JP2001271889A - Structure of a pair of involute gears - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide structure of a pair of involute gears which maintains strength of the tooth root, improving the contact ratio and sufficiently coping with the change of center distance, in the case the tooth number of a small gear is extremely small. SOLUTION: In this structure of a pair of involute gears, the pressure angle of the tooth end of the small gear is made smaller than that of the tooth root, and the pressure angle of the tooth end of the large gear is made equal to the pressure angle of the tooth root of the small gear. Furthermore, the pressure angle of the tooth root of the large gear is made equal to the pressure angle of the tooth end of the small gear.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pair of involute gears meshing with each other, wherein the number of teeth on the small gear side is 16 or less, and the pair of involute gears is made of a plastic material used in an environment where a temperature change is large. About. In addition, the present invention particularly relates to a gear applicable to a pair of involute gears made of plastic materials having different linear expansion coefficients.

[0002]

2. Description of the Related Art For a small gear having 16 or less teeth, a transition gear is used in the manufacture thereof in order to prevent the gear from being cut down.
In a positive transition, the root of the tooth root is shortened and the tooth pressure is increased, so that devaluation can be reduced or prevented. FIG. 3 shows a meshing state of a transition gear in which the pressure angle is 20 °, the number of teeth of the small gear is 10, and the number of teeth of the large gear is 61. FIG. 4 shows a similar engagement state at a pressure angle of 12 °.

[0003]

The pressure angle is large (20
°) In the state shown in FIG. 3, the downshift of the small gear can be prevented by the transition. However, there is a drawback that the tip of the tooth is shortened and the meshing ratio is reduced accordingly. In the state of FIG. 4 where the pressure angle is small (12 °),
Although the addendum is longer, the root of the tooth is cut down and the strength of the small gear is reduced. When such a gear is made of plastic, the depressed portion becomes narrow in a neck shape, and when the resin material is cooled and contracted during injection molding, the die cannot be removed,
Manufacturing of gears becomes difficult. As described above, there has been no practical plastic involute gear that can increase the contact ratio and can be used in a place where the temperature changes greatly under the condition that the number of teeth of the small gear is extremely small. In particular, in the case of a pair of involute gears made of plastic materials having different linear expansion coefficients, meshing often becomes impossible due to a change in environmental temperature. Therefore, an object of the present invention is to develop a gear that solves the above problems.

[0004]

According to the first aspect of the present invention, the first tooth profile 1 having a small number of teeth and the second tooth profile 2 having a large number of teeth are transmitted while meshing with each other. In the formed pair of involute gear structures, the first tooth profile 1 is:
The pressure angle α ₁ of the involute tooth profile 1a on the tip side,
The pressure angle α ₂ of the involute tooth profile 1b on the root side is α
₁ <α ₂ , and the second tooth form 2 has a pressure angle α ₃ of the involute tooth form 2a on the tip end side and a pressure angle α ₄ of the involute tooth form 2b on the root side, α ₃ = α. _2, α
₄ = is a pair of involute gears structure, characterized in that the alpha ₁ relationship. According to a second aspect of the present invention, in the first aspect, the number of teeth of the first tooth profile 1 is 16 or less, and the tooth profile is positively shifted, and the number of teeth of the second tooth profile 2 is 25 or more. In addition, the tooth profile is a pair of involute gear structures that are negatively or positively shifted or not shifted. According to a third aspect of the present invention, there is provided a pair of involute gear structures made of a plastic material according to the first or second aspect.

[0005]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an enlarged plan view showing a main part of a pair of involute spur gears of the present invention, and FIG. 2 is a reference diagram for comparatively explaining the operation and effect of the gear of the present invention.
In FIG. 1, a first tooth profile 1 constituting a small gear having 10 teeth has an involute tooth profile 1a on the tip end side with a pressure angle of 12 ° based on a base circle D ₁ having the first pressure angle. The involute tooth profile 1b on the root side has a pressure angle of 20 °
belongs to. And the involute tooth profile 1a on the appendix side
Is positive and the transfer coefficient of the involute tooth profile 1b on the root side is positive and 0.3. The second tooth profile 2 which is a large gear is an example in which the number of teeth is 61,
Based on the second pressure angle basic circle D _2, involute 2a of the addendum side is at a pressure angle of 20 °, pressure angle tooth root side of the involute tooth 2b is 12 °. The involute tooth profile 2a on the appendix side has a negative transfer coefficient and −
0.53, and the root-side involute tooth profile 2b is negative and has a transfer coefficient of -0.818. In this example, the reference pitch circle diameter of the first tooth profile 1 is 0.9 mm,
That of the second tooth profile 2 is 11.59 mm. The module size is 0.19.

The addendum on the side of the small gear (first tooth profile 1) is
In FIG. 2 which is a reference diagram, the tooth profile 3 of the first pressure angle indicated by a solid line.
The pressure angle of 12 ° is adopted, and the tooth root adopts the pressure angle of 20 ° of the tooth form 4 of the second pressure angle indicated by the dotted line. By doing so, the strength of the tooth root of the small gear is increased,
By increasing the length of the tooth tip, the contact ratio can be improved as much as possible, and a smooth tooth engagement can be ensured.

