Control of a novel switched mode variable ratio drive

A novel design of a variable ratio drive is described and analysed. The main feature of the drive is that, rather than giving a continuous conversion of input speed and torque, this drive operates in a pulsed manner, storing packets of input energy in a spring and releasing the energy to the load. By controlling the storage and release of energy by means of clutches, it is possible to make the drive emulate a wide range of gear ratios in both forward and reverse directions. The effective ratio can be altered as each pulse is transferred, allowing rapid adjustment of the output speed and torque. Furthermore, by consideration of the internal dynamics of the system, it is shown that it is possible to devise controllers which avoid clutch engagement when there is movement between plates, thus avoiding slip and reducing wear. A practical realisation of the drive is presented which can transmit up to 100 W of mechanical power with an effective ratio of between 1:3.2 and 1.3:1 at an efficiency greater than 70%.