DE102014222064B4 - Electric machine - Google Patents

Abstract

An electric machine (1) with electronic commutation, comprising: - a circular cylindrical stator (2) with spaced stator teeth (22), wherein a part of the stator teeth (22) of stator coils (3) are surrounded as single tooth windings, so that in any of the more than one coil side (31) of a stator coil (3), the stator coils (3) being subdivided into a plurality of groups, which are interconnected via separate neutral points, - a rotor (4), which is rotatably mounted relative to the stator (2) and has rotor poles (42) formed by surface-mounted permanent magnets (41), the ratio of the sum of a radial air gap width (h) in a d-axis of the rotor (4) and a radial air gap width (H) in a q-axis of the rotor (4) to a Nutöffnungsbreite (W) of a slot opening (25) is between 2 and 3.

Description

Technical area

The invention relates to electrical machines, in particular electronically commutated electrical machines with high reliability and fault tolerance.

State of the art

Depending on the application, it is necessary that electrical machines have a particularly high fault tolerance. This is the case, for example, in fuel pumps of aircraft engines and in steering motors in motor vehicles.

Fault-tolerant electrical machines must have some characteristics that distinguish them from conventional electronically commutated electrical machines. For example, the phases of the winding must be electrically insulated from one another and in particular be driven by a single single-phase power section. Furthermore, such electrical machines can be equipped with a high d-axis inductance to limit short-circuit currents in a faulty winding in a phase connection short circuit.

Without magnetic isolation, fault currents in one phase can cause high voltages in one or more of the remaining phases, making control of these phases difficult. In particular, such magnetic isolation is achieved by having in each of the stator slots only one phase, i. a phase strand or a phase conductor is arranged.

Furthermore, in fault-tolerant electrical machines, it may be provided that the magnetic flux generated by the stator coils and passing through the air gap to the rotor body does not interact with other phases.

With the US 5 874 795 A an electric machine has become known, on the stator teeth of which single tooth windings are arranged. In between, auxiliary teeth of the stator are arranged so that in each case only one coil side of a single tooth winding is located in the corresponding stator slots. In this case, the rotor has surface-mounted permanent magnets which interact with the single-tooth windings.

The DE 10 2012 101 006 A1 shows a drive circuit of an electromechanical power steering, the motor has a three-phase winding, which is divided into two groups. The two coil groups each have their own star point.

With the DE 10 2010 053 364 A1 a permanent magnet motor has become known whose rotor has a loaf-shaped permanent magnet.

The DE 103 49 252 A1 shows a rotor of an electric motor whose laminations are rotated in the circumferential direction against each other so that the rotor has a helix angle to reduce the cogging torque of the motor.

The US 2008/0 290 751 A1 also shows an electric machine whose stator has single-tooth windings. In each case auxiliary teeth are arranged between the teeth with the single-tooth windings, so that in each case only one coil side of a stator coil is located in a stator slot. The individual coils drive a rotor, on whose surfaces permanent magnets are arranged.

It is an object of the present invention to provide a fault tolerant electric machine having a low torque ripple and a low noise and vibration.

Disclosure of the invention

This object is achieved by the electric machine according to claim 1.

Further embodiments are specified in the dependent claims.

• - einen kreiszylindrischen Stator mit beabstandeten Statorzähnen, wobei ein Teil der Statorzähne von Statorspulen als Einzelzahnwicklungen umgeben sind, so dass sich in keiner der zwischen den Statorzähnen ausgebildeten Statornuten mehr als eine Spulenseite einer Statorspule befindet;
• - einen Läufer, der relativ zum Stator drehbeweglich gelagert ist und durch oberflächenmontierte Permanentmagnete gebildete Läuferpole aufweist; wobei die Statorspulen in mehrere Gruppen unterteilt sind, die über separate Sternpunkte verschaltet sind.

According to one aspect, there is provided an electronically commutated electric machine comprising:

• - A circular cylindrical stator with spaced stator teeth, wherein a part of the stator of stator coils are surrounded as single tooth windings, so that is located in any of the stator teeth formed between the stator more than one coil side of a stator coil;
• - A rotor which is mounted rotatably relative to the stator and having rotor poles formed by surface-mounted permanent magnets; wherein the stator coils are divided into several groups, which are interconnected via separate neutral points.

One idea for designing the electrical machine is to provide it with a multi-phase stator winding. The groups of stator coils of the stator winding are each connected via separate neutral points. The Stator coils are provided as single tooth windings around, not directly adjacent stator teeth, so that only one coil side is located in a stator.

As a result, all the phase coils can be arranged physically separated from one another, so that the possibility of a phase short circuit is reduced.

