JP7255354B2 - Worm reducer and electric assist device - Google Patents

Description

The present invention relates to a worm reduction gear including a worm and a worm wheel, and an electric assist device including the worm reduction gear.

2. Description of the Related Art In a steering apparatus for automobiles, when a driver rotates a steering wheel, the rotation of the steering wheel is transmitted to an input shaft of a steering gear unit via a steering shaft and an intermediate shaft. The rotation of the input shaft is converted into linear motion of the rack shaft of the steering gear unit, thereby pushing and pulling the pair of tie rods. As a result, a steering angle corresponding to the amount of operation of the steering wheels is imparted to the pair of steered wheels.

Japanese Patent Application Laid-Open No. 2004-306898 (Patent Document 1) discloses an electric power steering apparatus that uses an electric motor as an auxiliary power source to reduce the force required for a driver to operate a steering wheel. An electric power steering device includes a worm reduction gear for increasing the torque of an electric motor. The worm speed reducer includes a housing, a worm wheel rotatably supported by the housing and having wheel teeth on the outer peripheral surface thereof, and a worm gear rotatably supported by the housing and meshing with the wheel teeth on the outer peripheral surface. Equipped with a worm. The torque of the electric motor is increased by being transmitted to the worm wheel via the worm, and then applied as auxiliary power to steering force transmission members such as the steering shaft, the input shaft of the steering gear unit, or the rack shaft. This reduces the force required by the driver to operate the steering wheel.

By the way, in a worm speed reducer, there is unavoidable backlash at the meshing portion between the wheel teeth and the worm teeth due to the dimensional errors and assembly errors of the parts constituting the worm speed reducer. Due to the existence of the backlash, when the direction of rotation of the steering wheel is changed, an offensive rattling noise may be generated at the meshing portion.

Japanese Patent Laying-Open No. 2004-306898 describes a structure in which the tip of the worm is biased toward the worm wheel in order to suppress the generation of tooth rattling noise at the meshing portion between the wheel teeth and the worm teeth. ing. The structure described in Japanese Patent Application Laid-Open No. 2004-306898 includes a preload pad that is fitted on the tip of the worm and arranged to be movable relative to the worm wheel, and a housing that is installed between the preload pad and the housing. Equipped with a torsion coil spring. The torsion coil spring is elastically deformed, and the elastic restoring force of the torsion coil spring urges the preload pad toward the worm wheel. As a result, the backlash at the meshing portion between the wheel teeth and the worm teeth is suppressed, and the occurrence of rattling noise is suppressed.

Japanese Patent Application Laid-Open No. 2004-306898

In the structure disclosed in Japanese Patent Application Laid-Open No. 2004-306898, the outer peripheral surface of the preload pad fitted to the tip of the worm and the inner surface of the housing are arranged so that the tip of the worm can move farther and nearer with respect to the worm wheel. A gap is provided over the entire circumference between the peripheral surface. Therefore, the tip of the worm can also move in the radial direction perpendicular to the direction of the worm wheel, based on the presence of the gap. On the other hand, if movement in such a direction can be suppressed, the operability of the steering wheel can be further improved.

In view of the circumstances as described above, the present invention provides a worm reduction gear in which the tip of the worm is biased toward the worm wheel, wherein The purpose is to realize a structure that can suppress the movement of

A worm reduction gear according to the present invention includes a housing, a worm wheel rotatably supported by the housing and having wheel teeth on an outer peripheral surface thereof, and a worm wheel rotatably supported by the housing and meshing with the wheel teeth on the outer peripheral surface. a worm having worm teeth, a bearing externally fitted on the tip of the worm, a holder internally fitted with the bearing, and arranged inside the housing so as to be capable of moving farther and nearer with respect to the worm wheel; and a spring member that elastically biases the holder toward the worm wheel.
The holder includes a pair of inner spring holding portions that are circumferentially spaced apart from the worm wheel relative to the central axis of the holder, and the spring members that are arranged more than the pair of inner spring holding portions. an outer spring retainer disposed on the far side from the worm wheel in the first direction, which is the urging direction of the holder, and between the pair of inner spring retainers in the circumferential direction.
The spring member includes a base having radially outer surfaces in contact with the outer spring holding portions, and circumferentially extending from both circumferential ends of the base, and having radially inner surfaces contacting the pair of inner spring holding portions. a pair of arms that are in elastic contact with each other, and ends of the pair of arms that are farther from the base, and whose radial outer surfaces are in elastic contact with the inner peripheral surface of the housing. and a pair of pressed portions.

The holder includes a pair of holder-side first regulating surfaces arranged at two locations on both sides of an imaginary plane that includes the central axis of the worm and is parallel to the first direction, and a pair of holder-side second regulating surfaces arranged at two locations on the side farther from the worm wheel than the pair of holder-side first regulating surfaces and on both sides of the virtual plane; The housing has a pair of housing-side first regulation surfaces facing the pair of holder-side first regulation surfaces and a pair of housing-side second regulation surfaces facing the pair of holder-side second regulation surfaces. A configuration having a regulating surface can be employed.
In this case, preferably, the sum of the gaps existing between the pair of holder-side first restricting surfaces and the pair of housing-side first restricting surfaces is equal to the pair of holder-side second restricting surfaces. It is made smaller than the sum of the gaps existing between the pair of housing-side second regulation surfaces.
Preferably, at least one of the holder-side first regulating surface and the holder-side second regulating surface exists over the entire width of the holder in the axial direction.

A configuration may be employed in which the base has a recess that is recessed radially inward, and the recess is engaged with the outer spring retainer.

A configuration may be employed in which the holder has an axial direction restricting portion that restricts the axial displacement of the spring member with respect to the holder.

A configuration may be adopted in which each of the pair of arm portions is bent at an obtuse angle from both ends of the base portion in the circumferential direction toward the side closer to the worm wheel in the first direction.

A configuration may be employed in which the radially outer surface of the pressing portion is a convex curved surface.

A configuration may be employed in which the spring member is connected to the ends of the pair of pressing portions on the far side from the base portion and has a pair of locking portions having concave radial outer surfaces.
In this case, when the holder narrows the opening angle between the portions of the pair of arm portions farther from the base portion, the inner side of the concave surface that is the radially outer side surface of each of the pair of locking portions A configuration having an axial engagement hole at a location aligned with the space can be adopted.

A configuration may be adopted in which the engagement hole axially penetrates the holder.

A configuration in which the spring member is a leaf spring can be adopted.

An electric assist device of the present invention includes an electric motor and a worm speed reducer that increases the power of the electric motor and transmits it to a steering force transmission member. The worm speed reducer is the worm speed reducer of the present invention.

According to the worm speed reducer and the electric power assist device of the present invention, it is possible to suppress the movement of the tip portion of the worm in the radial direction perpendicular to the direction in which the worm wheel moves farther and nearer.

