JP7404688B2 - Worm reducer and electric assist device - Google Patents

Description

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

In a steering device for an automobile, when a driver operates (rotates) a steering wheel, the rotation of the steering wheel is transmitted to an input shaft of a steering gear unit through a steering shaft or an intermediate shaft. When the rack shaft of the steering gear unit is displaced in the width direction of the vehicle due to the rotation of the input shaft, the pair of tie rods are pushed and pulled, thereby imparting a steering angle to the steered wheels.

Japanese Patent Laid-Open No. 2005-42913 (Patent Document 1) and Japanese Patent Laid-Open No. 2004-306898 (Patent Document 2) disclose that an electric motor is used as an auxiliary power source when a driver uses a steering wheel to give a steering angle to the steered wheels. An electric power steering device is disclosed that reduces the force required to operate a wheel. In an electric power steering device, the torque of the electric motor is increased by a worm reducer, and then the torque of the electric motor is increased by a worm reducer, and then the torque of the electric motor is increased by a rotating shaft that rotates with the rotation of the steering wheel, such as a steering shaft or an input shaft of the steering gear unit, or the torque of the steering gear unit. It is applied to direct-acting shafts such as rack shafts and screw shafts.

FIG. 16 shows the structure of a worm reducer described in Japanese Patent Application Laid-open No. 2004-306898. The worm reducer 100 includes a housing 101, a worm wheel 102, and a worm 103.

The housing 101 includes a wheel accommodating portion 104 and a worm accommodating portion 105 whose central axis is twisted with respect to the central axis of the wheel accommodating portion 104 and whose axially intermediate portion opens into the wheel accommodating portion 104. and has.

The worm wheel 102 has wheel teeth 106 on its outer peripheral surface, and is supported and fixed coaxially around a rotating shaft 107 rotatably supported inside the wheel accommodating portion 104 .

The worm 103 has worm teeth 108 on the outer circumferential surface of the axially intermediate portion thereof, which mesh with the wheel teeth 106 . The worm 103 is rotatably supported inside the worm accommodating portion 105 by a pair of ball bearings 109a and 109b at two positions in the axial direction with the worm teeth 108 in between. Of the pair of ball bearings 109a and 109b, the outer ring of the ball bearing 109a on the tip side of the worm 103 (on the right side in FIG. 16) is fitted into a holder 110 that is fitted and fixed inside the rear end side of the worm accommodating portion 105. It is press-fitted. The inner ring of the ball bearing 109a is fitted onto a large-diameter portion 111 provided in a portion of the worm 103 located closer to the tip than the worm teeth 108 via a synthetic resin bush 112 by a clearance fit. . That is, the inner ring of the ball bearing 109a is fitted onto the bush 112, which is fitted onto the large diameter portion 111 of the worm 103 with a clearance fit, without wobbling. The outer ring of the ball bearing 109b on the base end side of the worm 103 (on the left side in FIG. 16) is press-fitted into the opening of the worm accommodating portion 105, and the inner ring of the ball bearing 109b is fitted onto the base end of the worm 103. ing. An output shaft of an electric motor 113 is connected to the base end of the worm 103 so that torque can be transmitted thereto. That is, the worm 103 can be rotationally driven by the electric motor 113.

In the worm reducer 100, unavoidable backlash exists at the meshing portion between the wheel teeth 106 and the worm teeth 108, based on dimensional errors and assembly errors of the components constituting the worm reducer 100. Due to the presence of this backlash, when changing the direction of rotation of the steering wheel, a harsh rattling sound may occur at the meshing portion. In the illustrated example, the tip of the worm 103 is elastically urged toward the worm wheel 102 in order to suppress the occurrence of such rattling noise.

That is, the base end portion of the worm 103 is supported by a ball bearing 109b having a radial clearance with respect to the worm accommodating portion 105 so as to be able to swing slightly. An annular gap exists between the outer circumferential surface of the large diameter portion 111 of the worm 103 and the inner circumferential surface of the bush 112 over the entire circumference. A pad 114 is tightly fitted onto the tip of the worm 103, and a torsion coil spring 115 is installed between the pad 114 and the holder 110. The torsion coil spring 115 elastically moves the pad 114 toward the worm wheel 102 in a first direction (vertical direction in FIG. 16) perpendicular to the central axis of the electric motor 113 and the central axis of the worm wheel 102. By pressing, the tip of the worm 103 is elastically pressed toward the worm wheel 102 in the first direction. As a result, backlash between the wheel teeth 106 and the worm teeth 108 is suppressed, and the occurrence of rattling noise is suppressed.

Japanese Patent Application Publication No. 2005-42913 JP2004-306898A

By the way, in order to ensure a large allowable range (dimensional tolerance) for dimensional errors and assembly errors of each of the parts constituting the worm reducer 100, the amount by which the tip of the worm 103 can be displaced in the first direction is increased. It is necessary to secure it.

In addition, in order to reduce the rattling noise generated at the meshing part between the worm teeth and the wheel teeth, and to reduce the weight, the worm wheel is made of synthetic resin with a metal inner wheel element and wheel teeth on the outer peripheral surface. A combination with an outer wheel element can be used. However, when such a worm wheel is used, the outer wheel element made of synthetic resin may expand due to water absorption, heat, etc., and the friction at the meshing portion between the worm teeth and the wheel teeth may increase. In order to prevent an increase in friction at the meshing portion between the worm teeth and the wheel teeth due to expansion of the outer wheel element, it is necessary to secure a large amount by which the tip of the worm 103 can be displaced in the first direction.

