Rotating electric machine

Abstract

Title: Rotating Electric Machine The invention relates to a rotating electric machine (2) having an axis of rotation, the machine comprising: - at least one rotor (8), - at least one stator (10) comprising: o a stator body (36) comprising slots (26), o a plurality of electrical windings passing in the slots (26), in particular the electrical windings being formed by conductive pins (38) housed partially in the slots (26) of the stator body (36) and electrically connected two by two via their ends to form electrical phases, o a fluid channel (40) configured for a flow of heat transfer fluid, in particular a dielectric fluid, the channel (40) extending axially within the stator body (36), the fluid channel (40) being adjacent to at least one of the slots (26) and being radially aligned with the slot (26). Figure for the summary: Fig. 2

Description

Title of the invention: Rotating electric machine

[0001] The present invention relates in particular to a rotating electrical machine.

[0002] In a way known per se, a rotating electrical machine comprises a stator and a rotor attached to a shaft, and it can operate as an alternator or motor or both (in which case it is called a reversible machine).

[0003] Currently, there is a need to obtain more power and torque for the rotating electrical machine, while reducing its size (smaller machine dimensions). However, increasing the power and torque of the electrical machine leads to thermal constraints, due to the heat generated by said machine, which limits its performance.

[0004] The invention aims in particular to overcome these aforementioned drawbacks.

[0005] The invention thus relates to a rotating electrical machine having an axis of rotation, comprising:

[0006] - at least one rotor,

[0007] - at least one stator comprising: • a stator body comprising notches, • a plurality of electrical windings passing through the slots, in particular the electrical windings being formed by conductive pins housed partially in the slots of the stator body and electrically connected in pairs via their ends to form electrical phases, • a fluid channel configured for the flow of a heat transfer fluid, in particular a dielectric fluid, the channel extending axially within the stator body, the fluid channel being adjacent to at least one of the slots and being radially aligned with the slot.

[0008] The fluid channel extending "axially" means that it extends along the axis of rotation of the electrical machine. The channel can therefore also be referred to as an axial channel.

[0009] The fluid channel is adjacent to the notch in the sense that the fluid channel is connected to the notch. In other words, the fluid channel is not separated from the notch.

[0010] The fluid channel is said to be "radially aligned with the notch" in the sense that, since the notch is inscribed within an angular sector, the fluid channel is also inscribed within that angular sector, namely that the fluid channel does not extend beyond the angular sector, or extends beyond that angular sector, on each side, by at most 10%, or at most 20%, of the angular sector considered. For example, if the notch is inscribed in an angular sector with an opening of 4°, then the fluid channel overflows at most, for example, by 0.4° on each side of the angular sector.

[0011] The invention makes it possible to increase, by means of fluid channels, the cross-section of passage of heat transfer fluid inside the rotating electrical machine, in particular the stator.

[0012] Each fluid channel is located as close as possible to the notch through which the electrical windings, which are heat sources, pass.

[0013] By passing the heat transfer fluid as close as possible to the electrical windings or coils, it is possible to cool them more effectively. The invention thus allows for better cooling of the rotating electrical machine. When the heat transfer fluid has a relatively low viscosity (for example, a kinematic viscosity of 2 mm² / s at 100°C for a dielectric oil compared to a viscosity of 5 mm² / s for a standard gearbox or electrical machine oil today), it is possible to increase the flow rate of this heat transfer fluid within the rotating electrical machine by increasing the cross-sectional area through which the heat transfer fluid passes. This increase in fluid flow rate is advantageously achieved without increasing pressure losses.

[0014] Moreover, the fact that the fluid channel is radially aligned with the notch helps to preserve the electrotechnical performance of the rotating electrical machine insofar as the location of this fluid channel disturbs the passage of magnetic flux between the rotor and the stator as little as possible.

[0015] It is possible, for example, to increase the flow rate from 10 L / min to approximately 15 L / min for the same level of pressure loss.

