The way that the internal combustion engine develops torque or performance through RPM, essentially requires a combination of clutch and gear box or converter and graduated/infinitely variable automatic gearbox. With a combination of its advantages, the automation of clutch and gear box is conquering the market. What ever the case may be, a changeable gear ratio and an acceleration assistance are necessary in the drive chain, the internal combustion engine however, works only at between 500 to 800 RPM and delivers in the most favourable case, as a diesel engine, appreciable torque at roughly 1300 RPM, the petrol engine somewhat later. If too much torque is demanded at low revs when pulling off, stalling of the engine will result.

Should the revs be too high when pulling off, the clutch will suffer through slipping. In addition, the driver, or some sort of automatic regulation, should be able to change the transmission ratio to the driving wheels in such a way that the engine functions either at the highest efficiency level, the highest torque, or the maximum performance. At the same time, of course, the exhaust emission of the engine, its position, as well as the gear-change comfort, the noise level and the production costs of the gearbox must be taken into consideration.

In the case of graduated gearboxes, different gearwheel combinations are incorporated into the power flow. In all manual gearboxes the power flow, when changing gear, must be interrupted for a short time, this does not apply to planetary gearboxes or to those with a dual-clutch gearbox. Except in the direct gear all graduated gearboxes can also be called torque converters. Continuosly variable transmissions allow a continuous, automatic adaptation to the engine traction force. The state of the art nowadays, are dual-clutch gearboxes or direct gearboxes. They are very quick and work almost without jerking. Unfortunately, they are also a little expensive. 09/08