FIG. 1 is a partially cutaway side view showing a column-assist type electric power steering apparatus incorporating an electric assist apparatus according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line AA of FIG. FIG. 3 is a partially cutaway perspective view of the electric assist device of the first embodiment of the present invention as seen from the front. FIG. 4 is a view corresponding to the right side of FIG. 3, shown in a partially exploded state. FIG. 5 is an enlarged view of the B portion in FIG. 6 is a cross-sectional view taken along line CC of FIG. 5. FIG. FIG. 7 is a cross-sectional view taken along line DD of FIG. 8 is a cross-sectional view taken along line EE of FIG. 6. FIG. FIG. 9 is a perspective view of a holder, a leaf spring, and a tip side bearing of the first example of the embodiment of the invention. FIG. 10 is a front view of the holder, the leaf spring, and the tip side bearing of the first embodiment of the present invention, viewed from the axial direction. 11 is a view seen from the right side of FIG. 10. FIG. FIG. 12 is a perspective view of the holder of the first example of the embodiment of the invention. FIG. 13 is a front view of the holder of the first example of the embodiment of the invention as seen from the axial direction. FIG. 12 is a perspective view of a leaf spring according to the first embodiment of the invention. FIG. 15 is a characteristic diagram showing the effect of leaf springs on the worm angle and worm torque in relation to the first embodiment of the present invention. FIG. 16 is a diagram corresponding to FIG. 6 regarding the second example of the embodiment of the present invention. FIG. 17 is a diagram corresponding to FIG. 6 regarding the third example of the embodiment of the present invention. FIG. 18 is a diagram corresponding to FIG. 9 regarding the third example of the embodiment of the present invention. FIG. 19 is a diagram corresponding to FIG. 6 regarding the fourth example of the embodiment of the present invention. FIG. 20 is a diagram corresponding to FIG. 7 regarding the fourth example of the embodiment of the present invention. FIG. 21 is a partially cut-away perspective view of a portion of the electric assist device of the fifth embodiment of the present invention, viewed from the front. Figure 22 is a view similar to Figure 21, shown in a partially exploded state; FIG. 23 is a diagram corresponding to FIG. 6 regarding the fifth example of the embodiment of the present invention. FIG. 24 is a diagram corresponding to FIG. 7 regarding the fifth example of the embodiment of the present invention. 25 is a cross-sectional view taken along line FF of FIG. 23. FIG. FIG. 26 is a perspective view of a holder, a leaf spring, and a tip side bearing of a fifth example of the embodiment of the invention.

[First example of embodiment]
A first example of an embodiment of the present invention will be described with reference to FIGS. 1 to 15. FIG.
This example is an example in which the electric power assist device of the present invention is applied to a column assist type electric power steering device.

As shown in FIG. 1 , in the electric power steering device 1 , when the driver rotates the steering wheel 2 , the rotation of the steering wheel 2 is transmitted to the input shaft 4 of the steering gear unit 3 . The rotation of the input shaft 4 is converted into linear motion of the rack shaft (not shown) of the steering gear unit 3, thereby pushing and pulling the pair of tie rods 5. As shown in FIG. As a result, a steering angle corresponding to the amount of operation of the steering wheel 2 is applied to the pair of steered wheels. The steering wheel 2 is supported and fixed to the rear end of a steering shaft 6 , and the steering shaft 6 is rotatably supported inside a steering column 7 . The front end of the steering shaft 6 is connected to the rear end of an intermediate shaft 9 via a universal joint 8a, and the front end of the intermediate shaft 9 is connected to the input shaft 4 via another universal joint 8b. .

The electric power steering device 1 includes an electric assist device 10 that applies auxiliary power to the steering shaft 6 in order to reduce the force required for the driver to operate the steering wheel 2 . The electric assist device 10 includes an electric motor 11 and a worm reduction gear 12 . That is, the electric assist device 10 increases the torque of the output shaft 13 of the electric motor 11 by the worm speed reducer 12, and then applies it to the steering shaft 6 as auxiliary power.

As shown in FIGS. 2 to 8, the worm reduction gear 12 is rotatably supported by a housing 14, a worm wheel 16 having wheel teeth 15 on its outer peripheral surface, and the housing 14. A worm 18 having worm teeth 17 meshing with the wheel teeth 15 on its outer peripheral surface, a tip side bearing 20 externally fitted to the tip of the worm 18, a holder 21 internally fitted with the tip side bearing 20, and a holder A plate spring 22 that is a spring member that elastically biases the worm wheel 16 toward the worm wheel 16 is provided.

In the following description, the direction in which the plate spring 22 biases the holder 21, that is, the extension direction of the vector representing the force P (see FIGS. 6 and 7) with which the plate spring 22 biases the holder 21 (see FIG. 2 7) is defined as the "first direction", and a first imaginary plane including the central axis O _W of the worm 18 and parallel to the first direction is defined as S ₁ (see FIGS. 6 and 7), A direction perpendicular to the first imaginary plane _S1 (front and back directions in FIGS. 2 and 5, left and right directions in FIGS. 6 and 7) is defined as a “second direction”, includes the central axis _OW of the worm 18, and is the second direction. A second virtual plane perpendicular to the first virtual plane S ₁ is defined as S ₂ (see FIGS. 6 and 7).

The housing 14 is made of, for example, light metal such as aluminum alloy or magnesium alloy, or synthetic resin (polymer material) such as polyamide (PA), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT). or made of reinforced synthetic resin in which reinforcing fibers (reinforcing materials) such as glass fiber, carbon fiber, and aramid fiber are mixed into the synthetic resin, and the wheel housing portion 23 housing the worm wheel 16 and the worm 18 are housed. and a worm housing portion 24 which is provided with a worm housing. The central axis of the worm housing portion 24 is arranged at a twisted position with respect to the central axis of the wheel housing portion 23 . Such a housing 14 is coupled and fixed to the front end portion of the steering column 7 so that the central axis of the wheel accommodating portion 23 and the central axis of the steering column 7 are coaxial.

The worm housing portion 24 has a cylindrical shape and is open on both axial sides and has an axial intermediate portion that opens into the wheel housing portion 23 . An opening on one side in the axial direction of the worm housing portion 24 is closed by a lid 25 , and an opening on the other side in the axial direction of the worm housing portion 24 is closed by an electric motor 11 coupled and fixed to the housing 14 . It's leaking.

Regarding the worm housing portion 24, the worm 18, and the holder 21, one axial side is the right side in FIGS. 2 to 5, and the other axial side is the left side in FIGS. Regarding the worm 18, one side in the axial direction is the distal side, and the other side in the axial direction is the proximal side.

