Worm reducer

Abstract

This invention comprises an elastic propelling means (6) and an elastic grasping means (7). The elastic propelling means (6) propels an inner diameter-side member (5) toward a worm wheel (3) side. The elastic grasping means (7) has, in a section between the outer circumferential surface of the inner diameter-side member (5) and the inner circumferential surface of an outer diameter-side member (9), a pair of grasping flat springs (41) disposed on either side of the inner diameter-side member (5) in a third direction. Each of the grasping flat springs (41) exhibits a non-linear spring characteristic such as the spring constant increasing with an increase in the amount of deflection in a direction that includes a third direction component.

Description

[Technical field]

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

[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 an electric motor. The worm reducer includes a housing, a worm wheel, and a worm. The housing includes a wheel accommodating section and a worm accommodating section having a central axis that is twisted relative to the central axis of the wheel accommodating section and an axially intermediate section that opens into the wheel accommodating section. The worm wheel has wheel teeth on its outer circumferential surface and is rotatably supported inside the wheel accommodating section. The worm has worm teeth on its outer circumferential surface that mesh with the wheel teeth and is rotatably supported inside the worm accommodating section. The torque of the electric motor is increased by being transmitted to the worm wheel via the worm, and is then applied as auxiliary power to a steering force transmission member such as a steering shaft or a pinion shaft or rack shaft of a steering gear unit. This reduces the force required for the driver to operate the steering wheel.

[0004] In a worm reduction gear, unavoidable backlash exists at the meshing portion between the wheel teeth and the worm teeth due to dimensional errors and assembly errors of the components that make up the worm reduction gear. Due to the existence of this backlash, when changing the direction of rotation of the steering wheel, However, an unpleasant clicking noise may occur at the meshing area.

[0005] Japanese Patent Publication No. 2020-128803 describes a structure for biasing the tip of the worm toward the worm wheel in order to suppress the generation of teeth rattle noise at the meshing portion between the wheel teeth and the worm teeth. The structure includes an outer fitting member that is fitted onto a support bearing that rotatably supports the tip of the worm and arranged so as to be movable toward and away from the worm wheel, and a biasing spring (elastic biasing means) installed between the outer fitting member and the worm accommodating portion. The biasing spring is elastically deformed, and biases the outer fitting member toward the worm wheel by the elastic restoring force of the biasing spring. This suppresses backlash at the meshing portion between the wheel teeth and the worm teeth, thereby suppressing the generation of teeth rattle noise.

[0006] In the structure described in JP 2020-128803 A, a gap is provided around the entire circumference between the outer peripheral surface of an outer fitting member that is fitted onto a support bearing that rotatably supports the tip of the worm and the inner peripheral surface of the worm accommodating part, so that the tip of the worm can move toward and away from the worm wheel. Therefore, based on the presence of the gap, the tip of the worm can also move in a third direction that is perpendicular to both the first direction, which is the biasing direction of the biasing spring, and the second direction, which is the axial direction of the worm accommodating part.

[0007] On the other hand, a meshing reaction force acts on the worm from the meshing portion between the worm teeth and the wheel teeth. The meshing reaction force includes a force of a third direction component. The direction of the third direction component is reversed depending on the rotation direction of the worm. In addition, when a car is driven, the third direction component of the vibration input in the reverse direction from the tire is transmitted to the worm. For this reason, if the tip of the worm is allowed to move in the third direction without resistance based on the existence of the gap, the third direction component of the meshing reaction force acting on the worm and the third direction component of the vibration input in the reverse direction to the worm will cause the outer peripheral surface of the outer fitting member to collide with the inner peripheral surface of the worm housing part with force in the third direction, which is likely to generate abnormal noises such as harsh hitting sounds and rattle sounds.

[0008] Therefore, in order to suppress the generation of such abnormal noise, the structure described in JP 2020-128803 A includes a pair of clamping leaf springs that clamp the outer fitting member from both sides in the third direction. The pair of clamping leaf springs suppress the momentum of the tip of the worm when it moves in the third direction, thereby suppressing the generation of the abnormal noise as described above. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2020-128803 Summary of the Invention [Problem to be solved by the invention]

[0010] The conventional structure described in JP 2020-128803 A has room for improvement in the following respects.

[0011] That is, in the conventional structure described in JP 2020-128803 A, in order to smooth the biasing action of the tip of the worm by the biasing spring, that is, to smooth the movement of the tip of the worm in the first direction, the spring constant of the pair of clamping leaf springs is required to be low. On the other hand, in order to sufficiently suppress the outer circumferential surface of the outer fitting member from colliding forcefully in the third direction with the inner circumferential surface of the worm accommodating portion due to the third direction component of the meshing reaction force acting on the worm and the third direction component of the vibration input in reverse to the worm, the spring constant of the pair of clamping leaf springs is required to be large.

[0012] However, in the conventional structure described in JP 2020-128803 A, the spring constant of the pair of clamping leaf springs is constant, making it difficult to meet the two above-mentioned requirements, which are in a contradictory relationship.

[0013] The present disclosure aims to provide a worm reducer that can smooth the biasing action of the tip of the worm by an elastic biasing means and that can easily suppress the force of collision between members in the third direction around the tip of the worm. [Means for solving the problem]

[0014] A worm reducer according to one aspect of the present disclosure includes a housing, a worm wheel, a worm, a support bearing, elastic biasing means, and elastic clamping means.

[0015] The housing has a wheel accommodating portion and a worm accommodating portion having a central axis that is skewed with respect to the central axis of the wheel accommodating portion and an axially intermediate portion that opens into the wheel accommodating portion.

[0016] The worm wheel has wheel teeth on its outer circumferential surface, and is rotatably supported inside the wheel accommodating portion.

[0017] The worm has worm teeth on its outer circumferential surface that mesh with the wheel teeth, and is rotatably supported inside the worm accommodating portion.

[0018] The support bearing is fitted onto the tip portion of the worm.

[0019] The elastic biasing means biases the inner diameter side member, which is the support bearing or an outer fitting member fitted onto the support bearing, towards the worm wheel.

[0020] The elastic clamping means has a pair of clamping leaf springs arranged on both sides of the inner diameter side member in a third direction perpendicular to both a first direction, which is the biasing direction by the elastic biasing means, and a second direction, which is the axial direction of the worm accommodating portion, in the portion between the outer peripheral surface of the inner diameter side member and the inner peripheral surface of an outer diameter side member which is the worm accommodating portion or an inner fitted member fitted into the worm accommodating portion.

[0021] In a worm reducer according to one aspect of the present disclosure, each of the pair of clamping leaf springs exhibits a nonlinear spring characteristic in which the spring constant increases with an increase in the amount of deflection in a direction including the third direction component. Here, the increase in the spring constant with an increase in the amount of deflection in a direction including the third direction component may be a stepwise increase or a continuous increase.

[0022] In one embodiment of the worm reducer disclosed herein, each of the pair of clamping leaf springs has a circumferential middle portion in contact with the inner surface of the outer diameter side member and each of both circumferential side portions in contact with the outer peripheral surface of the inner diameter side member, and further, as the amount of deflection in a direction including a component of the third direction increases, the distance between the contact portions of the circumferential side portions with respect to the outer peripheral surface of the inner diameter side member decreases, thereby increasing the spring constant.

[0023] In one embodiment of the worm reducer of the present disclosure, the circumferential middle portion of each of the pair of clamping leaf springs intersects with a third direction straight line Lx, which is a straight line that passes through the center of the worm and extends in the third direction, when viewed from the second direction.

[0024] In one embodiment of the worm reducer disclosed herein, the inner surface of the outer diameter side member has a portion that contacts the circumferential middle portion of each of the pair of clamping leaf springs, and the portion is formed of a planar portion extending in the first direction.

[0025] In one embodiment of the worm reducer of the present disclosure, the circumferential middle portion of one of the clamping leaf springs constituting the pair of clamping leaf springs, when viewed from the second direction, intersects with a radial line L1 including the vector of a meshing 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 predetermined direction, and the circumferential middle portion of the other clamping leaf spring constituting the pair of clamping leaf springs, when viewed from the second direction, intersects with a radial line L2 including the vector of a meshing reaction force F2 applied to the worm from the meshing portion when the worm rotates in the direction opposite to the predetermined direction.

[0026] In a worm reducer according to an embodiment of the present disclosure, in a target clamped leaf spring that is at least one of the pair of clamped leaf springs, the circumferential intermediate portion is configured by a first portion having a partially cylindrical shape curved along the outer circumferential surface of the inner diameter side member. Each of the circumferential side portions is configured by a second portion having a partially cylindrical shape curved along the outer circumferential surface of the inner diameter side member and smoothly continuing to the first portion. The radius of curvature of the radially inner surface of the first portion in a free state is smaller than the radius of curvature of the outer circumferential surface of the inner diameter side member. The radius of curvature of the radially inner surface of the second portion in a free state is larger than the radius of curvature of the radially inner surface of the first portion in a free state. Here, the radius of curvature of the radially inner surface of the second portion in a free state can be constant over the entire circumferential length, or can be changed stepwise or continuously in the circumferential direction.