The combination of the separate star points and the completely isolated arrangement of the stator coils, a very robust electric machine can be provided, in which a particularly high fault tolerance can be achieved. Furthermore, the thermal coupling between the phases is significantly reduced in that each stator slot is arranged only one coil side of a stator coil.

Further, the number of stator teeth may correspond to n * 2 * P (n = 2, 3...), Where P is the phase number of the electric machine 1 and the number of rotor poles is at least 8.

According to one embodiment, the rotor may have a soft-magnetic, in particular polygonal rotor body, on whose surface facing the stator, in particular, bread-shaped permanent magnets are arranged, which form the rotor poles.

In particular, the stator coils of a group may be adjacent to each other.

Furthermore, each stator coil of a group may be adjacent to another stator coil of another group.

A ratio of a stator slot opening width, i. Width of the slot opening, to a Nutöffnungshöhe can be between 2 and 5, in particular between 3 and 4.

Furthermore, tooth widths of tooth shanks of the (in particular all) not provided with stator coils stator teeth may be equal to or greater than the Zahnschaftbreiten of tooth shafts of the stator coils provided with stator coils.

A ratio of the diameter of an inner recess of the stator to an outer diameter of the stator can be between 0.54 and 0.58, in particular 0.57. In this case, the diameter preferably refers to the iron core of the stator, which is composed for example of individual stamped laminations.

Further, the ratio of a stator yoke width of a stator yoke of the stator to a tooth width of tooth shafts of the stator coil-provided stator teeth may be between 0.7 and 0.8, preferably between 0.74 and 0.76.

According to one embodiment, the ratio of the sum of the radial effective air gap width in the rotor d-axis and the radial effective air gap width in the rotor q-axis to a slot opening width (W _SO ) may be between 2.2 and 2.8.

In particular, the ratio of the height h _{PMe of} the permanent magnets at their edges to the height of the permanent magnets in their middle in the circumferential direction between 0.3 and 0.6, in particular between 0.4 and 0.5.

According to one embodiment, the ratio of the edge height of the permanent magnets to the radial width of an air gap between the stator and rotor at the edge of the permanent magnets can be between 0.9 and 1.2.

It can be provided that the permanent magnets in the circumferential direction have a ratio of an overlap angle to the pole pitch of the rotor pole of between 0.85 and 1.

Furthermore, the rotor can be provided with a skew.

list of figures

• 1 eine Querschnittsdarstellung einer elektrischen Maschine mit einer Wicklungsanordnung;
• 2 eine schematische Darstellung der Verschaltung der Statorspule gemäß einer ersten Wicklungsanordnung;
• 3 eine schematische Darstellung der Verschaltung der Statorspule gemäß einer zweiten Wicklungsanordnung;
• 4 eine Veranschaulichung der Dimensionierungen des Stators und des Läufers der elektrischen Maschine der 1.

Embodiments are explained below with reference to the accompanying drawings. Show it:

• 1 a cross-sectional view of an electrical machine with a winding assembly;
• 2 a schematic representation of the interconnection of the stator coil according to a first winding arrangement;
• 3 a schematic representation of the interconnection of the stator coil according to a second winding arrangement;
• 4 an illustration of the dimensions of the stator and the rotor of the electric machine 1 ,

Description of embodiments

1 shows a cross-sectional view through an electric machine 1 , The electric machine has a stator 2 on, the a circular cylindrical Statorjoch 21 and stator teeth protruding inward in the radial direction R 22 having. The stator teeth 22 are spaced apart in the circumferential direction U, so that between the stator teeth 22 Stator grooves 23 are located. The shown electric machine has 12 stator teeth, but other even numbers of stator teeth may be provided in other embodiments. Generally, the number of stator teeth may correspond to n * 2 * P (n = 2, 3...), Where P is the phase number of the electric machine 1 equivalent.

The stator teeth 22 have a toothed shaft with a substantially rectangular cross-section (with respect to the radial direction R) and can at its protruding end with tooth heads 24 be provided. The tooth heads 24 stand from the tooth shaft of the stator tooth 22 in the circumferential direction U, ie in the direction of arrangement of the stator teeth 22 about the slot opening 25 the stator grooves 23 towards an air gap 6 to reduce. The protruding ends of the stator teeth 22 form an inner recess 26 ,

The stator 2 is provided with a stator winding, which has several stator coils 3 includes. The stator coils 3 have coil sides 31 on, each individually in a stator slot 23 of the stator 2 are arranged so that a magnetic, thermal and physical insulation between the individual, through the stator coils 3 formed phases of the stator winding, can be ensured. This is between one with a stator coil 3 provided stator tooth 22 always one or more unwound, ie not with a stator coil 3 provided stator tooth 22 ,

In the interior recess 26 of the stator 2 is a runner 4 arranged by surface magnets 41 trained runner poles 42 having. The permanent magnets 41 are on a lateral surface of a soft magnetic rotor body 43 arranged, which is cylindrical and has a polygonal cross-section. The permanent magnets 41 are attached to lateral surface portions of the rotor body. The runner body 43 is on a wave 5 arranged and stored rotatably.