The worm housing portion 24 has a holder holding portion 26 on the inner peripheral surface of one end in the axial direction. The holder holding portion 26 has a sub-holding portion 28 which is recessed radially outward at the end (upper end in FIGS. 5 to 7) farther from the worm wheel 16, and the remaining portion of the sub-holding portion 28 deviated from the sub-holding portion 28. A portion has a main holding portion 27 which is a cylindrical surface centered on the central axis of the worm housing portion 24 .

The main holding portion 27 of the holder holding portion 26 has housing-side first regulating surfaces 29 at both end portions in the second direction. Further, the sub-holding portion 28 of the holder holding portion 26 has housing-side second restricting surfaces 30 on a pair of inner side surfaces facing each other in the second direction. The housing-side second regulation surface 30 is a flat surface orthogonal to the second direction, that is, a surface parallel to the first imaginary plane _S1 .

The worm wheel 16 has wheel teeth 15 on its outer peripheral surface. The worm wheel 16 is supported and fixed around the front end portion of the steering shaft 6 rotatably supported inside the wheel accommodating portion 23 so as to rotate together with the steering shaft 6 . In this example, the worm wheel 16 is made of a metal such as steel, and is made of polyamide (PA), polyphenylene sulfide (PPS), polycarbonate (PC), or polyacetal (POM) around a disk-shaped inner wheel element 31. or made of a reinforced synthetic resin obtained by mixing reinforcing fibers such as glass fiber, carbon fiber, and aramid fiber into the synthetic resin, and an outer wheel element 32 having wheel teeth 15 on the outer peripheral surface is coupled and fixed. .

The worm 18 is made of a metal such as steel, has worm teeth 17 on the outer peripheral surface of the axially intermediate portion, and has a columnar small diameter portion 33 at the tip to which the tip side bearing 20 is fitted. The worm 18 is rotatably supported inside the worm housing portion 24 by the proximal side bearing 19 and the distal side bearing 20 with the worm teeth 17 meshing with the wheel teeth 15 of the worm wheel 16 .

The proximal side bearing 19 is a ball bearing and supports the proximal side portion of the worm 18 on the other side in the axial direction so as to be rotatable with respect to the worm housing portion 24 . Also, the base end bearing 19 supports the worm 18 in a swingable manner with respect to the worm housing portion 24 . A base end portion, which is the other axial end portion of the worm 18 , is connected to the output shaft 13 of the electric motor 11 via a coupling 34 . The coupling 34 enables transmission of torque between the output shaft 13 and the worm 18 and swinging of the worm 18 with respect to the output shaft 13 . The method of connecting the output shaft 13 and the worm 18 is not particularly limited as long as the torque can be transmitted between the output shaft 13 and the worm 18 and the worm 18 can swing with respect to the output shaft 13. For example, A connection method by spline engagement can also be adopted.

The tip side bearing 20 is a ball bearing, and includes an inner ring 35 fitted and fixed to a small diameter portion 33 provided at the tip of the worm 18, and an outer ring 36 arranged coaxially with the inner ring 35 around the inner ring 35. , and a plurality of balls 37, each of which is a rolling element, disposed between the inner ring raceway provided on the outer peripheral surface of the inner ring 35 and the outer ring raceway provided on the inner peripheral surface of the outer ring 36 so as to be free to roll. Prepare. Note that, for example, a roller bearing, a needle bearing, or the like can also be used as the tip side bearing.

As shown in FIGS. 5 to 13, the holder 21 has an annular shape as a whole, fits and holds the distal bearing 20 inside, and is arranged inside a holder holding portion 26 of the housing 14 . The holder 21 is made of, for example, a light metal such as an aluminum alloy or a magnesium alloy, or a synthetic resin such as polyamide (PA), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). It is made of reinforced synthetic resin in which reinforcing fibers such as glass fiber, carbon fiber, and aramid fiber are mixed into synthetic resin.

The holder 21 has a holder cylinder portion 38 , a holder flange portion 39 and a holder extension portion 40 .

The holder tubular portion 38 is configured in a substantially cylindrical shape, and has a bearing holding portion 41 for internally fitting and holding the outer ring 36 of the tip end side bearing 20 on the inner peripheral surface of the intermediate portion in the axial direction. The holder tubular portion 38 has a small diameter side projecting portion 42 projecting radially outward at the end portion of the other side portion in the axial direction and the intermediate portion that is farther from the worm wheel 16 in the first direction. The small-diameter side projecting portion 42 has a rectangular shape when viewed in the axial direction, and has a pair of inner It has a spring retainer 45 . Each of the inner spring holding portions 45 is a cylindrical convex surface that smoothly connects the tip surface 43 and the side surface 44 . The holder tubular portion 38 is positioned symmetrically with respect to the first virtual plane S1 and on the farther side from _the worm wheel 16 than the second virtual plane _S2 , among the outer peripheral surfaces of the other side portion and the intermediate portion in the axial direction. Notches 46 that are recessed radially inward are provided at two locations.

The holder flange portion 39 has a substantially annular shape, and protrudes radially outward from one axial side portion of the holder cylindrical portion 38 over the entire circumference. The holder flange portion 39 has an outer peripheral shape that is substantially similar to the holder holding portion 26 and slightly smaller than the holder holding portion 26 .

Such a holder flange portion 39 has a flat non-contact portion 47 that does not come into contact with the main holding portion 27 of the holder holding portion 26 at the end portion of the outer peripheral surface that is closer to the worm wheel 16 in the first direction. have. Moreover, the holder flange portion 39 has a pair of convex portions 48 projecting radially outward at both end portions in the second direction. A radially outer end surface (tip surface) of each projection 48 serves as a holder-side first regulation surface 49 . The first holder-side restricting surface 49 is a cylindrical convex surface with the same radius of curvature as the first housing-side restricting surface 29 . However, the radius of curvature of the first holder-side regulation surface 49 can be smaller or larger than the radius of curvature of the first housing-side regulation surface 29 .

Further, the holder flange portion 39 has a large-diameter side projecting portion 50 projecting radially outward at the end portion on the far side from the worm wheel 16 in the first direction. The large-diameter side protrusion 50 has a rectangular shape when viewed from the axial direction, and has a width dimension in the second direction larger than that of the small-diameter side protrusion 42 . In addition, the large-diameter-side projecting portion 50 has holder-side second restricting surfaces 51 on a pair of outer side surfaces facing opposite sides in the second direction. The holder-side second regulation surface 51 is a flat surface perpendicular to the second direction. In addition, the holder flange portion 39 does not contact the corner portion present at the radially inner edge portion of the housing-side second regulation surface 30 at the portion adjacent to the radially inner side of the holder-side second regulation surface 51 . It has an escape recess 52 to keep it in place.

The holder extending portion 40 is configured in a semi-cylindrical shape and extends from the second direction central portion of the large diameter side projecting portion 50 toward the other side in the axial direction. The holder extending portion 40 has an outer spring holding portion 53, which is a semi-cylindrical convex surface, on a portion of the radial inner surface excluding the base end, which is one axial end. The holder extending portion 40 bulges outward from the outer spring holding portion 53 in the radial direction around the center axis of curvature of the outer spring holding portion 53 at a portion adjacent to the base end side of the outer spring holding portion 53 . It has a semi-circular bulging portion 54 .

