Operationally Reliable Brushless DC Electric Motor

Abstract

The present disclosure relates to a brushless DC electric motor, such as for an actuator unit of an implant, as for a cardiac assist system, with a stator with a hollow-cylindrical iron-free winding and a rotor which can rotate relative to the stator. A shaft has a number p of pairs of permanent-magnetic poles, and the winding has a number n of three-phase systems separate from one another. The number of n three-phase systems separate from one another, is varied based on a number p of pairs of permanent-magnetic poles, and the systems are arranged in a manner spatially offset from one another by an angle of 360°/n.

Claims

1. A brushless DC electric motor with comprising: a stator with a hollow-cylindrical iron-free winding; and a rotor arranged to rotate relative to said stator and having a shaft with a number p of pairs of permanent-magnetic poles, where said winding has a number n of three-phase systems separate from one another, wherein the number n of three-phase systems separate from one another is selected as follows: for a number p=1 of pairs of permanent-magnetic poles, n is two; and, for a number p>1 of pairs of permanent-magnetic poles, n corresponds either to: an integer divisor of p, where the integer divisor is unequal to 1, or the number p, or twice the number p of pairs of permanent-magnetic poles; where the number n of three-phase systems separate from one another in said hollow-cylindrical iron-free winding is arranged in a manner spatially offset from one another by an angle of 360°/n.

2. The brushless DC electric motor according to claim 1, comprising: at least a number p=2 of pairs of permanent-magnetic poles, and the number n of three-phase systems separate from one another corresponds to an integer divisor of p, where the integer divisor is unequal to 1, or to the number p of pairs of permanent-magnetic poles.

3. The brushless DC electric motor according to claim 2, comprising: at least a number p=2 of pairs of permanent-magnetic poles, and the number n of three-phase systems separate from one another corresponds exactly to the number p of pairs of permanent-magnetic poles.

4. The brushless DC electric motor according to claim 1, comprising, for each phase of said three-phase systems electrically separate from one another: at least a number of k=2 single coils connected in series, where a product k.Math.n of k single coils and said n separate phase systems corresponds to twice the number of pairs of permanent-magnetic poles, and where a spatial angle of said single coils, connected in series, of the respective phase of said three-phase systems separate from one another is 360°/n/k.

5. The brushless DC electric motor according to claim 4, wherein two single coils of a phase, connected in series, are electrically connected in said hollow-cylindrical iron-free winding in opposite winding directions.

6. The brushless DC electric motor according to claim 1, wherein the axial positions of said at least two three-phase systems separate from one another overlap in relation to said shaft at least in certain regions.

7. The brushless DC electric motor according to claim 1, wherein said single coils of said three-phase systems separate from one another are connected to one another in a star connection, where neutral points of said at least two three-phase systems separate from one another are preferably connected to one another.

8. The brushless DC electric motor according to claim 1, wherein said single coils of said individual three-phase systems separate from one another are connected to one another in series so that an electrical coupling of said individual three-phase systems, referred to as a delta connection, is created.

9. The brushless DC electric motor according to claim 1, wherein said single coils of said three-phase systems, that are separate from one another, are connected to one another in a single polygon connection.

10. The brushless DC electric motor according to claim 1, wherein a separate electronic commutator is provided for each of said three-phase systems that are separate from one another.

11. The brushless DC electric motor according to claim 1, wherein said stator comprises: a magnetic yoke.

12. The brushless DC electric motor according to claim 1, wherein an air gap between said rotor and said stator is configured to allow for a fluid flow through said air gap where said circumferential air gap is sized relative a radius of said rotor.

13. The brushless DC electric motor according to claim 1, in combination with: an actuator unit of an implant configured for a cardiac assist system.

14. The brushless DC electric motor according to claim 10, wherein the electronic commutator is an electronic block commutator.

15. The brushless DC electric motor according to claim 11, wherein the magnetic yoke is a laminated iron pack arranged around said hollow-cylindrical iron-free winding.

16. The brushless DC electric motor according to claim 13, wherein an air gap between said rotor and said stator is configured for human blood to flow through the gap, the gap being larger than 15% and/or larger than 25% relative to a radius of the rotor.

17. The brushless DC electric motor according to claim 3, comprising, for each phase of said three-phase systems electrically separate from one another: at least a number of k=2 single coils connected in series, where a product k n of k single coils and said n separate phase systems corresponds to twice the number of pairs of permanent-magnetic poles, and where a spatial angle of said single coils, connected in series, of the respective phase of said three-phase systems separate from one another is 360°/n/k.

18. The brushless DC electric motor according to claim 17, wherein a separate electronic commutator is provided for each of said three-phase systems that are separate from one another.

