DCT

We have heard from sources that shall remain nameless that the love affair with the DCT may be short lived at BMW for certain models and future products. There are other plans in the works for a transmission to provide greater efficiency, increased torque handling capabilities in a lighter, cost effective package.

It is also indicated that several European manufacturers of luxury vehicles are currently testing a new form of transmission. It has no true gears but uses a series of and rotors and a variator, the Infinitely Variable Transmission from Torotrak. It is more of a traction drive system than a transmission.

The IVT moves away from the constraints of stepped ratio automatic transmissions and unlike Continuously Variable Transmissions there is no torque limitation. The ratio range is provided not by a system of gears, as found in a conventional automatic transmission, but by a variator which consists of a set of discs and rollers and is termed a 'full toroidal' variator (more information on how the variator works can be found here). The IVT technology allows control of the complete powertrain enabling optimisation of the efficiency of the engine. In conventional transmissions the engine and transmission are controlled separately. The IVT is torque controlled rather than ratio controlled. The software determines the torque required at the road wheels and then requests torque from the transmission rather than setting a specific ratio. The engine can then be used to deliver the power at its most efficient operating point. In conventional automatics where the gear ratios are fixed the engine only runs at its most efficient operating points for short periods of time. This optimisation of the entire powertrain brings about a fuel economy benefit in three ways: Due to the geared neutral feature of the IVT the engine can be directly connected to the road wheels whilst the vehicle is stationary. There is no need for a separate starting device such as an inefficient torque converter. Due to its wide ratio spread the IVT provides the ability for the engine to run at a high overdrive of 74mph/1000rpm. Because the IVT does not have discrete ratio steps it can run the engine at optimum conditions for fuel economy and emissions. It has been verified that the IVT improves vehicle performance. Analysis by one of the world's leading transmission suppliers shows that 4 seconds, after a wide open throttle launch from rest, an IVT vehicle has 2 metre advantage over a typical 6-speed automatic. This is a major attraction to manufacturers of high performance vehicles.

Frank