FR3076113B1 - SYNCHRONOUS MACHINE WITH COIL INDUCTOR - Google Patents

Abstract

Flow switching machine, comprising a first pole piece and a second pole piece adjacent, the upper face of the first pole piece having an extension γr01 along the circumference of the rotor, the lower face of the first pole piece having an extension γri1 , the upper face of the second pole piece of the same pair having an extension γr02, the lower face of the second pole piece having an extension γri2, the two pole pieces being arranged so that an axial end surface of the first polar piece is facing an axial end surface of the second pole piece, with γri1 <γr01, γr02 <yri2, and γr01 = γr02.

Description

Synchronous machine with wound inductor

Synchronous machines with wound inductor, with flow switching, are known from the prior art, in particular used to supply electrical or mechanical power in a vehicle, for example in the publication Zhongze WU ICEMS 2016. "Design and Analysis of A Partitioned Stator Wound Field Switched Flux Machine for Electric Vehicle ”. A synchronous flow-switching rotary electric machine connected to a shaft via a bearing makes it possible to provide electrical power to power the electrical components of the vehicle or mechanical power to drive the vehicle, i.e. to provide proportional torque necessary for vehicle consumables. Such machines make it possible to obtain higher torques due to the higher total winding surface.

Such synchronous rotating electrical machines, with flow switching, comprise an excitation stator and an armature stator, the two stators being positioned in a radial concentric configuration, around an axis of rotation Z, the excitation stator being inside the armature stator, an air gap being defined between the two stators in which a rotor is housed, the excitation stator being formed by a stator body comprising a plurality of teeth extending from the body excitation stator towards the rotor, an excitation winding being wound around the plurality of teeth of said excitation stator, the armature stator being formed by a stator body comprising a plurality of teeth extending from the body armature stator to the rotor, an armature winding being wound around the plurality of teeth of said armature stator, and the rotor, having no winding or permanent magnets, is fo rmé by a set of pairs of pole pieces arranged circumferentially in the air gap opposite each of the stators, separated by a pole pitch.

Such machines have the disadvantage that during the movement of the rotor relative to the excitation and armature stators, the modifications of the field lines generate a disturbing induced voltage at the level of the excitation stator which generates losses, and degrades your machine performance. It is therefore a question of being able to optimize the torque generated by reducing said induced voltage.

Thus in a machine such as that which is the subject of the invention, a pair of pole pieces comprises a first pole piece and a second pole piece adjacent to the first pole piece, each pole piece having substantially the shape of a truncated pyramid. , each pole piece positioned in the air gap having two axial end surfaces facing one along the axis of the machine, two blanks facing you along the circumferential direction of the machine, two faces facing one of the other, an upper face facing the armature stator and a lower face facing the excitation stator, the upper face of the first pole piece having an extension along the circumference of the rotor defined by an angle of opening of said face opposite the armature stator between a first left blank and a first right blank γτΟ1, the underside of the first pole piece having an extension ion te along the circumference of the rotor defined by an opening angle of said face opposite the excitation stator between the first left blank and te first right blank yri1, the upper face of the second pole piece of the same pair having an extension along the circumference of the rotor defined by an opening angle of said face opposite the armature stator between a second left blank and a second right blank γτ02, the lower face of the second pole piece having an extension the along the circumference of the rotor defined by an opening angle of said face opposite the excitation stator between a second left blank and a second right blank γπ2, the two pole pieces being arranged so that an end surface axial of the first pole piece is opposite an axial end surface of the second pole piece, the blanks of the first pole piece being inclined so that e: γτΙ1 <γιΌ1, the blanks of the second pole piece being inclined so that: γτ02 <yri2, with γτΟ1 and γτ02 of the same order of magnitude.

Such a machine is of simple design in that it does not require slip rings, brushes or the like, the only movable part being the movable part with your pole pieces which does not require any power supply, and with an assembly of the pieces easy polar. In addition, the geometry and the particular arrangement of the pairs of pole pieces forming a rotor makes it possible, by limiting your abrupt variations in magnetic flux at the level of the excitation stator, to reduce the disturbing harmonics of induced voltage. The inclination of the blanks also contributes to the reduction of abrupt flux changes.