The holder 21 holds the outer ring 36 of the distal end side bearing 20 in the bearing holding portion 41 and is disposed inside the holder holding portion 26 , and the large diameter side projecting portion 50 serves as a secondary portion of the holder holding portion 26 . It is arranged inside the holding portion 28 , and the other portion is arranged inside the main holding portion 27 of the holder holding portion 26 .

Leaf spring 22 has a baseless trapezoidal shape, as shown in FIGS. Further, the plate spring 22 is assembled between the holder 21 and the holder holding portion 26 as shown in FIG. Regarding the plate spring 22, the terms “axial direction” and “radial direction” refer to the “axial direction” and “radial direction” regarding the holder 21 unless otherwise specified. Regarding the plate spring 22 , “radially outward” refers to the side farther from the central axis of the holder 21 , and “radial inner” refers to the side closer to the central axis of the holder 21 .

The leaf spring 22 is made of, for example, steel such as rolled steel or stainless steel, non-ferrous metal such as copper alloy, nickel alloy or titanium alloy, polyamide (PA), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), It is made of reinforced synthetic resin in which reinforcing fibers such as glass fiber, carbon fiber and aramid fiber are mixed into synthetic resin such as polybutylene terephthalate (PBT). When the leaf spring 22 is made of a reinforced synthetic resin, the spring constant of the leaf spring 22 can be finely adjusted by adjusting the amount of reinforcing fiber mixed.

The leaf spring 22 has a base portion 55 that is a base portion, a pair of arm plate portions 56 that are arm portions, and a pair of curved plate portions 57 that are pressing portions. The substrate portion 55 has a rectangular flat plate shape extending in the second direction. Each of the pair of arm plate portions 56 has a rectangular flat plate shape extending in the circumferential direction from both ends of the substrate portion 55 in the second direction. It is in the shape of a rectangular flat plate that is bent at an obtuse angle by the same angle toward the side near the worm wheel 16 with respect to the first direction. The pair of curved plate portions 57 are connected to the tip portions of the pair of arm plate portions 56 (end portions opposite to the substrate portion 55), and each has a partial cylindrical shape with a convex curved surface on the radial outer surface. is.

Such a plate spring 22 is assembled between the holder 21 and the holder holding portion 26 , and the second direction central portion of the radial outer surface of the substrate portion 55 is elastically brought into contact with the outer spring holding portion 53 . The base end side portions of the radially inner side surfaces of the pair of arm plate portions 56 are in elastic contact with the pair of inner spring holding portions 45, and the radially outer side portions of the pair of curved plate portions 57 are in contact with each other. The convex curved surface, which is the side surface, is in elastic contact with the portion on the side farther from the worm wheel 16 than the second imaginary plane S ₂ among the two side portions of the main holding portion 27 in the second direction. That is, in this state, the pair of arm plate portions 56 are elastically bent and deformed. Due to the elastic restoring force of the pair of arm plate portions 56 thus bent and deformed, an elastic biasing force P directed toward the worm wheel 16 side in the first direction is applied to the holder 21 .

That is, in a state in which the leaf spring 22 is assembled between the holder 21 and the holder holding portion 26, an elastic force acting on the pair of inner spring holding portions 45 from the radial inner side surfaces of the pair of arm plate portions 56 is applied. The pressing force includes a first directional component (component of force) directed toward the worm wheel 16 side in the first direction and a second directional component (component of force) directed in a direction toward each other in the second direction. I'm in. Then, the first direction component of this is applied to the holder 21 as the biasing force P. As shown in FIG.

In addition, only the portion of the one axial end surface of the leaf spring 22 corresponding to the second direction central portion of the base plate portion 55 is axially aligned with the radially inner end portion of the bulging portion 54 that is the axial direction restricting portion. , and the remaining portion is not in contact with the holder 21 . Grease is applied to contact portions between the radially outer side surfaces of the pair of curved plate portions 57 and the main holding portion 27 .

Further, in a state in which torque is not transmitted from the worm 18 to the worm wheel 16, the holder 21 is held at a neutral position by the plate spring 22 inside the holder holding portion 26, and the outer peripheral surface of the holder 21 is held by the holder holding portion 26. 26 , and a gap exists over the entire circumference between the outer peripheral surface of the holder 21 and the holder holding portion 26 . Further, in this state, the gap existing between the outer peripheral surface of the holder 21 and the holder holding portion 26 includes the gap existing between the holder-side first regulation surface 49 and the housing-side first regulation surface 29, and A gap existing between the holder-side second regulation surface 51 and the housing-side second regulation surface 30 is smaller than the gap existing in the remaining portion. Furthermore, in this state, a gap exists between the holder-side first restricting surface 49 and the housing-side first restricting surface 29, and exists between the holder-side second restricting surface 51 and the housing-side second restricting surface 30. is smaller than the gap to be In other words, the sum of the gaps existing between the pair of holder-side first regulating surfaces 49 and the pair of housing-side first regulating surfaces 29 is the sum of the pair of holder-side second regulating surfaces 51 and the pair of It is smaller than the sum of the gaps existing with the housing-side second regulation surface 30 .

When assembling the worm reduction gear 12 of this example, before inserting the holder 21 inside the holder holding portion 26, the plate spring 22 is attached to the holder 21 as shown in FIGS. Specifically, the second direction central portion of the radial outer surface of the base plate portion 55 of the plate spring 22 is elastically brought into contact with the outer spring holding portion 53, and the radial inner surfaces of the pair of arm plate portions 56 are brought into contact with each other. The proximal side is brought into elastic contact with a pair of inner spring retainers 45 . A portion of the one axial end surface of the leaf spring 22 corresponding to the second direction central portion of the base plate portion 55 is brought into axial contact with or closely opposed to the radial inner end portion of the bulging portion 54 .

The opening angle (θ') between the pair of arm plate portions 56 in this state is the same as that between the pair of arms in the single state (free state) of the plate spring 22 indicated by the imaginary line (two-dot chain line) in FIG. It is larger than the opening angle (θ) between the plate portions 56 (θ'>θ). That is, the plate spring 22 is attached to the holder 21 in a state of being elastically deformed so that the opening angle between the pair of arm plate portions 56 is larger than that of the single arm plate portion 56 . As a result, the second direction central portion of the radially outer side surface of the base plate portion 55 elastically contacts the outer spring holding portion 53, and the base end side portions of the radially inner side surfaces of the pair of arm plate portions 56 are brought into contact with each other. It is in elastic contact with the pair of inner spring retainers 45 . Furthermore, in this state, the radially outer side surfaces of the pair of curved plate portions 57 of the leaf spring 22 protrude radially outward from the outer peripheral surface of the holder flange portion 39, and the amount of protrusion is is larger than the amount of protrusion in the assembled state.