[0027] In a worm reducer according to one embodiment of the present disclosure, in a target clamped leaf spring that is at least one of the pair of clamped leaf springs, the circumferential intermediate portion is configured by a first portion having a partially cylindrical shape curved along the outer circumferential surface of the inner diameter side member. Each of the circumferential side portions is configured by a second portion having a partially cylindrical shape curved along the outer circumferential surface of the inner diameter side member and smoothly continuing to the first portion. The radii of curvature of the radially inner surfaces of the first portion and the second portion in a free state are equal to each other and smaller than the radius of curvature of the outer circumferential surface of the inner diameter side member. Each of the second portions has a low-rigidity leaf spring portion at a circumferential end portion on the first portion side, the low-rigidity leaf spring portion having a lower rigidity than the remaining portion in the circumferential direction and the first portion.

[0028] In this case, in a worm reducer according to one embodiment of the present disclosure, each of the clamped leaf springs constituting the pair of clamped leaf springs is the target clamped leaf spring, the elastic clamping means has a circumferential connecting portion that circumferentially connects the circumferential ends of the pair of clamped leaf springs closer to the worm wheel to each other, the circumferential connecting portion has a partially cylindrical shape curved along the outer circumferential surface of the inner diameter side member and is smoothly continuous with the pair of clamped leaf springs, and the radius of curvature of the radial inner surface of the circumferential connecting portion in a free state is equal to the radius of curvature of the radial inner surfaces of the first portion and the second portion in a free state.

[0029] In the worm reducer according to one aspect of the present disclosure, the elastic clamping means has a circumferential connection portion that circumferentially connects circumferential ends of the pair of clamping leaf springs that are closer to the worm wheel to each other.

[0030] In the worm reducer according to one aspect of the present disclosure, the circumferential connection portion has, in at least a portion in the circumferential direction, a low-rigidity connection portion having a rigidity lower than that of the pair of sandwiching leaf springs.

[0031] In the worm reduction gear according to one aspect of the present disclosure, each of the pair of sandwiched leaf springs has a residual stress applied to a portion of the sandwiched leaf spring that contacts the inner circumferential surface of the outer diameter side member.

[0032] In a worm reducer according to one aspect of the present disclosure, the elastic clamping means has a circumferential positioning piece that circumferentially engages with the inner diameter side member or the outer diameter side member.

[0033] In a worm reducer according to one aspect of the present disclosure, the elastic clamping means has an axial positioning piece that axially engages with the inner diameter side member or the outer diameter side member.

[0034] In one embodiment of the worm reducer of the present disclosure, the nonlinear spring characteristics are represented by a graph that is downwardly convex, with the horizontal axis representing the deflection in the third direction and the vertical axis representing the load, and whose slope increases as the deflection in the third direction increases.

[0035] The present disclosure can be implemented by appropriately combining the above-described aspects to the extent that no contradiction occurs. Effect of the Invention

[0036] According to the worm reducer of one aspect of the present disclosure, the biasing action of the tip of the worm by the elastic biasing means can be made smooth, and the force of collision between members in the third direction around the tip of the worm can be easily suppressed. [Brief description of the drawings]

[0037] [Figure 1] FIG. 1 is a diagram illustrating an electric power steering device incorporating a worm reduction gear according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Diagram 3] FIG. 3 is an enlarged view of the upper right portion of FIG. [Figure 4] FIG. 4 is an exploded perspective view of the portion shown in FIG. [Diagram 5] FIG. 5 is a view of the part shown in FIG. 3 from the right side with the cover and the retaining ring removed. [Figure 6] FIG. 6 is an enlarged view of part B in FIG. [Figure 7] FIG. 7 is an enlarged view of part C in FIG. [Figure 8] FIG. 8 is a view of the housing in the first example, seen from the right side of FIG. [Figure 9] FIG. 9 is a perspective view showing the support bearing, the elastic biasing means, and the elastic clamping means in the first example. [Figure 10] FIG. 10 is a view showing the components shown in FIG. 9 in isolation. [Figure 11] Figure 11(a) is a side view of the elastic biasing means in the first example, Figure 11(b) is a view from the top of Figure 11(a), Figure 11(c) is a view from the bottom of Figure 11(a), Figure 11(d) is a view from the left side of Figure 11(a), and Figure 11(e) is a view from the right side of Figure 11(a). [Figure 12] Figure 12(a) is a side view of the elastic clamping means in the first example, Figure 12(b) is a view from above Figure 12(a), Figure 12(c) is a view from below Figure 12(a), Figure 12(d) is a view from the left side of Figure 12(a), and Figure 12(e) is a view from the right side of Figure 12(a). [Figure 13] 13(a) to 13(d) are diagrams that diagrammatically show how the amount of deflection of the elastic biasing means in the first direction increases in the first example. [Figure 14] FIG. 14 is a diagram (conceptual diagram) showing the spring characteristics of the elastic biasing means in the first example. [Figure 15] 15(a) to 15(c) are diagrams that diagrammatically show how the amount of deflection in the third direction of the elastic clamping means (clamping leaf spring) in the first example increases. [Figure 16] FIG. 16 is a diagram (conceptual diagram) showing the spring characteristics of the elastic clamping means (clamping leaf spring) in the first example. [Figure 17] 17(a) to 17(c) are diagrams showing a state in which the amount of deflection in the third direction of the elastic clamping means (clamping leaf spring) in the first example does not change with movement in the first direction. [Figure 18] FIG. 18(a) is a side view of an elastic clamping means in a second example of an embodiment of the present disclosure, and FIG. 18(b) is a perspective view of the elastic clamping means. [Figure 19] 19(a) to 19(c) are diagrams that diagrammatically show how the amount of deflection in the third direction of the elastic clamping means (clamping leaf spring) in the second example increases. [Figure 20] FIG. 20 is an exaggerated schematic diagram showing a state in which the elastic clamping means (clamping leaf spring) in the second example is bent in the third direction. [Figure 21] FIG. 21 is a diagram corresponding to a part of FIG. 5 according to a third example of the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] [Example 1] A first example of an embodiment of the present disclosure will be described with reference to FIGS. 1 to 17. FIG.

[0039] (1) Worm reducer The worm reducer of the present disclosure is applicable to worm reducers incorporated into part of various mechanical devices, but in this example, a case will be described in which the present disclosure is applied to a worm reducer incorporated into part of an electric power steering device for an automobile.

[0040] As shown in FIGS. 1 to 5, the worm reduction gear 1 of this embodiment includes a housing 2, a worm wheel 3, a worm 4, a support bearing 5, elastic biasing means 6, and elastic clamping means .

[0041] The housing (2) includes a wheel accommodating portion (8) and a worm accommodating portion (9) having a central axis that is twisted with respect to the central axis of the wheel accommodating portion (8) and an axially intermediate portion that opens into the wheel accommodating portion (8).

[0042] The wheel receiving portion 8 is configured in a cylindrical shape. In Fig. 2, the central axis of the wheel receiving portion 8 extends in the front-to-rear direction.

[0043] The worm accommodating portion 9 is configured in a cylindrical shape, and has openings on both axial ends. In Fig. 2, the central axis of the worm accommodating portion 9 extends in the left-right direction. The opening on one axial side of the worm accommodating portion 9 is closed by a cover 10 attached to the opening by a retaining ring 47. The opening on the other axial side of the worm accommodating portion 9 is closed by an electric motor 11 coupled and fixed to the housing 2.

[0044] With respect to the worm housing portion 9 and each member housed in the worm housing portion 9, one axial side is the right side in FIG. 2, and the other axial side is the left side in FIG.

[0045] The worm wheel 3 has helical gear-shaped wheel teeth 12 on its outer circumferential surface, and is rotatably supported inside the wheel accommodating portion 8. In this example, the worm wheel 3 is fitted and fixed to an axial portion of a rotating shaft rotatably supported inside the wheel accommodating portion 8 (in this example, a front portion of the steering shaft 50 in the front-rear direction of the vehicle).

[0046] The worm 4 has, on the outer peripheral surface of an axially intermediate portion, screw-like worm teeth 13 that mesh with the wheel teeth 12 of the worm wheel 3, and is rotatably supported inside the worm accommodating portion 9. In this example, the twist direction of the worm teeth 13 is a right-handed thread direction. However, the twist direction may also be a left-handed thread direction.

[0047] The portion of the worm 4 near the base end (the portion near the left end in FIG. 2) is rotatably supported by a ball bearing 14 with respect to the worm housing portion 9. In this example, the outer ring of the ball bearing 14 is fitted inside the worm housing portion 9 with a radial gap therebetween, and the inner ring of the ball bearing 14 is fitted outside 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 so as to be rotatable and oscillatingly displaceable with respect to the worm housing portion 9. The outer ring of the ball bearing 14 can also be fitted inside the worm housing portion 9 with an interference fit. The structure for supporting the portion of the worm 4 near the base end to be rotatable and oscillatingly displaceable with respect to the worm housing portion 9 is not limited to the structure of this example, and various structures can be adopted.