19. The brushless DC electric motor according to claim 18, wherein said stator comprises: a magnetic yoke.

20. The brushless DC electric motor according to claim 19, in combination with: an actuator unit of an implant configured for a cardiac assist system.

Description

[0019] Non-restricting embodiments of the present invention shall be explained hereafter in more detail using exemplary drawings, where:

[0020] FIG. 1 shows a schematic exploded view of a brushless DC electric motor according to the invention,

[0021] FIG. 2 shows a schematic representation of the coil connection of the DC electric motor from FIG. 1 with two pairs of permanent-magnetic poles and two three-phase systems,

[0022] FIG. 3 shows a schematic representation of the independent magnetic fluxes for the circuit from FIG. 2 with two single coils for every phase,

[0023] FIG. 4 shows a schematic representation of the independent magnetic fluxes according to FIG. 3 with an internal short between turns, and

[0024] FIG. 5 shows a schematic representation of a winding configuration for the circuit from FIG. 2 with two single coils for every phase.

[0025] It applies to the following embodiments that like components are designated with like reference characters. Where a figure contains reference characters which are not explained in more detail in the associated figure description, then reference is made to preceding or subsequent figure descriptions.

[0026] The general structure of a brushless DC electric motor 1 according to the invention shall first be explained with reference to FIG. 1. The main components of this brushless DC electric motor 1 are rotatable rotor 2 with a permanent magnet 3 which is connected directly to shaft 4, as well as stator 5 in which rotor 2 is mounted to be rotatable, with a hollow-cylindrical iron-free winding 6 and yoke 7 arranged around winding 6 and connected to housing 8. Yoke 7 consists of a laminated iron pack for reducing the iron losses that occur due to rotating permanent magnet 3 of rotor 2. A printed board 10 provides for the electrical connection of winding 6 to associated power electronics by way of connecting wires 9. Sensors, for example Hall sensors, can also be arranged on printed board 10 and scan the position of permanent magnets 3 co-rotating with shaft 4.

[0027] Shaft 4 with permanent magnet 3 mounted thereon is mounted to be rotatable on two preloaded ball bearings 11. Two balancing rings 12 arranged between ball bearings 11 and permanent magnet 3 enable dynamic balancing of the rotor in that material can be removed selectively from two balancing rings 12. The balancing of the rotor by way of balancing rings 12 reduces the vibration and noise and thereby extends the service life of ball bearings 11 and entire electric motor 1, respectively, in particular at the high rotational speeds that can be reached with a brushless DC electric motor 1. Rotor 2 mounted in housing 8 can be secured with bearing flange 13 on the face side.

[0028] The connection of hollow-cylindrical iron-free winding 6 of DC electric motor 1 from FIG. 1 to a permanent magnet 3 consisting of two pairs of permanent-magnetic poles 14 and two three-phase systems 15 of winding 6, that are electrically isolated from one another, to single phases P.sub.1, P.sub.3 and P.sub.5 or P.sub.2, P.sub.4 and P.sub.6, respectively, is shown in FIG. 2. In addition to permanent magnet 3 with four magnetic poles, single phases P.sub.1, P.sub.3 und P.sub.5 and. P.sub.2, P.sub.4 und P.sub.6, respectively, each have two single coils 16 which are connected in series and arranged in winding 6 offset from one another by a spatial angle of 90°. Where a larger air gap 17 is provided between stator 5 with winding 6 and rotor 2 with permanent magnet 3, which allows for the flow of fluid, in particular for human blood to flow through. Furthermore, single phases P.sub.1, P.sub.3 and P.sub.5 and P.sub.2, P.sub.4 and P.sub.6, respectively, of respective three-phase systems 15 are electrically connected to one another in a star connection, where individual neutral points 18 of two three-phase systems 15 are merged with one another and are led out from winding 6 as a common neutral point 19. As an alternative to the star connection shown in FIG. 2, two three-phase systems 15 can also be connected accordingly as a six-phase polygon circuit without individual neutral points 18 or a common neutral point 19.