FIG. 5 shows another embodiment of the present invention, in which the number of teeth of a small gear (first tooth form 1) is ten and the number of teeth of a large gear (second tooth form 2) is ten. 61 is an example. Basically, it is the same as that of FIG. 1, and the addendum on the side of the small gear (first tooth profile 1) is the first solid line in FIG.
The pressure angle 12 ° of the tooth form 3 of the pressure angle is employed, and the tooth root employs the pressure angle 20 ° of the tooth form 4 of the second pressure angle indicated by the dotted line. By doing so, the strength of the root of the pinion of the pinion can be increased, and the end gear can be lengthened, the meshing rate can be improved as much as possible, and a smooth meshing can be ensured.

[0008]

According to the pair of involute gear structures of the present invention, the first tooth profile 1 of the small gear having a small number of teeth is provided.
Can secure the strength at the base of the tooth, and can increase the meshing ratio to perform smooth transmission. In other words, it is possible to increase the pressure angle at the root of the pinion and eliminate the devaluation, and to reduce the pressure angle at the tooth tip to lengthen the tooth tip and increase the meshing ratio. it can. In addition, since both the addendum and the root have involute tooth profiles, reliable transmission can be ensured and the production thereof is easy. Further, since the second tooth profile 2 has a large number of teeth, even if the pressure angle at the root of the tooth is smaller than that at the end of the tooth, there is no problem in strength.

According to the second aspect of the present invention, since the number of teeth of the first tooth profile 1 is 16 or less and the tooth profile is positively shifted, the end of the tooth is long. The original warp becomes shorter, the tooth pressure becomes thicker, preventing the undercut, and the strength of the small gear can be increased. The number of teeth of the second tooth profile 2 is 2
The gap is 5 or more, and the gap between the leading end of the large gear and the tooth bottom of the small gear is kept large, so that normal engagement can be maintained even if the distance between the shafts is shortened due to environmental temperature changes. Further, normal engagement can be maintained even when the distance between the shafts becomes long. This is because the addendum of the small gear is long, and the root of the large gear meshing with it is long.

According to a third aspect of the present invention, in the pair of involute gear structures of the respective inventions, the gears are made of a plastic material. According to the present invention, it is possible to prevent the undercut and eliminate the narrowing of the tooth root, so that even when the resin material is cooled and solidified and reduced during plastic molding, the product can be released from the mold. .
Therefore, a highly reliable and accurate plastic gear can be provided.

[Brief description of the drawings]

FIG. 1 is an enlarged plan view of a pair of involute tooth profiles of the present invention.

FIG. 2 is a comparative reference diagram for explaining a pair of involute tooth profiles of the present invention.

FIG. 3 shows a conventional gear, in which a transition angle gear having a pressure angle of 20 °, a small gear having 10 teeth, and a large gear having 61 teeth is meshed.

FIG. 4 shows a conventional gear, in which a transition angle gear having a pressure angle of 12 °, a small gear having 10 teeth, and a large gear having 61 teeth is meshed.

FIG. 5 is an enlarged plan view of another pair of involute tooth profiles of the present invention.

FIG. 6 is a comparative reference diagram for explaining a pair of involute tooth profiles of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 1st tooth profile 1a Involute tooth profile at the end of the tooth 1b Involute tooth profile at the root of the tooth 2 Second tooth profile 2a Involute tooth profile at the end of the tooth 2b Involute tooth profile at the root of the tooth D ₁ Base circle of the first pressure angle D ₂ 2 Basic circle of pressure angle D ₃ Basic circle of first pressure angle D ₀ Pitch circle 3 Tooth profile of first pressure angle 4 Tooth profile of second pressure angle

Claims (3)

[Claims] 1. A pair of involute gear structures formed so that a first tooth profile 1 having a small number of teeth and a second tooth profile 2 having a large number of teeth are meshed with each other and transmitted. 1 is an involute tooth profile 1a on the distal end side
A pressure angle alpha ₁ of the pressure angle alpha ₂ of the tooth root side of the involute tooth 1b is in the relationship of alpha ₁ <alpha _2, the second tooth 2, involute tooth 2a of the addendum side
A pressure angle alpha ₃ of the pressure angle alpha ₄ of the tooth root side of the involute tooth 2b _{is, α 3 = α 2, α} 4 = α a pair of involute gears structure, characterized in that in _one relationship. 2. The tooth profile of claim 1, wherein the number of teeth of the first tooth profile 1 is 16 or less and the tooth profile is positively shifted, and the number of teeth of the second tooth profile 2 is 25 or more and the tooth profile thereof. Is a pair of involute gear structures that are either negatively or positively shifted, or have no shift. 3. The pair of involute gear structures according to claim 1, wherein the pair of involute gears is made of a plastic material.