can be suppressed, and the preload at the meshing portion between the wheel teeth 11 and the worm teeth 12 can be maintained at an appropriate magnitude.

[0106] In the worm reducer 1 of this example, it is possible to prevent or suppress the generation of abnormal noise around the tip end of the worm 4 due to collision between members in the third reference direction.

[0107] That is, in the worm reducer 1 of this example, the biasing spring 6 has two third spring portions 33a, 33b. The two third spring portions 33a, 33b are provided at circumferential locations located at both ends in the third reference direction, and are in elastic contact with the retaining portion 19.

[0108] Therefore, the meshing reaction force acts on the worm 4, suppressing the momentum of the tip of the worm 4 moving in the third reference direction, thereby preventing or suppressing the generation of abnormal noise. Specifically, when the worm 4 starts to rotate in a predetermined direction, the elasticity of one third spring portion 33a can suppress the momentum of the tip of the worm 4 moving to one side in the third reference direction. Therefore, even if this movement causes the outer circumferential surface of the main body portion 30 of the biasing spring 6 to come into contact with the main holder 26, the generation of abnormal noise, which is a collision sound, can be prevented or suppressed. Furthermore, when the worm 4 starts to rotate in the direction opposite to the predetermined direction, the elasticity of the other third spring portion 33b can suppress the momentum of the tip of the worm 4 moving to the other side in the third reference direction. Therefore, even if this movement causes the outer circumferential surface of the main body portion 30 of the biasing spring 6 to come into contact with the main holder 26, the generation of abnormal noise, which is a collision sound, can be prevented or suppressed.

[0109] In the worm reducer 1 of this example, when the worm 4 starts to rotate in a predetermined direction, the elasticity of the first spring portion 31 also suppresses the momentum of the tip of the worm 4 moving to one side in relation to the third reference direction. Furthermore, when the worm 4 starts to rotate in the direction opposite to the predetermined direction, the elasticity of the second spring portion 32 also suppresses the momentum of the tip of the worm 4 moving to the other side in relation to the third reference direction.

[0110] In the worm reducer 1 of this example, the biasing spring 6 is configured as a single unit, in other words, it is configured from a single part. This reduces the cost of managing the biasing spring 6 and the labor cost of assembling the biasing spring 6 to the worm reducer 1. As a result, the worm reducer 1 can be manufactured at low cost.

[0111] In this example, the first spring portion 31 and the second spring portion 32 are disposed at different positions relative to the second reference direction, which makes it easier to ensure the support rigidity of the support bearing 5 relative to the retaining portion 19 compared to when the first spring portion 31 and the second spring portion 32 are disposed at the same position relative to the second reference direction.

[0112] In this example, the two third spring portions 33a, 33b are disposed at different positions relative to the second reference direction, which makes it easier to ensure the support rigidity of the support bearing 5 relative to the retaining portion 19 compared to when the two third spring portions 33a, 33b are disposed at the same position relative to the second reference direction.

[0113] In the worm reducer 1 of this example, the main body portion 30 of the biasing spring 6 has a one-side end portion 34, which is a portion located on one circumferential side of the portion to which the first spring portion 31 is connected, and a other-side end portion 35, which is a portion located on the other circumferential side of the portion to which the second spring portion 32 is connected, and the one-side end portion 34 and the other-side end portion 35 are disposed at mutually different positions in the second reference direction. Therefore, based on the presence of the one-side end portion 34 and the other-side end portion 35, the main body portion 30 can cover the outer peripheral surface of the support bearing 5 in a balanced manner in the circumferential and axial directions, and as a result, the biasing spring 6 can be assembled stably to the support bearing 5.

[0114] <Electric power steering device> As shown in FIG. 1, the electric power steering device 36 of this example includes a steering wheel 37, a steering shaft 38, a steering column 39, a pair of universal joints 40a, 40b, an intermediate shaft 41, a steering gear unit 42, the worm reducer 1 of this example, and the electric motor 10.

[0115] The steering wheel 37 is fixedly supported at the rear end of a steering shaft 38. The steering shaft 38 is rotatably supported inside a steering column 39 supported on the vehicle body. The front end of the steering shaft 38 is connected to a pinion shaft 43 of a steering gear unit 42 via a rear universal joint 40a, an intermediate shaft 41, and a front universal joint 40b. Therefore, when the driver turns the steering wheel 37, the rotation of the steering wheel 37 is transmitted to the pinion shaft 43 via the steering shaft 38, the pair of universal joints 40a and 40b, and the intermediate shaft 41. The rotation of the pinion shaft 43 is converted into linear motion of a rack shaft (not shown) of the steering gear unit 42 that meshes with the pinion shaft 43. As a result, a pair of tie rods 44 are pushed and pulled, and a steering angle corresponding to the amount of rotation of the steering wheel 37 is applied to the left and right steered wheels.