In the structure described in Japanese Unexamined Patent Publication No. 2004-306898, a gap exists between the outer peripheral surface of the large diameter portion 111 of the worm 103 and the inner peripheral surface of the bush 112 over the entire circumference. Therefore, in order to ensure a large amount of displacement of the tip of the worm 103 in the first direction, the gap in the first direction is increased in the gap in the direction perpendicular to the first direction (the front and back directions in FIG. 16). ) also becomes large. Therefore, when changing the direction of rotation of the steering wheel, the tip of the worm 103 may be displaced in a direction perpendicular to the pressing direction by the torsion coil spring 115 (front and back directions in FIG. 16).

In view of the above-mentioned circumstances, the present invention provides a worm reducer that includes means for imparting elasticity to the tip of the worm in a direction that approaches the worm wheel. The aim is to realize a structure that can suppress displacement.

The worm reducer of the present invention includes a housing, a worm wheel, a worm, a support bearing, elastic biasing means, and elastic clamping means.
The housing includes a wheel accommodating portion and a worm accommodating portion that is arranged in a twisted position with respect to the wheel accommodating portion and has an axially intermediate portion open to the wheel accommodating portion.
The worm wheel has wheel teeth on its outer circumferential surface and is rotatably supported inside the wheel accommodating portion.
The worm has worm teeth on its outer peripheral surface that mesh with the wheel teeth, and is rotatably supported inside the worm accommodating portion.
The support bearing includes an inner ring that is fitted onto the tip of the worm, and an outer ring that is disposed around the inner ring and coaxially with the inner ring.
The elastic biasing means elastically biases the support bearing toward the worm wheel directly or via another member fitted onto the outer ring.
The elastic holding means elastically holds the support bearing or the other member from both sides with respect to a first direction, which is the urging direction of the elastic urging means, and a second direction perpendicular to the central axis of the worm accommodating portion. be held between.

The worm reducer of the present invention further includes a guide member that fits the outer ring so that it can be displaced in the first direction, and that is fitted inside the worm accommodating portion, and the elastic clamping means: It can be arranged between the outer ring and the guide member.

The elastic biasing means may be arranged between the outer ring and the guide member or between the outer ring and the worm housing.

The guide member has a support that directly faces the outer ring at at least one location in the circumferential direction, preferably two locations spaced apart in the circumferential direction, on the inner circumferential surface of the side portion far from the worm wheel with respect to the first direction. A surface portion can be provided.

The worm reducer of the present invention may further include an elastic ring elastically held between an inner circumferential surface of the worm accommodating portion and an outer circumferential surface of the guide member.
In this case, the amount of elastic compression of the elastic ring in the side portion closer to the worm wheel can be made larger than the amount of elastic compression of the elastic ring in the side portion farther from the worm wheel.
Specifically, the elastic ring is arranged on the outer circumferential surface of the guide member, with the center axis of the elastic ring offset from the center axis of the guide member toward the side closer to the worm wheel in the first direction. It can be locked with.

The elastic biasing means is located on a side far from the worm wheel with respect to the first direction, in a portion between the outer ring and the guide member, or a portion between the outer ring and the inner circumferential surface of the worm accommodating portion. A first leaf spring may be provided, disposed in the portion.

The elastic clamping means may include a pair of second leaf springs disposed on both sides in the second direction in a portion between the outer ring and the guide member.

Each of the pair of second leaf springs includes a pair of distal arm portions disposed on both sides of the support surface portion in the axial direction of the guide member, and a proximal end of the pair of distal arm portions. The base portion may include a base portion connecting the two portions to each other and having an inner surface of the guide member in the radial direction elastically abutted against an outer circumferential surface of the outer ring.

Each of the pair of second leaf springs has a pair of close springs extending from both ends of the base in the axial direction of the guide member toward a side closer to the worm wheel in the first direction. The device may further include a lateral arm.

Each of the pair of second leaf springs may further include a locking piece for locking each of the pair of second leaf springs to the guide member.

The worm reducer of the present invention may further include a cover supported by an opening on the tip side of the worm in the guide member.

Alternatively, the worm reducer of the present invention may directly fit the outer ring into the inner circumferential surface of the worm accommodating portion so as to be able to be displaced in the first direction without providing a guide member. In this case, the elastic biasing means is arranged between the outer ring and the worm accommodating part, and the elastic clamping means is arranged between the outer ring and the worm accommodating part.

The electric assist device of the present invention includes an electric motor, and a worm reducer that increases the torque of the electric motor and applies it to a rotary shaft that rotates with rotation of a steering wheel or a linear shaft that constitutes a steering gear unit. Equipped with
In particular, in the electric assist device of the present invention, the worm reducer is the worm reducer of the present invention.

According to the worm reducer and electric assist device of the present invention as described above, when changing the rotational direction of the worm wheel, the tip of the worm is displaced in a direction perpendicular to the biasing direction by the elastic biasing means. can be suppressed.

