Magnetic coupling
The term magnetic coupling serves as a generic term for a number of types of coupling whose function is based on the effect of a magnetic field . These types of coupling include, among others, the electromagnetic coupling, the magnetic particle coupling, magnetorheological fluid coupling and the non-contact magnetic coupling.
Electromagnetic clutch
An electromagnetic clutch is an electrically remotely switchable, non-positive or positive clutch .
The shape, also known colloquially as a magnetic clutch , is similar in its basic structure to a single-disk dry clutch . The drive side is equipped with an electromagnet , which usually does not rotate as its magnetic field reaches the rotating coupling partner via an air gap. Depending on the electrical voltage applied, a magnetic field of different strengths acts on the slidingly mounted pressure plate on the driven side. The clutch disc is clamped or is axially movable and is pressed against a stationary part and thus transmits the rotary movement.
The clutch disks can also be toothed.
Magnetic couplings can be easily (remotely) controlled. It is often installed in motor vehicles to switch compressors and pumps. In the case of the starter , its axially displaceable armature serves as a movable element. It is drawn into the stator by the excitation field and the pinion engages the externally toothed flywheel of the internal combustion engine.
Magnetic clutches were used in machine and device construction to switch drives on and off and to reverse the direction of rotation.
Magnetic particle clutch
The magnetic particle clutch is a frictional coupling. A metal powder or metal gel is located in the gap between the drive pressure plate and the output pressure plate. The electromagnet housed in a pressure plate magnetizes the metal particles and stiffens them. This results in a non-positive connection. Changing the applied voltage creates a tight connection or slip . Without electricity, no forces are transmitted because the metal particles are placed on the drive pressure plate by centrifugal force . The magnetic particle clutch can be used as a starting clutch, but a dissipation of the heat from the slip operation must be ensured. The magnetic particle brake works according to the same principle .
Magnetorheological fluid coupling
A magnetorheological fluid coupling, or MRF coupling for short, is basically constructed like a magnetic particle coupling. Instead of the metal powder used, however, a magnetorheological fluid is used. Under the influence of a magnetic field, this changes its consistency from liquid to gel-like to solid. The advantage of an MRF coupling compared to a metal powder coupling is the better sealing of the transmission medium to the outside, lower internal friction in the separated state (less heat, less wear) and better heat dissipation, which allows longer or frequent operation in the slip state. Magnetorheological clutches can be manufactured in disk, bell and other shapes.
Contactless magnetic coupling
Their different types are used, among other things, to achieve power transmission through walls (e.g. hermetically sealed containers). You can work with permanent magnets or electromagnets. One example is the setpoint temperature adjustment on contact thermometers .
Magnetic couplings with permanent magnets on both sides have a wide range of applications in magnetic coupling pumps . They represent a variant of the centrifugal or displacement pump with regard to the sealing system. Due to the contactless, magnetic power transmission, the pump housing is not interrupted by a drive shaft. The main area of application is the pumping of toxic, odorous or dangerous fluids , e.g. B. in chemistry and petrochemistry.
In addition to rotary variants, there are also linear variants, e.g. B. for hermetically sealed pneumatic working cylinders or for contactless power transmission in magnetic levitation scales.
The driving side of a contactless magnetic coupling can also be the rotating field of the stator of an electric motor . In this case one speaks of canned motors . Examples are magnetic stirrers , heating circulation pumps, aquarium pumps, water meters and the drives for the rotating anodes of X-ray tubes .
In older vehicle speedometers , an aluminum disc with a return spring was moved by induction of an eddy current by means of a permanent magnet attached to the speedometer shaft .
Hysteresis clutch
Working method: Two segment-wise permanently excited ring magnets (outer disks) enclose a (middle) hysteresis disk. If the same poles are opposite each other, a maximum magnetic field acts on the hysteresis disc. This causes a flow of lines of force in the circumferential direction within the hysteresis disk, which generates the maximum torque. If there are unequal poles facing each other, the slightest magnetic field acts on the hysteresis disk and the flow of lines of force runs directly through it. This causes the minimum torque. By changing the angle of the pole superposition, the torque can be adjusted continuously and, since there are no touching surfaces, the setting is retained indefinitely.
Advantages of hysteresis brake clutches:
- no breakaway torque occurs
- noiseless operation
- no wear as the power transmission is not based on friction