Cycloid Gears

Design

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.

Cycloid Reduction Mechanism in Hybrid Vehicle Control Systems

A Hybrid Vehicle control system used in automobile application uses a Cycloid Reduction mechanism. The shift control actuator typically includes a Cycloid Gear reduction technology that increases the torque of the actuator. The main application of this is in parking. As soon as the vehicle is parked on a slope the parking lock is released.

Cycloid Reduction Mechanism:

The eccentric shaft rotates with the motor shaft, in the process, pressing the driven gear against the fixed gear.
Driven gear is able to rotate one tooth for every complete rotation of the motor shaft.
Reduction ratio of 61:1 can be achieved.