FIG. 1 is a partially cutaway side view showing a column assist type electric power steering device incorporating an electric assist device according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line AA in FIG. FIG. 3(A) is a perspective view showing the guide assembly taken out, and FIG. 3(B) is a perspective view seen from the opposite side to FIG. 3(A). 4(A) is a front view of the guide assembly viewed from the tip side in the axial direction of the worm, and FIG. 4(B) is a plan view viewed from above FIG. 4(A). 4(C) is a bottom view seen from below of FIG. 4(A), FIG. 4(D) is a side view seen from the right side of FIG. 4(A), and FIG. 4(E) is a bottom view of FIG. , is a rear view seen from the right side of FIG. 4(D). FIG. 5 is a sectional view taken along line BB in FIG. 4(A). FIG. 6 is a sectional view taken along line CC in FIG. 4(A). FIG. 7 is an exploded perspective view of the guide assembly. 8(A) is a front view of the guide member viewed from the tip side in the axial direction of the worm, and FIG. 8(B) is a plan view viewed from above FIG. 8(A). (C) is a bottom view seen from below of FIG. 8(A), and FIG. 8(D) is a side view seen from the right side of FIG. 8(A). FIG. 9 is a sectional view taken along line DD in FIG. 8(A). FIG. 10 is a sectional view taken along line EE in FIG. 8(A). FIG. 11(A) is a plan view showing the first leaf spring taken out, FIG. 11(B) is a front view seen from the bottom of FIG. 11(A), and FIG. 11(C) is a plan view showing the first leaf spring taken out. It is a side view seen from the left side of FIG. 11(A), and FIG. 11(D) is a side view seen from the right side of FIG. 11(A). 12(A) is a front view showing the second leaf spring taken out, FIG. 12(B) is a side view seen from the right side of FIG. 12(A), and FIG. 12(C) is a 12(A) as seen from above, and FIG. 12(D) is a rear view as seen from the right side of FIG. 12(B). 13(A) is a rear view of the cover seen from the proximal end side in the axial direction of the worm, and FIG. 13(B) is a plan view seen from above of FIG. 13(A). (C) is a bottom view seen from below of FIG. 13(A), and FIG. 13(D) is a side view seen from the right side of FIG. 13(A). FIG. 14 is a partially cutaway side view showing an example of a rack assist type electric power steering device into which the electric assist device of the present invention can be incorporated. FIG. 15 is a partially cutaway side view showing an example of a pinion assist type electric power steering device into which the electric assist device of the present invention can be incorporated. FIG. 16 is a sectional view showing an example of a conventional structure of a worm reducer.

1 to 13(D) show an example of an embodiment of the present invention. 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, the rotation of the steering wheel 2 is transmitted to the input shaft 4 of the steering gear unit 3, and as the input shaft 4 rotates, a pair of tie rods 5 are pushed. When pulled, a steering angle is imparted to the 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 applies the rotational torque of the output shaft 13 of the electric motor 11 to the steering shaft 6 while increasing it using the worm reducer 12 .

The worm reducer 12 includes a housing 14, a worm wheel 15, a worm 16, a support bearing 17, a guide member 18, a first leaf spring 19, and a pair of second leaf springs 20.

The housing 14 is a cast product of iron-based alloy, a die-cast molded product of light alloy such as aluminum, or an injection molded product of synthetic resin, and has a twist position relative to the wheel accommodating portion 21 . The worm accommodating portion 22 is disposed at the wheel accommodating portion 22 and has an axially intermediate portion open to the wheel accommodating portion 21 .

The wheel accommodating portion 21 is supported and fixed to the front end of the steering column 7 so that its central axis and the central axis of the steering column 7 are coaxial.

The worm accommodating portion 22 has a cylindrical shape and has openings at both ends in the axial direction. An opening on one side in the axial direction (the right side in FIG. 2) of the worm accommodating portion 22 is closed by the electric motor 11 that is coupled and fixed to the housing 14, and an opening on the other side in the axial direction (the left side in FIG. 2) of the worm accommodating portion 22 is closed. ) is closed by a lid 23.

Note that with respect to the worm accommodating portion 22, the worm 16 rotatably supported inside the worm accommodating portion 22, and members disposed around the worm 16, one side in the axial direction refers to the proximal end side of the worm 16. 2 refers to the right side in FIG. 2, and the other axial side refers to the tip side of the worm, which is the left side in FIG.

The worm accommodating portion 22 has a cylindrical surface portion 24 having a cylindrical surface shape on the inner circumferential surface of one side in the axial direction, and a stepped portion facing toward one side in the axial direction at the other end of the cylindrical surface portion 24 in the axial direction. It has 25. The worm accommodating portion 22 has a cylindrical guide holding portion 26 on the inner circumferential surface of the other side in the axial direction, and an inward portion protruding radially inward in a portion adjacent to one side of the guide holding portion 26 in the axial direction. It has a flange portion 27. Furthermore, the worm accommodating portion 22 has an engagement recess 28 that is recessed to one side in the axial direction at the end of the other axial side surface of the inward flange portion 27 that is further away from the wheel accommodating portion 21 in the circumferential direction.

The worm wheel 15 has wheel teeth 29, which are helical gears, on its outer peripheral surface, and is rotatably supported inside the wheel accommodating portion 21. In this example, the worm wheel 15 is supported and fixed around the front end of the steering shaft 6 which is rotatably supported inside the wheel accommodating portion 21 so as to rotate together with the steering shaft 6. The worm wheel 15 of this example is formed by bonding and fixing an outer wheel element 31 made of synthetic resin having wheel teeth 29 on the outer circumferential surface around an inner wheel element 30 made of metal and having a circular plate shape.

The worm 16 has screw-shaped worm teeth 32 on the outer circumferential surface of the axially intermediate portion thereof, which mesh with the wheel teeth 29 of the worm wheel 15, and is rotatably supported inside the worm accommodating portion 22. The worm 16 has a base end connected to the output shaft 13 of the electric motor 11 via a torque transmission joint 33 so that torque can be transmitted thereto.

The torque transmission joint 33 includes a drive-side transmission member 34 externally fitted and fixed to the tip end (left end in FIG. 2) of the output shaft 13 of the electric motor 11, and a driven side transmission member 34 externally fitted and fixed to the base end of the worm 16. It includes a side transmission member 35, a pair of elastic members 36 each made of an elastic material such as an elastomer such as rubber, and a coupling 37 made of a synthetic resin or metal material.

