A BRIGHT CONCEPT

Torotrak uses a toroidal variator in a power splitting scheme on a low regime going gradually from the reverse to forward motion through a complete stop. An infinite ratio span is so obtained. In high regime the planetary gear set is locked and all the power is directly transmitted by the variator.

OPERATION

The engine drives directly the planet carrier while the sun gear is driven via the variator, the annulus being connected to the driven wheels. When the variator is set in maximum overdrive, the sun gear revolves much faster than the planet carrier so that the annulus is driven in opposite direction, providing a fast reverse. By decreasing the overdrive ratio, the annulus slows down then stands still before restarting in forward motion. In this regime, the maximum speed is reached when the variator is in extreme underdrive ratio!

If the epicyclic gear set is then locked and the connection crankshaft / planet carrier disconnected, the power splitting operation stops and the variator begins to work in usual manner for a new range going to an extremely high overdrive, which lowers the average consumption of > 19 % according to the US CAFE cycle. The transition from a regime to the other one being made at synchronous revs it is therefore absolutely imperceptible.

In low regime, there's a power recirculation which harms a little the efficiency. But this regime is only used at low speed and in reverse.