[0029] FIG. 3 shows a schematic representation of the independent magnetic fluxes for a DC electric motor 1 according to the invention in the star connection shown in FIG. 2. The preferred embodiment of DC electric motor 1 with a four-pole permanent magnet 3 and two three-phase systems 15 is taken as a basis here again, each with 2 single coils 16 for every phase that are connected in series and that are arranged in winding 6 at a spatial angle of 90° relative to one another. FIG. 3 shows the diagram of independent magnetic fluxes ϕ.sub.1 to ϕ.sub.4 of four single coils 16 of two associated single phases, i.e. offset by 180°, of two three-phase systems 15 separate from one another. Two single coils 16 of the respective single phases are electrically connected in opposite winding directions, resulting in a magnetic coil coupling with a north and a south pole

[0030] The schematic representation in FIG. 4 shows the diagram of independent magnetic fluxes ϕ.sub.1 to ϕ.sub.4 of four single coils 16 for a faulty operating state in which a single coil 16 of winding 6 is short-circuited by an internal winding fault and ideally does not allow for any magnetic flux. In contrast to the undisturbed operating state of DC electric motor 1 in FIG. 3, a single coil 16 of single phase P.sub.1 is short-circuited in an unforeseen manner by an internal fault between turns, resulting in a short-circuit current being formed that counteracts the rotor field. Magnetic fluxes ϕ.sub.1 and ϕ.sub.2 are forced out of short-circuited single coil 16 of single phase P.sub.1 and must therefore close tangentially, i.e. in the circumferential direction, in air gap 17 between the surface of rotor 2 and the inner diameter of winding 6. Magnetic fluxes ϕ.sub.1 and ϕ.sub.2 therefore form only magnetic leakage flux components that are no longer detected by the winding system and can therefore no longer contribute to the electromechanical power conversion.

[0031] The magnetic coil flux consisting of magnetic fluxes ϕ.sub.1 and ϕ.sub.2 of single phase P.sub.1 is reduced by ¾ to ¼ due to the short between turns. However, the magnetic coil flux in oppositely disposed single phase P.sub.2 of winding 6 shows a reduction by only ¼ to ¾ of the flux that prevailed in the fault-free state in FIG. 3. After switching off short-circuited single phase P.sub.1, single phase P.sub.2 can still continue to be operated with a flux reduced by 25%. This relatively small impairment is due to the fact that directly adjacent pairs of poles are associated with the single phases. After switching off a faulty single phase, 10/12, i.e. about 83% of the winding system can still make a power contribution Accordingly, in emergency operation, the winding currents and, corresponding to the square of the current, the copper losses can also be reduced. Due to the higher degree of efficiency during emergency operation, DC electric motor 1 according to the invention can be classified as significantly more fault-tolerant than conventional electric motors with a simple three-phase winding 6. With DC electric motor 1 according to the invention, start-up from a standstill is also still possible during emergency operation.

[0032] The polyphase nature of DC electric motor 1 according to the invention with smaller voltage differences between adjacent single coils 16 reduces the current between adjacent single phases P.sub.1 to P.sub.6 during an emergency operation with internal shorts between turns. Emergency operation with an existing internal short between turns therefore causes lower additional losses and accordingly DC electric motor 1 according to the invention provides a better degree of efficiency during emergency operation. In contrast to bifilar wound windings 6, a magnetic flux can still form in the event of an internal shorts between turns in DC electric motor 1 according to the invention on more than half the circumference of winding 6 which allows for a slightly reduced voltage induction in remaining, unaffected single coils 16.

[0033] The winding configuration for DC electric motor 1 according to the invention shown in FIG. 2 is shown in the schematic representation of winding 6 with two single coils 16 for every single phase P.sub.1 to P.sub.6 in FIG. 5. Single phases P.sub.1 to P.sub.6 of two three-phase systems 15 separate from one another are connected to one another in a star connection, where neutral points 18 of at least two three-phase systems 15 separate from one another are connected to one another and can be led out of winding 6 as a common neutral point 19 and connected to power electronics. Single coils 16 of two three-phase systems 15 are configured in a rhombus-shaped winding shape in order to achieve the greatest possible turn density of hollow-cylindrical iron-free winding 6. This winding shape is also known as a diamond winding. Two single coils 16 of respective single phases P.sub.1 to P.sub.6 are electrically connected in the hollow-cylindrical iron-free winding in an opposite winding direction, resulting in a magnetic coil coupling with a north and a south pole and thereby to the increased fault tolerance of DC electric motor 1 according to the invention.

LIST OF REFERENCE CHARACTERS

[0034] 1 DC electric motor [0035] 2 rotor [0036] 3 permanent magnet [0037] 4 shaft [0038] 5 stator [0039] 6 winding [0040] 7 yoke [0041] 8 housing [0042] 9 connecting wires [0043] 10 printed board [0044] 11 ball bearing [0045] 12 balancing rings [0046] 13 bearing flange [0047] 14 pair of poles [0048] 15 three-phase system [0049] 16 single coils [0050] 17 air gap [0051] 18 neutral points [0052] 19 common neutral point [0053] P.sub.1-P.sub.6 single phases [0054] ϕ.sub.1-ϕ.sub.4 magnetic fluxes