The stator coils 3 can according to a first winding design according to the schematic representation of 2 be interconnected. 2 schematically shows a plan view of the ends of the stator teeth 22 in a linear projection, with every second stator tooth 22 from a stator coil 3 is surrounded, so that exactly one coil side 31 in each of the stator slots 23 is arranged. The first winding design comprises a plurality of, in the present case two sub-machines, the stator coils associated with each phase 3 exhibit that on the stator 2 are arranged adjacent to each other.

In the present embodiment, in the first winding design, as in FIG 2 shown, as first partial winding T1 three phases associated with each other adjacent stator coils 3 on the stator teeth 1 . 3 and 5 arranged, which are connected in a neutral connection with a first neutral point S1. This is followed by a second partial winding T2, the stator coils associated with three phases 3 on the stator teeth 7 . 9 and 11 exhibit. The stator coils 3 the second partial winding T2 are electrically connected via a common second neutral point S2. The two partial windings T1, T2 can be controlled via separate power units, by a corresponding current supply of the stator coils 3 to generate a rotating stator magnetic field.

By the above-described arrangement of the stator coils 3 For example, the partial windings T1, T2 can be provided and controlled completely physically separated from one another, thereby obtaining an ideal fault-tolerant winding system.

In a second winding design, which in the schematic representation of 3 are shown, unlike the first winding design of the 2 the stator coils 3 so interconnected that each immediately adjacent stator coils 3 are assigned to different star points S1, S2. In particular, the stator coils 3 are on the stator teeth 1 . 5 and 9 interconnected via a first neutral point S1 to a first partial winding T1, while the stator coils 3 on the stator teeth 3 . 7 and 11 are connected via a second neutral point S2 to a second partial winding T2. Such an arrangement reduces the development of running noise and vibration in the operation of the electric machine 1 compared to the interconnection of the first winding design.

In 4 is an enlarged fragmentary cross-sectional view of the electric machine 1 shown with dimensions to explain the preferred for the above electrical machine dimensioning and dimensioning.

In particular, the embodiment of the electric machine 1 with twelve stator slots 23 and eight rotor poles 42 creates a magnetic circuit with a rotational symmetry of four. This in turn creates a spatial ordering of the radial stress wave in the air gap of the machine generated by the rotor field of four. Accordingly, the lowest structural mode of the stator core that can be excited by this voltage wave is the fourth. This ensures that the stator core can not be excited with the second pattern mode (ovalizing mode), thereby the machine has low noise and vibration.

By providing only one coil side 31 in the stator grooves 23 ie, a single-layer winding, a larger phase inductance is achieved compared to electric machines with eg two coil sides per Statornut, ie a two-layer winding. To avoid too high a phase inductance, surface mounted permanent magnets are attached to the rotor 4 used, and a large slot width W _so that the width of the slot opening 25 corresponds in the circumferential direction U, and a low slot opening height h _SO , the thickness of the tooth tips 24 in the radial direction R, used. The ratio of the slot opening width W _SO to the slot opening height h _SO is preferably 3.5. An optimum ratio is in a range of 2 to 5, preferably in a range between 3 and 4.

Preferably, the wound and unwound stator teeth 22 identical geometries, so that their tooth widths W _T and Nutöffnungshöhen h _{SO are} identical. This avoids high amplitude sub-harmonic excitations due to the non-uniform reluctance of the wound and unwound stator teeth. Accordingly, very low cogging and torque ripples can be achieved.

By providing identical tooth widths W _{T of} the wound and unwound stator teeth 22 prevents the unwound stator teeth from saturating when in the stator coils 3 a short circuit fault occurs with high fault currents and high induced fluxes. The use of the thicker unwound stator tooth avoids the flow induced by the fault on adjacent non-saturated wound stator teeth 22 is derived and thus proper, ie not short-circuited stator coils influenced.

Furthermore, it can also be provided to form the tooth shanks of the unwound stator teeth 22 wider than the tooth shanks of the wound stator teeth 22 ,

The division ratio of the diameter of the inner recess D _SB to the outer diameter of the stator D _SO is preferably between 0.54 and 0.58, particularly preferably 0.57. This concerns in particular an electric machine 1 with eight rotor poles 42 and with surface-mounted permanent magnets.

