Cycloid Gears
The cycloidal gear profile is basically a form of toothed gear. The Cycloid
gears find extensive use in use in clocks of the mechanical types. The gear
tooth profile of a Cycloid gear is primarily based on the curves of the
nature of epicycloid and hypocycloid. These are the curves which gets
generated by a circle that rolls around outside (respectively inside) of a
different circle.
Why use Cycloidal Gears
There are basically two reasons that inspite of difficulties Cycloidal
Gears are preferred.
- The pinions are very simple to make. The part of the pinion that acts
is nothing but a flat radial surface.
- They are traditional to make
Cycloid Gear Design
The diagram below explains the structure of Cycloid Gears.
In a basic Cycloid Gear design, addenda is referred to the curves of the
teeth which is outside the pitch circle. While dedenda is the name given to
the curves of the tooth spaces that is inside the pitch circle. Addendum of
one gear rests on the interior of dedendum of the other gear.
In case of cycloidal gears, the addenda (as described above) the wheel
teeth shows the nature of convex epi-cycloidal curves. While the dedenda of
the pinion are of the type concave hypocycloidal curves. These are generated
by an identical generating circle. This type of design allows the motion of
one gear to be easily transferred to the other at a locally unchanged
angular velocity.
The pitch circle is drawn at the centre of either of the gear at a point
through which the tooth makes contact with each other.
Application of Cycloid Gears
Cycloidal tooth forms are mainly used in the clocks for a number of
reasons:
- They generate a less sliding friction.
- They show less wear.
- Higher gear ratios can be easily be achieved without tooth
interference.
Cycloidal Gears with modified flank
This particular tooth form which has the flanks removed is particularly
suitable for clocks. As they are slow moving, and have a lighter load gears.
Features:
- The gears are not engaged till the pitch circles come in really close
contact.
- Only a single pair of teeth is engaged at one point of time.
- The touching time of the gears are also reduced.
- The teeth are generally narrower and simple to make.
