Everyone knows that magnets tend to attract metals. Also, one magnet can attract another. But the interaction between them is not limited to attraction, they can repel each other. The matter is in the poles of the magnet - opposite poles attract, the same poles repel. This property is the basis of all electric motors, and quite powerful ones.
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 has been put into 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 stationary part (stator) by magnetic flux forces is called a magnetic bearing. When the mechanism is in operation, it is influenced by physical forces that tend to shift the axis. To overcome them, the magnetic bearing was equipped with a control system that monitors the load and gives a signal to control the strength of the magnetic flux. Magnets, in turn, are stronger orhas less effect on the rotor, keeping it in the center position.
Magnetic bearing has been widely used in industry. These are basically powerful turbomachines. Due to the absence of friction and, accordingly, the need to use lubricants, the reliability of machines is many times increased. Wear of nodes is practically not observed. It also improves the quality of dynamic characteristics and increases efficiency.
Active magnetic bearings
Magnetic bearing, where the force field is created with the help of electromagnets, is called active. Positional electromagnets are located in the bearing stator, the rotor is represented by a metal shaft. The entire system that holds the shaft in the unit is called active magnetic suspension (AMP). It has a complex structure and consists of two parts:
- bearing block;
- electronic control systems.
Basic elements of the AMP
Radial bearing. A device that has electromagnets on the stator. They hold the rotor. The rotor has special ferromagnet plates. When the rotor is suspended at the midpoint, there is no contact with the stator. Inductive sensors track the slightest deviation of the rotor position in space from the nominal. Signals from them control the strength of the magnets at one point or another to restore balance in the system. The radial clearance is 0.50-1.00 mm, the axial clearance is 0.60-1.80 mm
- Magnetic bearingthrust works in the same way as radial. A thrust disk is fixed on the rotor shaft, on both sides of which there are electromagnets mounted on the stator.
- Safety bearings are designed to hold the rotor when the device is off or in emergency situations. During operation, auxiliary magnetic bearings are not involved. The gap between them and the rotor shaft is half that of a magnetic bearing. Safety elements are assembled on the basis of ball devices or plain bearings.
- Control electronics includes rotor shaft position sensors, converters and amplifiers. The whole system works on the principle of adjusting the magnetic flux in each individual electromagnet module.
Passive magnetic type bearings
Permanent magnet bearings are rotor shaft holding systems that do not use a feedback control circuit. 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 the formation of friction and reduces the reliability of the system. The magnetic stop in the technical sense has not yet been implemented in this scheme. Therefore, in practice, a passive bearing is used infrequently. There is a patented model, for example, a Nikolaev suspension, which has not yet been repeated.
Magnetic tape in wheel bearing
Concept"magnetic wheel bearing" refers to the ASB system, which is widely used in modern cars. The ASB bearing is different in that it has a built-in wheel speed sensor inside. This sensor is an active device embedded in the bearing spacer. It is built on the basis of a magnetic ring on which the poles of an element that reads the change in magnetic flux alternate.
When the bearing rotates, there is a constant change in the magnetic field created by the magnetic ring. The sensor registers this change, generating a signal. The signal is then sent to the microprocessor. Thanks to it, systems such as ABS and ESP work. Already they correct the work of the car. ESP is responsible for electronic stabilization, ABS regulates the rotation of the wheels, the level of pressure in the system is the brake. It monitors the operation of the steering system, acceleration in the lateral direction, and also corrects the operation of the transmission and engine.
The main advantage of the ASB bearing is the ability to control the speed of rotation even at very low speeds. At the same time, the weight and size indicators of the hub are improved, the installation of the bearing is simplified.
How to make a magnetic bearing
The simplest do-it-yourself magnetic bearing is easy to make. It is not suitable for practical use, but it will clearly show 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, for example, a piece of plastic tube, and an emphasis,for example, a half-liter glass jar. Magnets of a smaller diameter are attached to the ends of the tube with hot glue in such a way that a coil is obtained. In the middle of one of these magnets, a plastic ball is glued on the outside. Identical poles should face outward. Four magnets with the same poles up are laid out in pairs at a distance of the length of the tube segment. The rotor is placed over the lying magnets and on the side where the plastic ball is glued, it is supported with a plastic jar. Here is the magnetic bearing and ready.