Next, the holder 21 to which the plate spring 22 is attached as described above, together with the tip end side bearing 20 internally fitted and held in the holder 21, is moved in the axial direction of the worm accommodating portion 24 of the housing 14 as shown in FIGS. It is inserted inside the holder holding portion 26 from the opening on one side. As a result, the large-diameter side projecting portion 50 and the holder extending portion 40 of the holder 21 are arranged inside the sub-holding portion 28, and the remaining portion of the holder 21 is arranged inside the main holding portion 27, The inner ring 35 of the bearing 20 is externally fitted and fixed to the small diameter portion 33 provided at the tip of the worm 18 .

In this example, the operation of inserting the holder 21 with the leaf springs 22 attached thereto from the opening on one side in the axial direction of the worm housing portion 24 into the inside of the holder holding portion 26 is performed by one pair of the leaf springs 22. By elastically narrowing the opening angle of the tip side portion of the arm plate portion 56, the radial outer side surfaces of the pair of curved plate portions 57 of the plate spring 22 are radially outward from the outer peripheral surface of the holder flange portion 39. Do it in a state where it does not protrude. After the insertion, when the opening angle of the tip side portions of the pair of arm plate portions 56 is elastically restored a little, the radial outer surfaces of the pair of curved plate portions 57 move toward the second direction of the main holding portion 27 . It is in a state of elastic contact with the portion of the both side portions farther from the worm wheel 16 than the second imaginary plane _S2 .

In the electric power assist device 10 of the present embodiment as described above, when the electric motor 11 is energized and torque is transmitted from the worm 18 to the worm wheel 16, the meshing portion between the wheel teeth 15 and the worm teeth 17 meshes with the worm 18. A reaction force is added. The meshing reaction force includes not only the component in the first direction (component of force) but also the component in the second direction (component of force). The direction of the second direction component of the meshing reaction force is opposite to each other when the worm 18 rotates in a predetermined direction and when the worm 18 rotates in a direction opposite to the predetermined direction. That is, when torque is transmitted between the worm 18 and the worm wheel 16, as shown in FIGS. 6 and 7, the meshing reaction force F ₁ or F ₂ is added.

In the electric power steering apparatus 1 of the present embodiment as described above, the elastic restoring force of each of the pair of arm plate portions 56 constituting the leaf spring 22 causes the holder 21 to move toward the worm wheel 16 in the first direction. A directed elastic biasing force P is applied. Therefore, when the biasing force P is applied to the tip of the worm 18 via the holder 21 and the tip side bearing 20, the worm teeth 17 are biased toward the wheel teeth 15, and the worm teeth 17 and the wheel teeth 15 are biased. The backlash of the meshing part with is suppressed.

In addition, in the assembled state of the worm reduction gear 12, the position of the worm 18 in the first direction is affected by dimensional errors and assembly errors of the members that make up the worm reduction gear 12, and the resin material that makes up the housing 14 and the outer wheel element 32. It changes due to temperature changes, dimensional changes due to water absorption, wear of the worm teeth 17 and wheel teeth 15, and the like. In this example, the amount of elastic deformation (amount of bending) of the pair of arm plate portions 56 of the leaf spring 22 changes in accordance with such a change, thereby causing the meshing portion between the worm tooth 17 and the wheel tooth 15 to back up. The frictional force of the meshing portion can be maintained at an appropriate level while suppressing lash.

In addition, in this example, not only are the radial outer surfaces of the pair of curved plate portions 57 of the leaf spring 22 elastically contacting both side portions of the main holding portion 27 in the second direction, but also one of the leaf springs 22 The radial inner side surfaces of the pair of arm plate portions 56 are in elastic contact with the pair of inner spring holding portions 45 of the holder 21 . In this state, elastic pressing forces acting on the pair of inner spring holding portions 45 from the radially inner side surfaces of the pair of arm plate portions 56 are applied to the first direction, respectively, toward the worm wheel 16 side in the first direction. It includes not only directional components, but also second directional components each oriented towards each other with respect to a second direction. Therefore, it is possible to prevent the tip of the worm 18 from moving (rattling) in the second direction based on such a second direction component.

In this way, in this example, one leaf spring 22 can be used to perform the above-described biasing and suppression of movement in the second direction. The number of parts can be reduced as compared with the case of carrying out.

In this example, when torque is transmitted between the worm 18 and the worm wheel 16, the first direction component of the meshing reaction force _F1 or _F2 applied to the worm 18 causes the tip of the worm 18 to move. , when moving away from the worm wheel 16 in the first direction, the movement can be permitted by increasing the amount of elastic deformation of the pair of arm plate portions 56 of the leaf spring 22 .

On the other hand, when the tip of the worm 18 moves in the second direction due to the second direction component of the meshing reaction force _F1 or _F2 applied to the worm 18, the pair of arm plate portions of the plate spring 22 The movement can be permitted by increasing the amount of elastic deformation of the arm plate portion 56 positioned forward in the direction of the movement.

Further, in this example, when torque is not transmitted from the worm 18 to the worm wheel 16, the gap that exists between the outer peripheral surface of the holder 21 and the holder holding portion 26 is between the holder side first regulation surface 49 and the housing. The gap existing between the side first restricting surface 29 and the gap existing between the holder side second restricting surface 51 and the housing side second restricting surface 30 are smaller than the gaps existing in the remaining portions. It's becoming Furthermore, in this state, a gap exists between the holder-side first restricting surface 49 and the housing-side first restricting surface 29, and exists between the holder-side second restricting surface 51 and the housing-side second restricting surface 30. is smaller than the gap to be

Therefore, when the tip of the worm 18 moves in the first direction and the second direction due to the meshing reaction force F ₁ (the first direction component and the second direction component), X ₁ , the holder-side first restricting surface 49 contacts the housing-side first restricting surface 29 . Then, when the holder 21 swings around the contact portion, the holder-side second restricting surface 51 contacts the housing-side second restricting surface 30 at the _X2 portion, and then the _X3A portion and the _X3B portion. The outer peripheral surface of the holder 21 contacts the holder holding portion 26 at at least one of the portions. As a result, movement of the tip of the worm 18 in the first direction and the second direction can be restricted. As for the _X3A part and the _X3B part, by adjusting the gap between both parts, it is possible to make contact with only one part, or contact with both parts. You can also make In addition, when contact is made at both parts, contact can be made at both parts at the same time, or contact can be made at both parts one after the other. can.

