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          A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Seven-gears Automatic
    Transmission







More and more gears for high-torque engines

These automatic gearboxes (see above) are usually combined with engines which due to their large cubic capacity and a wide usable RPM range, do not necessitate such a gearbox. Of course the acceleration can be easily improved by having so many gears. Also, because of the wider spreading of the gear ratio in the highest gear, an improvement can be had, after all, the driver doesn't have to do any gear-changing her-/himself.

Fuel saving but not fast...

In the practice this gearbox changes into the highest gear as quickly as possible to save fuel, then, changing down 1, 2 or even 3 gears with every small accelerator pedal movement. Not quite ideal as far as comfort goes, because during the downshift with a full load even modern automatic gearboxes cannot function free of jerking. In addition, there are the small pauses, which when added together give the driver the feeling that, compared with the gear box or the direct gear box the acceleration is not quite as direct.

Similar construction to five-speed gearboxes

Not only can a saving be achieved through using longer transmission ranges, but also, e.g., by the use of a multi-disc-converter by-pass-clutch (on the top left in the figure) which can be applied, if needs be, right down to the first gear. The only thing that is new about the torque converter, is the depiction which allows a look right into the freewheel of the guide wheel. Following this is the Ravigneaux set-up and two simple planetary systems, only one more than in the five-speed gearbox. In winter and during difficult conditions starting off is carried out more gently and in a higher gear.

In spite of more gears hardly any increase in weight

The fact that in spite of more parts the weight has not changed substantially, is also due to the casing being made from a magnesium alloy. Dealing with the technical development of automatic gearboxes one must also have a close look at the higher fuel consumption that they cause. It should be quite clear that more gears influence the efficiency positively, when at the same time the gear ratio spread is increased. In addition the torque converter by-pass-clutch is deployed in every gear with short interruptions for the gear changing operation. For this reason it's not clear why the manufacturers still maintain considerable differences in the maximum speed for manual gear cars and for automatic vehicles. All that remains, except for the oil to be moved in the torque converter, only the primary- and perhaps a secondary pump as an efficiency brake. It is interesting to note that, not the manual gear-box, but rather the automatic system has a direct gear ratio in the highest gear.

Economical through more intelligent gear-changing

The originally planned consumption difference of just 10% or 1 litre/100 km can no longer be substantiated, particularly not when a diesel engine is used with the automatic. Should the especially economical 3-litre car perform this feat only in the automatic version, is the potential of the automatic for the normal harried driver in heavy traffic or in tail-backs further accentuated. This is naturally assuming, that one does not use the selector lever or steering wheel paddle unwisely to achieve a pointless acceleration advantage. 09/08


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Translator: Don Leslie - Email: lesdon@t-online.de

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