JP4479403B2 - Worm, worm reducer, and electric power steering device - Google Patents

Description

  The present invention is suitable for an electric power steering device that generates auxiliary steering torque from an electric motor in response to a steering torque applied to a steering wheel, decelerates it, and transmits it to an output shaft of a steering mechanism. The present invention relates to a reduction gear, and more particularly to an electric power steering device including the worm reduction gear.

  In a steering system of an automobile, a so-called power steering device that performs steering assist using an external power source is widely adopted. Conventionally, vane type hydraulic pumps have been used as power sources for power steering devices, and many of these hydraulic pumps are driven by an engine. However, this type of power steering device has a large engine drive loss due to the constant drive of the hydraulic pump (several horsepower to about 10 horsepower at the maximum load), so it can be used in light vehicles with small displacement. It was difficult, and it was unavoidable that the fuel consumption of a car with a relatively large displacement was reduced to a level that could not be ignored.

  Therefore, in order to solve these problems, an electric power steering device (Electric Power Steering, hereinafter referred to as EPS) using an electric motor as a power source has attracted attention in recent years. The EPS uses an in-vehicle battery as a power source for the electric motor, so there is no direct engine drive loss, and since the electric motor is started only at the steering assist time, a decrease in driving fuel consumption is suppressed, and electronic control is performed. It has the feature that it can be done very easily.

  In EPS, an auxiliary steering torque is generated from an electric motor in response to a steering torque applied to a steering wheel, and is decelerated by a power transmission mechanism (worm reducer) and transmitted to an output shaft of the steering mechanism. ing.

  FIG. 5 is a longitudinal sectional view of an electric power steering apparatus according to a conventional example. 6A, 6B, and 6C are side views of a worm according to a conventional example.

  As shown in FIG. 5, a worm 3 is rotatably supported on the gear housing 1 via a pair of bearings 2a and 2b. A recess 4 is formed at the base end of the worm 3, and a female spline is formed in the recess 4. A drive shaft 5 of an electric motor (not shown) on which a male spline is formed is connected to the spline. The worm 3 is allowed to move in the axial direction.

  A pair of dampers 7a and 7b are formed between both flange portions 6a and 6b of the worm 3 and both inner rings of the pair of bearings 2a and 2b, respectively. Supports the generation of rattle noises.

  As shown in FIGS. 6A and 6B, the worm 3 is formed with a complete screw portion 20 at the center thereof, and the gear teeth of the worm wheel 8 mesh with the complete screw portion 20. It is.

  Further, as shown in FIGS. 6A and 6B, relief portions 22 having a small diameter are formed on both sides of the complete screw portion 20.

  Furthermore, in the example shown in FIG. 6C, both sides of the complete screw portion 20 are outside the intersection range where the outer diameter of the worm 3 and the outer diameter of the worm wheel 8 intersect (that is, both end portions from the intersection range). An incomplete thread 21 is formed on the side. Further, the outer diameter of the incomplete screw portion 21 is equal to the outer diameter of the complete screw portion 20. If the inside of the intersection range where the outer diameter of the worm 3 and the outer diameter of the worm wheel 8 intersect with each other and the inner side of the position where the complete screw portion is located, interference occurs.

  However, in recent years, in order to improve the layout of the vehicle, there has been a demand for reduction in size and weight, and downsizing of the worm reduction gear is no exception, and reduction in the overall length of the worm is required.

  When the complete screw portion of the worm meshes with the gear teeth of the worm wheel, the axial length of the complete screw portion is set so that the incomplete screw portion and the gear teeth of the worm wheel do not interfere with each other. Conventionally, the length is limited and shortening is difficult.

  The present invention has been made in view of the circumstances as described above, and shortens the axial length of the complete screw portion to shorten the overall length of the worm, thereby reducing the size and weight of the electric power steering device. It is an object of the present invention to provide a worm, a worm reducer, and an electric power steering device that can be realized.

In order to achieve the above object, a worm according to claim 1 of the present invention is a worm having a complete threaded portion at an approximately central portion in the axial direction and an incomplete threaded portion at both ends , and meshing with a worm wheel .
Substantially inboard from the intersection range and outer diameter of the worm wheel of the worm intersect, Yes forms part of the incomplete thread portion, respectively,
The incomplete screw part is characterized in that at least a part of the outer diameter is set smaller than the outer diameter of the complete screw part and larger than the root diameter.

  A worm speed reducer according to a second aspect of the present invention includes the worm according to the first aspect.