[0016] Thanks to the invention, the flow rate of the heat transfer fluid in the channel can be increased at a given electric pump power, this pump being intended to allow the circulation of the heat transfer fluid in the fluid channel. This avoids oversizing the electric machine and the electric pump, and thus optimizes their compactness.

[0017] Thus, increasing the flow rate of the heat transfer fluid can lead to an increase in the circulation speed of the heat transfer fluid, thereby increasing the heat dissipation from the rotating electrical machine via the heat transfer fluid. This results in a more compact rotating electrical machine, while optimizing electrotechnical performance.

[0018] The features, variations, and different embodiments of the invention can be combined with one another in various ways, provided they are not incompatible or mutually exclusive. In particular, variations of the invention may be imagined that do not include that a selection of features described subsequently in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0019] According to one aspect of the invention, the fluid channel is inscribed in the same angular sector as the notch. In other words, the fluid channel and the notch have dimensions, along the circumference of the stator, that are substantially equal.

[0020] Alternatively, the fluid channel extends onto only one side of the angular sector.

[0021] Alternatively, the fluid channel extends over two opposite sides of the angular sector.

[0022] According to one aspect of the invention, the angular sector is taken from the geometric center of the stator, between two geometric radii of the stator.

[0023] According to one aspect of the invention, the fluid channel extends axially parallel to the notch.

[0024] According to one aspect of the invention, the fluid channel opens onto two opposite axial end faces of the stator body.

[0025] According to one aspect of the invention, the notches are distributed along a circumference of the stator body. In particular, the notches are open on a first axial end face and a second axial end face of the stator body. In other words, the notches pass axially through the stator body and open onto the two opposite axial end faces of the stator.

[0026] According to one aspect of the invention, the fluid channel has a radial dimension, in the direction of a geometric radius of the stator, which is at most 50%, or at most 30% or 20%, of a radial dimension of the slot. Thus, if the slot measures radially Dslot, then the associated fluid channel measures radially (Dcnal) at most Dslot*0.5, or at most Dslot*0.3, or Dslot*0.2. Advantageously, the fluid channel has a radial dimension that is between 5% and 40% of a radial dimension of the slot.

[0027] Advantageously, the stator body comprises at least one fluid channel per slot. For example, the stator body comprises as many fluid channels as slots, for example 36 in number.

[0028] According to one aspect of the invention, the fluid channel extends over the outermost radial end of the slot. In other words, the outermost radial end of the slot corresponds to the radial end located opposite the air gap between the rotor and the stator. Thus, such a positioning of the fluid channel makes it possible to efficiently dissipate heat from the rotating electrical machine via the heat transfer fluid while minimizing the impact on the machine's electrotechnical performance.

[0029] According to one aspect of the invention, the fluid channel extends over the innermost radial end of the slot. In other words, the innermost radial end of the slot corresponds to the radial end closest to the air gap between the rotor and the stator.

[0030] According to one aspect of the invention, the fluid channel has a neck (narrowed portion) at the junction with the notch.

[0031] According to one aspect of the invention, each radial end of the notch opens onto a fluid channel.

[0032] Alternatively, only one of the radial ends of the notch opens onto a fluid channel.

[0033] According to one aspect of the invention, the slot is opened radially towards the air gap between the rotor and the stator. In this case, the slot is formed between two non-contiguous tooth roots. These two consecutive tooth roots form an axial slot between them.

[0034] Alternatively, the notch is closed on the side of the air gap between the rotor and the stator.

[0035] According to one aspect of the invention, at least one of the fluid channels is formed within the notch by a space left free by the absence of electrical winding.

[0036] For example, the space left free is due to the absence of a conductive pin in a row of conductive pins inserted in the notch.

[0037] In this case, the fluid channel is located within the notch itself, and the fluid channel is also said to be adjacent to the notch.

[0038] In this case, the notch can be closed from each radial end.

[0039] According to one aspect of the invention, the fluid channels on the stator body are identical.