[0116] The electric power steering device 36 of this example is configured to reduce the force required by the driver to operate the steering wheel 37 by increasing the auxiliary power of the electric motor 10 using the worm reducer 1 and then applying it to the front end of the steering shaft 38.

[0117] When implementing the worm reducer of the present disclosure, the worm reducer 1 and the electric motor 10 can be disposed at a position where auxiliary power is applied to the pinion shaft or rack shaft of the steering gear unit.

[0118] [Example 2] A second example of the embodiment of the present disclosure will be described with reference to FIGS. 8 to 11(c).

[0119] In this example, the biasing spring 6a further has a fourth spring portion 45. The fourth spring portion 45 is provided to protrude radially outward from the main body portion 30 at a circumferential location located at the end farther from the worm wheel 3 in the first reference direction, and is in elastic contact with the retaining portion 19a.

[0120] In this example, the elastic force of the fourth spring portion 45 is used in addition to the elastic force of the first spring portion 31 and the second spring portion 32 to bias the tip end portion of the worm 4 toward the worm wheel 3 side.

[0121] In this example, the retaining portion 19a has a fourth recess 46 that is recessed radially outward at a circumferential location located at the end farther from the worm wheel 3 in the first reference direction. The fourth spring portion 45 is disposed inside the fourth recess 46. The fourth recess 46 has a pair of inner surfaces 46A that face each other in the circumferential direction and a bottom surface 46B that connects the radially outer ends of the pair of inner surfaces 46A. The bottom surface 46B is formed by a partial cylindrical surface centered on the central axis of the main retaining portion 26. The fourth spring portion 45 is in elastic contact with the bottom surface 46B of the fourth recess 46.

[0122] In this example, the fourth spring portion 45 is made up of multiple spring pieces. This makes it easy to design the fourth spring portion 45 to adjust its elasticity. Specifically, in this example, the fourth spring portion 45 is made up of two spring pieces 47a, 47b. However, when implementing the present disclosure, the fourth spring portion can also be made up of a single spring portion.

[0123] In this example, the two spring pieces 47a, 47b are arranged at different positions relative to the second reference direction, which makes it easier to ensure the support rigidity of the support bearing 5 relative to the retaining portion 19a compared to when the two spring pieces 47a, 47b are arranged at the same position relative to the second reference direction.

[0124] In this example, one spring piece 47a has a semi-cylindrical base portion 47aA bent radially outward from the tip of one end portion 34 of the main body portion 30, and a partially cylindrical pressing portion 47aB extending from the radially outer end portion of the base portion 47aA to the other circumferential side. The radius of curvature of the radially outer surface of the pressing portion 47aB is approximately equal to the radius of curvature of the bottom surface 46B of the fourth recessed portion 46.

[0125] The other spring piece 47b has a semi-cylindrical base portion 47bA bent radially outward from the tip of the other end portion 35 of the main body portion 30, and a partially cylindrical pressing portion 47bB extending circumferentially to one side from the radially outer end portion of the base portion 47bA. The radius of curvature of the radially outer surface of the pressing portion 47bB is approximately equal to the radius of curvature of the bottom surface 46B of the fourth recess 46.

[0126] The two spring pieces 47a, 47b are arranged inside the fourth recess 46, and the radially outer surfaces of the pressing portions 47aB, 47bB are in elastic contact with the bottom surface 46B of the fourth recess 46.

[0127] In this example, the radial depth of the fourth recess 46 is smaller than the radial depths of the first recess 27 and the second recess 28. In this example, when the meshing reaction force acting on the worm 4 is zero, the radial height of the fourth spring portion 45 is smaller than the radial heights of the first spring portion 31 and the second spring portion 32. Therefore, the fourth spring portion 45 is less likely to wear out than the first spring portion 31 and the second spring portion 32. Therefore, even after the first spring portion 31 and the second spring portion 32 wear out after long-term use, the elasticity of the fourth spring 45 can maintain the state in which the tip end of the worm 4 is biased toward the worm wheel 3.

[0128] The other configurations and effects of the second example are the same as those of the first example.

[0129] [Example 3] A third example of the embodiment of the present disclosure will be described with reference to FIGS.