The ratio of the stator yoke width W _Y to the stator tooth width W _T is between 0.7 and 0.8, preferably between 0.74 and 0.76, for example 0.75. This means a stiffer stator yoke 21 , whereby the vibration resistance is increased and the noise is reduced during operation of the electric machine. Furthermore, by the radially widened stator yoke 21 a saturation in the stator yoke 21 be avoided, whereby a linear torque-current dependence is achieved. In particular, ensures a wider stator yoke 21 greater stability when constructed with stator segments.

To ensure that only one self-inductance component of the phase inductance remains, the entire stator flux of an energized, wound stator tooth should pass through the stator slot 23 and groove opening 25 to the adjacent unwound stator tooth 22 run and over the Statorjoch 21 flow back. To achieve this, the groove opening widths W _SO should be smaller than twice the effective air gap width between the inner recess of the stator 2 and the rotor body 43. Thus it can be avoided that a magnetic flux runs to the rotor body 43 and then possibly to other stator coils 3 acts back so that a coupling inductance is generated.

The effective air gap (or effective magnetic air gap) is the total gap (radial distance) between the inner recess of the stator 2 (ie, the stator bore) to the rotor body 43 , This entire gap includes the "true" air gap, the nonmagnetic retainer, and the permanent magnets. The permanent magnets have a permeability of almost 1 (about 1.05) and therefore can be considered as magnetic as air. (Air has a permeability of exactly 1). The retaining sleeve also has a permeability of 1 (non-magnetic steel) and therefore can also be regarded as magnetic, such as air.

This still requires relatively thick surface mounted permanent magnets 41 in conjunction with a non-magnetic retaining sleeve 7 that the runner 4 surrounds and at the permanent magnet 41 is applied. As a result, the necessary wide effective air gap is achieved. Due to the octagonal shape of the rotor body 43 There are different effective air gap widths between the inner recess of the stator 2 and the runner body 43 namely, the radial air gap width h _d in the d-axis of the rotor and the radial air-gap width h _q in the q-axis of the rotor, wherein the slot width W _{SO is} smaller than h _d + h _q . In particular, h _d + h _{q should be} increased by a factor 2 to 3 , Preferably between 2.2 and 2.8 larger than W _SO, in particular greater by a factor of 2.4.

The permanent magnets 41 are preferably formed from a rare earth material and are loaf-shaped to achieve a sinusoidal phase electromotive force (EMF) necessary to achieve low torque ripple in sinusoidal phase currents. A Brotlaibform is appropriate, since this has a flat surface which is in a simple manner with the rotor body 43 can be connected, for example by gluing. The loaf shape of the surface mounted permanent magnets 41 has a certain outer contour, which generates a very low cogging torque and minimizes the 5th, 7th, 11th, and 13th harmonics of the airgap flux. This achieves an almost sinusoidal course of the phases EMF, which is necessary for a very low torque ripple (if sinusoidal phase currents are used).

In particular, since the torque of a machine is generated only with the air-gap flux interlinked with the winding, the proportion of the fundamental wave of the air-gap flux should be maximized to an electric machine 1 with a high torque density. In particular, the 3rd harmonic in the air gap flow should be allowed for this purpose. The 3 , Theoretically, harmonic is not with the stator coils 3 coupled, so that no unwanted third harmonics are generated in the phase EMF, because the 3rd harmonic winding factor of the winding used theoretically (assuming a slot width of 0) is zero. However, if a very small amount of the 3rd harmonic occurs in the phase EMF (with a finite width of the slot openings), this does not lead to an undesirable effect, because in ideally balanced 3-phase machines with star connection, the 3rd harmonic of the individual phases in the chained phase EMF (between the terminals) cancel out by superposition.

The ratio of the edge _height h _PMe (in the radial direction) of the permanent magnets 41 (Height at their edges) to the height h _{PMm of} the permanent magnet 41 in its center (seen in the circumferential direction U) is approximately between 0.3 and 0.6, in particular between 0.4 and 0.5, for example at 0.45. This ratio, in conjunction with the above sinusoidal waveform of the phases EMF, ensures that the above suppression of the 5th, 7th, 11th, and 13th harmonics of the air gap flux is achieved. It also increases the robustness of the electric machine 1 to tolerances in the width of the permanent magnet 41 and their position on the rotor body 43 ,

The ratio of the edge _height h _{PMe of} the permanent magnets 41 to the radial height h _{ge of} the air gap at this outer edge of the permanent magnets 41 to the inner diameter of the stator 2 is about 1, for a local, irreversible demagnetization at the outer edges of the permanent magnets 41 at full load, especially when low cost rare earth rare earth permanent magnets (without dysprosium) are used. However, this ratio should not be less than about 0.9.

