Converter unit and clutch

The so-called centrifugal clutch is one of the central elements of the automatic drive in the scooter. More precisely, the rear part of the automatic transmission consists of a converter, a clutch, several clutch shoes and a clutch bell. These elements are completed by clutch springs and a counterpressure spring.

Hoy it works

The central task of a coupling consists of a "separating" connection between motor and gear. The engine power is transmitted to the crankshaft by means of an angular momentum, which sets the front converter in motion. The V-belt running inside the crankshaft then transfers the energy to the rear converter and finally to the rear wheel. For a more detailed description, see topic: Variomatik. If there were no clutch on the rear converter in between, the engine energy would be transferred directly and without delay to the rear wheel. The scooter would then either shoot forward or the engine would be stalled. Also an idle speed or idle throttle would not be possible.

The centrifugal clutch also serves the same purpose, i.e. the separating connection between engine and gearbox. However, the clutch is not connected manually but automatically. The clutch is located inside the clutch bell, which in turn is firmly connected to the gearbox. There is a certain distance between the clutch and the bell so that free rotation is possible. The V-belt causes the torque converter and thus the clutch to rotate, whereby the clutch jaws installed on the latter are pressed outwards by the centrifugal forces. At a certain speed, the centrifugal force is so high that the jaws rest firmly against the bell, thus also setting it in a rotary motion and the so-called frictional connection with the gear takes place. The clutch has now engaged the first "gear". When the speed drops again, the centrifugal force acting on the jaws also drops and the clutch disengages from the clutch bell.

In order to illustrate this process of stepless wiring even more clearly, the comparison with the bicycle is again a good idea. If the bicycle chain is on a small cogwheel at the front and on a large cogwheel at the rear, you move slower, but it is easier to ride up a hill. If, on the other hand, a large gearwheel is set at the front and a small one at the rear, you move much faster with more effort.

In scooters and maxi scooters this principle is perfected by the two converters front and rear have been. If you want to start, the V-belt lies in a small orbit around the converter at the front and in a large orbit around the rear and allows the scooter to start with little effort. If the variator contracts at the front due to the increased speed and forces the V-belt into a higher orbit, the rear converter is pulled apart at the same time and the belt rotates in a narrower orbit. The transmission ratio has now changed in favour of faster travel. If the scooter moves slower again and reduces the engine speed, the V-belt falls back into a lower position at the front and rises back into a higher orbit at the rear.

The fact that the rear converter expands or contracts again is due to the counterpressure spring, which gives way to the tensile force of the V-belt above a certain strength and lets it sink lower or pushes it up again when the tension decreases.

Wissenswertes - (nicht) nur für Tuningfreunde

The radial design of roller clutches enables full use to be made of the area available for connection for the frictional connection and thus guarantees almost 100% efficiency in the transmission of motor power to the gearbox. However, adequate ventilation or cooling of the clutch is absolutely necessary for optimum function. If, for example, the clutch becomes too hot, the clutch shoes can glaze, i.e. they become too smooth and no longer grip properly, making it much more difficult to "take along" the clutch bell and thus to shift gears. A low temperature thus extends the service life of your clutch, as well as kevlar-reinforced clutch shoes. For these purposes you will find different types of clutch bells, which supply the clutch with a lot of fresh air and keep the temperature permanently low by means of adapted blades. An example is the high performance clutch bell R-Vent 107mm from Naraku, which provokes exactly this effect.

The so-called clutch shoes are attached to the clutch, which are pressed against the clutch bell by the centrifugal force at higher speeds. These jaws are connected to each other by various springs, the strength of which affects the force required to press the jaws against the bell. If, for example, the springs need more force to be stretched apart, the frictional connection takes place at a later point in time, i.e. at a higher speed. The result is an increased acceleration, as the motor has to turn higher before engagement can take place and thus more power can be provided for starting. If the scooter does not move properly, this could be due to incorrect springs in your clutch.

To increase the performance of your scooter, Racing Planet offers different sets of springs in different degrees of hardness, clutches and complete rear converter units from Stage6, Malossi, Polini and Naraku, which allow an individual and optimal adjustment of your scooter. Particularly when purchasing a complete converter unit, the often complicated installation and adjustment of the back pressure spring is no longer necessary.