When the torque transmitted between the output shaft 13 of the electric motor 11 and the worm 16 is relatively small, the torque transmission joint 33 transmits the rotational torque of the output shaft 13 from the drive-side transmission member 34 to an elastic member on one side in the axial direction. 36 to the coupling 37, and further, the rotation torque of the coupling 37 is transmitted to the driven side transmission member 35 via the elastic member 36 on the other side in the axial direction. On the other hand, when the torque transmitted between the output shaft 13 of the electric motor 11 and the worm 16 is large, the pair of elastic members 36 are elastically crushed in the circumferential direction. The rotational torque of the output shaft 13 is directly transmitted from the drive-side transmission member 34 to the coupling 37, and further, the rotational torque of the coupling 37 is directly transmitted to the driven-side transmission member 35.

In addition, regarding the specific structure of the torque transmission joint 33, various conventionally known structures can be adopted. In any case, in this example, the tip end of the output shaft 13 of the electric motor 11 and the base end of the worm 16 are connected via the torque transmission joint 33 so that torque can be transmitted. This prevents rattling noise from occurring at the torque transmission section between the output shaft 13 and the worm 16, and allows the worm 16 to swing relative to the output shaft 13. However, as long as it is possible to transmit torque between the output shaft 13 of the electric motor 11 and the worm 16 and to swing the worm 16 with respect to the output shaft 13, the tip of the output shaft 13 of the electric motor 11 and the worm The method of connection with the base end portion of 16 is not particularly limited, and connection may be made by spline engagement or the like.

The worm 16 is fitted in order from the proximal end side (one side in the axial direction) between the proximal end portion to which the driven side transmission member 35 is externally fitted and fixed, and the axially intermediate portion provided with the worm teeth 32. It includes a mating tube portion 38 and a flange portion 39 that projects outward in the radial direction. The worm 16 rotatably supports the fitting cylindrical portion 38 with respect to the cylindrical surface portion 24 of the worm accommodating portion 22 by a ball bearing 40 . The ball bearing 40 includes an outer ring 41, an inner ring 42, and a plurality of balls 43.

The outer ring 41 is fitted into the cylindrical surface portion 24 of the worm accommodating portion 22 with a clearance fit, and is held between the stepped portion 25 and a retaining ring 44 that is locked to the cylindrical surface portion 24 from both sides in the axial direction. . In other words, the outer ring 41 has the other axial side surface abutted against the stepped portion 25 and one axial side surface abutted against the retaining ring 44 . However, the outer ring 41 can also be internally fitted into the cylindrical surface portion 24 of the worm accommodating portion 22 by tight fitting.

The inner ring 42 is externally fitted onto the fitting cylindrical portion 38 of the worm 16 without play, and a driven side transmission member is externally fitted and fixed onto one axial side surface of the flange 39 and the base end of the worm 16. It is held between the other axial side surface of 35 via a pair of elastic members 76 from both sides in the axial direction. In other words, the inner ring 42 has one axial side surface abutted against the other axial side surface of the driven transmission member 35 via the elastic member 76 on one axial side, and the other axial side surface is axially It abuts against one side surface in the axial direction of the collar portion 39 via the elastic member 76 on the other side.

The plurality of balls 43 are rotatably arranged between an outer ring raceway provided on the inner peripheral surface of the outer ring 41 and an inner ring raceway provided on the outer peripheral surface of the inner ring 42 .

The ball bearing 40 has a radial gap between the outer ring 41, the inner ring 42, and the balls 43. Therefore, the fitting cylinder part 38 of the worm 16 is supported by the cylindrical surface part 24 of the worm accommodating part 22 so as to be rotatable and swingable.

Further, the worm 16 has a small-diameter cylindrical portion 45 at the tip (the other end in the axial direction) that has a smaller outer diameter than the portion adjacent to the proximal end (on one side in the axial direction). The worm 16 supports the small diameter cylindrical portion 45 with respect to the guide holding portion 26 of the worm accommodating portion 22 so as to be freely rotatable and movable toward and away from the worm wheel 15 by means of a support bearing 17 and a guide member 18. ing.

The support bearing 17 includes an inner ring 46 externally fitted and fixed to a small diameter cylindrical portion 45, an outer ring 47 disposed coaxially around the inner ring 46, and an inner ring raceway and an outer ring provided on the outer peripheral surface of the inner ring 46. A plurality of rolling elements 48 are disposed so as to be freely rollable between the outer ring raceway provided on the inner circumferential surface of the roller 47. In this example, a ball bearing in which the rolling elements 48 are balls is used as the support bearing 17, but a radial roller bearing or a radial needle bearing may also be used.

The support bearing 17 of this example is arranged inside the guide holding part 26 of the worm accommodating part 22 via the guide member 18 so as to be able to move toward and away from the worm wheel 15 . The support bearing 17 is elastically biased toward the worm wheel 15 by a first leaf spring 19 disposed at the end of the portion between the outer ring 47 and the guide member 18 that is far from the worm wheel 15. be done. Further, the support bearing 17 is arranged in a first direction (vertical direction in FIGS. 2, 4A, and 6), which is the direction in which the first plate spring 19 urges the portion between the outer ring 47 and the guide member 18. A pair of second leaf springs 20 disposed on both sides in a second direction (left-right direction in FIGS. 4A and 5) orthogonal to the center axis of the worm accommodating portion 22 It is elastically clamped from the That is, in this example, the elastic biasing means that elastically biases the support bearing 17 toward the worm wheel 15 side is constituted by the first plate spring 19, and The elastic clamping means for clamping from the base is composed of a pair of second leaf springs 20.

The guide member 18 is made of synthetic resin and includes a cylindrical main body 49 and one side surface of the main body 49 in the axial direction that is farthest from the worm wheel 15 in the first direction and is spaced apart in the second direction. A pair of engaging protrusions 50 are provided that protrude toward one side in the axial direction from two positions.