According to one embodiment, the machine is such that γτΟ1 = γτ02 == γτ0 and checking the inequalities 0.5 <Rri1 <0.9, 0.9 <Rri2 <0.95 and 0.7 <Rr0 <0.75, where the angular polar step is defined by polar step = 360 / Ner where Ner designates the number of teeth on the rotor, and RrO = γτθ / non-polar, Rri1 = γτϊ1 / non-polar, Rri2 = yri2 / non-polar.

According to one embodiment, the machine is such that Rri2 is equal to 0.95, Rrit is equal to 0.54.

According to one embodiment, for each pole piece your two axial end faces are substantially parallel to each other and transverse to the upper and lower faces, the distance between the upper and lower faces called thickness for each pole piece is the same for your two pole pieces , the distance between your axial end faces called depth for each pole piece is the same for the two pole pieces, the left side of the first pole piece is the same inclination in a direction opposite to the right side of the first pole piece and the right blank of the first pole piece is of the same inclination in a direction opposite to the left blank of the second pole piece, your two pole pieces being positioned so that the upper face of the first pole piece is in continuity with the upper face of the second pole piece along the axis of the machine.

According to one embodiment, each pole piece is substantially symmetrical, the two blanks of the first pole piece being inclined substantially at the same inclination ς relative to the plane transverse to the upper face, in two opposite directions, your two blanks of the second piece polar also being inclined by the same inclination ς in two opposite directions.

According to one embodiment, N pairs of pole pieces are arranged two by two adjacent to you along the axial direction of the machine, two adjacent pairs of N pairs being offset along the circumference of the rotor by a distance less than the pole pitch, your adjacent pairs being two to two offset along the circumference of the rotor, offset V along the circumferential direction of the rotor between the first and the last of the N pairs of pole pieces given by the relationship N * 2 * p * tan ôsk where Gsk denotes the twist angle.

According to one embodiment, an electrical twist angle T is included in the interval [80 °, 90 °] and advantageously of the order of 84 ° for a machine comprising twelve teeth on each of the stators, regardless of the number of pairs pole piece between ten and fourteen, the electrical twist angle T given by the relation: T = esk * X, where X is the number of pairs of poles seen by each stator. According to one embodiment, the number of teeth of each of the stators is twelve and the number of pairs of pole pieces is ten, for γτΟ included in the interval (25 °, 27 °), the opening angle of the face opposite the excitation stator yri1 of the first pole piece is within the interval (18 °, 32.4 °) and advantageously of the order of 19.4 ° and the opening angle of the face opposite the stator excitation γτΙ2 of the second pole piece is in the interval (32.4 °, 34.2 °) and advantageously of the order of 34.2 °.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given only by way of illustration but in no way limit the invention.

Figure 1 shows a perspective view of the rotary electric machine with a magnification of the pair of pole pieces;

FIG. 2 represents the flux lines for different positions of the rotor relative to the stators;

Figures 3a and 3b show the pair of pole pieces from two perspectives; FIG. 4 represents the pair of pole pieces in the case of asymmetrical pole pieces;

FIG. 5 represents the attenuation of the voltage induced by the coupling of pole pieces;

Figures 6a and 6b illustrate the voltage induced for the harmonic of order 6 without or with coupling of pole pieces;

Figure 7 illustrates the case of twisting;

Figure 8 shows the influence of the twist angle on the induced tension.

The rotary electrical machine illustrated in FIG. 1 comprises a fixed excitation stator 12, carrying the excitation, and an armature stator 11 also fixed. The two stators 11, 12 are mounted in a radial concentric configuration around an axis of rotation Z which is the axis of the machine and separated by an air gap. A rotor 20 is rotatably mounted in the air gap between the two fixed stators, around an axis of rotation X.

The excitation stator 12 made of soft magnetic material has a stator body and teeth extending radially from the stator body. An excitation coil 102 is wound on each of the teeth of the excitation stator. The excitation winding 102 is traversed by an excitation current of. Said current of is adapted to polarize the branches of the stator and acts as an inductor. The excitation coils are connected to create a predetermined number of poles.

