JP2004351989A - Electric power steering device and manufacturing method of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device reducing the number of part items and its weight by preventing slippage between a large gear and a ball nut, and also to provide a manufacturing method of the electric power steering device. <P>SOLUTION: The large gear 8 is constituted of a metallic tooth core part 8b and a synthetic resin made tooth member 8a. The tooth core part 8b is peripherally provided on an outer periphery 7a of the metallic cylindrical ball nut 7 so as to be integral with it. The tooth core part 8b is rectangular on its cross-section in the axial direction, a projected part 8c a cross-section in the axial direction of which is roughly rectangular is peripherally provided in width smaller than width of the tooth core part 8b on a central part of an outer periphery of the tooth core part 8b, and dimensions in the axial direction of the projected part 8c are formed so that the outer peripheral side becomes longer than the inner peripheral side. The tooth member 8a is peripherally provided in the same width as the tooth core part 8b on the outer periphery of the tooth core part 8b, and gear cutting work is applied on an outer peripheral head end part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device that transmits driving of a motor to a rack shaft to assist steering and a method of manufacturing the electric power steering device.
[0002]
[Prior art]
Conventionally, an electric power steering device referred to as a rack assist type includes a rack shaft having rack teeth meshing with a pinion provided on a pinion shaft connected to a steering shaft, and a ball screw portion formed on the rack shaft. A ball screw mechanism having a ball nut externally fitted to the ball screw portion, a large gear attached to the outer periphery of the ball nut, and a small gear provided at an end of an output shaft of the motor and meshing with the large gear. And assists the steering by moving the rack shaft in the axial direction by driving a motor.
[0003]
A spiral groove is formed on the inner periphery of the ball nut, and by filling a plurality of balls into a track formed by a combination of the spiral groove and the ball screw portion of the rack shaft, a smooth rotation of the ball nut is ensured. The rotation of the ball nut moves the ball in the track to move the rack shaft in the axial direction. On the outer periphery of the ball nut, a large gear is fitted and attached, and by engaging the large gear with a small gear attached to the output shaft of the motor, the rotation of the output shaft of the motor causes the small gear and the large gear to rotate. , The ball nut can be rotated at a reduced speed, and the rotation of the ball nut moves the rack shaft in the axial direction to assist the steering.
[0004]
The gear is composed of a metal cylindrical tooth core member and a synthetic resin tooth member, and after the tooth core member is loaded in a mold, a synthetic resin is injected to melt the tooth core member with molten resin. The tooth member is molded by wrapping and hardening, and the gear member is attached by press-fitting the large gear into a ball nut (for example, see Patent Document 1).
Further, as another conventional example, the key groove provided on the inner periphery of the metal cylindrical tooth core member of the large gear and the key groove provided on the outer periphery of the cylindrical ball nut are opposed to each other. The gear is attached to the ball nut by externally fitting the gear to a ball nut, inserting a key member into a mounting hole formed by the key groove, and fixing the key member with a lock nut. There is also.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-225734
[Problems to be solved by the invention]
In the electric power steering apparatus described in Patent Literature 1, there is a possibility that the large gear and the ball nut may slip with the increase in the output of the motor that auxiliary drives the rack shaft.
Further, in the other conventional example, the number of parts is increased and the weight is increased as compared with the case where the large gear is press-fitted into the ball nut.
Further, in any of the above cases, there is a possibility that the concentric accuracy between the ball nut and the large gear may be impaired due to a mounting error occurring at the time of mounting.
[0007]
The present invention has been made in view of such circumstances, and a tooth center portion of a large gear is formed integrally with an outer periphery of a ball nut, and a tooth member of the large gear is formed on the tooth center portion. It is an object of the present invention to provide an electric power steering device in which slip between a gear and a ball nut is prevented, the number of parts is reduced and the weight is reduced, and a method of manufacturing the electric power steering device.
It is another object of the present invention to provide an electric power steering device in which the strength of the large gear is increased by increasing the contact area between the tooth member of the large gear and the tooth center, and a method of manufacturing the electric power steering device.
Furthermore, a method for manufacturing an electric power steering apparatus in which the precision of concentricity between a gear and a ball nut is improved by forming a tooth member by performing gear cutting after a pre-machining tooth member is formed at a tooth center portion of the gear. The purpose is to provide.