The guide member 18 includes a locking groove 51 having a rectangular cross-sectional shape on the outer peripheral surface of the main body portion 49 over the entire circumference. The guide member 18 has the main body portion 49 fitted inside the guide holding portion 26 of the worm accommodating portion 22 with the elastic ring 52 being locked in the locking groove 51 . In this example, the amount of elastic compression of the elastic ring 52 in the side portion close to the worm wheel 15 is made larger than the amount of elastic compression in the side portion far from the worm wheel 15. For this purpose, specifically, the center axis of the locking groove 51 is offset from the center axis of the main body portion 49 toward the side closer to the worm wheel 15 in the first direction. As a result, the guide member 18 is elastically urged toward the side far from the worm wheel 15 in the first direction. By pressing against the guide member 18, wobbling of the guide member 18 is suppressed. In this example, the elastic ring 52 is constituted by an O-ring having a circular cross-sectional shape in a free state before being locked in the locking groove 51. However, the cross-sectional shape of the elastic ring 52 is not limited to a circular shape, but can also be an elliptical shape, a rectangular shape, or the like.

The main body portion 49 includes partially cylindrical support surface portions 53 at two positions spaced apart in the circumferential direction on the side portion far from the worm wheel 15 in the first direction on the inner circumferential surface of the axially intermediate portion. Each of the support surface portions 53 has a radius of curvature that is the same as or slightly larger than the radius of curvature of the outer peripheral surface of the outer ring 47 of the support bearing 17 . Further, in this example, the main body portion 49 has a substantially semi-cylindrical concave curved surface portion 54 on the side portion of the inner circumferential surface of the axially intermediate portion near the worm wheel 15 in the first direction. The concave curved surface portion 54 has a radius of curvature that is the same as or slightly larger than the radius of curvature of the outer peripheral surface of the outer ring 47 of the support bearing 17 .

The main body portion 49 has engagement surface portions 55 on a pair of inner surfaces facing each other in the second direction, which are approximately H-shaped when viewed from the second direction, and for disposing the second leaf spring 20. Equipped with The engagement surface portions 55 are arranged at the four corners of a flat engagement base portion 56 that is orthogonal to the second direction, axially both side portions sandwiching the bearing surface portion 53, and axially both side portions sandwiching the concave curved surface portion 54. , and includes pedestal surface portions 57a and 57b that protrude beyond the engagement base 56, and a restraining surface portion 58 that protrudes from near the center of the engagement base 56. Each of the pedestal surface parts 57a and 57b exists on the same virtual plane orthogonal to the second direction. The amount of protrusion of the pedestal surface portions 57a and 57b from the engagement base 56 is larger than the amount of protrusion of the restraining surface portion 58 from the engagement base 56.

The main body part 49 is an end part of the inner circumferential surface of the axially intermediate part on the side far from the worm wheel 15 in the first direction, and is located between the support surface part 53 in the circumferential direction. The locking recess 79 is recessed toward the side far from the worm wheel 15 in the first direction, and the locking convex portion 59 is provided on the bottom surface of the locking recess 79 and protruding toward the side closer to the worm wheel 15 in the first direction. Be prepared. Note that the end portions on both axial sides of the locking recess 79 are open to both axial side surfaces of the main body portion 49 .

The main body portion 49 has a cutout portion 60 at both end portions in the first direction on the other axial side surface, and is a portion circumferentially removed from the cutout portion 60. Side wall portions 61 having a substantially arcuate shape when viewed from the axial direction are provided on both sides in two directions. Further, the main body portion 49 has grooves 62 extending in the first direction on both side portions in the second direction of the outer circumferential surface of the other axial portion. Furthermore, the main body portion 49 has locking notches 63a and 63b, which radially penetrate through the end portions in the second direction of both axial side surfaces. Of the locking notches 63a and 63b, the locking notch 63a provided on the other axial side surface passes through the center of the side wall 61 in the radial direction, and the locking notch 63a is provided on the other axial side surface of the groove 62. It opens in the center.

The pair of engagement convex portions 50 are arranged inside the engagement recess 28 of the worm accommodating portion 22 with the main body portion 49 being fitted inside the guide holding portion 26 of the worm accommodating portion 22 . Thereby, the phase of the guide member 18 in the circumferential direction with respect to the worm housing part 22 is determined, and the guide member 18 is prevented from rotating inside the worm housing part 22.

The first plate spring 19 is formed by bending an elastic metal plate such as a steel plate into a substantially U-shape, as shown in FIGS. 11(A) to 11(D). In this example, the first leaf spring 19 includes a base 64 , a folded portion 65 that is folded back in a U-shape from the end of one longitudinal direction of the base 64 (one side of the guide member 18 in the axial direction), and the folded portion 65 . A curved portion 66 is curved into a partially cylindrical shape so that the side closer to the worm wheel 15 in the first direction is convex from the tip end portion (the other end of the guide member 18 in the axial direction). Furthermore, the first leaf spring 19 has a rectangular locking hole 67 in the base 64 .

The first leaf spring 19 is constructed by arranging (inserting) the base portion 64 inside the locking recess 79 of the guide member 18 and fitting the locking hole 67 into the locking protrusion 59 so that the guide member It is supported inside 18. While being supported inside the guide member 18 , the curved portion 66 of the first leaf spring 19 causes the outer peripheral surface of the outer ring 47 of the support bearing 17 disposed inside the guide member 18 to be connected to the side far from the worm wheel 15 . By elastically pressing the end portion of the support bearing 17, the support bearing 17 is elastically urged toward the worm wheel 15 side. Note that with the first leaf spring 19 supported inside the guide member 18 , the folded portion 65 is arranged between the pair of engagement protrusions 50 of the guide member 18 .