The rotor 20 positioned radially between the excitation stator 12 and the armature stator 11 is formed of pole pieces arranged circumferentially in the air gap. The pole pieces are made of soft ferromagnetic material. The pole pieces are mounted on a movable annular support. The mobile support is made from a non-magnetic, non-electric conductive material, for example stainless steel or plastic.

The rotor 20 is facing the teeth of the excitation stator 12. The rotor is also facing the armature stator 11.

The armature stator 11 is formed by a stator body and teeth extending radially from the armature stator body towards the rotor 20. The armature winding 101 is wound on each of the teeth of the armature stator 11. The armature winding is traversed by an excitation current ac.

Advantageously, the machine will include in this embodiment one or more phases of conductive coils. In the embodiment illustrated in Figure 1 it will be a three-phase machine, such a configuration will be favorable in terms of control and stability.

In these machines, the torque performance will be improved in particular when the number of magnetic poles and pole pieces verify one of the following relationships: ns ^ pl + ph or ns = ph-pl or ns ^ pl-ph, where ns is the number of pole piece pairs in the rotor, ph is the number of pole pairs in the armature stator and pl is the number of pole pairs in the excitation stator. When one of these relations is verified, each stator sees, in its interaction with the rotor, the same number X of pairs of poles on both sides of the rotor. The pairs of pole pieces 21 of the rotor by modulating the flux density therefore make it possible to transform each stator into a stator with a different number of poles.

The field density in the air gap has many harmonics and one of the most important harmonics created in the air gap between the rotor 20 and the armature stator 11 will typically be the harmonic of order pl-ph or pl-s- ph.

The number of poles on the stators is defined by the choice of the winding and its power supply.

Numerically, for the machine illustrated in FIG. 1, in which the rotor 20 comprises ten pole pieces 21, the number of poles will therefore be chosen so that the excitation stator has 8 magnetic poles (pl-4) and that the stator d induced has 12 poles (ph = 6). In the air gap on the armature stator side, the rotor 20 transforms the magnetic flux from the 8-pole excitation stator to the 12-pole armature stator: ns-pM0-4 = 6, which corresponds to the number ph of pairs of poles in the armature stator. In the air gap on the excitation stator side, the rotor 20 transforms the flux from the 12-pole armature stator to the 8-pole excitation stator: ns-ph = 10-6 = 4 which corresponds to the number pl of pairs of poles in the excitation stator.

In operation, the current of, by traversing the coils of the excitation stator 12, creates a magnetization at the level of each of the branches of the excitation stator 12 corresponding alternately to north and south poles. A rotating magnetic field is then created in the air gap by the interaction between the magnetization of the excitation stator and the pole pieces of the rotor 20 which take the magnetization of the teeth of the excitation stator 12 opposite. The armature stator 11 traversed by a current ac creates a variable rotating field which interacts with the previous rotating field to create a torque. The interaction between these two fields results in field lines shown in Figure 2.

The rotation of the rotor 20, that is to say pairs of pole pieces, relative to the stators 11,12 generates modifications of the flux path which crosses the excitation coil according to the position of the pole pieces.

In the case of the machine illustrated in FIG. 1, the number of teeth on the excitation stator is identical to the number of teeth on the armature stator, each tooth of the excitation stator 12 being opposite a notch defined between two teeth of the armature stator 11, the pairs of pole pieces being positioned between the excitation stator and the armature stator.

FIG. 2 illustrates the flux seen by the armature stator 11 as a function of the position of the rotor 20 in the case of the machine illustrated in FIG. 1. The flux seen by the armature stator 11 passes through a maximum positive value and negative minimum during the rotation of the rotor 20, which corresponds to the case where the passage of the flux in one or the other of the pole pieces surrounding the stator is favored.

By considering a portion of the machine in which a tooth of the armature stator between two consecutive teeth of the excitation stator, when the rotor 20 is in the position in which a pole piece 21 is both opposite a tooth of the excitation stator, and a tooth of the armature stator (theta = 0 ° or 180 °) the flow loops through the armature stator 11. This corresponds to the extremes of flux seen by the armature stator. When the pole piece 21 is opposite a notch between two teeth of the excitation stator 12 and facing a tooth of the armature stator 11 (theta - 90 °), the flow loops directly between the pole piece 21 and the two consecutive teeth of the excitation stator. This corresponds to a zero flux seen by the armature stator 11. When two adjacent pole pieces are opposite the two consecutive teeth of the excitation stator, the tooth of the armature stator considered is not facing any part polar, (theta = 270 °), the flux loops directly through the two teeth adjacent to the tooth considered of the armature stator and the flux seen by the tooth of the armature stator considered is zero. As a variant, the number of teeth on the two stators will be different.

