Field of the Invention

The invention relates to an electric motor for use in power-demanding applications with a requirement for safe operation, particularly for aerospace applications.

Background of the Invention

Electric motors are machines, according to other sources electric rotating machines, used to convert electrical energy into mechanical work, for which they use the force effects of magnetic fields. According to Lorentz's law of force, a force proportional to the perpendicular component of magnetic induction and the magnitude of the electric current acts on a conductor lying in a magnetic field and flowed with an electric current. In essence, we can say that the mutual attraction and repulsion of two electromagnets, or an electromagnet and a permanent magnet, is exploited.

As a rotating machine, an electric motor has basically two main parts, which are the rotor and the stator. The stator is the fixed part of the electric motor and the rotor is the rotating part of the electric motor. By design, the rotor can be inside the stator or vice versa. In a very common configuration of an electric motor, the rotor is inside the stator, with the stator having electromagnets and the rotor having permanent magnets.

Nowadays, to increase the efficiency of converting electrical energy into mechanical work, the design of electric motors is improved by arranging the permanent magnets used in the electric motor in a Halbach magnet array, which can intensify the magnetic field of permanent magnets up to four times. Examples of such a consideration are the inventions known from document US 2019/0058384 Al, or from document US 2008/0224557 Al.

The disadvantages of the current trend of modifying the design of electric motors to maximize the efficiency of their operation are that the materials, technologies and designs used are brought to the edge of their capabilities and there is a risk of failure of the electric motor (machine). The combination of high rotor speeds, including the associated centrifugal forces, and the multiple intensification of magnetic fluxes in the electric motor due to the arrangement of the permanent magnets of the rotor in a Halbach magnet array, leads to extreme stresses that can lead to the destruction of the electric motor with a small error in the choice of materials or in the quality of the work done.

An example of such destruction of an electric motor can be the disintegration or loosening of some permanent magnets of the rotor, which leads to the total breakage of the rotor and in many cases also to the breakage of other parts of the electric motor, thus causing the sudden stop of the electric motor. The sudden interruption of the conversion of electrical energy into mechanical work, or even the immediate jamming and stopping of the rotor rotation, can have quite fatal consequences, e.g. in aviation, automotive transport, etc.

Another disadvantage that goes hand in hand with the above stresses is the thermal load. The intensification of magnetic fluxes in the electric motor leads to a greater production of waste heat, which not only stresses the materials of construction of the electric motor, but also reduces its performance, since the increasing temperature results in an increase in electrical resistance in the electrically conductive components of the electric motor. The most thermally stressed part of the electric motor are the coils of electrical wire wound on the armature.

Waste heat removal is usually accomplished by air rinsing, where in stationary electric motor applications, fan blades are attached to the extended end of the rotating shaft of the electric motors. The blades blow ambient air into the rotor and stator gaps during motor operation. When an electric motor is used in a mobile application, such as a vehicle, it is typically flushed with ambient air in response to the movement of the vehicle. Electric motors have ribbing on their casing to maximize the air-flushed area.

This standard cooling solution is applicable to electric motors that can be sufficiently air flushed, or that can be oversized, or that are not driven to the limit of their material and design capabilities. If it is necessary to remove heat more efficiently, the air rinse is replaced by a rinse with an electrically inert cooling medium, e.g. oil. Examples of such a solution are the inventions known from documents FR2823382 (Al), US 2005206258 (Al), or US 2011042967 (Al). The disadvantages of a direct oil rinsing are that it is necessary to create rinsing channels, in particular between the windings of the electric motor, which reduces the performance of the electric motor. Another disadvantage is associated with free immersion of the electric motor, as the hot oil does not circulate well when free immersing, rises upwards, and does not wash the electric motor parts evenly. In addition, the free immersion as well as the design of the rinsing channels between the windings contributes to the overall size of the electric motor, which loses the advantage of high performance in a small size.