The second plate spring 20 is formed by punching an elastic metal plate such as a steel plate into a substantially H-shape, as shown in FIGS. 12(A) to 12(D). Specifically, the second leaf spring 20 has a substantially flat plate shape as a whole, and among the base 68 and both side edges of the base 68 in the first direction, the longitudinal direction (the axial direction of the guide member 18) The four arm portions 69a and 69b extending in the first direction from both end portions and the longitudinal direction (axial direction of the guide member 18) both side edges of the base portion 68 are separated from the support bearing 17 in the plate thickness direction of the base portion 68. A pair of locking pieces 70 are provided that are bent in the direction (radially outward of the guide member 18). The second leaf spring 20 is constructed by bringing the four arm portions 69a, 69b into contact with the pedestal surface portions 57a, 57b of the engagement surface portion 55, and by hooking the locking piece 70 onto the locking notches 63a, 63b. , supported inside the guide member 18. In this way, the pair of second leaf springs 20 supported on both sides in the second direction of the inner peripheral surface of the guide member 18 elastically support the outer ring 47 of the support bearing 17 from both sides in the second direction. to hold. Note that when the second leaf spring 20 is supported inside the guide member 18, the distance between the arms 69a on the side far from the worm wheel 15 (distal arm portion) among the four arm portions 69a and 69b is The support surface portion 53 protrudes from the worm wheel 15, and the concave curved surface portion 54 protrudes from between the arm portions (proximal arm portions) 69b on the side closer to the worm wheel 15. In other words, the arm portion 69a on the side far from the worm wheel 15 is arranged on both sides of the support surface portion 53 in the axial direction of the guide member 18, and the arm portion 69b on the side closer to the worm wheel 15 is arranged on both sides of the support surface portion 53 in the axial direction of the guide member 18. They are arranged on both sides of the concave curved surface portion 54 in the axial direction.

The worm reducer 12 of this example further includes a cover 71 that supports the opening on the other axial side of the guide member 18. As shown in FIGS. 13(A) to 13(D), the cover 71 has a substantially oval end face shape when viewed from the axial direction of the guide member 18. The cover 71 has a circular hole 72 in the center, and a pair of locks protruding in the axial direction of the guide member 18 on both sides in the first direction of one side surface in the axial direction of the guide member 18. It has a claw 73. However, the circular hole 72 can also be omitted. The cover 71 is supported by the guide member 18 by hooking the locking claw 73 onto the other end of the main body 49 in the axial direction while being disposed between the pair of side walls 61 of the main body 49. be done.

When assembling the worm reducer 12, after arranging the first leaf spring 19, a pair of second leaf springs, and the support bearing 17 inside the guide member 18, the cover 71 is placed inside the guide member 18. By supporting the opening on the other side in the axial direction, a guide assembly 77 as shown in FIGS. 3(A) to 4(E) is constructed. By inserting (press-fitting) such a guide assembly 77 between the guide holding part 26 of the worm accommodating part 22 and the small diameter cylindrical part 45 of the worm 16, the tip of the worm 16 is held in the guide. It is rotatably supported inside the portion 26 and is given elasticity toward the worm wheel 15 side. After inserting the guide assembly 77 between the guide holding part 26 of the worm housing part 22 and the small diameter cylindrical part 45 of the worm 16, a retaining ring 78 is engaged with the other end of the guide holding part 26 in the axial direction. Stop. This prevents the guide assembly 77 from being displaced to the other side in the axial direction, and also prevents the cover 71 from falling off (coming off) from the guide member 18.

In the electric assist device 10 of this example, the small diameter cylinder portion 45 provided at the tip of the worm 16 is rotated with respect to the guide holding portion 26 of the worm housing portion 22 via the support bearing 17 and the guide member 18. It supports the worm wheel 15 so that it can freely move toward and away from the worm wheel 15. Furthermore, since the support bearing 17 is elastically biased toward the worm wheel 15 in the first direction by the first leaf spring 19, backlash between the worm teeth 32 and the wheel teeth 29 is prevented. It can be suppressed.

Furthermore, in the electric assist device 10 of this example, the support bearing 17 is elastically held from both sides in the second direction by the pair of second leaf springs 20. Therefore, even if the rotation direction of the worm wheel 15 supported and fixed to the steering shaft 6 changes based on the driver's operation of the steering wheel 2, the tip of the worm 16 is displaced in the second direction. can be suppressed.

Note that when torque is transmitted from the worm 16 to the worm wheel 15 by energizing the electric motor 11, a meshing reaction force is applied to the worm 16 from the meshing portion between the wheel teeth 29 and the worm teeth 32. This meshing reaction force includes not only a component related to the first direction but also a component related to a second direction perpendicular to the first direction. The directions of the components of the meshing reaction force in the second direction are opposite to each other when the worm 16 rotates in one direction and when it similarly rotates in the other direction. That is, when transmitting torque between the worm 16 and the worm wheel 15, a meshing reaction force that is inclined with respect to the first direction is applied to the tip of the worm 16, depending on the rotational direction of the worm 16.

When transmitting torque between the worm 16 and the worm wheel 15, if the component in the first direction of the meshing reaction force applied to the worm 16 becomes larger than the elastic urging force by the first leaf spring 19, The tip of the worm 16 is displaced in a direction away from the worm wheel 15 in the first direction. In this example, when the tip of the worm 16 is displaced in a direction away from the worm wheel 15, the outer circumferential surface of the outer ring 47 of the support bearing 17 comes into contact with the support surface 53 provided on the inner circumferential surface of the guide member 18, and the guide The outer circumferential surface of the member 18 is pressed against the guide holding portion 26 of the worm housing portion 22, thereby supporting the meshing reaction force. In this example, the support surface portions 53 are provided at two positions spaced apart in the circumferential direction on the inner circumferential surface of the guide member 18, on a side portion far from the worm wheel 15. Therefore, regardless of the rotational direction of the worm 16, the contact portion between the outer peripheral surface of the outer ring 47 and the bearing surface portion 53 can be positioned in the direction of the meshing reaction force, and the meshing reaction force can be absorbed by the housing 14. It can be supported efficiently.

