Beltless Continuously Variable Transmission

What is a transmission? A transmission is a device which is used to provide a set of discrete angular velocity outputs from a constant velocity source.

What is a continuously variable transmission? A continuously variable transmission (CVT) serves the same function as a traditional transmission. The difference, however, is that an indiscrete range of outputs is produced.

Where are CVTs incorporated? Although this design has been used to modify a drill press, the concept can also be implemented into milling machines, lathes, automobiles, and various other devices.

Is the CVT a new concept? No. In 1886, the first CVT was built by Daimler and Benz, two German automotive engineers. Their design was based on a rubber V-belt that would ride between two shallow angle cones and has remained relatively unchanged for the past century.

Traditional CVT design.

The Design

The design consists of three components: the torque conversion cones, the double-idler assembly, and the main housing.

Torque Conversion Cones
The concept of the CVT design is based upon two aluminum cones which, when placed together, form a semicircular profile and produce the required angular velocity ratios, due to their varied surface diameter. They are mounted on steel rods and supported by both radial and thrust bearings.

Double-Idler Assembly
The double-idler consists of two polyurethane rubber wheels positioned at 90 degrees to one another and connected via a pair of mitre gears. This assembly results in a 1:1 angular velocity ratio between it's input and output wheels. Depending upon the orientation of this assembly, the aforementioned velocity ratios between the cones may be achieved.

The double-idler is set upon a carriage that is held in place between the torque conversion cones by a means of a pivot at the centre of the described circle. The idler assembly can also be adjusted along the plane of the carriage such that the wheels are always in contact with the cones. This is achieved by tightening a spring against the housing of the double-idler. To obtain the desired output ratio, the idler is oriented by a speed control mounted on the main housing.

Main Housing
The main housing encases the double-idler assembly and torque conversion cones in a small and easily mountable envelope.

Technical Specifications
For a 12 inch drill press:
Minimum output: 200 rpm
Maximum output: 5000 rpm

How is this design unique? Traditional CVTs have always had a problem delivering the required torque since excessive amounts have caused the belts to fail. To address this problem, the design team developed a CVT which was not based on a belt system. Having removed the belt and designed the mechanism so that it could be varied during the machine's operation, this desing is more versatile and safer to use.

The beltless CVT.

Design team members: (l-r) Noru Gogovitza, Professor W.L. Cleghorn, Adrienne Chee Hing, Christopher Daniel.

To see the "CVT" in action, click here. WARNING: This clip is a 1.2MB MPEG Movie file.