[0040] Alternatively, the fluid channels on the stator body are of different shapes, at least for some of the fluid channels.

[0041] For example, the fluid channels are of two different types, for example two different shapes. The fluid channels of different shapes are, for example, arranged alternately.

[0042] According to one aspect of the invention, the cross-sectional shape of the fluid channel(s) is, for example, polygonal, rectangular, or trapezoidal. The shape may be rounded.

[0043] According to one aspect of the invention, the fluid channel may have a symmetrical shape with respect to a plane containing the axis of rotation of the machine.

[0044] Alternatively, the fluid channel may have a non-symmetrical shape with respect to a plane containing the axis of rotation of the machine.

[0045] According to one aspect of the invention, the cumulative cross-sections of the fluid channels of the stator represent 10% to 60% at most of the cumulative cross-sections of the slots.

[0046] According to one aspect of the invention, the stator body comprises at least one additional fluid channel separate from the fluid channel adjacent to the notch, in particular a plurality of additional fluid channels separate from the fluid channels adjacent to the notches.

[0047] According to one aspect of the invention, the rotating electrical machine is configured to provide a passage for the heat transfer fluid in the air gap between the rotor and the stator. The heat transfer fluid does not remain in the air gap and is discharged into a lower part of the rotating electrical machine. In this way, pressure losses due to friction of the heat transfer fluid are avoided, particularly at high rotor speeds.

[0048] According to one aspect of the invention, the electrical windings of the stator form at the axial ends of the stator body coils which are cooled by the heat transfer fluid, in particular the dielectric fluid.

[0049] According to one aspect of the invention, the heat transfer fluid, in particular the dielectric fluid, is injected into the fluid channels of the stator, for example, using distribution elements assembled with the stator.

[0050] According to one aspect of the invention, the electrical windings being formed by conductive pins, each conductive pin comprises two substantially parallel conductive segments connected by a bent connecting portion to form a "U" (called a "U-pin"). The conductive segments are inserted, in particular, at a first axial end face of the stator, into two separate slots, such that the conductive segments are substantially parallel to the axis of revolution of the stator. A single slot can accommodate several segments belonging to separate conductive pins, which are thus stacked and form different layers of conductive segment. Each slot, for example, receives between 4 and 10 conductive pins.

[0051] According to one aspect of the invention, the conductive pins are for example made of copper.

[0052] Alternatively, the electrical windings are formed by continuous electrical wires.

[0053] According to one aspect of the invention, the heat transfer fluid circulates in a fluid circuit that passes through the rotating electrical machine. The fluid circuit includes, for example, an electric pump for forced circulation of the heat transfer fluid. This fluid circuit includes the fluid channel(s).

[0054] According to one aspect of the invention, the heat transfer fluid, in particular a dielectric fluid, is an oil.

[0055] According to one aspect of the invention, the rotating electrical machine is of the radial flux type.

[0056] According to one aspect of the invention, the rotating electrical machine is reversible, being able to operate in motor mode and in alternator mode.

[0057] According to one aspect of the invention, the stator body is formed by a stack of laminations.

[0058] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0059] [Fig-1] Fig. 1 is schematically and partially a cross-sectional view of a rotating electric machine;

[0060] [Fig.2] Fig.2 schematically and partially represents, in cross-section, a rotating electric machine according to an example of an embodiment of the invention;

[0061] [Fig.3] Fig.3 schematically and partially represents, in cross-section, a rotating electric machine according to another embodiment of the invention;

[0062] [Fig.4] Fig.4 schematically and partially represents, in cross-section, a rotating electric machine according to another embodiment of the invention;

[0063] [Fig. 5] [Fig. 5] Schematically and partially represents, in cross-section, a stator of a rotating electrical machine according to another embodiment of the invention;

[0064] [Fig.6] Fig.6 schematically and partially represents, in cross-section, a stator of a rotating electrical machine according to another embodiment of the invention;

