Adjacent to friction, torque probably appears as a physical value in the automobile most frequently. As the above figure shows, it appears in the piston engine initially in the crankshaft and then increasingly in the gearbox (in the first three gears). This happens once again in the final drive in such a way that, e.g., in the first gear the engine torque to the driving wheels is increased approx. 14-fold. Of course the whole drive-train assembly must be adjusted for this increase. With especially strong diesel engines the torque development must be partially reduced because the accordingly reinforced gearbox is not available. Truck gearboxes have, with only a few more gear wheels, often four times the size of a motor car gearbox.
Torque appears everywhere where a shaft alone or a (gear) wheel or lever turns on it. This is made clear when driving, e.g., in the steering, where one even needs the support of hydraulics or electric power steering. One should not only consider driven gear-, chain- or belt wheels. Also the braking of a turning wheel has to do with torque, if e.g., when downshifting, the engine speed increases through the energy of the moving car.
For the mechanic, torque is important because it must be observed when tightening screws or bolts. Therefore, he uses tools, eg., a torque wrench, which are designed to register the exact amount of torque being used at the time to avoid tightening too much. Of course the tool must be adjusted according to the respective screw or bolt. A wheel bolt that is tightened too much can prevent the successful wheel change in the event of a breakdown. Not to mention the possible resulting damage to the brake disk, wheel rim and/or the bolt itself.
Sometimes torque is called 'turning force', but a force can only be achieved if the torque is shared by the lever. In this case, it's not about the direction which is so important for the force. At most, it's an orientation which indicates the rotary direction of the shaft. Force becomes torque if it works through a rocker arm onto a rotary component. Furthermore, torque becomes performance if one considers the time in which it works on the shaft.Torque increases either with the force that works on the lever, or with the lever itself. Standstill is reached on the lever if the right and the left torque are equal. In the case of a rocker arm, the cam must, through the tappets, produce the same amount of torque as the valve spring produces on the valve. For the opening of the valve even a higher torque is necessary. 05/10