Centrifugal clutch

Tangential centrifugal clutch (without bell) from a moped

Tangential centrifugal clutch with additional indirect action (without bell) in a moped

Radial centrifugal clutch in a chainsaw

A centrifugal clutch is a clutch in which a frictional connection is established by the centrifugal force pulling movable flaps or slides with clutch linings outwards as the speed increases , making contact with the inner wall of the clutch housing (clutch bell), which also serves as an output .

Alternatively, has the centrifugal force controlled clutch , usually simply also centrifugal clutch called, found wide. In contrast to the arrangement described here, it is a disk or multi-plate clutch that is controlled by a structurally separate, liner-free centrifugal pendulum .

properties

Centrifugal clutches work independently. The torque that can be transmitted depends on the speed. When the speed drops, they separate automatically by a single revolving return spring or a return spring per flap or slide.

Via the spring force , for. B. set that the engine is disengaged at idle . If you increase the speed, the clutch engages and the motor delivers torque to the output shaft . As a result, without additional control intervention by the operator, for. B. a start-up of an internal combustion engine is possible.

Since only one side of the clutch can influence the deflection of the flaps or slides, a centrifugal clutch acts in a direction-dependent manner when it is not engaged; this directional dependency relates to the direction of the torque flow, not to the direction of rotation. However, once the frictional connection has been established, the torque to maintain the speed and thus the engagement can be applied from both sides.

Designs

Tangential

In the tangential design, flaps are mounted at pivot points near the circumference. This design has the advantage of being simple and robust. The disadvantage is that only a small part of the bell's circumference (usually less than 50%) can be used for power transmission . Since the pads should be worn evenly , they must not be attached too close to the axes of rotation of the flaps.

An additional indirect effect to increase the contact pressure is also possible. For this purpose, the flaps are also provided with a covering along the radius (see illustration). If the flap swings outwards, this covering is tilted and thereby additionally presses the loose end of the adjacent flap against the bell. This design can achieve a high contact pressure even at low speeds.

Radial

In the radial version, no flaps, but slides move along two or more radii of the bell. As a result, the entire slide surface towards the bell can be provided with a covering and used, so the bell surface utilization rate is almost 100%. The disadvantage of this design is the slide mechanism, which is sensitive to tilting and must therefore be manufactured more precisely than an axis of rotation.

Areas of application

The moped shown in the middle picture has two antiparallel centrifugal clutches on one axle: the inner one acts as a kick starter to connect the starter pedals and the engine (middle illustration), the outer one as an idle clutch that connects the engine and wheel (upper illustration). The combined construction uses the bell of one clutch as a carrier for the flaps of the other.

Kickstarter

The inner clutch flaps are mounted on the outer bell that belongs to the outer clutch. The inner bell - not visible in the middle picture - is attached above the inner flaps. When you step on the pedals, the inner flaps rotate. Once a sufficient speed has been reached (one step is enough), the inner bell is coupled and the motor connected to its axle is started.

Idle clutch

After the shown moped has started, the axis of the inner clutch bell now rotates due to the torque of the engine. The pedals are still again, the kick starter clutch is released. The output (outer bell) is at rest, the drive (inner bell) is idling. By accelerating, the speed of the motor, the inner bell and the outer flaps attached to it are increased (picture above). When the speed is sufficient, the outer bell is coupled and the motor is connected to the wheel.

The centrifugal clutch was also used more frequently in the past for electric motors that have a large centrifugal mass to move (e.g. a heavy agitator , a so-called heavy start ). It was used to relieve the motor in the lower speed range, since asynchronous motors without a current displacement rotor have their stable operating point beyond a torque mountain at high speed and this operating point cannot therefore be reached during heavy starting. However, due to the development of special rotor types, start-up circuits and frequency converters , this is no longer a common use.

Slip clutch

In karts a robust centrifugal clutch is installed like because characterized simultaneous braking and acceleration is possible (high speed of the drive, clutch slips at the braked driven). Kart engines have their highest torque at high speeds. This driving technique is therefore used in bends in order to have the full engine torque available again immediately after releasing the brake at the end of the bend.

The centrifugal clutch is also used in this form as a safety element. Blocks z. B. the prime mover, the clutch opens due to the reduced speed and the output runs freely. This can save the prime mover from serious damage.

Centrifugal brake

If you fix the output side, you get a centrifugal brake . It protects machines or structures with rotating elements from overspeeding. Centrifugal brakes are often used in summer toboggan runs .