Such variations in the flow through the excitation coil as a function of time generates an induced voltage across the excitation coil.

The axial direction Z of the machine is the direction along the axis of the machine. The circumferential direction is the direction which, in a plane transverse to the axis of the machine Z, follows the circumference of the rotor. The radial direction of the machine is the direction given by the radius of the rotor in the plane transverse to the direction of the Z axis.

In this machine, illustrated in perspective in Figure 1, each pole piece 22, 23 is in the form of a truncated pyramid having six faces in pairs opposite illustrated in Figure 3. Each pole piece is advantageously substantially symmetrical.

Each pole piece is placed in the air gap between the two stators 11, 12 so that two faces are opposite the stators. These two faces are the upper and lower faces, the upper face 220, 230 being opposite the armature stator and the lower face 221, 231 being opposite the excitation stator 12. These two faces are slightly curved to follow the very slight curvature of the stators. These two faces are substantially parallel to each other facing each other along the radial direction. The two upper and lower faces are separated by a thickness e.

§

The two other opposite faces along the axial direction Z are the two axial end faces 224, 225, 234, 235. Said two axial end faces are substantially transverse to the upper and lower faces and parallel to one another. the other. The two axial end faces are separated by a depth p.

The last two faces facing each other along the circumferential direction are your blanks of the pole piece 21. The left blank 222, 232 and the right blank 223, 233 are defined with respect to the direction of movement. along the circumference of the rotor. Said blanks are inclined relative to the transverse plane to the upper, lower and axial faces, in opposite directions. The inclined sides of the truncated pyramid help to reduce the induced voltage due to abrupt variations in magnetic flux.

The extension of the first pole piece 22 along the circumferential direction is given by an angle which is determined from the center of the machine, as illustrated in FIG. 3a. The two faces of the pole piece 21 facing the stator do not have the same extension along the circumference. The upper face of the first pole piece 21 has an extension along the circumference of the rotor defined by an opening angle of said face opposite the armature stator between the first left blank and the first right blank γτΟ1. The underside of the first pole piece has an extension te along the circumference of the rotor defined by an opening angle of said face opposite the excitation stator between the first left blank and the first right blank γπ1. The two different opening angles defining the geometry of the first pole piece γπ1, γτΟ1, verify the relationship γπ1 <γτΟ1, which defines the inclination of the right and left blanks of the first pole piece.

The second adjacent pole piece 23, of geometry similar to the first pole piece will also have the shape of a truncated pyramid, of the same thickness e and the same depth p.

The upper face of the second pole piece 230 has an extension te along the circumference of the rotor defined by an opening angle of said face γτΟ2 opposite the induced stator between the second left blank 232 and the second right blank 233. The underside of the second pole piece 231 has an extension along the circumference of the rotor defined by an opening angle yri2 of said face opposite the excitation stator between the second left blank 232 and the second right blank

233. The two different opening angles defining the geometry of the second pole piece γπ2, γτ02, verify the relationship γπ2> γτ02, which defines the inclination of the right and left blanks of the second pole piece.

The two blanks of the same pole piece are advantageously inclined at substantially the same angle ξ in two opposite directions.

As a variant, your two blanks are inclined by two different angles ξΐ and ξ2.

In a preferred embodiment, your angles γτΟ1, yr02 will be substantially identical equal to yrO, the upper face of the first pole piece being substantially the same dimension as the upper face of the second pole piece.

The opening angles of the two pole pieces of the same pair will therefore verify the following relationship:

yri! <γτΟ <γπ2

The two pole pieces 22, 23 will therefore be two truncated pyramids head to tail, the first pole piece corresponding to a pyramid oriented towards the inside of the machine and the second pole piece corresponds to a pyramid oriented towards the outside of the machine.