[0008]
[Means for Solving the Problems]
An electric power steering apparatus according to a first aspect of the present invention includes a large gear provided on an outer periphery of a ball nut externally fitted to a ball screw formed on a rack shaft interlocked with a steering shaft, and a motor output. An electric power steering device that is provided on a shaft and includes a small gear that meshes with the large gear, and that drives the motor to move the rack shaft to assist in steering, wherein the large gear is provided on an outer periphery of the ball nut. It is characterized by comprising an integrally formed tooth core and a tooth member provided on the outer periphery of the tooth core.
[0009]
In the electric power steering apparatus according to the second aspect of the present invention, the tooth center in the first aspect is provided with a projection having a substantially rectangular cross section in the axial direction around the outer periphery of the tooth center having a rectangular cross section in the axial direction. It is characterized by having done.
[0010]
An electric power steering apparatus according to a third aspect of the present invention is characterized in that the axial dimension of the projection in the second aspect is formed such that the outer peripheral side is longer than the inner peripheral side.
[0011]
An electric power steering apparatus according to a fourth invention of the present invention is characterized in that a plurality of tooth centers in the first invention have a substantially rectangular cross section in the axial direction and are spaced apart from each other.
[0012]
An electric power steering apparatus according to a fifth aspect of the present invention is characterized in that the tooth center portion according to the first aspect is formed in a substantially rectangular shape in an axial section at a bottom of a groove formed in the ball nut. I do.
[0013]
An electric power steering device according to a sixth aspect of the present invention is characterized in that the axial dimension of the tooth core in the fourth or fifth aspect is formed such that the outer peripheral side is longer than the inner peripheral side. I do.
[0014]
A method for manufacturing an electric power steering device according to a seventh aspect of the present invention is the method for manufacturing an electric power steering device for manufacturing the electric power steering device according to any of the first to sixth aspects, wherein the large gear is provided on the outer periphery of the ball nut. Are formed integrally with each other, a pre-processed tooth member is formed on the outer periphery of the tooth center portion, and the pre-processed tooth member is subjected to tooth cutting to form a tooth member.
[0015]
According to the first aspect, the tooth center portion of the large gear is formed integrally with the ball nut to prevent slippage between the large gear and the ball nut even when the steering assist driving force is increased. Since the key member and the lock nut can be omitted, the number of parts can be reduced and the weight can be reduced.
[0016]
In the second invention, the third invention, the fourth invention, the fifth invention, and the sixth invention, the contact area between the tooth member of the large gear and the tooth core is increased, and the strength of the large gear is reduced. To increase.
[0017]
According to the seventh aspect of the present invention, by forming a tooth member by forming a pre-working tooth member at the tooth center portion of the gear and then performing tooth cutting to eliminate the mounting error, the concentric accuracy between the gear and the ball nut is eliminated. Can be improved.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings showing the embodiments.
Embodiment 1
FIG. 1 is a partially broken front view showing a configuration of an electric power steering device according to the present invention. In the figure, reference numeral 5 denotes a long cylindrical housing horizontally placed in the left-right direction of the vehicle. A rack shaft 3 is supported inside the housing 5 so as to be movable in the left-right direction. At one end of the rack shaft 3, rack teeth 3a are formed. A steering wheel 1 is attached to an upper end of a steering shaft 2 provided in the vertical direction, and a pinion shaft (not shown) having a pinion (not shown) is connected to a lower end of the steering shaft 2, and the pinion is connected to the rack teeth 3a. Has been engaged. Steering of wheels (not shown) connected via knuckle arms (not shown) attached to left and right ends of the rack shaft 3 causes the rack shaft 3 to rotate in conjunction with rotation of the steering shaft 2 by operating the steered wheels 1. This is performed by being moved in the left-right direction.
[0019]
A ball screw portion 3b is formed at the other end of the rack shaft 3, and a metal cylindrical ball nut 7 is fitted to the ball screw portion 3b. The large gear 8 provided on the outer periphery 7a of the ball nut 7 is meshed with a small gear 9 provided at the end of the output shaft 4a of the motor 4. The motor 4 is attached to a motor support 5a provided in the housing 5.
[0020]
The steering torque applied to the steering shaft 2 via the steered wheels 1 is detected by a torque sensor (not shown), and the drive of the motor 4 is controlled according to the detected torque. The rotation of the output shaft 4a of the motor 4 is transmitted to the large gear 8 via the small gear 9 to rotate the ball nut 7 at a reduced speed, and the rack shaft 3 moves in the left-right direction to assist steering.