[0065] [Fig.7] Fig.7 schematically and partially represents, in cross-section, a stator of a rotating electrical machine according to another embodiment of the invention;

[0066] [Fig.8] Fig.8 schematically and partially represents, in cross-section, a stator of a rotating electrical machine according to another embodiment of the invention;

[0067] [Fig.9] Fig.9 schematically and partially represents, in cross-section, a rotating electric machine according to another embodiment of the invention;

[0068] [Fig. 10] [Fig. 10] schematically and partially represents, in cross-section, a rotating electric machine according to another embodiment of the invention;

[0069] [Fig. 11] [Fig. 11] schematically and partially represents, in cross-section, a rotating electric machine according to another embodiment of the invention;

[0070] [Fig. 12] The [Fig. 12] schematically and partially represents, in cross-section, a rotating electrical machine according to another embodiment of the invention.

[0071] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0072] Figure 1 shows an example of a compact, polyphase rotating electrical machine 2, particularly for use in motor vehicles. This machine 2 converts mechanical energy into electrical energy in alternator mode and can operate in motor mode to convert electrical energy into mechanical energy. This rotating electrical machine 2 is, for example, an alternator, a starter-alternator, a reversible machine, or an electric motor.

[0073] The rotating electrical machine 2 comprises a housing 4. Inside this housing 4, the machine further comprises a shaft 6, a rotor 8 fixed to the shaft 6 for rotation, and a stator 10 surrounding the rotor 8. The rotation of the rotor 8 occurs about an axis of rotation X. The housing 4 comprises a front flange 12a and a rear flange 12b which are assembled together. These flanges 12a and 12b are hollow and each centrally carries a bearing coupled to a respective ball bearing 18 for the rotational mounting of the shaft 6. In addition, the housing 4 comprises mounting means 14 for mounting the rotating electrical machine 2 in the vehicle.

[0074] A drive member 20 such as a pulley or a pinion can be fixed on a front end of the shaft 6. This drive member 20 allows the rotational motion to be transmitted to the shaft 6 or the shaft 6 to transmit its rotational motion.

[0075] The front flange 12a and the rear flange 12b are arranged here to form a chamber 22 for the circulation of a heat transfer fluid such as oil.

[0076] The rotor 8 is formed of a lamination pack housing permanent magnets forming the magnetic poles. Alternatively, the rotor 8 could be a claw rotor comprising two pole wheels and a rotor coil. According to another embodiment, the rotor may be a wound rotor formed of a lamination pack mounted coaxially on the rotor shaft, said lamination pack having a plurality of radially salient poles and at least one axial opening, a winding of electrically conductive wire being intended to be wound around each pole.

[0077] The stator 10 comprises a frame 24 formed from a stack of laminations. The frame 24, which defines a stator body 36, is provided with slots 26 for mounting electrical windings 28. The electrical windings 28, formed by conductive pins or continuous wires, pass through the slots 26 of the frame 24 and form front 30a and rear 30b coils on either side of the frame 21 of the stator 10. Furthermore, the electrical windings 28 are formed of several phases comprising a plurality of electrical conductors and being electrically connected to an electronic assembly 32.

[0078] The electronic assembly 32, which is mounted here on the housing 4, includes a power electronic module (not shown) for controlling the phases of the electrical windings 28. Alternatively, the electronic assembly 32 could be located remotely from the rotating electrical machine 2. A battery with a nominal voltage greater than 300 V can be used to supply the rotating electrical machine with direct current.

[0079] Figure 2 shows a detail of the rotating electrical machine 2 of Figure 1, with an axis of rotation X. This rotating electrical machine 2 comprises:

[0080] - the rotor 8,

[0081] - the stator 10 comprising:

[0082] or a stator body 36 comprising notches 26,

[0083] or a plurality of electrical windings 28 passing through the slots 26, the electrical windings 28 being formed here by conductive pins 38 housed partially in the slots 26 of the stator body 36 and electrically connected two by two via their ends to form electrical phases,

[0084] o fluid channels 40 configured for a flow of heat transfer fluid, here an oil, the channels 40 extending axially within the stator body 36, the fluid channels 40 being adjacent each to one of the notches 26 and being radially aligned with the respective notch 26.

