Mechanical Clutches
Mechanical clutches in combination with mechanical stepped transmissions are widely used in passenger cars and are normally realised in the form of dry single-plate clutches. In this case, the friction between input and output shafts is produced over circular disks which rub against each other. The figure illustrates the conversion of the engine characteristic graph by a mechanical clutch.
As the vehicle starts, the engine in the operating point C produces the torque MC at speed nC.. This input torque is transferred to the output side at the same magnitude as long as nO is smaller than nC. The starting vehicle accelerates until a speed equality is achieved, resulting in: nI = nO = nC. Once the clutch is entirely closed, it is be driven according to the engine graph.
In the case of the disk clutch, the magnitude of the transferable torque depends on the applied force FC between the disks, the frictional coefficient μC of the friction pairing, the effective frictional radius rmC and the number of frictional pairs zC


The mean frictional radius (new condition) is then calculated by



where: reC = external radius of clutch disk
riC = internal radius of clutch disk
It can also be approximately calculated using a simplified formula.



The axial force is generally produced by a preloaded spring. By varying the spring travel, in the vehicle the transferred moment can be adjusted as one likes between "zero" and "maximum" using the clutch pedal.
Due to poor heat dissipation, the mechanical dry clutch can only absorb a limited loss of heat. As a result of this, the speed conversion is timewise limited. Today's linings consist of so-called Fillers. Metallic splinters are sometimes part of it. They are held together by an organic bonding agent. They can deal with high temperatures and are abrasion and wear-resistant. Their life often corresponds to the entire vehicle life.