Further, in this example, each of the pair of second leaf springs 20 is formed into a substantially H-shape and a substantially flat plate shape. Therefore, the second leaf spring 20 can be manufactured at low cost, and when attaching the second leaf spring 20 to the guide member 18, there is no need to consider the directionality with respect to the first direction, which improves assembly efficiency. can be achieved. However, the elastic clamping means that clamps the support bearing from both sides in the second direction can also be configured as a whole. That is, the elastic clamping means can have a structure in which the ends of the pair of second leaf springs 20 that are closer to the worm wheel 15 in the first direction are connected to each other. Furthermore, the elastic clamping means and elastic urging means for elastically urging the support bearing toward the worm wheel may be integrally configured.

In addition, in this example, since the cover 71 is supported at the opening on the other axial side of the guide member 18, even before the guide assembly 77 is installed in a predetermined position, the cover 71 can be accessed from the inside of the guide member 18. It is possible to prevent the support bearing 17, the first leaf spring 19, and the pair of second leaf springs 20 from falling off. Therefore, the support bearing 17, the guide member 18, the first leaf spring 19, the pair of second leaf springs 20, and the cover 71 can be handled as a subassembly, and the worm reducer 12 can be assembled. can improve sexual performance. Furthermore, in this example, with the guide assembly 77 disposed between the guide holding part 26 of the worm housing part 22 and the small diameter cylinder part 45 of the worm 16, the other end of the guide holding part 26 in the axial direction is A retaining ring 78 that is engaged with the guide member 77 prevents the guide assembly 77 from moving to the other side in the axial direction, and also prevents the cover 71 from falling off (coming off) from the guide member 18 . Therefore, even if a force directed toward the other side in the axial direction is applied to the worm 16 due to the transmission of torque between the worm wheel 15 and the worm 16, the worm 16 will not be excessively displaced to the other side in the axial direction. This can prevent the meshing portion between the wheel teeth 29 and the worm teeth 32 from locking.

Further, in this example, a case has been described in which the present invention is applied to a structure in which the central axis of the worm wheel 15 and the central axis of the worm 16 are perpendicular to each other when viewed from the first direction. The reducer can also be applied to a structure in which the central axis of the worm wheel and the central axis of the worm obliquely intersect (form an acute angle) when viewed from the first direction.

In this example, a first leaf spring 19 that constitutes an elastic biasing means is provided between a guide member 18 that is arranged without rattling inside the worm accommodating portion 22 of the housing 14 and an outer ring 47 of the support bearing 17; Although a pair of second leaf springs 20 constituting the elastic clamping means are arranged, the first leaf spring can also be arranged between the worm accommodating portion and the outer ring of the support bearing. Alternatively, in the worm reducer of the present invention, the outer ring of the support bearing is directly fitted into the inner peripheral surface of the worm accommodating portion so as to be able to be displaced in the first direction, and the elastic biasing means and the elastic clamping means are provided. It can also be arranged between the worm accommodating portion and the outer ring or another member (holder member) fitted onto the outer ring.

The electric power assist device of the present invention is not limited to a column assist type electric power steering device, but can be incorporated into electric power steering devices having various structures.

Specifically, for example, in a rack assist type electric power steering device 1a as shown in FIG. A rotary shaft 74 is disposed, and pinion teeth provided at the tip of the rotary shaft 74 are meshed with teeth of a rack 75 constituting the steering gear unit 3.

Further, in a pinion assist type electric power steering device 1b as shown in FIG. 15, a worm wheel 15 of a worm reducer 12 is supported and fixed to an input shaft 4a of a steering gear unit 3a.

Moreover, the worm reducer of the present invention can be incorporated not only in an electric assist device but also in various mechanical devices.

1, 1a, 1b electric power steering device 2 steering wheel 3, 3a steering gear unit 4, 4a input shaft 5 tie rod 6 steering shaft 7 steering column 8a, 8b universal joint 9 intermediate shaft 10, 10a electric assist device 11 electric motor 12 worm Reducer 13 Output shaft 14 Housing 15 Worm wheel 16 Worm 17 Support bearing 18 Guide member 19 First leaf spring 20 Second leaf spring 21 Wheel housing portion 22 Worm housing portion 23 Lid body 24 Cylindrical surface portion 25 Step portion 26 Guide holding portion 27 Inward flange portion 28 Engagement recess 29 Wheel tooth 30 Inner wheel element 31 Outer wheel element 32 Worm tooth 33 Torque transmission joint 34 Drive side transmission member 35 Driven side transmission member 36 Elastic member 37 Coupling 38 Fitting cylinder portion 39 Flange portion 40 Ball bearing 41 Outer ring 42 Inner ring 43 Ball 44 Retaining ring 45 Small diameter cylindrical portion 46 Inner ring 47 Outer ring 48 Rolling element 49 Main body 50 Engagement convex portion 51 Locking groove 52 Elastic ring 53 Bearing surface portion 54 Concave curved surface portion 55 Engagement surface portion 56 Engagement base 57a, 57b Pedestal surface 58 Retaining surface 59 Locking protrusion 60 Notch 61 Side wall 62 Groove 63a, 63b Locking notch 64 Base 65 Folded portion 66 Curved portion 67 Locking hole 68 Base 69a, 69b Arm portion 70 Locking piece 71 Cover 72 Circular hole 73 Locking pawl 74 Rotating shaft 75 Rack 76 Elastic member 77 Guide assembly 78 Retaining ring 79 Locking recess 100 Worm reducer 101 Housing 102 Worm wheel 103 Worm 104 Wheel accommodating portion 105 Worm housing section 106 Wheel teeth 107 Rotating shaft 108 Worm teeth 109a, 109b Ball bearing 110 Holder 111 Large diameter section 112 Bush 113 Electric motor 114 Pad 115 Torsion coil spring