The two pole pieces are arranged so that the rear axial end surface of the first piece 225 is opposite the front axial end surface of the second pole piece 234. The two end surfaces are therefore in contact on the entire end surface of the first pole piece, the two upper faces of the two pole pieces forming a rectangle of width 2 * p and of longitudinal extension te along the circumference of the machine corresponding to the angle γτΟ (Figure 3b ).

The two pole pieces 22, 23 are advantageously bonded to each other at these end surfaces. This avoids unfavorable flow leaks between the two pole pieces.

Thus your two pole pieces of the pair form a block of thickness e, of depth 2 * p and having, over part of its depth, notches hollowed out in the axial direction and in the circumferential direction.

As a variant, the pair of pole pieces 21 could be machined in one piece, that is to say that the morphology of two adjacent pole pieces described above will be formed by machining a single piece of material.

As a variant illustrated in FIG. 4, when the two blanks of a pole piece will have different inclinations ξ1 and ξ2, the pole piece being thus asymmetrical, the same asymmetry will be reproduced for the other pole piece of the pair. Thus, as illustrated in FIG. 4, the two pole pieces will be arranged so that 5 the left tilt blank ς1 of the first pole piece will have the same tilt inaison1 as the right blank of the second pole piece but in the opposite direction . The right blank of the first pole piece with tilt ξ2 will have the same tilt as the left blank of the second pole piece.

As a variant, the two axial end faces may not be transverse to the upper and lower faces, but inclined relative to the direction transverse to the upper and lower faces.

The angular polar step depending on the geometry of the machine is defined by: polar-step = 360 / Ner where Ner designates the number of pairs of pole pieces in the case described here.

By setting the coupling of the pole pieces by the following ratios:

RrO - yrO / non-polar

Rri1 = γπ1 / polar-step

Rri2 ^ Tri2 / pas-polar the coupling will be particularly effective in the configuration in which the ratios will verify the following inequalities:

0.5 <Rri1 <0.9,

0.9 <Rri2 <0.95

0.7 <rr0 <0.75

The coupling will be in particular optimal in the case where Rri2 is equal to 25 0.95 and Rri1 is equal to 0.54 regardless of the number of teeth on the two stators (11, 12), which corresponds to the angular condition to have an optimal coupling whatever or the number of teeth on the stators.

The insertion of such pairs of pole pieces 120 in place of the usual simple pole pieces, known from the prior art, will make it possible to erase the abrupt flux transitions between each of the stators 11, 12 and the rotor 20, when the rotor moves opposite the stators and passes opposite the stator teeth and the notches defined between the stator teeth. In fact, the second pole piece creates an additional flow 180 ° out of phase with the flow created by the first pole piece so that the two flows offset each other for a zero sum, as illustrated in FIG. 5.

For a machine geometry corresponding to FIG. 1 for which the number of teeth on the excitation stator is identical to the number of teeth on the armature stator of twelve and for a rotor comprising ten pairs of pole pieces, the abrupt path modifications flux seen by the excitation coil during the movement of the rotor as a function of the position of the pole pieces with respect to the two stators generates an induced voltage therefore harmonics at the level of the excitation signal of which the preponderant harmonic in this configuration will be the harmonic of order 6 (figure 5).

By adding pairs of pole pieces 21 as described above, a significant reduction in peak-to-peak voltage will be observed for this harmonic of order 6 in particular while maintaining a high average torque of the machine. The harmonic of order 6 will be strongly attenuated in the case where the pole pieces will have the following dimensions γτΟ = 25.2 °, γτϊ1 = 19.5 °, γτί2 ------ 35 °. as illustrated in Figures 6a and 6b.

As a variant, a pair of pole pieces from the air gap may be replaced by N pairs of pole pieces. The pairs of pole pieces of a plurality will be two by two adjacent along the axial direction of the machine Z. Two pairs of pole pieces 21 adjacent will be offset along the circumferential direction of the rotor. The rear axial end face of the second pole piece 235 of the first pair is partially bonded to the front axial end face 224 of the first pole piece of the adjacent pair along Z. The offset between two consecutive pairs will advantageously be regular .

