Active magnetic bearing

Everyone knows that magnets have the property of attracting metals. Also one magnet can pull the other. But the interaction between them is not limited only to attraction, they can repel each other. The thing at the poles of the magnet is that opposite poles are attracted, the same poles are repelled. This property is the basis of all electric motors, and quite powerful.

There is also such a thing as levitation under the influence of a magnetic field, when an object placed over a magnet (having a pole similar to it) hangs in space. This effect was applied in practice in the so-called magnetic bearing.

What is a magnetic bearing

An electromagnetic type device in which a rotating shaft (rotor) is supported in a fixed part (stator) by forces of a magnetic flux is called a magnetic bearing. When the mechanism is in operation, it is influenced by physical forces that tend to displace the axis. To overcome them, the magnetic bearing is equipped with a monitoring system that monitors the load and provides a control signal for the magnetic flux. Magnets, in turn, are stronger or weaker on the rotor, keeping it in a central position.

The magnetic bearing has found wide application in the industry. These are mainly powerful turbomachines. Due to the lack of friction and, accordingly, the need to use lubricants, the reliability of machines is greatly increased. The wear of the knots is practically not observed. Also, the quality of dynamic characteristics is increased and the efficiency is increased.

Active magnetic bearings

A magnetic bearing, where a force field is created by means of electromagnets, is called active. Electromagnetic positional are located in the bearing stator, the rotor is represented by a metal shaft. The entire system, which ensures the retention of the shaft in the unit, is called the active magnetic suspension (AMP). It has a complex structure and consists of two parts:

• Bearing block;
• Electronic control systems.

The main elements of AMP

• The bearing is radial. A device that has electromagnets on the stator. They hold the rotor. There are special plates from the ferromagnet on the rotor. When the rotor is suspended in the middle point, its contact with the stator is absent. Inductive sensors monitor the slightest deviation of the rotor position in space from the nominal. Signals from them control the strength of the magnets at a particular point to restore equilibrium in the system. The radial clearance is 0.50-1.00 mm, the axial clearance is 0.60-1.80 mm.

• The magnetic thrust bearing works in the same way as the radial bearing . On the shaft of the rotor fixed thrust disk, on both sides of which are located electromagnets, fixed on the stator.
• Thrust bearings are designed to hold the rotor when the device is off or in emergency situations. During operation, the auxiliary magnetic bearings are not engaged. The gap between them and the rotor shaft is half that of the magnetic bearing. The safety elements are assembled on the basis of ball bearings or sliding bearings.
• The control electronics include rotor shaft position sensors, converters and amplifiers. The entire system operates on the principle of magnetic flux adjustment in each individual electromagnet module.

Passive bearings of magnetic type

Magnetic bearings on permanent magnets are rotor shaft holding systems that do not use a control circuit that includes feedback. Levitation is carried out only due to the forces of high-energy permanent magnets.

The disadvantage of such a suspension is the need to use a mechanical stop, which leads to friction and reduced reliability of the system. The magnetic emphasis in the technical sense has not yet been realized in this scheme. Therefore, in practice, a passive bearing is used infrequently. There is a patented model, for example, Nikolaev's suspension, which has not yet been replicated.

Magnetic tape in hub bearing

The term "magnetic hub bearing" refers to the ASB system, which is widely used in modern cars. The ASB bearing is characterized by the built-in wheel speed sensor inside. This sensor is an active device embedded in the bearing shim. It is built on the basis of a magnetic ring, on which the poles of the element that reads the change in the magnetic flux alternate.

When the bearing rotates, the magnetic field produced by the magnetic ring changes continuously. The sensor records this change by forming a signal. Then the signal enters the microprocessor. Thanks to it, such systems as ABS and ESP work. They are already correcting the car. ESP is responsible for electronic stabilization, ABS regulates the rotation of the wheels, the level of pressure in the system is braking. It monitors the operation of the steering system, acceleration in the lateral direction, and also corrects the operation of the transmission and the engine.

The main advantage of the ASB bearing is the ability to control the speed of rotation even at very low rpm. At the same time, the dimensions of the hub are improved, the mounting of the bearing is simplified.

How to make a magnetic bearing

The simplest magnetic bearing with its own hands is easy to make. It is not suitable for practical use, but it clearly demonstrates the possibilities of magnetic force. To do this, you need four neodymium magnets of the same diameter, two magnets of a slightly smaller diameter, a shaft, such as a piece of a plastic tube, and a stop, such as a glass half-liter can. Magnets of smaller diameter with the help of hot melt are fixed to the ends of the tube in such a way that a coil appears. In the middle of one of these magnets, a plastic ball is glued from the outside. The same poles should look outwards. Four magnets with the same poles up are laid out in pairs at a distance of the length of the length of the tube. The rotor is placed over the lying magnets and on the side where the plastic ball is glued, prop it with a plastic jar. Here is the magnetic bearing and is ready.