[0048] The base end of the worm 4 is connected to the tip end of the output shaft 15 of the electric motor 11 by using a coupling 16 so as to enable torque transmission and oscillating displacement. Note that the base end of the worm 4 can also be connected to the tip end of the output shaft 15 of the electric motor 11 by spline engagement or the like so as to enable torque transmission and oscillating displacement.

[0049] The support bearing 5 is fitted onto the tip end of the worm 4. The tip end of the worm 4 is a tip end on one axial side (the right end in FIG. 2) in a "second direction" which is the axial direction of the worm housing part 9 (the left-right direction in FIG. 2 and FIG. 3, the front-back direction in FIG. 5).

[0050] In this example, the support bearing 5 is configured as a ball bearing. That is, as shown in Fig. 3, the support bearing 5 includes an inner ring 17, an outer ring 18, and a plurality of balls 19 arranged between an inner ring raceway provided on the outer peripheral surface of the inner ring 17 and an outer ring raceway provided on the inner peripheral surface of the outer ring 18. The inner ring 17 is fitted and fixed to the tip portion of the worm 4. Note that when implementing the present disclosure, the support bearing may also be configured as another type of bearing, such as a roller bearing.

[0051] In this example, the inner peripheral surface of the worm housing portion 9 has a small-diameter cylindrical surface portion 20, which is smaller in diameter than the outer peripheral surface of the support bearing 5, i.e., the outer peripheral surface of the outer ring 18, in a portion near one end in the axial direction, and has a retaining portion 21, which is larger in diameter than the small-diameter cylindrical surface portion 20, in a portion adjacent to one 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 one axial side. In this example, the support bearing 5 is disposed inside the retaining portion 21 so as to be movable in the radial direction.

[0052] In the following description, the direction in which the worm 4 moves toward or away from the worm wheel 3, which is the biasing direction of the elastic biasing means 6 (the up-down direction in Figures 2, 3, and 5), is referred to as the "first direction", the axial direction of the worm accommodating portion 9 (the left-right direction in Figures 2 and 3, the front-to-back direction in Figure 5) is referred to as the "second direction", and the direction perpendicular to both the first and second directions (the front-to-back direction in Figures 2 and 3, the left-to-right direction in Figure 5) is referred to as the "third direction".

[0053] As shown in Fig. 5 and Fig. 8, the holding portion 21 of the worm accommodating portion 9 includes a main holding portion 23, an auxiliary holding portion 24, and a locking portion 25. The main holding portion 23 is disposed approximately coaxially with the small diameter cylindrical surface portion 20, and has an approximately cylindrical shape that is one size larger than the outer circumferential surface of the support bearing 5. The auxiliary holding portion 24 protrudes outward from an end portion of the main holding portion 23 that is farther from the worm wheel 3 in the first direction (the upper side in Fig. 5 and Fig. 8). The locking portion 25 protrudes outward from an end portion of the main holding portion 23 that is closer to the worm wheel 3 in the first direction.

[0054] The main holding portion 23 is a portion inside which the support bearing 5 is disposed so as to be movable in the radial direction. The ends of the main holding portion 23 on both sides in the third direction are constituted by a pair of flat portions 26 (see FIG. 7 ) each extending in the first direction. The pair of flat portions 26 are portions with which the circumferential intermediate portions of the pair of clamping leaf springs 41 constituting the elastic clamping means 7 come into contact. The distance between the pair of flat portions 26 in the third direction is greater 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 greater than the stroke amount by which the elastic clamping means 7 can move in the first direction together with the tip end of the worm 4 and the support bearing 5 during operation. This allows the pair of clamping leaf springs 41 constituting the elastic clamping means 7 to maintain a state of contact with the pair of flat portions 26 regardless of the movement of the elastic clamping means 7 in the first direction.

[0055] Of the main retaining portion 23, a portion that is circumferentially offset from the pair of flat portions 26 is configured with a cylindrical surface portion 27 having a larger diameter than the outer circumferential surface of the support bearing 5. When implementing the present disclosure, the pair of flat portions of the main retaining portion may be omitted, and the main retaining portion may be configured with only the cylindrical surface portion.

[0056] In the worm reduction gear 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 12 and the worm teeth 13. The meshing reaction force includes not only a first direction component but also a third direction component. The direction of the third direction component of the meshing reaction force 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. The ratio of the first direction component and the third direction component included in the meshing reaction force is different between when the worm 4 rotates in a predetermined direction and when the worm 4 rotates in the opposite direction. That is, when torque is transmitted between the worm 4 and the worm wheel 3, a meshing reaction force F1 or F2 as shown in FIG. 5 is applied to the tip of the worm 4 depending on the rotation direction of the worm 4. The meshing reaction forces F1 and F2 are oriented in directions asymmetric to each other with respect to the third direction. In this example, the twist direction of the worm teeth 13 is a right-handed thread direction, but when the twist direction of the worm teeth 13 is a left-handed thread direction, the directions of the meshing reaction forces F1 and F2 in Fig. 5 are reversed with respect to the third direction. In this case, the structure of the part of this example shown in Fig. 5 can be reversed with respect to the third direction, that is, reversed left and right in Fig. 5.

[0057] 5, the circumferential range in which the cylindrical surface portion 27 of the main holding portion 23 exists includes the same circumferential positions as the vectors of the meshing reaction forces F1, F2 when viewed from the second direction. In other words, the radial lines L1, L2 including the vectors of the meshing reaction forces F1, F2 intersect with a circumferential portion of the cylindrical surface portion 27 of the main holding portion 23.

[0058] The auxiliary holding portion 24 is a portion on the inside of which the elastic biasing means 6 is disposed. The auxiliary holding portion 24 has a large recess 28 recessed toward one side in the third direction in a portion on one side in the third direction (the right side in Figs. 5 and 8). The auxiliary holding portion 24 has a small recess 29 recessed toward the side farther from the worm wheel 3 in the first direction in a portion on the other side in the third direction (the left side in Figs. 5 and 8). The auxiliary holding portion 24 has a first inclined surface portion 30 and a second inclined surface portion 31 between the large recess 28 and the small recess 29, in that order from the side of the large recess 28. Each of the first inclined surface portion 30 and the second inclined surface portion 31 is formed by a flat surface inclined toward the other side in the third direction and toward the side farther from the worm wheel 3 in the first direction. As shown in FIG. 6, the inclination angle θ2 of the second inclined surface portion 31 with respect to the third direction is larger than the inclination angle θ1 of the first inclined surface portion 30 with respect to the third direction (θ2>θ1). In this example, the length of the second inclined surface portion 31 is longer than the length of the first inclined surface portion 30 when viewed from the second direction. The large recess 28 and the first inclined surface portion 30 are connected by a first corner portion 32. The first inclined surface portion 30 and the second inclined surface portion 31 are connected by a second corner portion 33. The second inclined surface portion 31 and the small recess 29 are connected by a third corner portion 34. That is, the first corner 32, the second corner 33, and the third corner 34 are located in this order in the direction away from the pin 36 arranged in the large recess 28 in the third direction (leftward in Figs. 5, 6, and 8), and the first corner 32, the second corner 33, and the third corner 34 are located in this order in the direction away from the worm wheel 3 in the first direction (upward in Figs. 5, 6, and 8). The first corner 32, the second corner 33, and the third corner 34 are portions that come into contact with the elastic biasing means 6 during operation.

[0059] 5 and 8, the locking portion 25 is a portion for circumferentially engaging a portion of the elastic clamping means 7. In the example shown in the figures, the locking portion 25 is configured by a semi-cylindrical concave surface.

[0060] In this example, the worm accommodating portion 9 has a recess 35 that opens into a portion of the step surface 22 that is located inside the large recess 28. 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 used to hold the elastic biasing means 6.

[0061] The elastic biasing means 6 biases the support bearing 5, which corresponds to the inner diameter side member, toward the worm wheel 3. This suppresses backlash between the wheel teeth 12 and the worm teeth 13, thereby suppressing the generation of teeth rattle noise. Note that when implementing the present disclosure, an external fitting member that is fitted onto the support bearing 5 can also be used as the inner diameter side member. In other words, the elastic biasing means can bias the external fitting member toward the worm wheel.

[0062] In this example, the elastic biasing means 6 exhibits non-linear spring characteristics in which the spring constant increases as the amount of deflection in the first direction increases when the elastic biasing means 6 is installed in a place of use.

[0063] For this reason, in this example, the elastic biasing means 6 has a configuration as shown in Figs. 11(a) to 11(e) and uses a metallic biasing leaf spring 37 arranged as shown in Fig. 5.

[0064] As shown in Figures 11(a) to 11(e), the biasing leaf spring 37 comprises a rectangular, flat band plate portion 38 having a large aspect ratio, a base plate portion 39 bent at an obtuse angle from the edge portion of the base end side of the longitudinal direction of the band plate portion 38 (right side of Figure 11(a)) to one side in the thickness direction (lower side of Figure 11(a)), and a folded plate portion 40 folded back 180 degrees to one side in the thickness direction from the edge portion of the tip side of the longitudinal direction of the band plate portion 38 (left side of Figure 11(a)), with the tip side portion being overlapped with the tip side portion of the band plate portion 38.