As illustrated in FIG. 7, a twist angle 0sk can be defined, which will define the overall offset of the plurality of pairs of juxtaposed pole pieces, relative to the direction Z, that is to say the offset between the first and the last pair of the plurality in the circumferential direction. The twist will also make it possible to soften the flux by reducing the influence of harmonic 6 in the induced voltage. By denoting P the depth of the plurality of N pairs of pole pieces along the axis of rotation Z, each pair having the properties described above, P = N * 2 * p.

The twisting parameter V along the circumferential direction is therefore given by V = P * tan 0sk.

The offset along the circumferential direction between two pairs of consecutive pole pieces will then be given by v - 2p * tan Osk. As a variant, it is possible to consider an irregular offset between pairs of adjacent pole pieces.

The twist makes it possible to soften the flow by making it more sinusoidal by limiting the influence of the preponderant harmonics.

The mechanical twist angle Ôsk is connected to the electrical twist angle T by the relation:

T = 0sk * X where X is the number of pairs of poles seen by each stator.

In the case of the previous machine comprising 12 teeth on each of the stators, the number of pairs of pole pieces being between 10 and 14, the electrical twist angle will advantageously be in the interval [80 °, 90 °] and in particular of the order of 84 °, as illustrated in FIG. 8. This gives an optimum angle so as not to decrease the torque too much while limiting the influence of the harmonic 6.

In the case of a machine comprising an excitation stator and an armature stator each having 12 teeth and a rotor comprising 11 pairs of pole pieces, the harmonic of order 6 will be greatly attenuated in the case where the pole pieces will have the following dimensions γτΟ = 23 °, yri 1 == 15 °, γπ2 - 31 °.

In such a configuration there is a significant reduction in peak-to-peak voltage while maintaining a high average torque of the machine.

In the case of a machine comprising an excitation stator and an armature stator each having 12 teeth and a rotor comprising 13 pairs of pole pieces, the harmonic of order 6 will be greatly attenuated in the case where your pole pieces will have the following dimensions γτΟ = 19.4 °, γτΐ1 = 21.5 °, γτί2 = 27 °.

In the case of a machine comprising an excitation stator and an armature stator each having 12 teeth and a rotor comprising 14 pairs of pole pieces, the harmonic of order 6 will be greatly attenuated in the case where the pole pieces will have the following dimensions γτΟ ~ 18 °, γτϊ1 = 14.5 °, γτί2 = 24 °.

The reduction of the peak to peak voltage of this harmonic in systems with 12 teeth with stators and a number of teeth with rotor of 11, 13 or 14 is illustrated in FIGS. 6a and 6b.

In all of the above, the pole pieces of the rotor will typically be made of soft magnetic material such as ferromagnetic steel sheets FeSI, FeCo or FeNi.

The dimensions will be such that p will typically be around 35mm and e will typically be around 6mm.

Claims (8)

