For the manual gearbox, seven speeds is the maximum.
Would you have known, that one can't simply choose a transmission with a torque-compatibility which is suited to the maximum torque development of the engine in an off-road vehicle? Just imagine, when on an uphill gradient, the maximum torque of the engine is confronted with particularly sluggish- or even for a short time, wheels that are turning backwards.
These are called torque-peaks and one would be well advised to ensure that there is a surplus. This happens with the seven-speed double-clutch transmission shown in the above picture for a maximum of 600 Nm and 275 kW of performance. Apart from the reinforcements in the gearbox itself, there are more and wider clutch-plates. Wet clutches can manage the heat development caused by high amount of torque better, because the lubrication oil flows through them from the inside to the outside
Up to now, six-speeds were more or less the standard. Indeed, seven-speeds are not there simply to make the prospectus more interesting. After all, this gearbox is also and in fact, especially intended for all-wheel drive, where the transmission spread in the direction of low ratio, to provide a sort of off-road gear, is very important. For the highest gear, this configuration is like an overdrive which has a positive influence on the fuel consumption..
In view of the dividing of the gearbox into two groups, the odd-numbered gear-speeds prove to be favourable, because due to the additional reverse-gear, a balanced draw is arrived at. This gearbox from 2011 also achieves a spread of 7,3. That much more is still possible, is in the meantime, proved by the nine-speed automatic transmissions, which with 9,7, are getting close to the double figures. Then, the top-speed may even be able to be reached in seventh gear.
The 1st, 3rd, 5th and 7th gears face the 2nd, 4th, and 6th gears.
As far as the structure is concerned, a lot has been changed compared with the original manual gearbox. If the connection for the rear axle is also flanged on, then together with the mechatronics, we're dealing with three oil reservoirs, each with its own oil-level and fortunately, with longer oil-change intervals. They are, by the way, filled from below. The oil filter is normally not changed at all and the system also needs an oil-cooling-heat exchanger at the top.
Actually, the DCTs are not really similar to an automatic transmission. However, both do need an oil pump for the oil circulation, which is driven directly from the engine through the converter casing or the double clutch. The oil pump drains off up to 3 kW (4 HP), e.g., to press the clutch plates together with substantially more than 10 bar of pressure. Coil springs open the clutch when the pressure has been reduced to 2 bar. 08/15