Designing my own CVT module

Our objective was to design a CVT module with the given limitations. REMEMBER THAT THIS IS JUST A MODULE AND DISPLAYS THE WORKING PRINCIPALS OF MODERN CVT.

Objective: Design and constructing a CVT/ automatic transmission within 3 weeks that is economical and will render us capable of understanding CVT technology for future developments.

The Process: First we chose the best type of CVT to design. As most common and developed CVT used by the automobile industry is the Variable Diameter CVT we thought that it would be a good experience from a future prospective as Mechatronics engineers.

Limitations: We had initially designed a more practical CVT( I will post later on) but the problem was that in Pakistan machining is the weakest link in our industry. We spent hours finding a machinist that could give us the right angles and pulleys but either they dint understand the drawings or required supervision or they would ask for enough money so that they could take a trip to the Figi Islands so we opted for the next best thing! Scrap metal! We spent hours in Rawalpindi, City Sadar Road and finally found our saviors at a place called "Astuble" in Rawalpindi were they sell scrap metal, spare parts, springs and other useful stuff ( mechanical engineers do visit). Any ways we further modified our second design according to the what we had found.

Its Working

The new CVT design worked on a similar principle except that it used centrifugal tension in the belt to push the Variator open. The detail of it working is as follows:

This design has two pulleys; one on the driver shaft and one on the driven shaft both connected through a light duty gauge V-Belt. The driver pulley can slide open varying the diameter that the belt is griping and the driven pulley has a fixed diameter. Along with the driver pulley a spring of force F is attached which initially restricts the pulley from sliding open.

As the r.p.m increases on the driver pulley, the centrifugal tension Tc increases in the V-Belt griping the driver pulley. When the reaction component of Tc on the pulley exceeds spring force F it allows the spring to get compressed thus allowing the pulley to open up causing the V-Belt to slide down hence griping a smaller diameter on the driver pulley. When this happens the pulley diameter ratio changes hence changing gearing ratio between the two pulleys.

The next post will give the details of how we built this machine, where we got the components from, their cost in Pak Rs and calculations for the CVT in the design stages.