It is the object of the invention to create an electric motor that could be used in applications requiring the best possible result of a high power/size ratio, further requiring protection against sudden stopping of the electric motor, and further requiring compactness of the electric motor in the form of a monoblock.

Summary of the Invention

This task is solved by means of an electric motor created according to the invention described below.

An electric motor for power-demanding applications consists of a rotor, a stator and an electric motor jacket. The rotor is fitted with permanent magnets in a Halbach array to amplify the magnetic effect. The stator is provided with windings wound on stator armature.

The subject matter of the invention is that a partition is arranged in the air gap between the stator windings and the permanent magnets of the rotor, which together with the electric motor jacket forms a sealed chamber with the stator located inside the chamber. At the same time, at least one distribution channel of the cooling medium is formed in the chamber and is routed along at least one of the sides of the windings of at least a portion of the stator, and at the same time the distribution channel is routed along the back of the armature of at least a portion of the stator. The distribution channel includes at least one inlet and at least one outlet of the cooling medium.

The inventive arrangement of the electric motor enables more efficient heat removal from the windings of the electric motor. The cooling medium flows around the winding from the sides, thereby removing a large amount of waste heat from the winding. The cooling medium also circulates along the back of the stator armature, from which it draws waste heat before leaving the chamber. In the course of developing the invention, it has become apparent that it is possible to implement heat removal with the flow of the cooling medium in both directions of the distribution channel. It has been shown that rinsing the winding from the sides of the winding allows very good heat transfer to the cooling medium without having to provide the winding with flow channels, thereby reducing the winding density. In addition, this winding wrapping solution is suitable for high-performance electric motors whose power is increased by the Halbach array of permanent magnets.

In the course of the development of the invention, an embodiment of the electric motor has been proven, in which the chamber is provided with a distribution channel of the cooling medium which runs simultaneously along both sides of the stator windings along the entire circumference of the stator. The distribution channel is further routed around the back of the armature along the entire circumference of the stator. The space of the cooling medium surrounding the winding sides and the space behind the armature backs are preferably connected by at least one passageway. Preferably, the distribution channel has a mirror symmetrical structure. It is the symmetry of the structure of the distribution channel, which imaginatively divides the electric motor into halves each containing one side of the winding, that has proven to be an ideal solution in terms of cooling efficiency and in terms of the complexity of the structure in the electric motor chamber.

In a preferred embodiment of the electric motor according to the invention, the rotor is provided with a bandage threaded through the permanent magnets of the rotor and fixed to the rotor. The bandage holds the permanent magnet assembly together so that should any of the permanent magnets crack and break into shards, the bandage will hold the damaged part together, thereby eliminating the risk of any of the shards becoming wedged and bringing the machine to an abrupt stop. In addition, the bandage evenly distributes the centrifugal forces applied, reducing the risk of the permanent magnet breaking through a hidden manufacturing defect. Also, the bandage protects the bulkhead in the gap between the rotor and the stator to prevent it from puncturing and leaking cooling medium or oil.

In a further preferred embodiment of the electric motor according to the invention, a cooling medium line is connected to the inlet and the outlet of the cooling medium from the chamber by the inlet and the outlet of the sealless pump. The combination of a sealless pump and an electric motor according to the invention increases safety, since the sealless pump is designed for lossless circulation flow. Preferably, the sealless pump is connected to the rotor to transfer the rotational motion from the rotor to the sealless pump and thus does not need its own source of mechanical power.

It is advantageous if the sealless pump is integrated into the electric motor jacket to form a monoblock. The monoblock is particularly used in the aerospace industry, where emphasis is placed on minimizing and compacting the power units.

Also among the preferred embodiments of the electric motor is one in which the jacket is ribbed in the chamber area. The ribbing of the jacket increases the surface area for heat dissipation to the surrounding environment.