claims 1- Synchronous rotating electrical machine, flow switching, comprising an excitation stator (12) and an armature stator (11), the two stators (11, 12) being positioned in a concentric radial configuration, around an axis of rotation (Z), the excitation stator (12) being inside the armature stator (11), an air gap being defined between the two stators in which is housed a rotor (20), the stator excitation (12) being formed by a stator body having a plurality of teeth extending from the excitation stator body towards the rotor (20), an excitation winding (102) being wound around the plurality teeth of said excitation stator, the armature stator (11) being formed by a stator body comprising a plurality of teeth extending from the armature stator body (11) towards the rotor (20), an armature winding (101) being wound around the plurality of teeth of said armature stator, the rotor (20), devoid of winding or permanent magnets being formed by a set of pairs of pole pieces (21) arranged circumferentially in the air gap opposite each of the stators, separated by a pole pitch, characterized in that: a pair of pole pieces (21) comprises a first pole piece (22) and a second pole piece (23) adjacent to the first pole piece, each pole piece having the shape of a truncated pyramid, each pole piece positioned in the air gap having: two axial end surfaces facing one another along the axis of the machine, two blanks facing each other along the circumferential direction of the machine, two faces facing each other, one upper face facing the armature stator and a lower face facing the excitation stator, the upper face of the first pole piece (220) having an extension along the circumference of the rotor defined by an opening angle γτΟ1 of said facing side of the armature stator between a first left blank (222) and a first right blank (223), the underside of the first pole piece (221) having an extension along the circumference of the deflected rotor negated by an opening angle γπ1 of said face opposite the excitation stator between the first left blank (222) and the first right blank (223), 5 the upper face of the second pole piece (230) of the same pair having an extension along the circumference of the rotor defined by an opening angle γτ02 of said face opposite the armature stator between a second left blank ( 232) and a second straight blank (233) the underside of the second pole piece (231) having an extension the 10 along the circumference of the rotor defined by an opening angle γπ2 of said face opposite the excitation stator between a second left blank (232) and a second right blank (233), the two pole pieces (22, 23 ) being arranged so that an axial end surface of the first pole piece is opposite an axial end surface 15 of the second pole piece, the blanks of the first pole piece being inclined so that: γτΗ <γτΟ1, the blanks of the second pole piece being inclined so that: γτ02 <γτΙ2 ₃ with γτΟ1 and γτ02 of the same order of magnitude. 2- Machine according to claim 1 in which γτΟ1 = γτ02 = γτ0, γτΟ being an opening angle and verifying the inequalities: 0.5 <Rri1 <0.9, 0.9 <Rri2 <0.95 25 and 0.7 <Rr0 <0.75 Where the angular polar step is defined by: polar-step = 360 / Ner where Ner designates the number of teeth on the rotor. And: RrO = γτθ / polar step 30 Rri 1 - γτ! 1 / not-polar Rri2 = Tri2 / non-polar 3- Machine seton claim 2 in which when Rri2 is equal to 0.95, Rri1 is equal to 0.54. 4- Machine according to any one of claims 1 to 3 wherein for each pole piece (22, 23) the two axial end faces are substantially parallel to each other and transverse to the upper and lower faces, the distance between the upper faces and lower said thickness (e) for each pole piece is the same for the two pole pieces, the distance between the axial end faces said depth (p) for each pole piece is the same for the two pole pieces, the left blank of the first pole piece (222) has the same inclination in a direction opposite to the right blank of the first pole piece (223) and the right blank of the first pole piece (232) has the same inclination in a direction opposite to the left blank of the second pole piece (233), the two pole pieces being positioned so that the upper face of the first pole piece (220) is in continuity with the fa this upper of the second pole piece (230) along the axis of the machine. 5- Machine according to claim 4 in which: each pole piece is substantially symmetrical, the two blanks of the first pole piece (222, 223) being inclined at the same inclination ξ relative to the plane transverse to the upper face, in two opposite directions, the two blanks of the second piece polar (232, 233) also being inclined by the same inclination ξ in two opposite directions. 6- Machine according to one of claims 1 to 5 wherein N pairs of pole pieces are arranged two by two adjacent along the axial direction of the machine, two adjacent pairs of N pairs being offset along the circumference of the rotor by a distance less than the pole pitch, the adjacent pairs being two by two offset along the circumference of the rotor, the offset V along the circumferential direction of the rotor between the first and the last of the N pairs of pole pieces being given by relation: V = N * 2 * p * tan Osk where 0sk denotes the twist angle, and p denotes the depth of a pole piece along the axis (Z). 7- Machine according to claim 6 wherein an electrical twist angle T is in the interval [80 °, 90 °] and advantageously of the order of 84 ° for a machine comprising twelve teeth to each of the stators (11, 12), whatever the number of pairs of pole pieces between ten and fourteen, the electrical twist angle T given by the relation: T = 0sk * X Where X is the number of pairs of poles seen by each stator . 8 ~ Machine according to one of claims 1 to 7 wherein the number of teeth of each of the stators (11, 12) is twelve and the number of pairs of pole pieces is ten, for yrO included in the interval (25 °, 27 °), the opening angle of the face opposite the excitation stator γτίΐ of the first pole piece is within the interval (18 °, 32.4 °) and advantageously of the order of 19.4 ° and the opening angle of the face opposite the yri2 excitation stator of the second pole piece is in the interval (32.4 °, 34.2 °) and advantageously of the order of 34.2 °.