On the other hand, when the tip of the worm 18 moves in the first direction and the second direction due to the meshing reaction force F ₂ (the first direction component and the second direction component), in FIG. The holder-side _first restricting surface 49 contacts the housing-side first restricting surface 29 at a portion mirror-symmetrical to the _X1 portion across the one imaginary plane S1. Next, when the holder 21 swings around the contact portion, the holder-side second regulating surface 51 becomes the housing-side second regulating surface at a portion mirror-symmetrical to _{the X2} portion across the first imaginary plane S1. 30, the outer peripheral surface of the holder 21 contacts the holder holding portion 26 in at least one of the portions mirror-symmetrical to the portions _X3A and _X3B across the first imaginary plane _S1 . As a result, movement of the tip of the worm 18 in the first direction and the second direction can be restricted.

In particular, in this example, as described above, the holder-side first restricting surface 49 first contacts the housing-side first restricting surface 29, and then the holder-side second restricting surface 51 contacts the housing-side second restricting surface 30. Due to contact, when the movement of the tip portion of the worm 18 in the second direction is restricted, a rapid increase in surface pressure (worm torque) acting on the meshing portion between the worm tooth 17 and the wheel tooth 15 is suppressed. can.

That is, unlike the present example, when the holder-side first restricting surface 49 contacts the housing-side first restricting surface 29 and the holder-side second restricting surface 51 contacts the housing-side second restricting surface 30 at the same time, Since the movement of the tip of the worm 18 in the second direction is abruptly restricted, the tip of the worm 18 is positioned in the second direction as indicated by the dashed line α between two points C ₁ and C ₂ in FIG. The amount of change in the surface pressure (worm torque) of the meshing portion with respect to the change in (worm angle) increases sharply. On the other hand, as in this example, the first holder-side restricting surface 49 contacts the first housing-side restricting surface 29 first, and then the second holder-side restricting surface 51 contacts the second housing-side restricting surface 30 . Upon contact, the movement of the tip of the worm 18 in the second direction _is gradually restricted ( _stepwise ). Between the contact (point C ₁ ) and the next contact (point C ₂ ), the amount of change in the surface pressure (worm torque) of the meshing portion with respect to the change in the second direction position (worm angle) of the tip of the worm 18 is It can be increased slowly. As a result, when the movement of the tip of the worm 18 in the second direction is restricted, it is possible to prevent the driver operating the steering wheel 2 from feeling uncomfortable.

Further, unlike the case of this example, when the holder-side first restricting surface 49 contacts the housing-side first restricting surface 29 and the holder-side second restricting surface 51 contacts the housing-side second restricting surface 30 at the same time, The impact and hammering sound at the time of contact tend to be louder. On the other hand, in this example, the first holder-side restricting surface 49 first contacts the first housing-side restricting surface 29 , and then the second holder-side restricting surface 51 contacts the second housing-side restricting surface 30 . Therefore, it is possible to suppress impact and hammering noise at the time of contact.

Further, in this example, when the holder 21 moves inside the holder holding portion 26, the elastic deformation amount of the pair of arm plate portions 56 of the plate spring 22 changes, and the pair of plate springs 22 The contact portion between the radially outer surface of the curved plate portion 57 and the main holding portion 27 slips. However, since the contact portion is coated with grease, the slip can be smoothly performed.

Further, in this example, the shape of the leaf spring 22 is a simple trapezoidal shape, so the leaf spring 22 can be manufactured at low cost. Further, in this example, the opening angle between the pair of arm plate portions 56 of the plate spring 22 is regulated to a constant size (θ′) with the plate spring 22 attached to the holder 21 . Therefore, it is not necessary to precisely regulate the opening angle (θ) of the leaf spring 22 as a single piece. Accordingly, the leaf spring 22 can be manufactured at a reduced cost.

Further, in this example, the plate spring 22 is elastically deformed with respect to the holder 21 so that the opening angle becomes larger than that of the single piece, and the outer spring holding portion 53 and the pair of inner spring holding portions 45 are attached. It is held at three locations in total. Therefore, the leaf spring 22 can be attached to the holder 21 without rattling.

Further, in this example, only the portion of the one axial end surface of the leaf spring 22 corresponding to the second direction central portion of the base plate portion 55 is in contact with the radially inner end portion of the bulging portion 54 or is axially closely opposed to the bulging portion 54 . , and the remaining portion is not in contact with the holder 21 . Therefore, the change in the amount of elastic deformation of the leaf spring 22 is not hindered by the holder 21, and in other words, the leaf spring 22 can appropriately bias the holder 21. FIG.

In this example, the operation of inserting the holder 21 with the leaf spring 22 attached inside the holder holding portion 26 is performed while narrowing the opening angle between the tip side portions of the pair of arm plate portions 56 of the leaf spring 22. However, at this time, the pair of curved plate portions 57 of the leaf spring 22 can be inserted into the notches 46 of the holder. Therefore, it is easy to narrow the opening angle between the tip side portions of the pair of arm plate portions 56 of the leaf spring 22 .

In this example, only the radial outer surfaces of the pair of curved plate portions 57 of the leaf spring 22 are the second imaginary side portions of the main holding portion 27 in the second direction when the worm reduction gear 12 is assembled. It elastically contacts the part farther from the worm wheel 16 than the plane _S2 . That is, the contact portion of the leaf spring 22 with respect to the holder holding portion 26 is uniquely determined. Therefore, variations in the biasing force P can be suppressed.

[Second example of embodiment]
A second example of the embodiment of the invention will be described with reference to FIG.

In this example, the leaf spring 22a has a leaf spring engaging portion 58 in the middle portion in the second direction of the substrate portion 55a. The leaf spring engaging portion 58 has a semi-cylindrical shape along the outer spring holding portion 53 of the holder 21 . A radially inward recessed portion, which is a radially outer surface of the plate spring engaging portion 58 , is engaged with the outer spring holding portion 53 . In this example, the radial outer surface of the plate spring engaging portion 58 and the outer spring holding portion 53, which are engaged with each other, have arcuate cross-sectional shapes. For the cross-sectional shape of each of the radial outer surface of the leaf spring engaging portion and the outer spring holding portion, various shapes such as U-shape (square shape) and V-shape (triangular shape) may be adopted. can be done.

In the structure of this example as described above, by engaging the leaf spring engaging portion 58 with the outer spring holding portion 53, it is possible to prevent the leaf spring 22a from shifting in the second direction with respect to the holder 21. FIG. Therefore, the direction and magnitude of the biasing force P (see FIG. 6) can be stabilized.

Further, when adopting a structure that can prevent the leaf spring from shifting in the second direction with respect to the holder by engaging the leaf spring engaging portion with the outer spring holding portion as in the structure of this example, can adjust the direction and magnitude of the biasing force by varying the lengths of the pair of arm plate portions that constitute the leaf spring.
Other configurations and effects are the same as those of the first embodiment.

[Third example of embodiment]
A third example of the embodiment of the invention will be described with reference to FIGS. 17 and 18. FIG.

