Gear form constructions

Details Gear form constructions Gear form constructions

1998-04-08

2001-01-30

Fenstermacher, David (Department: 3682)

Machine element or mechanism

Gearing

Teeth

C074S42100R

Reexamination Certificate

active

06178840

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the construction of profiles of conjugate gears. In particular, the present invention may be applied directly to spur gears and other gear forms.
BACKGROUND OF THE INVENTION
Several attempts have been made to reduce the contact stress in gear teeth, because a high contact stress can cause pitting and eventually failure of the teeth. Many of these attempts have been based on the Wildhaber or Novikov types of gearing, in addition to the more common involute forms. In Novikov gears, the profiles in the transverse sections are circular arcs, the pinion being convex and the gear being concave. The problem with circular arc profiles is that they are not conjugate. With conjugate profiles, the angular velocity ratio is exactly constant. In each transverse section, there is continuous contact throughout the meshing cycle and the contact point moves along each profile towards the tip of the driving tooth and towards the root of the driven tooth.
Because a variable angular velocity ratio is not acceptable, Novikov gears are made helical. This means that in each transverse section, only one pair of points come into contact. At any instant, there will be one transverse section where contact occurs and this contact point moves axially along the tooth face as the gears rotate. Such gears are generally noisy and have not been widely used. The same comments apply to Wildhaber gears which are shaped as circular arcs in the normal sections.
More recently, other profiles have been proposed in which there are two or more contact points in each transverse section. Gears having such profiles still suffer, though, from the disadvantages just described.
SUMMARY OF THE INVENTION
A gearing system, constructed in accordance with the present invention, includes a first gear having a first plurality of teeth each having a first tooth profile lying entirely within the pitch circle of the first gear and a mating gear having a second plurality of teeth each having a second tooth profile lying entirely outside the pitch circle of the mating gear. The second tooth profile of the second plurality of teeth of the mating gear is conjugate to the first tooth profile of the first plurality of teeth of the first gear. Either the relative curvature of the first tooth profile of the first gear and the second tooth profile of the mating gear is a constant, or the following function of the radius of curvature &rgr;
1
of the first tooth profile of the first gear, the radius of curvature &rgr;
2
of the second tooth profile of the mating gear, and the gear pair pressure angle &phgr; of the first gear and the mating gear is a constant, as follows:
1
cos
⁢
 
⁢
φ
⁢
(
1
ρ
1
+
1
ρ
2
)
=
C


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