[0065] The biasing leaf spring 37 is entirely disposed inside the worm housing portion 9. Specifically, as shown in FIG. 5, the biasing leaf spring 37 is disposed on the side farther from the worm wheel 3 in the first direction in the portion between the outer circumferential surface of the support bearing 5 and the retaining portion 21 provided on the inner circumferential surface of the worm housing portion 9 corresponding to the outer diameter side member. More specifically, the biasing leaf spring 37 is disposed inside the auxiliary retaining portion 24 constituting the retaining portion 21. Note that, when implementing the present disclosure, an inner fitting member that is fitted into the worm housing portion can also be used as the outer diameter side member. That is, the inner circumferential surface of the inner fitting member can also be provided with the retaining portion 21.

[0066] In this example, the biasing leaf spring 37 is installed at the location of use and is biased against the surrounding parts when the worm reduction gear 1 is in an unloaded state, 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 tip of the worm 4 are zero. , arranged as follows:

[0067] The base end of the base plate portion 39 is in elastic contact with the bottom of the large recess 28 constituting the auxiliary holding portion 24. One side surface in the thickness direction of the connection portion between the band plate portion 38 and the base plate portion 39, that is, the concave side surface (lower side surface in FIG. 5), is in elastic contact with the outer circumferential surface of the pin 36. The other side surface in the thickness direction (upper side surface in FIG. 5) of the intermediate portion of the band plate portion 38 is in elastic contact with the first corner portion 32 constituting the auxiliary holding portion 24. One side surface in the thickness direction (lower side surface in FIG. 5) of the tip portion of the folded plate portion 40 is in elastic contact with the end portion of the outer circumferential surface of the support bearing 5 that is farther from the worm wheel 3 in the first direction. The band plate portion 38 is not in contact with the second corner portion 33 and the third corner portion 34, and there are gaps between the band plate portion 38 and the second corner portion 33 and the third corner portion 34.

[0068] In this state, the biasing leaf spring 37 elastically biases the support bearing 5 toward the worm wheel 3, with the contact portion with the first corner portion 32 serving as a fulcrum S and the contact portion with the outer circumferential surface of the support bearing 5 serving as a load point P (see FIG. 13(a)). In this example, the biasing leaf spring 37 is held at the location of use by frictional force acting on the contact portion with the worm housing portion 9 and the pin 36. The load point P is located at approximately the same position as the third corner portion 34 of the auxiliary retaining portion 24 in the third direction.

[0069] In this example, when the torque transmitted from the worm 4 to the worm wheel 3 increases, the meshing reaction force F1 or F2 applied to the tip of the worm 4 increases, and the pressing force applied from the support bearing 5 to the load point P of the biasing leaf spring 37 increases, and the deflection amount of the biasing leaf spring 37 (strip plate portion 38) in the first direction increases. Figs. 13(a) to 13(d) are schematic diagrams showing how the deflection amount increases. In this example, when the deflection amount of the biasing leaf spring 37 in the first direction increases, the elastic contact position of the biasing leaf spring 37 with the auxiliary retaining portion 24 changes as shown in the order of Figs. 13(a) to 13(d). That is, the position of the fulcrum S of the biasing leaf spring 37 changes stepwise in the direction approaching the load point P. As a result, the spring constant of the biasing leaf spring 37 increases stepwise as shown in Fig. 14 (conceptual diagram).

[0070] More specifically, in this example, when the amount of deflection of the biasing leaf spring 37 in the first direction increases, the elastic contact position of the biasing leaf spring 37 with the auxiliary retaining portion 24 changes from the first corner portion 32 (one location) shown in Figure 13(a) to the first corner portion 32 and the second corner portion 33 (two locations) shown in Figure 13(b), then to the second corner portion 33 (one location) shown in Figure 13(c), and then to the second corner portion 33 and the third corner portion 34 (two locations) shown in Figure 13(d).

[0071] 13(a), in a state in which the biasing leaf spring 37 is in elastic contact only with the first corner portion 32 (one location), the fulcrum S of the biasing leaf spring 37 becomes the contact portion with the first corner portion 32. The spring constant of the biasing leaf spring 37 in this state (first stage) is relatively small, as shown in FIG. 14. In this example, during normal operation in which no large meshing reaction force acts on the worm, the amount of deflection of the biasing leaf spring 37 in the first direction is kept small, and the biasing leaf spring 37 is always in contact with the first corner portion 32.

[0072] 13(b), in a state in which the biasing leaf spring 37 is in elastic contact with the first corner 32 and the second corner 33 (two locations), and in a state in which the biasing leaf spring 37 is in elastic contact only with the second corner 33 (one location), as shown in Fig. 13(c), the fulcrum S of the biasing leaf spring 37 becomes the contact portion with the second corner 33. The spring constant of the biasing leaf spring 37 in this state (second stage) is relatively large as shown in Fig. 14, specifically, it is larger than in the first stage. .

[0073] As shown in FIG. 13(d), when the biasing leaf spring 37 elastically contacts the second corner portion 33 and the third corner portion 34 (two locations), the biasing leaf spring 37 can no longer increase the amount of deflection in the first direction any further, and reaches a so-called bottoming out state.

[0074] That is, in this example, the spring constant of the biasing leaf spring 37 changes in two stages according to the amount of deflection in the first direction of the biasing leaf spring 37. Specifically, the spring constant of the biasing leaf spring 37 increases from a relatively small value (first stage) to a relatively large value (second stage) as the amount of deflection in the first direction of the biasing leaf spring 37 increases.

[0075] Therefore, the torque transmitted from the worm 4 to the worm wheel 3 increases, and the amount of deflection of the biasing leaf spring 37 in the first direction increases, so that the spring constant of the biasing leaf spring 37 can be set to a relatively large value (second stage) just before the biasing leaf spring 37 hits the third corner portion 34 as shown in Fig. 13(d). Therefore, the force of the collision can be efficiently suppressed by the large elasticity of the biasing leaf spring 37. This makes it possible to efficiently suppress the generation of collision noise.

[0076] Furthermore, by reversing the rotational direction of the worm 4 from the state shown in Fig. 13(d), the spring constant of the biasing leaf spring 37 can be set to a relatively small value (first stage) just before the deflection amount of the biasing leaf spring 37 in the first direction decreases to the state shown in Fig. 13(a). Therefore, the force of the collision between the wheel teeth 12 and the worm teeth 13 caused by reversing the rotational direction of the worm 4 can be efficiently suppressed by reducing the biasing force of the biasing leaf spring 37. This makes it possible to efficiently suppress the generation of teeth-clash noise between the wheel teeth 12 and the worm teeth 13.

[0077] In this embodiment, the corners that serve as the fulcrum S of the biasing leaf spring 37 are the first corner 32 and the second corner 33. However, when implementing this disclosure, the number of the corners can be increased from that of this embodiment, thereby changing the spring constant of the biasing leaf spring 37 to three or more stages. In addition, the portion of the auxiliary retainer 24 with which the biasing leaf spring 37 elastically contacts, for example, the portion between the first corner 32 and the second corner 33, or the portion between the second corner 33 and the third corner 34, can be made into a convex curved surface. By adopting such a configuration, the biasing leaf spring 37 curves along the convex curved surface as the deflection amount of the biasing leaf spring 37 in the first direction increases. Therefore, the position of the fulcrum S of the biasing leaf spring 37 can be continuously changed in a direction approaching the load point P, and the spring constant of the biasing leaf spring 37 can be continuously increased.

[0078] When implementing the present disclosure, the spring characteristics of the elastic biasing means do not have to be nonlinear, but may be linear. When implementing the present disclosure and using a leaf spring as the elastic biasing means, the shape of the leaf spring may be different from that of the present example. When implementing the present disclosure, various springs other than leaf springs, such as coil springs, or rubber, may be used as the elastic biasing means.

[0079] The elastic holding means 7 has a pair of holding leaf springs 41 arranged on both sides of the support bearing 5 in the third direction in a portion between the outer circumferential surface of the support bearing 5 corresponding to the inner diameter side member and the retaining portion 21 provided on the inner circumferential surface of the worm accommodating portion 9 corresponding to the outer diameter side member. Each of the pair of holding leaf springs 41 exhibits nonlinear spring characteristics in which the spring constant increases with an increase in the amount of deflection in a direction including a component of the third direction (in this example, the amount of deflection in the third direction).

[0080] In this example, as shown in Fig. 12(a) to Fig. 12(e), the elastic holding means 7 is configured by a metal leaf spring having an overall notched cylindrical shape (C-shape). A pair of holding leaf springs 41 configure both circumferential side portions of the elastic holding means 7. The elastic holding means 7 has a circumferential connection portion 42 that circumferentially connects the circumferential ends of the pair of holding leaf springs 41 that are closer to the worm wheel 3 to each other. In Fig. 12(a), the dashed line α indicates the boundary between the pair of holding leaf springs 41 and the circumferential connection portion 42.

