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Axial flux technology

Axial flux machine

The core business of AXCO-Motors is to manufacture axial flux electrical machines, both axial flux motors and generators, for variable-speed drives (VSD). In the variable-speed drives, the control of the electric motor is implemented by a frequency converter, a device that changes the frequency of the alternating current and voltage.

Axial flux permanent magnet machine

For medium- and high-speed applications, our products are based on axial flux induction machine technology, where axial flux permanent magnet machines operate as low-speed applications. Permanent magnet machines are very suitable for applications such as wind generators, vehicle motors or servo motors.

Axial flux induction motor

With a frequency converter, axial flux induction motors are applicable to various pump, compressor, blower or similar applications, where the variable-speed technology shows significant energy savings compared with a fixed-speed (on-off) type drive or other traditional process control methods, such as valves. Because of the obtained energy savings, the VSD technology is well adapted to industrial use, and the number of variable-speed drives is steadily increasing. As for motors, our motors meet the high-efficiency motor (eff1 motor) specifications for electric motors.

Industrial applications

In several industrial applications, radial flux induction machines are used with step-down or step-up gearboxes to reach the desired rotational speed for the driven machinery. Alternatively, a belt drive may be employed instead of a gear; this is a very common solution, especially with small machines.

Korotusvaihde

Traditional radial flux machine running the operating unit via step-up gear. The construction is a standard solution in several applications.

Direct drive solutions

The products of AXCO-Motors are customized according to the customer’s specifications for direct drive solutions, in which the electrical machine is directly coupled to the driven machinery. If the axial length of the machine is limited by the application or there is a possibility to integrate the rotor directly into the driven machinery, the electrical machine based on the axial flux topology is an advisable choice. It is known that axial flux machines offer high torque and power density values. With the integrated medium- or high-speed motor, a compact light-weight system is achieved.

An actuator icluding the adabtable one stator axco motor.

Depending on the application, the motor requires either a single or double stator. The selection of the motor type must be established by cost and performance argumentation.

Single stator construction

This is a low-cost solution thanks to the one stator–one rotor configuration; generally, it is the most suitable choice for machines of low torque rating, typically Tmax ∼ 100 Nm.

The first explanation for the above statement is that if a double stator machine is employed for low torque ratings, the double air-gap structure degrades the performance of the motor, if compared with an equivalent single-sided configuration.

The second justification is related to the inherent characteristic of an axial flux machine to produce axial force. This is due to the magnetic pull in the air-gap. The magnetic force is directly proportional to the air-gap area of the machine, and consequently, in some cases, the magnitude of the force is difficult to withstand. The main concern here is the bearing lifetime, which depends on the bearing load.

However, there are several solutions, in which the bearings of the machinery are rigid enough to bear the axial force produced by the electrical machine.

One stator one rotor AXCO-Motors construction.

Double stator construction

This construction is a favourable choice for machines, the high torque rating of which is typically above 200 Nm. Benefits of the construction are a high torque density of the motor and balanced axial forces. Further, a very light-weight rotor construction (patented by AXCO-Motors) is obtained, which may be the solution for rotor dynamic issues. The short axial length and the light-weight rotor form a system, the natural frequencies of which are far above the operation range of the machine, even for high operation speeds.

Considering the cost of the machine, two stators are usually more expensive to manufacture, when compared with a single-sided equivalent, especially in the case of small machines. This is related to the amount of copper in the stator winding and also related to the time required to manufacture the winding. In machines with a higher torque rating, the difference in the manufacturing cost is smaller between single-sided and double-sided machines.

Our technical staff at AXCO-Motors will gladly help you find the most optimal motor solution for your applications.

Double stator one rotor AXCO-Motors construction.

History of the Axial Flux Electrical Machine

The first electrical machine was a primitive axial flux machine constructed by Michael Faraday. Since then, continuous development of electrical machines resulted in the prevalence of the radial flux machine technology which already early in the 1900's held the market of electric machines. At that time, development trends were pushed by the materials and manufacturing methods available. Since 1980 the applicability of axial flux machines to low-speed, direct-drive electrical drive applications has been studied. For instance, for the realization of the Monospace™-lift designed by Kone Elevators an axial flux motor type solution is used.

The expensive axial flux induction motor manufacturing technology has been an important limiting factor for the wide application of this motor type. Furthermore, the rotor construction of the machine has also been too weak to tolerate elevated rotational speeds. AXCO-Motors' innovations and its successful exploitation of the new technology - this is the key process that has enabled AXCO-Motors to cost-savingly manufacture the machine and, in addition, to increase the machine performance up to a level comparable to that of a traditional radial flux induction machine.

Pancake Motor

Pancake Motor

A light construction and excellent mechanical and dynamical performance are properties that make the axial flux induction machine well adaptable to medium-speed (3000 … 15000 rpm) applications.

 
   

AXCO-Motors Oy, Lappeenranta, info(at)axcomotors.com