Everything began in 1885 with the adoption of the first clutch used by Benz in his first automobile, a leather belt that transmitted the movement from a free pulley to a pulley connected to the crankshaft. However, it was not until the first half of the last century that the system, improved to mitigate friction between discs, became widespread. We are talking about the clutch introduced by De Dion Bouton in 1920.

The transmission clutch is a mechanism that joins or separates two shafts. This separation must take place whether the shafts are moving or stationary. In cars, the function of this element is to transmit the movement coming from the engine to our wheels at our will. This is very necessary because to start the direction of the cars, we must transmit the engine torque at low engine speed in a progressive way by mechanical or viscous slip until we get the complete coupling.

If all this technical mumbo-jumbo did not make much sense, the translation is that it transmits the engine power, controls the transmission of torque from the engine to the wheels. That is the function of the clutch, one of the fundamental parts of a car or industrial machinery.

Nowadays, we can choose between different types of clutch according to their characteristics.

According to the number of discs:

• Hydraulic: it has no discs; it is typical of industrial vehicles.
• Single-disc: the most commonly used in the automotive industry.
• Bidisc: consists of two discs.
• Multidisc: uses a package of discs and is used in motorcycles since it transmits a much higher torque to the gearbox.

By type of cooling:

• Dry: air cooling.
• Wet: oil cooling

By type of pressure on the pressure plate for coupling with the disc:

• Spring-loaded: the springs on which the force is applied are located on the periphery of the clutch disc.
• Diaphragm: the springs are replaced by an elastic carbon steel diaphragm.
• Centrifugal: typical of automatic driving, clutch engagement and disengagement are entrusted to counterweights that operate by the centrifugal force of engine rotation. Thus, it can be considered a transmission clutch that acts automatically from a certain speed of rotation of the motor shaft.

According to the type of drive:

• Mechanical friction: it consists of the flywheel on which the gearbox’s primary shaft is supported thanks to a bronze bushing. It is the most common in passenger cars. It works using liquid or using a cable.
• Hydraulic: acts as an automatic clutch between the engine and the gearbox, allowing the engine to transmit torque when it reaches a certain speed. The energy is sent by a centrifugal pump that communicates with a turbine.
• Electromagnetic or electronic assisted: it takes advantage of the strength of the electromagnetic field for torque transmission.

It is one of the elements that suffer the most stress and, therefore, has a more significant degradation throughout its useful life. It is made up of four main elements that perform the following functions:

• Flywheel: it is bolted to the crankshaft and rotates in unison with the engine. Bi-mass flywheels reduce vibrations but are more prone to failure.

A Clutch hub is also called a pressure plate; it is bolted to the flywheel, rotating together. It consists of a diaphragm or springs, which are responsible for compressing or releasing the clutch disc.

The friction disc has two faces covered with a material similar to the brake pads and is coupled to the gearbox via a shaft. When the clutch pedal is released, it rotates in conjunction with the flywheel and the hub. When depressed, it disengages, and the transmission of torque to the wheels is interrupted.

• Actuating mechanism: a bearing mounted on a fork rest on the diaphragm and pushes it to release or press the disc. This fork is the one we move when operating the clutch pedal.