[0021]
FIG. 2 is an axial sectional view showing the large gear 8 according to the present invention. The large gear 8 includes a metal tooth core 8b and a synthetic resin tooth member 8a. The tooth core 8b is provided so as to be integral with the outer periphery 7a of the metal cylindrical ball nut 7. The tooth core 8b has a projection 8c having a rectangular cross section in the axial direction and a substantially rectangular cross section in the axial direction over a width smaller than the width of the tooth core 8b at the center of the outer periphery of the tooth core 8b. The projection 8c is formed so that the dimension in the axial direction of the projection 8c is longer on the outer circumference than on the inner circumference. Note that a plurality of protrusions 8c may be provided on the outer periphery of the tooth core 8b. The tooth member 8a is provided around the outer circumference of the tooth core 8b with the same width as the tooth core 8b, and the outer peripheral tip is subjected to gear cutting.
[0022]
Next, molding of the tooth member 8a will be described. After the tooth core portion 8b is loaded into a mold having a substantially hollow cylinder having a diameter equivalent to the diameter of the large gear 8 and a length equivalent to the tooth thickness of the large gear 8, the synthetic resin (for example, reinforcing fiber is mixed). Nylon resin) is injected into the mold, and a molten synthetic resin is flowed around the outer periphery of the tooth core 8b and hardened. Mold. The outer peripheral tip of the pre-machining tooth member is subjected to gear cutting with a required dimension and accuracy to form the tooth member 8a.
Note that the tooth member 8a may be formed by performing an outsert molding in which a synthetic resin is adhered and fixed to the tooth core 8b by molding, and then a gear cutting process is performed.
[0023]
By forming the tooth core 8b of the large gear 8 integrally with the outer periphery 7a of the ball nut 7, slippage between the large gear 8 and the ball nut 7 is eliminated, and a key member for attaching the large gear 8 to the ball nut 7 is provided. Further, the need for a lock nut is eliminated, and the number of parts can be reduced and the weight can be reduced. In addition, since the tooth member 8a is formed by wrapping the protrusion 8c provided around the outer periphery of the tooth core 8b, the contact area between the tooth member 8a and the tooth core 8b is increased, and the strength of the large gear 8 is reduced. To increase. Further, since the tooth cutting is performed on the outer periphery of the tooth core portion 8b and then the tooth cutting process is performed to form the tooth member 8a, an error due to mounting is eliminated, and the concentric accuracy between the large gear 8 and the ball nut 7 is reduced. Is improved. Further, since the tooth member 8a having teeth integrally formed thereon is formed on the outer periphery of the tooth core portion 8b, mounting errors are eliminated, and concentric accuracy between the large gear 8 and the ball nut 7 is improved.
[0024]
Embodiment 2
FIG. 3 is an axial sectional view showing the large gear 8 according to the present invention. The large gear 8 is composed of two metal core portions 8b, 8b and a synthetic resin tooth member 8a. Each of the tooth cores 8b, 8b has an appropriate separation width, and has a substantially rectangular axial cross section outwardly over an appropriate width so as to be integrated with the outer periphery 7a of the metal cylindrical ball nut 7. Is provided. Each side surface of the tooth cores 8b, 8b, which is opposite to the side facing the tooth cores 8b, 8b, is formed perpendicular to the axial direction. Each of the opposing side surfaces is formed such that the axial dimension of the tooth core 8b is longer on the outer peripheral side than on the inner peripheral side. The tooth member 8a has the same width as the separation width between the opposite side surfaces of the tooth cores 8b, 8b, and is provided around the outer circumference of the tooth cores 8b, 8b. Is given.
[0025]
The molding of the tooth member 8a is the same as that of the first embodiment, and the description is omitted.
By arranging the two tooth centers 8b, 8b on the outer circumference 7a of the ball nut 7 at a distance from each other, the tooth centers 8b, 8b and the tooth member 8a are compared with the case where one tooth center 8b is installed. The contact area with the large gear 8 increases, and the strength of the large gear 8 increases.
[0026]
Embodiment 3
FIG. 4 is an axial sectional view showing the large gear 8 according to the present invention. A groove 10 having a rectangular vertical cross section is provided around the outer periphery 7a of the metal cylindrical ball nut 7 over an appropriate width. The tooth core 8 b is provided around the center of the bottom of the groove 10 so as to have a substantially rectangular axial section in the outward direction and is formed integrally with the ball nut 7. The axial dimension of the tooth core 8b is longer on the outer peripheral side than on the inner peripheral side, and the height of the tooth core 8b is formed to be the same dimension as the depth of the groove 10. Note that the height of the tooth core 8b may be higher than the depth of the groove 10. The tooth member 8a is provided around the outer periphery of the tooth core 8b with the same width as the width of the groove 10.