The width of the permanent magnets 41 in the circumferential direction U is chosen as large as possible and covers an entire pole pitch τ _p minus the width of very small positioning lugs 44 , The ratio of an overlap angle β _PM to the pole pitch τ _p is preferably between 0.85 and 1, in particular 0.88, the overlap angle β _{PM being} defined by the width of the loaf-shaped permanent magnet 41 is determined in the circumferential direction.

The runner 4 can be provided with a skew to reduce the cogging torque. In particular, the runner 4 to be divided by several, in particular 3 axial sections, each section in the circumferential direction U relative to the adjacent section by an angle of 4 to 6 °, in particular 5 °, is offset.

Claims (14)

An electric machine (1) with electronic commutation, comprising: - a circular cylindrical stator (2) with spaced stator teeth (22), wherein a part of the stator teeth (22) of stator coils (3) are surrounded as single tooth windings, so that in any of the the stator teeth (22) formed stator (23) more than one coil side (31) of a stator coil (3), wherein the stator coils (3) are divided into a plurality of groups, which are connected via separate neutral points; - a rotor (4) which is rotatably mounted relative to the stator (2) and by means of surface-mounted permanent magnets (41) formed rotor poles (42); - Where the ratio of the sum of a radial air gap width (h _d ) in a d-axis of the rotor (4) and a radial air gap width (h _q ) in a q-axis of the rotor (4) to a Nutöffnungsbreite (W _SO ) of a slot opening (25) is between 2 and 3. Electric machine (1) after Claim 1 , wherein the number of stator teeth is n * 2 * P (n = 2, 3...), where P is the phase number of the electric machine (1) and wherein the number of rotor poles (42) is at least 8. Electric machine (1) after Claim 1 or 2 , wherein the rotor (4) has a magnetically conductive polygonal rotor body (43), on whose surface facing the stator (2) bread-shaped permanent magnets (41) are arranged, which form the rotor poles (42). Electric machine (1) according to one of Claims 1 to 3 wherein the stator coils (3) of a group are adjacent to each other. Electric machine (1) according to one of Claims 1 to 3 wherein each stator coil (3) of a group is adjacent to another stator coil (3) of another group. Electric machine (1) according to one of Claims 1 to 5 wherein a ratio of the groove opening width (W _so ) to a groove opening height (h _SO ) of the groove opening (25) is between 2 and 5. Electric machine (1) according to one of Claims 1 to 6 in which tooth widths of tooth shanks of the stator teeth (22) not provided with stator coils (3) are equal to or greater than the tooth widths of tooth shanks of the stator teeth (22) provided with stator coils (3). Electric machine (1) according to one of Claims 1 to 7 wherein the ratio of the diameter of an inner recess (D _SB ) of the stator (2) to an outer diameter (Dso) of the stator (2) is between 0.54 and 0.58. Electric machine (1) according to one of Claims 1 to 8th wherein the ratio of a stator yoke width (W _Y ) of a stator yoke (21) of the stator (2) to a tooth width (W _T ) of tooth shafts of the stator teeth (22) provided with stator coils (3) is between 0.74 and 0.76 , Electric machine (1) according to one of Claims 1 to 9 wherein the ratio of the sum of a radial air gap width (h _d ) in the d-axis of the rotor (4) and a radial air-gap width (h _q ) in the q-axis of the rotor (4) to a slot opening width (W _SO ) of the slot opening (25) is between 2.2 and 2.8. Electric machine (1) according to one of Claims 1 to 10 Wherein a ratio of the edge height (h _PMe) of the permanent magnets (41) to the height (h _PMm) of the permanent magnets (41) located at its center in the circumferential direction U between 0.4 and 0.5. Electric machine (1) according to one of Claims 1 to 11 wherein a ratio of the edge _height (h _PMe ) of the permanent magnets 41 to the radial width (h _ge ) of an air gap (6) between the stator (2) and rotor (4) at the edge of the permanent magnets 41 is between 0.9 and 1.2 , Electric machine (1) according to one of Claims 1 to 12 wherein the permanent magnets (41) in the circumferential direction (U) have an overlap angle (β _PM ) with respect to the pole angle (τ _p ) of the rotor pole of between 0.85 and 1. Electric machine (1) according to one of Claims 1 to 13 , wherein the rotor (4) is provided with a skew.

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