[0081] In this example, each of the pair of sandwiched leaf springs 41 has a first portion 43 that constitutes a circumferential middle portion and a second portion 44 that constitutes each of the circumferential both side portions. In FIG. 12(a), a dashed line β indicates the boundary between the first portion 43 and the second portion 44.

[0082] The first part 43 has a partial cylindrical shape curved along the outer peripheral surface of the support bearing 5. Each of the second parts 44 has a partial cylindrical shape curved along the outer peripheral surface of the support bearing 5 and is smoothly continuous with the first part 43. That is, when viewed from the axial direction of the worm 4, the first part 43 and the second parts 44 are connected such that the circumferential ends of their radially inner surfaces share a common tangent line, and the circumferential ends of their radially outer surfaces share a common tangent line.

[0083] The radius of curvature R1 of the radially inner surface of the first part 43 in the free state is smaller than the radius of curvature Rs (see FIG. 5) of the outer peripheral surface of the support bearing 5 (R1 < Rs). The radius of curvature R2 of the radially inner surface of the second part 44 in the free state is larger than the radius of curvature R1 of the radially inner surface of the first part 43 in the free state (R2 > R1). In this example, the radius of curvature R2 is made equal to the radius of curvature Rs of the outer peripheral surface of the support bearing 5 (R2 = Rs). However, when implementing the present disclosure, the radius of curvature R2 can also be made slightly larger or smaller than the radius of curvature Rs.

[0084] In this example, residual stress is applied to the first part 43 corresponding to the portion that contacts the holding portion 21 provided on the inner peripheral surface of the worm housing portion 9 in each of the pair of clamping plate springs 41 that constitute the clamping plate springs 41. This makes it easier to ensure the durability of the first part 43, which is more likely to have a large amount of elastic deformation during operation compared to other parts. When implementing the present disclosure, the application of the residual stress can also be omitted.

[0085] The circumferential connection portion 42 has a partially cylindrical shape curved along the outer circumferential surface of the support bearing 5, and is smoothly continuous with each of the sandwiched leaf springs 41 constituting the pair of sandwiched leaf springs 41. That is, the sandwiched leaf springs 41 and the circumferential connection portion 42 are connected so that the circumferential ends of their radially inner surfaces have a common tangent when viewed from the axial direction of the worm 4, and are connected so that the circumferential ends of their radially outer surfaces have a common tangent. In this example, the radius of curvature Rj of the radially inner surface of the circumferential connection portion 42 in the free state is set to be equal to the radius of curvature R2 of the radially inner surface of the second portion 44 in the free state (Rj=R2). Note that, when implementing the present disclosure, the circumferential connection portion may be omitted, that is, the pair of sandwiched leaf springs 41 may be separated from each other.

[0086] In this example, the elastic clamping means 7 has a circumferential positioning piece 45 which engages with the worm receiving portion 9 in the circumferential direction.

[0087] In this example, two circumferential positioning pieces 45 are provided at a circumferential middle portion of the circumferential connecting portion 42, spaced apart from each other in the circumferential direction. The two circumferential positioning pieces 45 are provided so as to protrude 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 provided by forming an H-shaped through hole in the circumferential middle portion of the circumferential connecting portion 42 radially outward. The circumferential positioning piece 45 is a portion for circumferentially positioning the elastic clamping means 7 and preventing rotation by engaging with the locking portion 25 of the holding portion 21 in the circumferential direction.

[0088] In addition, when the present disclosure is implemented and circumferential positioning pieces are provided, the shape, number, circumferential position, etc. of the circumferential positioning pieces may be different from those in the present example. In addition, the circumferential positioning pieces may be provided so as to circumferentially engage with an inner diameter side member that is a support bearing or an outer fitting member that is fitted onto the support bearing.

[0089] In this example, the circumferential connection portion 42 has a low-rigidity connection portion 60 in a circumferential intermediate portion, specifically, in a portion between two circumferential positioning pieces 45, which has a lower rigidity than both circumferential side portions of the circumferential connection portion 42 and the pair of sandwiched leaf springs 41, which are the remaining portions in the circumferential direction. In this example, in order to reduce the rigidity of the low-rigidity connection portion 60, a rectangular through hole 61 is formed in the circumferential portion where the low-rigidity connection portion 60 is located, thereby reducing the section modulus of the circumferential portion. The low-rigidity connection portion 60 is provided to reduce the interaction of the pair of sandwiched leaf springs 41 by reducing the deflection resistance of the low-rigidity connection portion 60. When implementing the present disclosure, a low-rigidity portion can be provided in at least a portion of the circumferential direction of the circumferential connection portion. It is also possible to omit providing a low-rigidity portion in the circumferential connection portion.

[0090] In addition, when implementing the present disclosure, means for reducing the rigidity of the low rigidity portion may be adopted that is different from the present example, such as reducing the plate thickness of the low rigidity portion.

[0091] In this example, the elastic clamping means 7 has an axial positioning piece 46 which engages with the support bearing 5 in the axial direction.

[0092] In this example, two axial positioning pieces 46 are provided circumferentially spaced apart on each of the pair of sandwiching leaf springs 41. More specifically, the axial positioning pieces 46 are provided so as to bend radially inward from one axial end of a circumferentially intermediate portion of each of the second portions 44.

[0093] In addition, when the present disclosure is implemented and axial positioning pieces are provided, the shape, number, circumferential position, axial position, etc. of the axial positioning pieces may be different from those in this example. Also, the axial positioning pieces may be provided so as to axially engage with an inner diameter side member made of a worm housing portion or an inner fitting member fitted into the worm housing portion.

[0094] 5, the elastic clamping means 7 is disposed between the outer circumferential surface of the support bearing 5 and a retaining portion 21 provided on the inner circumferential surface of the worm accommodating portion 9. Specifically, the elastic clamping means 7 is fitted onto the outside of the support bearing 5, and is disposed inside a main retaining portion 23 constituting the retaining portion 21.

[0095] In this state, the two circumferential positioning pieces 45 provided on the elastic clamping means 7 are disposed inside the locking portion 25 constituting the holding portion 21, and are engaged with the locking portion 25 in the circumferential direction. As a result, the elastic clamping means 7 is positioned in the circumferential direction, and the pair of clamping leaf springs 41 constituting the elastic clamping means 7 are disposed on both sides in the third direction in the portion between the outer circumferential 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 locking portion 25. This allows for slight displacement of the two circumferential positioning pieces 45 relative to the locking portion 25 in the first direction and the third direction, which is necessary during operation. In this example, the first direction dimensions of the two circumferential positioning pieces 45 are set so that the amount of penetration of the two circumferential positioning pieces 45 into the engagement portion 25 in the first direction is always sufficient, regardless of whether the elastic clamping means 7 moves in the first direction together with the tip end of the worm 4 and the support bearing 5 during operation.

[0096] Each of the axial positioning pieces 46 provided on the elastic clamping means 7 abuts against a side surface on one axial side of the outer ring 18 of the support bearing 5, thereby engaging with the outer ring 18 in the axial direction. In this way, the elastic clamping means 7 is positioned in the axial direction with respect to the support bearing 5.

[0097] In this example, the first portion 43 (more specifically, the circumferential center portion of the first portion 43), which is the circumferential middle portion of each of the pair of clamping leaf springs 41, intersects with the third direction straight line Lx, which is a straight line that passes through the center O4 of the worm 4 and extends in the third direction, when viewed from the second direction.

[0098] More specifically, each of the sandwiching leaf springs 41 constituting the pair of sandwiching leaf springs 41 is disposed as follows relative to the surrounding parts when the meshing reaction forces F1, F2 are zero.

[0099] The circumferential center of the radially outer surface of the first portion 43 contacts the flat portion 26 constituting the main holder 23 at point Q1 shown in FIG. 15(a). The circumferentially outer end of the radially inner surface of each of the second portions 44, i.e., the end of the second portion 44 farther from the first portion 43 in the circumferential direction, contacts the outer circumferential surface of the support bearing 5 at point Q2 shown in FIG. 15(a). The radially inner side surface of the first portion 43 does not contact the outer circumferential surface of the support bearing 5, and a gap exists between the radially inner side surface of the first portion 43 and the outer circumferential surface of the support bearing 5. The radially outer side surface of each of the second portions 44 does not contact the main holder 23, and a gap exists between the radially outer side surface of each of the second portions 44 and the main holder 23. That is, the clamping leaf spring 41 contacts the main holding portion 23 at only one point (point Q1 shown in FIG. 15(a)), and contacts the outer circumferential surface of the support bearing 5 at only two points (point Q2 shown in FIG. 15(a)). When the meshing reaction forces F1 and F2 are zero, an initial deflection in the third direction occurs in each of the clamping leaf springs 41 constituting the pair of clamping leaf springs 41. This prevents the support bearing 5 from rattling in the third direction inside the main holding portion 23, even when the meshing reaction forces F1 and F2 are zero. However, from the viewpoint of keeping the frictional force of the pair of clamping leaf springs 41 against the flat portion 26 small when the meshing reaction forces F1 and F2 are zero, it is preferable to set the initial deflection in the third direction as small as possible.