Further preferably, the electric motor according to the invention comprises a thermostatic plate arranged at the outlet of the cooling medium from the distribution channel. The plate responds to the temperature of the flowing cooling medium by changing the flow rate of the cooling medium in the distribution channel, so that it can alter the distribution of the cooling medium. Preferably, a plate is used at each outlet of the cooling medium. Should hotter cooling medium accumulate in any of the distribution channels, the plate will increase the flow of the cooling medium through that particular distribution channel by thermally changing its shape, thereby compensating for the increased heating of the cooling medium in the distribution channel. Among the advantages of the invention is that the electric motor is efficiently cooled without having to interleave its windings with cooling channels or cooling elements, thereby reducing its density. Further, the electric motor still operates in the event of a breakdown of one of the permanent magnets and does not suddenly stop, allowing the electric motor to safely stop operating, which is particularly advantageous for aerospace applications.

Brief description of the drawings

The invention will be explained in more detail in the following illustrations, where:

Figure 1 shows a side view of an electric motor according to the invention,

Figure 2 shows a view of the bottom of the electric motor,

Figure 3 shows the electric motor jacket with a recess forming part of the distribution channel,

Figure 4 shows the electric motor jacket with the recess forming part of the distribution channel including the releases,

Figure 5 shows a perspective view into the electric motor with the side jacket cover removed,

Figure 6 shows a diagram of the flow of the cooling medium in a design where the side windings are cooled first.

Examples of preferred embodiments of the invention

It is understood that the specific embodiments of the invention described and illustrated hereinafter are presented for purposes of illustration and not as a limitation of the invention to the examples provided. Those skilled in the art will find or be able to provide, using routine experimentation, a greater or lesser number of equivalents to the specific embodiments of the invention described herein.

Figure 1 shows a side view of an electric motor according to the invention. Compared to the real state, the side cover of the jacket 6 of the electric motor is not shown in order to show the internal space and the arrangement of the main components of the electric motor, of an electric rotating machine. At the same time, all the windings 4 of the stator 3 are not depicted in Figure 1 to make the figure clearer. The main components of the electric motor include the rotor 1, which is circumferentially provided with permanent magnets 2. The orientation of the permanent magnets 2_is alternated to create a Halbach field with an enhanced magnetic effect towards the windings 4 and the armature 5 of the stator 2, while the magnetic effect towards the center of the rotor 1 is minimized by the Halbach arrangement. The rotor 1 is located inside the stator 3. The stator 3 is formed by an array of armature 5_running along the entire inner circumference of the stator 3. The armature 5 faces towards the rotor 1_ and is wrapped by the winding 4 to form an electromagnet. The stator 3 is surrounded around its circumference by an electric motor jacket 6. In the air gap between the rotor j_ and the stator 3 is a partition 7 made of electrically inactive material. The partition 7_serves to form a sealed chamber together with the jacket 6 for enclosing the stator 3. The sides of the chamber are sealed by the electric motor lids, which were described above as being part of the jacket 6.

Figure 2 shows the bottom of the electric motor. The casing 6 of the electric motor is visible. Also visible is a flange which houses the inlet 9 of the cooling medium to the chamber and distribution channel 8, respectively, and the outlets 10 of the cooling medium from the chamber and distribution channel 8, respectively. The inlets 9 and the outlets 10 are connected to a conventional oil distributor known to the person skilled in the art from the field of oil hydraulic distribution. A more detailed description of the hydraulic lines carrying the cooling medium from the electric motor to the cooler and back is not within the scope of the invention, and the skilled person will be able to design a variety of embodiments of hydraulic lines by routine work.

Fig. 3 shows only the peripheral jacket 6 without the stator 3 and the rotor 1. As can be seen from the figure, there are two inlets 9 of the cooling medium to the chamber on the inner circumference of the jacket 6. There are two inlets 9 because the windings 4_have two side faces and it is necessary to rinse both of these side faces with the cooling medium. Furthermore, grooves for guiding distribution channels 8 along the backs of the armatures 5 are visible, which terminate at the outlets 10 of the cooling medium from the chamber. One half of the distribution channel 8 is not obvious at first glance, but is the space in the chamber surrounding the sides of the windings 4. The other half of the distribution channel 8 is more obvious, as it is formed by a groove in the inner circumference of the jacket 6 to allow the cooling medium to return along the backs of the armature 5 of the stator 3.