Claims (13)

A housing including a wheel housing part and a worm housing part that is arranged in a twisted position relative to the wheel housing part and has an axially intermediate portion open to the wheel housing part;
a worm wheel having wheel teeth on its outer peripheral surface and rotatably supported inside the wheel housing portion;
a worm having worm teeth on an outer circumferential surface that mesh with the wheel teeth, and rotatably supported inside the worm accommodating portion;
a support bearing having an inner ring fitted around the tip of the worm, and an outer ring disposed around the inner ring coaxially with the inner ring;
Elastic biasing means for elastically biasing the support bearing toward the worm wheel, either directly or via another member fitted onto the outer ring;
Elastic clamping, in which the support bearing or the other member is elastically clamped from both sides with respect to a first direction, which is the biasing direction by the elastic biasing means, and a second direction, which is orthogonal to the central axis of the worm housing part. means and
a guide member that fits the outer ring so as to be displaced in the first direction, and that is fitted inside the worm accommodating portion;
Equipped with
The elastic clamping means includes a pair of second leaf springs each having a substantially flat plate shape and arranged on both sides with respect to the second direction in a portion between the outer ring and the guide member,
The guide member has a pair of engagement surfaces for arranging the pair of second leaf springs on a pair of inner surfaces facing each other in the first direction among the inner circumferential surfaces,
Each of the pair of engagement surfaces includes a flat engagement base perpendicular to the second direction, and is disposed on both sides of the engagement base in the first direction, and It has a pedestal surface part that protrudes more than the
Each of the pair of second leaf springs is in contact with the pedestal surface portion of each of the pair of engagement surface portions,
Worm reducer. The guide member includes a support surface directly facing the outer ring at at least one location in the circumferential direction of the inner circumferential surface of the side farthest from the worm wheel.
The worm reducer according to claim 1 . Each of the pair of second leaf springs includes a pair of distal arm portions disposed on both sides of the support surface portion in the axial direction of the guide member, and a proximal end of the pair of distal arm portions. a base portion connecting the two portions to each other, and having an inner surface of the guide member in a radial direction elastically abutted against an outer circumferential surface of the outer ring;
The worm reducer according to claim 2 . A housing including a wheel housing part and a worm housing part that is arranged in a twisted position relative to the wheel housing part and has an axially intermediate portion open to the wheel housing part;
a worm wheel having wheel teeth on its outer peripheral surface and rotatably supported inside the wheel housing portion;
a worm having worm teeth on an outer circumferential surface that mesh with the wheel teeth, and rotatably supported inside the worm accommodating portion;
a support bearing having an inner ring fitted around the tip of the worm, and an outer ring disposed around the inner ring coaxially with the inner ring;
Elastic biasing means for elastically biasing the support bearing toward the worm wheel, either directly or via another member fitted onto the outer ring;
Elastic clamping, in which the support bearing or the other member is elastically clamped from both sides with respect to a first direction, which is the biasing direction by the elastic biasing means, and a second direction, which is orthogonal to the central axis of the worm housing part. means and
a guide member that fits the outer ring so as to be displaced in the first direction, and that is fitted inside the worm accommodating portion;
Equipped with
The guide member has a support surface portion that directly faces the outer ring at at least one location in the circumferential direction of the inner peripheral surface of the portion farthest from the worm wheel;
The elastic clamping means includes a pair of second leaf springs disposed on both sides in the second direction in a portion between the outer ring and the guide member,
Each of the pair of second leaf springs includes a pair of distal arm portions disposed on both sides of the support surface portion in the axial direction of the guide member, and a proximal end of the pair of distal arm portions. a base portion connecting the two portions to each other, and having an inner surface of the guide member in a radial direction elastically abutted against an outer circumferential surface of the outer ring;
Worm reducer. Each of the pair of second leaf springs has a pair of close springs extending from both ends of the base in the axial direction of the guide member toward a side closer to the worm wheel in the first direction. further comprising a lateral arm;
The worm reducer according to claim 3 or 4 . The elastic biasing means is disposed between the outer ring and the guide member, or between the outer ring and the worm housing part.
The worm reducer according to any one of claims 1 to 5 . further comprising an elastic ring elastically held between an inner circumferential surface of the worm accommodating portion and an outer circumferential surface of the guide member;
The worm reducer according to any one of claims 1 to 6 . The amount of elastic compression of the elastic ring in a side portion closer to the worm wheel is larger than the amount of elastic compression of the elastic ring in a side portion farther from the worm wheel.
The worm reducer according to claim 7 . The elastic ring is locked to the outer circumferential surface of the guide member in a state in which the center axis of the elastic ring is offset from the center axis of the guide member toward the side closer to the worm wheel with respect to the first direction. There is,
The worm reducer according to claim 8 . The elastic biasing means is located on a side far from the worm wheel with respect to the first direction, in a portion between the outer ring and the guide member, or a portion between the outer ring and the inner circumferential surface of the worm accommodating portion. a first leaf spring disposed in the portion;
The worm reducer according to any one of claims 1 to 9 . Each of the pair of second leaf springs further includes a locking piece for locking each of the pair of second leaf springs to the guide member.
The worm reducer according to any one of claims 1 to 10 . The guide member further includes a cover supported by an opening on the tip side of the worm.
The worm reducer according to any one of claims 1 to 11 . electric motor and
a worm reducer that increases the torque of the electric motor and applies it to a rotating shaft that rotates with rotation of a steering wheel or a linear shaft that constitutes a steering gear unit;
Equipped with
An electric assist device, wherein the worm reducer is the worm reducer according to any one of claims 1 to 12 .

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