[0130] In the structure of this example, each of the first spring portion 31a and the second spring portion 32a that constitute the biasing spring 6b is made up of a plurality of spring pieces that are arranged at different positions with respect to the second reference direction.

[0131] Specifically, in this example, the first spring portion 31a has a slit 48 in its axial center. The slit 48 axially divides the base portion 31aA, the pressing portion 31aB, and the return portion 31aC of the first spring portion 31a into two. That is, the first spring portion 31a is composed of two spring pieces 49 located on both sides of the slit 48 in the axial direction. In this example, the base ends of the two spring pieces 49 are connected to both axial sides of one circumferential end of the main body portion 30a. In this example, the first recess 27a of the retaining portion 19b that houses the first spring portion 31a is provided over the entire axial range of the retaining portion 19b.

[0132] In this example, the spring force of the first spring portion 31a can be adjusted by changing the axial width of each of the two spring pieces 49, for example, by changing the axial width of the slit .

[0133] In this example, the second spring portion 32a has a slit 50 in the axial center. The slit 50 divides the base portion 32aA, the pressing portion 32aB, and the return portion 32aC of the second spring portion 32a into two in the axial direction. That is, the second spring portion 32a is composed of two spring pieces 51 located on both sides in the axial direction with the slit 50 in between. In this example, the base ends of the two spring pieces 51 are connected to both axial sides of the other circumferential end of the main body portion 30a.

[0134] In this example, the spring force of the second spring portion 32a can be adjusted by changing the axial width of each of the two spring pieces 51, for example, by changing the axial width of the slit 50.

[0135] When implementing the worm reducer of the present disclosure, at least one of the two third spring portions 33a, 33b can be configured with a plurality of spring pieces arranged at different positions with respect to the second reference direction.

[0136] The other configurations and effects of the third example are the same as those of the first example.

[0137] [Example 4] A fourth example of the embodiment of the present disclosure will be described with reference to FIG.

[0138] In this example, the first spring portion 31b and the second spring portion 32b constituting the biasing spring 6c are each provided across the entire width of the main body portion 30a in the second reference direction. In this example, the second recess (not shown) of the holding portion that accommodates the first spring portion 31b is provided across the entire axial range of the holding portion.

[0139] The other configurations and effects of the fourth example are the same as those of the first example.

[0140] The worm reducer of the present disclosure can be implemented by appropriately combining the structures of the above-described embodiments within the scope of no contradiction. [Explanation of symbols]

[0141] 1 Worm reducer 2. Housing 3 worm wheels 4. Warm 5 Support bearing 6, 6a, 6b, 6c bias spring 7 Wheel housing 8 Worm housing 9 Lid 10 Electric motor 11 Wheel Teeth 12 worm teeth 13 Ball bearings 14 Output shaft 15 Coupling 16 Inner Circle 17 Outer ring 18 balls 19, 19a, 19b holding part 20 Large diameter section 21 Step surface 22 Locking groove 23 Retaining ring 24 Small diameter section 25 Step surface 26 Main holding part 27, 27a First recess 27A Inner side 27B Bottom 27C Wall 28 Second recess 28A Inner side 28B Bottom 29a Third recess 29aA inner surface 29aB Bottom 29b Third recess 29bA inner surface 29bB bottom 29bC Wall 30 Main part 31, 31a, 31b First spring part 31A, 31aA base 31B, 31aB pressing portion 31C, 31aC return part 32, 32a, 32b Second spring part 32A, 32aA base 32B, 32aB pressing part 32C, 32aC return part 33a Third spring part 33aA base 33aB Pressing part 33aC Return part 33b Third spring part 33bA base 33bB pressing part 33bC Return part 34 One side end 35 Other side end 36 Electric power steering device 37 Steering Wheel 38 Steering shaft 39 Steering column 40a, 40b universal joint 41 Intermediate shaft 42 Steering gear unit 43 Pinion shaft 44 tie rod 45 Fourth spring section 46 4th recess 46A Inner side 46B Bottom 47a, 47b Spring pieces 47aA base 47aB Pressing part 47bA base 47bB pressing part 48 Slit 49 Spring piece 50 slits 51 Spring piece 52 outer ring 53 Inner circle 54 Worm damper