[0100] Of the pair of sandwiched leaf springs 41, one sandwiched leaf spring 41 located on the other side in the third direction (the left side in FIG. 5) has a second portion 44 on the side remote from the worm wheel 3 that intersects with a radial line L1 including a vector of the meshing reaction force F1 when viewed from the second direction. Of the pair of sandwiched leaf springs 41, the other sandwiched leaf spring 41 located on one side in the third direction (the right side in FIG. 5) has a second portion 44 on the side remote from the worm wheel 3 that intersects with a radial line L2 including a vector of the meshing reaction force F2 when viewed from the second direction.

[0101] In the above state, the elastic clamping means 7 clamps the support bearing 5 from both sides in the third direction with the pair of clamping leaf springs 41. This suppresses the momentum of the tip of the worm 4 when it moves in the third direction, thereby suppressing the generation of abnormal noise.

[0102] That is, in the structure of this example, in order to allow the tip of the worm 4 to move toward and away from the worm wheel 3 in the first direction, the main holder 23 arranged around the support bearing 5 is formed to be slightly larger than the outer circumferential surface of the support bearing 5. Therefore, the tip of the worm 4 can also move in the third direction.

[0103] On the other hand, the meshing reaction forces F1 and F2 acting on the worm 4 include not only a component in the first direction but also a force in the third direction. The direction of the third direction component is reversed depending on the rotation direction of the worm 4. In addition, when a machine (in this example, an automobile) incorporating the worm reduction gear 1 of this example is operated, if vibration is input in reverse to the worm reduction gear 1 from a portion (in this example, a tire) located downstream of the worm reduction gear 1 in terms of the power transmission direction, the third direction component of the vibration is transmitted to the worm 4. For this reason, if the tip end of the worm 4 is allowed to move in the third direction without resistance, the third direction components of the meshing reaction forces F1 and F2 acting on the worm 4 and the third direction component of the vibration input in reverse to the worm 4 will cause the outer circumferential surface of the support bearing 5 to collide with the main holder 23 with force in the third direction, which is likely to generate abnormal noises such as harsh hitting sounds and rattle sounds.

[0104] 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 in the third direction by a pair of clamping leaf springs 41 constituting the elastic clamping means 7. This suppresses the generation of abnormal noise by suppressing the momentum of the tip end of the worm 4 when it moves in the third direction.

[0105] In this example, when the torque transmitted from the worm 4 to the worm wheel 3 increases, and thus the meshing reaction force F1 or F2 applied to the tip of the worm 4 increases, the pressing force in the third direction acting on the sandwiched leaf spring 41 located on one side (the left side in FIG. 5) or the other side (the right side in FIG. 5) in the third direction from the support bearing 5 increases. This increases the amount of deflection of the sandwiched leaf spring 41 in the third direction. FIGS. 15(a) to 15(c) are diagrams that typically show how the amount of deflection increases.

[0106] In this example, as the deflection amount of the sandwiched leaf spring 41 in the third direction increases, the distance W in the first direction between the contact portions (points Q2) of the radially inner surfaces of the two second portions 44 with the outer peripheral surface of the support bearing 5 decreases continuously as shown in the order of Figs. 15(a) to 15(c). As shown in Fig. 15(c), when the first portion 43 of the sandwiched leaf spring 41 is sandwiched between the flat portion 26 of the main holder 23 and the outer peripheral surface of the support bearing 5, the sandwiched leaf spring 41 cannot increase the deflection amount in the third direction any more, and reaches a so-called bottoming out state. That is, in this example, until the bottoming out state is reached, the distance W decreases continuously as the deflection amount of the sandwiched leaf spring 41 in the third direction increases, and the spring constant of the sandwiched leaf spring 41 increases continuously as shown in Fig. 16 (conceptual diagram). That is, as described above, the clamping leaf spring 41 exhibits a nonlinear spring characteristic in which the spring constant increases as the deflection in the third direction increases. In particular, in the example of FIG. 16, when the horizontal axis represents the deflection in the third direction and the vertical axis represents the load, a graph representing the nonlinear spring characteristic is downwardly convex, and the slope increases as the deflection in the third direction increases. Note that the spring characteristic is not limited to the example of FIG. 16, and any nonlinear characteristic can be applied. For example, the spring characteristic may be represented by a graph that is upwardly convex, and the slope decreases as the deflection in the third direction increases. Alternatively, the spring characteristic may be represented by a graph that combines a plurality of curves and / or straight lines.

[0107] Therefore, in the structure of this example, the biasing action of the biasing leaf spring 37 on the tip of the worm 4 and the support bearing 5 can be made smooth, and the force of collision between components in the third direction around the tip of the worm 4 can be easily suppressed.

[0108] That is, since the spring constant of the clamping leaf spring 41 is small at a stage where the deflection in the third direction is small (low load region), the frictional force acting between the clamping leaf spring 41 and the flat portion 26 of the main holding portion 23 and the frictional force acting between the clamping leaf spring 41 and the outer circumferential surface of the support bearing 5 are small at this stage. This makes it possible to smooth the movement of the tip end of the worm 4 and the support bearing 5 in the first direction. This in turn makes it possible to smooth the biasing action of the biasing leaf spring 37 on the tip end of the worm 4 and the support bearing 5.

[0109] On the other hand, the spring constant of the clamping leaf spring 41 becomes large at the stage where the deflection in the third direction becomes large (high load region), so the momentum of the movement of the support bearing 5 in the third direction just before it hits the bottom as shown in Fig. 15(c) can be efficiently suppressed by the large elasticity of the clamping leaf spring 41. This makes it possible to efficiently suppress the generation of impact noise when hitting the bottom.

[0110] Furthermore, by reversing the rotational direction of the worm 4 from the state shown in Fig. 15(c), the spring constant of the clamping leaf spring 41 can be reduced just before the deflection amount in the third direction of the clamping leaf spring 41 decreases to the state shown in Fig. 15(a). Therefore, the force of the collision between the wheel teeth 12 and the worm teeth 13 caused by reversing the rotational direction of the worm 4 can be efficiently suppressed by reducing the biasing force of the clamping leaf spring 41. This makes it possible to efficiently suppress the generation of teeth-clash noise between the wheel teeth 12 and the worm teeth 13.

[0111] In this example, the radius of curvature of the radially inner surface of the second portion 44 constituting both circumferential sides of the clamping leaf spring 41 is constant, but when implementing this disclosure, the radius of curvature of the radially inner surface of the second portion can also be changed stepwise or continuously in the circumferential direction.

[0112] In this example, the portions of the main holding portion 23 with which the pair of clamping leaf springs 41 make elastic contact are formed of flat portions 26 extending in the first direction. Therefore, as shown in Figs. 17(a) to 17(c), even if the elastic clamping means 7 moves in the first direction, the deflection amount of the pair of clamping leaf springs 41 in the third direction, i.e., the distance W, does not change, and the spring constant of each of the clamping leaf springs 41 making up the pair of clamping leaf springs 41 can be kept constant. Therefore, stable spring characteristics can be ensured for the elastic biasing means 6 and the elastic clamping means 7. When implementing the present disclosure, the length of the pair of flat portions 26 in the first direction can be made smaller than the stroke amount by which the elastic clamping means 7 can move in the first direction together with the tip 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, the elastic contact portion of the clamping leaf spring 41 with the main holder 23 can move from the flat portions 26 onto the cylindrical surface portion 27. Even in this case, the spring constant of the clamping leaf spring 41 can be kept constant while the contact portion is present on the flat portions 26.

[0113] In this example, the radial lines L1 and L2 including the vectors of the meshing reaction forces F1 and F2 intersect with a circumferential portion of the cylindrical surface portion 27 of the main holding portion 23 when viewed from the second direction. In addition, the second portion 44 of the sandwiching leaf spring 41 located on the other side (left side in FIG. 5) in the third direction, among the pair of sandwiching leaf springs 41, on the side farther from the worm wheel 3, intersects with the radial line L1 including the vector of the meshing reaction force F1 when viewed from the second direction. In addition, the second portion 44 of the sandwiching leaf spring 41 located on one side (right side in FIG. 5) in the third direction, among the pair of sandwiching leaf springs 41, on the side farther from the worm wheel 3, intersects with the radial line L2 including the vector of the meshing reaction force F2 when viewed from the second direction.

[0114] For this reason, even if the support bearing 5 tends to move in the direction of the meshing reaction force F1 during operation, the momentum of the movement can be suppressed by the elasticity of the second portion 44 of the sandwiching leaf spring 41 located on one side in the third direction, which is on the side farther from the worm wheel 3. Furthermore, the meshing reaction force F1 can be supported by the cylindrical surface portion 27 of the main holder 23.