If the cooling medium is allowed to flow in the opposite direction, starting at the back of the armature 5 and only afterwards rinsing the side walls of the winding 4, the inputs 9 and outputs 10 in the figures must be simply renumbered by swapping the relationship markers. In this configuration, the output oil distributor, which is connected to inputs 9 and outputs 10, must also be modified.

In Figure 4 a different view of the jacket 6 is shown to show the passages 11 through which the cooling medium leaves one part of the distribution channels 8 and enters the other part of the distribution channels 8. At the same time, the oil distribution flange is not shown, so that it can be seen that there are two inlets 9 of the cooling medium in the jacket 6 for rinsing both sides of the winding 4. To better visualize the first half of the distribution channel 8 for rinsing the sides of the windings 4, Fig. 5 is provided in which the inlet 9 of the cooling medium can be seen in the area where the sides of the windings 4_are located (the windings 4 are not shown in Fig. 5, only the armatures 5 on which the windings 4 are located are visible).

Figure 6 shows a diagram of the flow of the cooling medium for a complete understanding of the invention. In the diagram, only a stator section 3 having four armature 5 and a winding 4 is depicted. The coolant flow first passes from the inlet 9 along the sides of the winding 4, and only subsequently returns along the backs of the armature 5 to the outlet 10. The coolant flow can be reversed in the diagram, with the inlets 9 and outlets 10 being interchanged.

In an undisplayed example of the embodiment of the invention, an electric motor is provided with a safety device comprising a bandage which is threaded through the permanent magnets 2 around the circumference of the rotor 1_. The bandage is fixed to the rotor 1_ in order to distribute the centrifugal force exerted by the permanent magnets 2 into the body of the rotor 1. The bandage is a sandwich structure made of a high-strength composite material, which is made of elastic knitted fabric that forms the matrix of the composite and is subsequently hardened, for example, with an acrylate varnish that serves as a binder. The skilled person will be able, by routine work, to devise further variations of the material for use as a matrix and as a binder.

In a further, not illustrated, example of the embodiment, the jacket 6 forms a monoblock which serves as a protective cover and further as a rigid frame for carrying the components of the electric motor. The lines for the cooling medium are formed in the monoblock to carry the cooling medium from the radiator to the inlets 9 and outlets 10 of the sealed chamber. A sealless pump is used to drive the cooling medium, such as gear oil, in a sealless manner. The cooling medium pump may also be an external device or may be rigidly coupled to an electric motor to form a monoblock.

In a penultimate, non- illustrated example embodiment of the invention, the jacket 6 of the electric motor may be provided with fins to maximize the heat transfer surface content for transferring waste heat to the surrounding environment.

In the last, not illustrated example of an embodiment of the invention, a thermo-planchet formed by a bimetallic plate, which is separate for each distribution channel or outlet 10 thereof, is clamped in the streams (flows) of the cooling medium coming out of the distribution channels 8 in the oil distributor, and which is provided with a small central flow hole which ensures a minimum flow of the cooling medium even in the case of closure of this planchet. When the temperature of the flowing medium rises above the set limit, the respective diaphragm, on the basis of its physical properties, bends and opens the respective distribution channel 8 according to the current and set temperature. The cooling medium of the particular side of the electric motor then flows into the common mixing channel and then into the cooler. At the same time, the plate prevents the coolant from flowing back from one side of the chamber to the other side of the chamber through the distribution channels 8 and vice versa. The plate thus also acts as a check valve. Industrial applicability

The electric motor according to the invention will find applications in fields where the best power/size ratio of the electric motor is needed, such as aviation.

Overview of the Positions

1 rotor

2 permanent magnet

3 stator

4 windings

5 armature

6 jacket

7 partition

8 distribution channel

9 inlet of the cooling medium into the chamber

10 outlet of the cooling medium from the chamber

11 release