Claims

1. a housing having a wheel accommodating portion and a worm accommodating portion having a central axis that is twisted relative to the central axis of the wheel accommodating portion and an axially intermediate portion that opens to the wheel accommodating portion; a worm wheel having wheel teeth on an outer peripheral surface and rotatably supported inside the wheel accommodating portion; a worm having worm teeth on an outer peripheral surface thereof that mesh with the wheel teeth and that is rotatably supported inside the worm accommodating portion; a support bearing fitted onto the tip end of the worm; a biasing spring that is disposed between the support bearing and a retaining portion that is a portion of the inner circumferential surface of the worm accommodating portion that is positioned around the support bearing, and that elastically biases the support bearing toward the worm wheel; Equipped with The biasing spring is The whole is composed as a whole, a main body portion having a circular or semicircular ring shape fitted onto the support bearing; a first spring portion disposed at a circumferential location in a first radial direction, which is the direction of a component of a meshing reaction force applied to the worm from the meshing portion between the wheel teeth and the worm teeth when the worm rotates in a predetermined direction, the first spring portion being provided so as to protrude radially outward from the main body portion and being in elastic contact with the retaining portion; a second spring portion disposed at a circumferential location in a second radial direction, which is a direction of a component force in the imaginary plane of a meshing reaction force applied to the worm from the meshing portion when the worm rotates in a direction opposite to the predetermined direction, and provided so as to protrude radially outward from the main body portion and in elastic contact with the retaining portion; a pair of third spring portions provided at circumferential locations on both ends of a third reference direction perpendicular to both a first reference direction which is the biasing direction of the biasing spring and a second reference direction which is the axial direction of the worm accommodating portion, the third spring portions being provided so as to protrude radially outward from the main body portion and being in elastic contact with the retaining portion; having Worm reducer.

2. The worm reducer according to claim 1 , wherein the first spring portion and the second spring portion are disposed at different positions relative to the second reference direction.

3. The main body portion is configured in a segmented ring shape, the first spring portion has a base portion connected to a portion of the main body portion near one end in the circumferential direction, the second spring portion has a base portion connected to a portion of the main body portion near the other end in the circumferential direction, a first end portion of the main body portion located on one side in the circumferential direction from a portion to which the base portion of the first spring portion is connected, and a second end portion of the main body portion located on the other side in the circumferential direction from a portion to which the base portion of the second spring portion is connected, the first end portion being disposed at different positions from each other in the second reference direction; 3. The worm reducer according to claim 2.

4. 2. The worm reducer according to claim 1, wherein a third spring portion of the pair of third spring portions arranged on one side in the third reference direction and a third spring portion of the pair of third spring portions arranged on the other side in the third reference direction are arranged at different positions with respect to the second reference direction.

5. the retaining portion has a first recess provided to be recessed radially outward at a circumferential location located in the first radial direction, a second recess provided to be recessed radially outward at a circumferential location located in the second radial direction, and a pair of third recesses provided to be recessed radially outward at circumferential locations located at both end portions in the third reference direction, the first spring portion is disposed inside the first recess and is in elastic contact with a bottom surface of the first recess, the second spring portion is disposed inside the second recess and is in elastic contact with a bottom surface of the second recess, one of the pair of third spring portions that is disposed on one side in the third reference direction is disposed inside one of the pair of third recesses that is disposed on one side in the third reference direction, and is in elastic contact with a bottom surface of the third recess; the third spring portion of the pair of third spring portions that is disposed on the other side in the third reference direction is disposed inside the third recess portion of the pair of third recess portions that is disposed on the other side in the third reference direction, and is in elastic contact with a bottom surface of the third recess portion; The worm reducer according to claim 1.

6. 2. The worm reducer according to claim 1, wherein at least one of the first spring portion, the second spring portion, and the pair of third spring portions is configured with a plurality of spring pieces arranged at different positions with respect to the second reference direction.

7. 2. The worm reducer according to claim 1, wherein the biasing spring has a fourth spring portion that is arranged at a circumferential location located at an end farther from the worm wheel in the first reference direction, that is provided so as to protrude radially outward than the main body portion, and that elastically contacts the retaining portion.

8. the retaining portion has a fourth recessed portion provided to recess radially outward at a circumferential location located at an end portion farther from the worm wheel in relation to the first reference direction, the fourth spring portion is disposed inside the fourth recess and is in elastic contact with a bottom surface of the fourth recess; 8. The worm reducer according to claim 7.

9. The worm reducer according to claim 7 , wherein the fourth spring portion is made up of a plurality of spring pieces.

10. The worm reducer according to claim 9 , wherein the plurality of spring pieces constituting the fourth spring portion are disposed at different positions relative to the second reference direction.

11. The worm reducer according to claim 7 , wherein a radial height of the fourth spring portion is smaller than a radial height of the first spring portion and smaller than a radial height of the second spring portion.

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