  An electric power steering apparatus according to a third aspect of the present invention includes the worm speed reducer according to the second aspect.

According to the present invention, a substantially inboard from the intersection range and the outer diameter of the worm of the outer diameter and the worm wheel intersect, Yes forms part of the incomplete thread portion, respectively, the incomplete thread portion, that Since at least a part of the outer diameter is smaller than the outer diameter of the complete threaded portion, there is a gap (margin) that does not interfere with the gear teeth of the other worm wheel.

  Therefore, in the complete screw portion, the axial length of the complete screw portion can be shortened by reducing the outer diameter of the incomplete screw portion at both ends of the complete screw portion. As a result, the overall length of the worm can be shortened, and as a result, the electric power steering device can be reduced in size and weight.

  Hereinafter, a worm, a worm reducer, and an electric power steering device according to embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a longitudinal sectional view of an electric power steering apparatus according to an embodiment of the present invention.

  FIG. 2 is a longitudinal sectional view of the electric power steering apparatus according to the embodiment of the present invention.

FIG. 3A is a longitudinal sectional view of an electric power steering apparatus according to a reference example of the present invention, and FIG. 3B is an enlarged sectional view of a portion surrounded by a circle in FIG.

  4 (a) and 4 (b) are side views of the worm according to the embodiment of the present invention.

  As shown in FIG. 1, a worm 3 is rotatably supported on the gear housing 1 through a pair of bearings 2a and 2b. A recess 4 is formed at the base end of the worm 3, and a female spline is formed in the recess 4. A drive shaft 5 of an electric motor (not shown) on which a male spline is formed is connected to the spline. The worm 3 is allowed to move in the axial direction.

  A pair of dampers 7a and 7b are formed between both flange portions 6a and 6b of the worm 3 and both inner rings of the pair of bearings 2a and 2b, respectively. Supports the generation of rattle noises.

  As shown in FIGS. 4 (a) and 4 (b), the worm 3 has a complete screw portion 10 formed at the center thereof, and the gear teeth of the worm wheel 8 mesh with the complete screw portion 10. It is.

Further, as shown in FIG. 2, on both sides of the complete screw portion 10, inside the intersection range where the outer diameter of the worm 3 and the outer diameter of the worm wheel 8 intersect (that is, near the center from the intersection range). A pair of incomplete threaded portions 11, 11 are formed .

  The incomplete screw portions 11 and 11 are set such that at least a part of the outer diameter is smaller than the outer diameter of the complete screw portion 10 and larger than the root diameter.

  With this configuration, as shown in FIG. 3B, the hatched portion is removed, the outer diameter of the incomplete screw portion is reduced, and a gap (margin) that does not interfere with the gear teeth of the worm wheel 8 of the other party is provided. it can.

  Therefore, in the complete screw portion 10, the axial length of the complete screw portion 10 can be shortened by reducing the outer diameter of the incomplete screw portions 11, 11 at both ends of the complete screw portion 10. . As a result, the overall length of the worm 3 can be shortened, and as a result, the electric power steering device can be reduced in size and weight.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible.

1 is a longitudinal sectional view of an electric power steering device according to an embodiment of the present invention. 1 is a longitudinal sectional view of an electric power steering device according to an embodiment of the present invention. (A) is a longitudinal cross-sectional view of the electric power steering apparatus which concerns on the reference example of this invention, (b) is an expanded sectional view of the part enclosed by the circle in (a). (A) and (b) are side views of the worm according to the embodiment of the present invention, respectively. It is a longitudinal cross-sectional view of the electric power steering apparatus which concerns on a prior art example. (A) (b) (c) is a side view of the worm | warm which concerns on a prior art example, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gear housing 2a, 2b Bearing 3 Worm 4 Recessed part 5 Drive shaft 6a, 6b Gutter part 7a, 7b Damper 8 Worm wheel 10 Completely threaded part 11 Incompletely threaded part 20 Completely threaded part 21 Incompletely threaded part 22 Escape part

Claims (3)

In a worm that has a complete thread part in the substantially central part in the axial direction and incomplete thread parts at both ends , and meshes with the worm wheel .
Substantially inboard from the intersection range and outer diameter of the worm wheel of the worm intersect, Yes forms part of the incomplete thread portion, respectively,
The worm is characterized in that at least a part of the outer diameter of the incomplete screw portion is smaller than the outer diameter of the complete screw portion and larger than the root diameter.   A worm speed reducer comprising the worm according to claim 1.   An electric power steering apparatus comprising the worm speed reducer according to claim 2.

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