The mechanical energy produced by engines, usually in the form rotary motion is transmitted to the bodies conducted through the transmission components.
Depending on the gear ratio (i.e. the ratio between the speed of rotation of the drive wheel and the
driven wheel) the transmission components are distinguished in:
- components that do not involve changes in gear ratio; they are shafts, joints and couplings;
- components entailing changes in gear ratio; they are called transmissions.
Transmission components without variation of the transmission ratio
The shafts make the connection between sprockets, pulleys, couplings, clutches etc. fixed or axial sliding. Depending on its function, shafts can be straight, telescopic, flexible or crank (shaft) [fig. 1].
Joints connect the shafts permanently. They can be rigid (for example, keyed shafts), elastic (for example, elastic tile joints that allow small reciprocal changes of joint parts) and articulated. Joints also allow the connection of shafts not axially aligned, the most common of which are those cardanic [fig. 2].
Couplings connect the shafts to allow a rapid disingagement. They can be:
- form couplings, usually made through toothed couplings; the shaft alignment must be perfect and at the time of engagement and disengagement the motion must be arrested to avoid damage [fig 3];
- force couplings, usually made through clutch couplings [fig. 4]; they deliver the motion transmitted by the friction generated between two surfaces pressed against each other and have the peculiarity to start or end transmission of motion even when the parts are moving; the motor vehicle clutch is an example of strong coupling;
- hydraulic couplings, used in special cases and in presence of limited efforts; are characterized by the absence of contact mechanical parts, because they exploit only the mass of the moving fluid. The turbine that in power stations plants has the function to produce electricity, is
a classic example of hydraulic coupling in which one first impeller pushes the fluid against a second.
Transmission components with variation of the gear ratio
The transmission components with variation of the gear ratio can be classified according to the gear ratio or according to the type of coupling.
Transmission according to the gear ratio
Depending on the way the gear ratio varies, transmission components can be:
- fixed ratio: are those that allow only one gear ratio; this category includes the speed reducers gearboxes, that transmit to the led shaft a rotation speed lower than that of motor [fig. 5];
- discrete ratio: are those that permit a predefined number of gear ratios; gearboxes of motor vehicles belong to this type [fig. 6];
- continuously variable ratios or continuous variators: are those that allow you to get an unlimited number of gear ratios.
Transmission according to the type of coupling
Depending on the way the connection is made, transmissions with variation of the gear ratio can
- with shape coupling: are those in which the geometric shape of the driving part fits with that of the part conducted dragging it in motion; the main shape coupling transmissions are the toothed belt, chain or toothed wheels [fig. 7];
- with strength coupling: they are those which realize the motion transmittion by the friction generated between two surfaces pressed against each other; the most widespread transmissions of this kind are flat belts, v-belts or cylindrical belts [fig. 8].