[0115] Even if the support bearing 5 tends to move in the direction of the meshing reaction force F2 during operation, the momentum of the movement can be suppressed by the elasticity of the second portion 44 of the sandwiching leaf spring 41 located on the other side in the third direction, which is on the side farther from the worm wheel 3. Furthermore, the meshing reaction force F2 can be supported by the cylindrical surface portion 27 of the main holding portion 23.

[0116] In this example, as shown in Fig. 5, the circumferential range of the cylindrical surface portion 27 of the main holding portion 23 is restricted to intersect with the radial lines L1 and L2 including the vectors of the meshing reaction forces F1 and F2, but since 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, the circumferential edge portion E2 on the radial line L2 side (right side in Fig. 5) with respect to the third direction of the cylindrical surface portion 27 can be disposed closer to the worm wheel 3 with respect to the first direction (lower side in Fig. 5) than the circumferential edge portion E1 on the radial line L1 side (left side in Fig. 5). For this reason, in this example, the large recess 28, which is a portion where the pin 36 is disposed, of the auxiliary holding portion 24 that protrudes outward from the end portion on the side farther from the worm wheel 3 with respect to the first direction (upper side in Figs. 5 and 8) of the main holding portion 23 is disposed on the radial line L2 side with respect to the third direction (right side in Fig. 5). This allows the large recess 28 to be disposed closer to the worm wheel 3 in the first direction than when the large recess 28 is disposed on the radial line L1 side (left side in FIG. 5) in the third direction. In other words, by adopting such an arrangement, the width dimension in the first direction of the entire holding portion 21 including the main holding portion 23 and the sub holding portion 24 can be minimized.

[0117] (2) Electric power steering device As shown in FIG. 1, 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 52a, 52b, an intermediate shaft 53, a steering gear unit 54, the worm reduction gear 1 and the electric motor 11 of this example.

[0118] The steering wheel 49 is supported and fixed to the rear end of the steering shaft 50. The steering shaft 50 is rotatably supported inside a steering column 51 supported on the vehicle body. The front end of the steering shaft 50 is connected to a pinion shaft 55 of a steering gear unit 54 via a rear universal joint 52a, an intermediate shaft 53, and a front universal joint 52b. 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, the pair of universal joints 52a and 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 that meshes with the pinion shaft 55. As a result, a pair of tie rods 56 are pushed and pulled, and a steering angle according to the amount of rotation of the steering wheel 49 is applied to the left and right steered wheels.

[0119] The electric power steering device 48 of this example is configured to reduce the force required by the driver to operate the steering wheel 49 by increasing the auxiliary power of the electric motor 11 by the worm reduction gear 1 and then applying it to the front end of the steering shaft 50.

[0120] When implementing the present disclosure, the worm reduction gear 1 and the electric motor 11 can be disposed at a position where auxiliary power is applied to the pinion shaft or rack shaft of the steering gear unit.

[0121] [Example 2] A second example of the embodiment of the present disclosure will be described with reference to FIGS.

[0122] In this example, the specific structure of the elastic clamping means 7a is different from that of the first example.

[0123] Specifically, in a free state, the elastic clamping means 7a in this example has a cylindrical shape with a discontinuous portion (gap) 57 at one location in the circumferential direction, as shown in Figures 18(a) and 18(b), and the radius of curvature of the inner surface is constant around the entire circumference.

[0124] More specifically, for each of the sandwiched leaf springs 41a constituting the pair of sandwiched leaf springs 41a, the radial inner surface of the first portion 43a located in the circumferential middle portion is smoothly continuous with the radial inner surface of the second portion 44a located on both circumferential sides, and the radius of curvature R1 of the radial inner surface of the first portion 43a and the radius of curvature R2 of the radial inner surface of the second portion 44a are equal to each other (R1=R2). In addition, the radial inner surface of each of the sandwiched leaf springs 41a constituting the pair of sandwiched leaf springs 41a and the radial inner surface of the circumferential connecting portion 42a are smoothly continuous with each other, and the radii of curvature R1, R2 of the radial inner surface of the sandwiched leaf spring 41a and the radius of curvature Rj of the radial inner surface of the circumferential connecting portion 42a are equal to each other (R1=R2=Rj). Moreover, the circumferential ends of the pair of sandwiched leaf springs 41a opposite the circumferential connection parts 42a are butted against each other, and the butted parts form discontinuous parts 57. However, when implementing the present disclosure, the discontinuous parts 57 may be gap parts where the circumferential ends of the pair of sandwiched leaf springs 41a opposite the circumferential connection parts 42a are circumferentially separated, or overlapping parts where the circumferential ends of the pair of sandwiched leaf springs 41a opposite the circumferential connection parts 42a overlap in the radial direction.

[0125] In this example, in the free state of the elastic clamping means 7a, the radii of curvature R1, R2, and Rj of the radially inner surfaces of the first portion 43a, the second portion 44a, and the circumferential connecting portion 42a are smaller than the radius of curvature Rs (see FIG. 5) of the outer circumferential surface of the support bearing 5 (R1=R2=Rj). <Rs)。

[0126] In this example, each of the second portions 44a has a low-rigidity leaf spring portion 58 at its circumferential end on the first portion 43a side, the low-rigidity leaf spring portion 58 having a lower rigidity than the remaining circumferential portion and the first portion 43a. 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.

[0127] In addition, when implementing the present disclosure, means for reducing the rigidity of the low rigidity portion may be adopted that is different from the present example, such as reducing the plate thickness of the low rigidity portion.

[0128] The elastic clamping means 7a is fitted onto the support bearing 5 (see FIG. 5) by elastically expanding its inner diameter, and is disposed inside the main holding portion 23 (see FIG. 5) constituting the holding portion 21. In this state, a pair of clamping leaf springs 41a constituting the elastic clamping means 7a are disposed on both sides in the third direction in the portion between the outer circumferential surface of the support bearing 5 and the main holding portion 23.

[0129] In this example, each of the pair of sandwiched leaf springs 41a is disposed relative to the surrounding parts as shown in FIG. 19(a) when the meshing reaction forces F1 and F2 are zero. That is, the circumferential center of the radially outer surface of the first part 43a contacts the flat part 26 constituting the main holding part 23 at point Q1. The circumferentially outer end of each of the second parts 44a, i.e., the end of the second part 44a farther from the first part 43a in the circumferential direction, contacts the outer circumferential surface of the support bearing 5 at point Q2. The radially inner side surfaces of each of the first part 43a and the second part 44a do not contact the outer circumferential surface of the support bearing 5, and there is a gap between the radially inner side surfaces of each of the first part 43a and the second part 44a and the outer circumferential surface of the support bearing 5. The radial outer surface of each of the second portions 44a does not contact the main holding portion 23, and a gap exists between the radial outer surface of each of the second portions 44a and the main holding portion 23. That is, the sandwiched leaf spring 41a contacts the main holding portion 23 at only one point (point Q1), and contacts the outer circumferential surface of the support bearing 5 at only two points (point Q2).

[0130] In this example, when the meshing reaction force F1 or F2 increases, the pressing force in the third direction acting on the sandwiching leaf spring 41a located on one side or the other side in the third direction from the support bearing 5 increases. This increases the amount of deflection of the sandwiching leaf spring 41a in the third direction. Figures 19(a) to 19(c) are diagrams that typically show how the amount of deflection increases.

[0131] In this example, as the amount of deflection of the clamping leaf spring 41a in the third direction increases, the distance W in the first direction between the contact portions of the two second portions 44a with the outer peripheral surface of the support bearing 5 decreases stepwise as shown in the order of Figures 19(a) to 19(c).

[0132] That is, in the stage where the deflection amount in the third direction is small (low load region), the distance W does not change much as shown in FIG. 19(a) and FIG. 19(b). In contrast, in the stage where the deflection amount in the third direction is relatively large (high load region), as shown in FIG. 19(c), each of the two second parts 44a comes into contact with the outer peripheral surface of the support bearing 5 at point Q3 not only at the outer circumferential end but also at the inner circumferential end, i.e., the low-rigidity leaf spring portion 58. This is because, as shown in an exaggerated manner in FIG. 20, the low-rigidity leaf spring portion 58 is curved more than other portions and approaches the outer peripheral surface of the support bearing 5. In the state shown in FIG. 19(c), the distance between the contact portions of the low-rigidity leaf spring portions 58 of the two second parts 44a with the outer peripheral surface of the support bearing 5 is the distance W, and the distance W is suddenly reduced compared to the state shown in FIG. 19(a) and FIG. 19(b). In other words, in this example, the spring constant of the sandwiching leaf spring 41a changes in two stages as the deflection amount in the third direction increases, thereby exhibiting a nonlinear spring characteristic.

[0133] In this example, the elastic clamping means 7a has a simple shape in which the radius of curvature of the inner peripheral surface is constant over the entire circumference in a free state, so that the manufacturing cost of the elastic clamping means 7a can be reduced. The other configurations and effects of the second example are the same as those of the first example.

[0134] [Example 3] A third example of the embodiment of the present disclosure will be described with reference to FIG.