In this example, the holder extending portion 40a of the holder 21a has an outer engaging portion 59 protruding radially inward at a portion adjacent to the outer spring holding portion 53 on the other side in the axial direction. An outer engaging portion 59, which is an axial restricting portion, is engaged with the other axial side end surface of the leaf spring engaging portion 58 that constitutes the leaf spring 22a. Further, the holder tubular portion 38a of the holder 21a has an inner engaging portion 60 protruding radially outward at a portion adjacent to the pair of inner spring holding portions 45 on the other side in the axial direction. Each of the inner engaging portions 60, which are the axial restricting portions, is engaged with the other axial end surface of the arm plate portion 56 of the plate spring 22a.

In the structure of this example as described above, the outer engaging portion 59 is engaged with the end surface of the plate spring engaging portion 58 on the other side in the axial direction, and the inner engaging portions 60 are engaged with the arm plate portion 56 on the other side in the axial direction. By engaging the side end face, it is possible to prevent the leaf spring 22a from shifting to the other side in the axial direction with respect to the holder 21a. Therefore, the direction and magnitude of the biasing force P (see FIG. 6) can be stabilized. Moreover, it is possible to prevent the leaf spring 22a from falling off from the holder 21a toward the other side in the axial direction.
Other configurations and effects are the same as those of the first and second examples of the embodiment.

[Fourth example of embodiment]
A fourth example of the embodiment of the invention will be described with reference to FIGS. 19 and 20. FIG.

In this example, the plate spring 22b has locking plate portions 65, which are locking portions, connected to the distal end portions of the pair of curved plate portions 57. As shown in FIG. The locking plate portion 65 is arranged radially inside the curved plate portion 57 and has a partially cylindrical shape with a concave radial outer surface. The curved plate portion 57 and locking plate portion 65 connected to each other have a cylindrical shape when viewed from the axial direction. Further, the holder flange portion 39a is formed on the radial outer side surfaces of the pair of locking plate portions 65 when the opening angle between the tip side portions of the pair of arm plate portions 56 constituting the plate spring 22b is narrowed. An axial engagement hole 61 is provided at a location aligned with a certain concave inner space (particularly, in this example, a circular hole existing between the curved plate portion 57 and the locking plate portion 65 that are connected to each other). . In this example, each of the engagement holes 61 axially penetrates the holder flange portion 39a.

In the structure of this example as described above, when inserting the holder 21b to which the plate spring 22b is attached inside the holder holding portion 26 of the housing 14, the pair of locking plate portions 65 constituting the plate spring 22b are A jig such as pliers or a pin is engaged with the concave surface (especially, in this example, a circular hole existing between the curved plate portion 57 and the locking plate portion 65 that are connected to each other), which is the radial outer surface of the For example, the jig can easily narrow the opening angle between the tip side portions of the pair of arm plate portions 56 constituting the leaf spring 22b. Further, when the jig is inserted into the engagement hole 61 of the holder 21b and engaged with the pair of arm plate portions 56 narrowing the opening angle between the tip side portions thereof, the pair of arms can be The narrowed opening angle between the tip side portions of the plate portion 56 can be maintained without holding hands. Therefore, the operation of inserting the holder 21b to which the plate spring 22b is attached into the holder holding portion 26 can be easily performed. Further, since the engaging hole 61 passes through the holder 21b in the axial direction, the jig can be engaged when the inserting work is performed in the same axial direction as in the case of the first embodiment. It can be pulled out from the inner side of the hole 61 to the back side of the holder flange portion 39a (the opposite side to the installation portion of the plate spring 22b) in the axial direction.
Other configurations and effects are the same as those of the first to third examples of the embodiment.

[Fifth example of embodiment]
A fifth example of the embodiment of the invention will be described with reference to FIGS. 21 to 26. FIG.

In this example, as shown in FIGS. 21 and 22, the axial direction of assembly of the holder 21c with respect to the holder holding portion 26 of the housing 14 is opposite to that in the first example of the embodiment.

The holder 21c has a holder-side first regulation surface 49a over the full width in the axial direction. For this reason, the holder 21c has a pair of sub-protrusions 62 projecting radially outward from both ends in the second direction of a portion of the holder tubular portion 38b axially deviated from the holder flange portion 39b. The radially outer surface of the sub-protruding portion 62 and the radially outer surface of the protrusion 48 of the holder flange portion 39b, which are surfaces that are continuous with each other, are defined as the holder-side first regulating surface 49a.

The holder 21c has a holder-side second regulation surface 51a over the entire width in the axial direction. For this reason, the holder 21c has a flat plate-like eaves portion 63 projecting from the full width in the second direction of the radially outer portion of the large-diameter side projecting portion 50 to one side in the axial direction. The second direction side surface of the eaves portion 63 and the second direction side surface of the large-diameter side projecting portion 50, which are surfaces that are continuous with each other, are used as a holder-side second restricting surface 51a. In this example, the radially outer portion of the holder extension portion 40a is integrally coupled to the radially inner portion of the second direction central portion of the eaves portion 63 .

The holder 21c has a recess 64 that is recessed radially inward in the second direction intermediate portion of the distal end surface 43a of the small-diameter side projecting portion 42a.

Also in this example, the leaf spring 22c has locking plate portions 65a connected to the distal end portions of the pair of curved plate portions 57. As shown in FIG. The locking plate portion 65a has a partially cylindrical shape with a concave radial outer surface. However, in this example, the locking plate portion 65a is disposed on the opposite side of the arm plate portion 56 with the curved plate portion 57 interposed therebetween, and the curved plate portion 57 and the locking plate portion 65a connected to each other are arranged axially. The shape seen from the top is S-shaped. Also in the case of this example, the holder flange portion 39b is arranged so that the pair of locking plate portions 65a are separated from each other when the opening angle between the tip side portions of the pair of arm plate portions 56 constituting the plate spring 22c is narrowed. An axial engagement hole 61a is provided at a location aligned with the inner space of the concave surface that is the radially outer surface of the . In this example, each of the engaging holes 61a axially penetrates the holder flange portion 39b.

In the case of the structure of this example as described above, the operation of inserting the holder 21c with the plate spring 22c attached inside the holder holding portion 26 of the housing 14 is performed by engaging the locking plate portion 65a of the plate spring 22c and the holder 21c. This can be easily done by using the joint hole 61a.

Further, in this example, the holder 21c has the holder-side first regulation surface 49a and the holder-side second regulation surface 51a over the entire width in the axial direction. For this reason, the rigidity of the holder 21c is increased when the holder-side first regulating surface 49a is brought into contact with the housing-side first regulating surface 29 and the holder-side second regulating surface 51a is brought into contact with the housing-side second regulating surface 30. can be improved. Furthermore, since the inner ring 35 and the outer ring 36 of the tip end side bearing 20 are less likely to tilt in this state, an increase in the torque of the tip end side bearing 20 can be suppressed. In this example, each of the holder-side first restricting surface 49a and the holder-side second restricting surface 51a exists over the entire width of the holder 21c in the axial direction. Only one of the side first regulating surface and the holder side second regulating surface can be present over the entire width of the holder in the axial direction.

