The IVT can be designed with mutliple regimes. A dual regime system is described on this page.
Low Regime
The following diagram is a generic simplified layout of the major components in the IVT in low regime mode.
When a vehicle with a Torotrak IVT moves from rest, in either forwards or reverse, it is operating in low regime - the low regime clutch is engaged.
As the driver depresses the accelerator, hydraulic pressure applied to the rollers in the variator produces a driving effort at the road wheels. The engine generates power to satisfy demand and the vehicle accelerates.
The variator progressively shifts to a higher ratio as vehicle speed increases. The planet carrier of the epicyclic gear (connected directly to the engine) dominates causing the output annulus to increase in speed. Eventually - at a transmission ratio roughly equivalent to second gear of a conventional transmission - the variator ratio reaches its upper limit and the transmission moves, smoothly, into high regime mode.
High Regime
The shift to high regime occurs by switching in the high regime clutch and switching out the low regime clutch.
First the high regime clutch is engaged - synchronously, since at this point there is no relative motion across its plates. Next the variator is set up for high regime operation.
Since both clutches are engaged and taking the drive the variator can be set up without loss of control. Finally the low regime clutch is released and operation continues in high regime. The epicyclic has been disengaged and the variator is now directly connected to the vehicle's wheels.
Changing the variator control during the shift sequence reverses the forces applied to the variator rollers. The rollers can now sweep back across the whole width of the discs in response to the driver's demand for acceleration, producing a smooth transition to high overdrive.
The change from low to high regime is achieved without slip, shock, wear or power loss.
An animation showing the two regimes can be found in the related links section below.