[0135] In this example, a pair of clamping leaf springs 41 constituting the elastic clamping means 7b are disposed farther from the worm wheel 3 in the first direction than in the first example. Specifically, in this example, of the pair of clamping leaf springs 41, a first portion 43 (more specifically, a circumferential center portion of the first portion 43) which is a circumferential intermediate portion of one of the pair of clamping leaf springs 41 located on the other side (left side in FIG. 21) in the third direction intersects with a radial line L1 including a vector of the meshing reaction force F1 when viewed from the second direction. Also, of the pair of clamping leaf springs 41, a first portion 43 (more specifically, a circumferential center portion of the first portion 43) which is a circumferential intermediate portion of the other of the pair of clamping leaf springs 41 located on the one side (right side in FIG. 21) in the third direction intersects with a radial line L2 including a vector of the meshing reaction force F2 when viewed from the second direction.

[0136] In this example, one of the sandwiched leaf springs 41 exhibits a nonlinear spring characteristic in which the spring constant increases with an increase in the amount of deflection in a direction including a component in the third direction (specifically, the amount of deflection in the direction of the meshing reaction force F1).The other sandwiched leaf spring 41 exhibits a nonlinear spring characteristic in which the spring constant increases with an increase in the amount of deflection in a direction including a component in the third direction (specifically, the amount of deflection in the direction of the meshing reaction force F2).

[0137] 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 elasticity of one of the sandwiching leaf springs 41. Also, when the support bearing 5 tends to move in the direction of the meshing reaction force F2, the momentum of the movement can be efficiently suppressed by the elasticity of the other sandwiching leaf spring 41.

[0138] In this example, main holding portion 23 constituting holding portion 21 does not have a pair of flat portions extending in the first direction at both ends in the third direction, and the entire circumferential direction is composed of cylindrical surface portion 27. The other configurations and effects of the third example are similar to those of the first example.

[0139] The present disclosure can be implemented by appropriately combining the structures of the above-described embodiments to the extent that no contradiction occurs.

[0140] This application is based on a Japanese patent application (Patent Application No. 2022-123209) filed on August 2, 2022, the contents of which are incorporated by reference into this application. [Explanation of symbols]

[0141] 1 Worm reducer 2. Housing 3 Worm Wheel 4. Warm 5 Support bearing 6 Elastic biasing means 7, 7a, 7b Elastic clamping means 8 Wheel storage area 9 Worm housing 10 Lid 11 Electric motor 12 Wheel Teeth 13 worm teeth 14 Ball bearing 15 Output shaft 16 Coupling 17 Inner Circle 18 Outer ring 19 balls 20 Small diameter cylindrical surface part 21 Holding part 22 Step surface 23 Main holding part 24 Sub holding part 25 Locking part 26 Plane section 27 Cylindrical surface part 28 Large recess 29 Small recess 30 First slope section 31 2nd slope section 32 1st corner 33 Second corner 34 Third corner 35 Recess 36 pin 37 Leaf spring 38 Band part 39 Circuit Board 40 Folding plate section 41, 41a Clamping leaf spring 42, 42a Circumferential connection part 43, 43a Part 1 44, 44a 2nd part 45 Circumferential positioning piece 46 Axial positioning piece 47 Retaining ring 48 Electric power steering device 49 Steering Wheel 50 Steering shaft 51 Steering column 52a, 52b Universal joint 53 Intermediate shaft 54 Steering gear unit 55 Pinion shaft 56 Tie rod 57 Discontinuities 58 Low rigidity leaf spring 59 Through hole 60 Low rigidity connection 61 Through hole

Claims

1. a housing having a wheel accommodating portion and a worm accommodating portion having a central axis that is twisted with respect to the central axis of the wheel accommodating portion and an axially intermediate portion that opens into the wheel accommodating portion; a worm wheel having wheel teeth on an outer circumferential surface and rotatably supported inside the wheel accommodating portion; a worm having worm teeth on an outer circumferential 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; an elastic biasing means for biasing an inner diameter side member, which is the support bearing or an outer fitting member fitted onto the support bearing, toward the worm wheel; an elastic clamping means having a pair of clamping leaf springs arranged on both sides of the inner diameter side member in a third direction perpendicular to both a first direction which is a biasing direction by the elastic biasing means and a second direction which is an axial direction of the worm accommodating portion, in a portion between an outer peripheral surface of the inner diameter side member and an inner peripheral surface of an outer diameter side member which is the worm accommodating portion or an inner fitting member fitted into the worm accommodating portion; A worm reducer, wherein each of the pair of clamping leaf springs exhibits nonlinear spring characteristics in which the spring constant increases as the amount of deflection in a direction including a component of the third direction increases.

2. 2. The worm reducer according to claim 1, wherein each of the pair of clamping leaf springs has a circumferential middle portion in contact with the inner peripheral surface of the outer diameter side member and each of both circumferential side portions in contact with the outer peripheral surface of the inner diameter side member, and further wherein as the amount of deflection in a direction including a component of the third direction increases, a distance between the contact portions of the circumferential side portions with respect to the outer peripheral surface of the inner diameter side member decreases, thereby increasing the spring constant.

3. 3. The worm reducer according to claim 2, wherein a circumferential middle portion of each of the pair of clamping leaf springs intersects with a third direction straight line Lx that passes through a center of the worm and extends in the third direction when viewed from the second direction.

4. 4. The worm reducer according to claim 3, wherein a portion of the inner surface of the outer diameter side member that comes into contact with a circumferential middle portion of each of the pair of clamping leaf springs is configured by a flat portion extending in the first direction.

5. a circumferential intermediate portion of one of the pair of clamping leaf springs intersects, as viewed from a second direction, a radial 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 wheel teeth when the worm rotates in a predetermined direction; 3. The worm reducer according to claim 2, wherein a circumferential middle portion of the other clamping leaf spring constituting the pair of clamping leaf springs intersects with a radial line L2 including a vector of a meshing reaction force F2 applied to the worm from the meshing portion when the worm rotates in a direction opposite to the predetermined direction, as viewed from a second direction.

6. In a target clamped leaf spring, which is at least one of the pair of clamped leaf springs, the circumferential intermediate portion is configured by a first portion having a partially cylindrical shape curved along an outer circumferential surface of the inner diameter side member, Each of the circumferential side portions has a partially cylindrical shape curved along an outer circumferential surface of the inner diameter side member, and is configured with a second portion smoothly continuing to the first portion, a radius of curvature of a radially inner surface of the first portion in a free state is smaller than a radius of curvature of an outer peripheral surface of the inner diameter side member; The worm reduction gear according to claim 2 , wherein a radius of curvature of a radially inner surface of the second portion in a free state is larger than a radius of curvature of a radially inner surface of the first portion in a free state.

7. In a target clamped leaf spring, which is at least one of the pair of clamped leaf springs, the circumferential intermediate portion is configured by a first portion having a partially cylindrical shape curved along an outer circumferential surface of the inner diameter side member, Each of the circumferential side portions has a partially cylindrical shape curved along an outer circumferential surface of the inner diameter side member, and is configured with a second portion smoothly continuing to the first portion, the radii of curvature of radially inner surfaces of the first portion and the second portion in a free state are equal to each other and smaller than the radius of curvature of the outer circumferential surface of the inner diameter side member; The worm reducer according to claim 2 , wherein each of the second portions has a low-rigidity leaf spring portion at a circumferential end portion on the first portion side, the low-rigidity leaf spring portion having a lower rigidity than a remaining portion in the circumferential direction and the first portion.

8. Each of the pair of clamping leaf springs is a target clamping leaf spring, the elastic clamping means has a circumferential connection portion that circumferentially connects circumferential ends of the pair of clamping leaf springs that are closer to the worm wheel to each other, the circumferential connection portion has a partially cylindrical shape curved along an outer circumferential surface of the inner diameter side member and smoothly continues to the pair of sandwiching leaf springs, The worm reduction gear according to claim 7 , wherein a radius of curvature of a radially inner surface of the circumferential connection portion in a free state is equal to a radius of curvature of a radially inner surface of each of the first portion and the second portion in a free state.

9. 2. The worm reduction gear according to claim 1, wherein the elastic clamping means has a circumferential connecting portion that circumferentially connects circumferential ends of the pair of clamping leaf springs that are closer to the worm wheel to each other.

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

11. 2. The worm reduction gear according to claim 1, wherein each of the pair of sandwiched leaf springs has a residual stress applied to a portion that contacts the inner circumferential surface of the outer diameter side member.

12. 2. The worm reduction gear according to claim 1, wherein the elastic clamping means has a circumferential positioning piece that circumferentially engages with the inner diameter side member or the outer diameter side member.

13. 2. The worm reduction gear according to claim 1, wherein the elastic clamping means has an axial positioning piece that axially engages with the inner diameter side member or the outer diameter side member.

14. 2. The worm reduction gear according to claim 1, wherein the nonlinear spring characteristic is represented by a graph that is downwardly convex with the horizontal axis representing the deflection in the third direction and the vertical axis representing the load, and in which the slope increases as the deflection in the third direction increases.

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