In this example, the holder 21c has a recess 64 that is recessed radially inward in the second direction intermediate portion of the radially outer surface of the small diameter side projecting portion 42a. For this reason, the operation of axially inserting the leaf spring 22c between the holder extending portion 40a and the small-diameter side projecting portion 42a of the holder 21c is performed by making the base portion 55a of the leaf spring 22c convex on the inner diameter side and concave on the outer diameter side. The second-direction intermediate portion of the substrate portion 55 a can enter the concave portion 64 when the substrate portion 55 a is bent elastically so as to be bent. Therefore, the insertion work can be easily performed.
Other configurations and effects are the same as those of the first to third examples of the embodiment.

The electric power assist device of the present invention is not limited to the column assist type electric power steering device, and can be incorporated in electric power steering devices of various structures. Specifically, for example, a pinion assist type electric power steering device that employs an input shaft (pinion shaft) of a steering gear unit as a steering force transmission member that imparts auxiliary power, and a steering force transmission that imparts auxiliary power. The electric assist device of the present invention can be incorporated into a rack assist type electric power steering device that employs the rack shaft of the steering gear unit as a member.

Moreover, the worm speed reducer of the present invention can be incorporated in various mechanical devices, not limited to the electric assist device.
Moreover, the spring member that constitutes the worm speed reducer of the present invention is not limited to a leaf spring, and may be a spring member that is made of a wire material such as an elastic metal.

Reference Signs List 1 electric power steering device 2 steering wheel 3 steering gear unit 4 input shaft 5 tie rod 6 steering shaft 7 steering column 8a, 8b universal joint 9 intermediate shaft 10 electric assist device 11 electric motor 12 worm reduction gear 13 output shaft 14 housing 15 wheel teeth 16 worm wheel 17 worm tooth 18 worm 19 base end bearing 20 tip end bearing 21, 21a, 21b, 21c holder 22, 22a, 22b leaf spring 23 wheel housing portion 24 worm housing portion 25 lid body 26 holder holding portion 27 main holding portion Part 28 Sub-holding part 29 Housing-side first restricting surface 30 Housing-side second restricting surface 31 Inner wheel element 32 Outer wheel element 33 Small diameter part 34 Coupling 35 Inner ring 36 Outer ring 37 Ball 38, 38a, 38b Holder cylindrical part 39, 39a , 39b holder flange portion 40, 40a holder extending portion 41 bearing holding portion 42, 42a small diameter side projecting portion 43, 43a tip end surface 44 side surface 45 inner spring holding portion 46 notch 47 non-contact portion 48 convex portion 49, 49a holder side first 1 restricting surface 50 large diameter side projecting portion 51, 51a holder side second restricting surface 52 escape recess 53 outer spring holding portion 54 bulging portion 55, 55a substrate portion 56 arm plate portion 57, 57a curved plate portion 58 leaf spring engagement Part 59 Outer Engagement Part 60 Inner Engagement Part 61, 61a Engagement Hole 62 Sub-Protrusion 63 Eaves Part 64 Recess 65, 65a Locking Plate Part

Claims (12)

a housing;
a worm wheel rotatably supported by the housing and having wheel teeth on its outer peripheral surface;
a worm rotatably supported by the housing and having worm teeth on its outer peripheral surface that mesh with the wheel teeth;
a bearing externally fitted to the tip of the worm;
a holder in which the bearing is fitted and which is arranged inside the housing so as to be movable with respect to the worm wheel;
a spring member that elastically biases the holder toward the worm wheel,
The holder includes a pair of inner spring holding portions that are circumferentially spaced apart from the worm wheel relative to the central axis of the holder, and the spring members that are arranged more than the pair of inner spring holding portions. an outer spring retainer disposed on the far side from the worm wheel in the first direction, which is the urging direction of the holder, and between the pair of inner spring retainers in the circumferential direction. ,
The spring member includes a base having radially outer surfaces in contact with the outer spring holding portions, and circumferentially extending from both circumferential ends of the base, and having radially inner surfaces contacting the pair of inner spring holding portions. a pair of arms that are in elastic contact with each other, and ends of the pair of arms that are farther from the base, and whose radial outer surfaces are in elastic contact with the inner peripheral surface of the housing. and a pair of pressed parts,
Worm reducer. The holder includes a pair of holder-side first regulating surfaces arranged at two locations on both sides of an imaginary plane that includes the central axis of the worm and is parallel to the first direction, and a pair of holder-side second regulating surfaces arranged at two locations on the side farther from the worm wheel than the pair of holder-side first regulating surfaces and on both sides of the virtual plane; cage,
The housing has a pair of housing-side first regulation surfaces facing the pair of holder-side first regulation surfaces and a pair of housing-side second regulation surfaces facing the pair of holder-side second regulation surfaces. and
The sum of the gaps existing between the pair of holder-side first restricting surfaces and the pair of housing-side first restricting surfaces is the sum of the pair of holder-side second restricting surfaces and the pair of housing-side first restricting surfaces. is smaller than the sum of the gaps existing between the two regulation surfaces,
A worm reduction gear according to claim 1. At least one of the holder-side first regulating surface and the holder-side second regulating surface exists over the entire width of the holder in the axial direction,
A worm speed reducer according to claim 2. the base has a radially inwardly recessed recess engaging the outer spring retainer;
A worm speed reducer according to any one of claims 1 to 3. The holder has an axial regulation portion that regulates axial displacement of the spring member with respect to the holder.
A worm speed reducer according to any one of claims 1 to 4. Each of the pair of arm portions is bent at an obtuse angle from both ends of the base portion in the circumferential direction toward a side closer to the worm wheel with respect to the first direction,
A worm speed reducer according to any one of claims 1 to 5. A radial outer surface of the pressing portion is a convex curved surface,
A worm speed reducer according to any one of claims 1 to 6. The spring member has a pair of locking portions that are connected to ends of the pair of pressing portions farther from the base portion and have concave radial outer surfaces,
A worm speed reducer according to any one of claims 1 to 7. The holder aligns with the inner space of the concave surface, which is the radial outer surface of each of the pair of locking portions, when the opening angle between the portions of the pair of arm portions on the far side from the base portion is narrowed. having an axial engagement hole at a location,
A worm reduction gear according to claim 8. The engagement hole axially penetrates the holder,
A worm reduction gear according to claim 9 . wherein the spring member is a leaf spring;
A worm speed reducer according to any one of claims 1 to 10. an electric motor, and a worm reduction gear that increases the power of the electric motor and transmits it to a steering force transmission member;
An electric assist device, wherein the worm reduction gear is the worm reduction gear according to any one of claims 1 to 11.

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