Having reached eight speeds in a fully automatic system, it's high time that we discuss the energy aspect. The manufacturer promises a 14% saving on the basis of a five-speed. How does one come to this conclusion? Firstly, one can use the larger gear-spreading argument. The number 7 (!) is slowly approached and nevertheless allows, using an extreme overdrive, high acceleration dynamics.
Whether, however, a six- or eight-cylinder engine, even when travelling fast, runs at 2500 or 3000 RPM, cannot of course, fully explain the efficiency increase mentioned above. Since the five-speed gearbox, a change of thinking has taken place among the designers. Thus, we no longer have freewheels, and for the number of gears, impressively few multiple-disc clutches, multiple-disc brakes as well as simple and combined planetary systems. This means reduced losses through less drag on any components that are, at the moment, not required.
A third source of saving arises through the new and innovative construction and control of the torque converter/bypass-clutch (on the left in the figure). Their area of responsibility has been immensely increased, since for the gear-change, one multiple-disc clutch lets the clutch out gently, using variable pressure, while at the same time the other is gently let in. The (Multidisc-) bypass clutch in the converter is opened only to start off and saves, in comparison to its predecessors, the energy used by opening up during gear changing in the Torque converter. 09/08