[0027]
The molding of the tooth member 8a is the same as that of the first embodiment, and the description is omitted.
When the groove 10 having an appropriate width is provided on the outer periphery 7a of the ball nut 7, and the tooth core 8b is provided around the bottom center of the groove 10, so that the tooth core 8b is provided around the outer periphery 7a of the ball nut 7. The contact area on the side surface of the groove 10 increases, the contact area between the tooth core 8b and the tooth member 8a increases, and the strength of the large gear 8 increases.
In the above-described embodiment, instead of the above-described tooth cutting, a molten synthetic resin is caused to flow around the outer periphery of the tooth core 8b and hardened, so that the teeth having the required dimensions and accuracy are integrally formed. The member 8a may be formed. Thereby, the gear cutting process can be omitted.
[0028]
【The invention's effect】
As described in detail above, in the present invention, the gear center of the gear wheel is formed integrally with the outer periphery of the ball nut, and the gear member of the gear wheel is formed on the gear core, so that the gear wheel Sliding with the ball nut can be prevented. Further, since a key member and a lock nut for attaching the large gear to the ball nut are not required, the number of parts can be reduced and the weight can be reduced.
[0029]
Further, in the present invention, the contact area between the tooth member of the large gear and the tooth center increases, and the strength of the large gear increases.
[0030]
Further, according to the present invention, by forming a tooth member by forming a pre-working tooth member at a tooth core portion formed integrally with a ball nut and then forming a tooth member, errors due to mounting are eliminated, and the large gear and the ball are removed. Concentricity with the nut can be improved. Furthermore, by forming a tooth member in which teeth having the required dimensions and precision are integrally formed, mounting errors are eliminated, and concentric precision between the large gear and the ball nut can be improved.
[Brief description of the drawings]
FIG. 1 is a partially broken front view showing a configuration of an electric power steering device according to the present invention.
FIG. 2 is an axial sectional view showing a large gear according to the present invention.
FIG. 3 is an axial cross-sectional view showing a large gear according to the present invention.
FIG. 4 is an axial sectional view showing a large gear according to the present invention.
[Explanation of symbols]
2 Steering shaft 3 Rack shaft 3b Ball screw 4 Motor 4a Output shaft 7 Ball nut 7a Ball nut outer circumference 8 Large gear 8a Tooth member 8b Tooth core 8c Projection 9 Small gear 10 Groove

Claims (7)

A large gear provided on the outer periphery of a ball nut externally fitted to a ball screw portion formed on a rack shaft interlocked with the steering shaft, and a small gear provided on the output shaft of the motor and meshing with the large gear. In the electric power steering device that comprises, to move the rack shaft by driving the motor to assist in steering,
The electric power steering apparatus according to claim 1, wherein the large gear includes a toothed portion integrally formed on an outer periphery of the ball nut and a tooth member provided on an outer periphery of the toothed portion. 2. The electric power steering apparatus according to claim 1, wherein the tooth center portion is provided with a projection having a substantially rectangular cross section in the axial direction around an outer periphery of the tooth center portion having a rectangular cross section in the axial direction. 3. The electric power steering apparatus according to claim 2, wherein an axial dimension of the protrusion is formed so that an outer peripheral side is longer than an inner peripheral side. The electric power steering apparatus according to claim 1, wherein a plurality of the tooth cores are formed so as to be spaced apart from each other in a substantially rectangular shape in the axial direction. The electric power steering device according to claim 1, wherein the tooth center portion has a substantially rectangular cross section in an axial direction at a bottom of a groove formed in the ball nut. 6. The electric power steering apparatus according to claim 4, wherein an axial dimension of the tooth center portion is formed such that an outer peripheral side is longer than an inner peripheral side. A method for manufacturing an electric power steering apparatus for manufacturing the electric power steering apparatus according to claim 1, wherein:
A toothed portion of the large gear is integrally formed on the outer periphery of the ball nut, a processed front tooth member is formed on the outer periphery of the toothed portion, and the toothed portion is formed by cutting the processed front tooth member. Manufacturing method of an electric power steering device.

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