[0085] Each conductive pin 38 comprises two substantially parallel conductive segments connected by a bent connecting portion to form a "U" (called a "U-pin"). The conductive segments are inserted at a first axial end face of the stator 10, into two separate slots 26, such that the conductive segments are substantially parallel to the axis of revolution of the stator 10. A single slot 26 can accommodate several segments belonging to separate conductive pins 38, which are thus stacked and form different layers of conductive segment. Each slot 26, for example, receives six conductive pins 38.

[0086] The fluid channels 40 extending "axially" means that they extend along the axis of rotation X.

[0087] The cumulative cross-sections of the fluid channels 40 of the stator 10 represent 10% to 60% at most of the cumulative cross-sections of the slots 26.

[0088] The fluid channels 40 are adjacent to the notches 26 in the sense that the fluid channels 40 are connected to the notches 26. In other words, the fluid channels 40 are not separated from the notches 26.

[0089] A heat transfer fluid passage is formed in the air gap 42 between the rotor 8 and the stator 10. Thus, the heat transfer fluid does not remain in the air gap 42 and is discharged into a lower part of the rotating electrical machine 2. In this way, pressure losses due to friction of the heat transfer fluid are avoided, particularly at high rotational speeds of the rotor 8.

[0090] The heat transfer fluid circulates in a fluid circuit that passes through the rotating electrical machine 2. The fluid circuit includes, for example, an electric pump (not shown) for forced circulation of the heat transfer fluid. This fluid circuit includes the fluid channels 40.

[0091] In the example of [Fig. 2], the stator body 36 comprises a single fluid channel 40 per slot. For example, the stator body 36 comprises as many fluid channels 40 as there are slots, for example, 36 in number.

[0092] The fluid channels 40 are said to be "radially aligned with the notches 26" in the sense that, since the notches 26 are inscribed within angular sectors 50, the fluid channels 40 are also inscribed within these angular sectors 50; that is, the fluid channels 40 do not extend beyond the angular sector, or extend beyond these angular sectors 50, on each side, by at most 10%, or at most 20%, of the angular sectors 50 considered. In the example of [Fig. 1], the fluid channels 40 do not extend beyond the angular sector.

[0093] The angular sector 50 is taken from the geometric center Ct of the stator 10, between two geometric radii R of the stator 10. The fluid channels 40 are inscribed in the same angular sectors 50 as the notches 26. In other words, the fluid channels 40 and the notches 26 have dimensions, along the circumference of the stator 10, which are substantially equal.

[0094] Alternatively, as can be seen in particular in [Fig.8], the fluid channel extends on only one side of the angular sector 50.

[0095] As shown in [Fig. 2], the fluid channels 40 have a radial dimension, in the direction of a geometric radius R of the stator 10, which is at most 50%, or at most 30% or 20%, of a radial dimension of the slots 26. Thus, if the slots 26 measure radially Dslot, then the associated fluid channels 40 measure radially (Dcnal) at most Dslot*0.5, or at most Dslot*0.3, or Dslot*0.2. Advantageously, the fluid channels have radial dimensions that are between 5% and 40% of the radial dimensions of the slots 26.

[0096] The fluid channels 40 open onto two opposite axial end faces of the stator body 36.

[0097] The notches 26 are distributed along a circumference of the stator body 36. The notches 26 are open on a first axial end face and a second axial end face of the stator body 36. In other words, the notches 26 pass axially through the stator body 36 and open onto the two opposite axial end faces of the stator 10.

[0098] In the example of [Fig.2], the fluid channels 40 extend over the outermost radial ends of the notches 26, opposite the air gap 42 formed between the rotor 8 and the stator 10.

[0099] In another embodiment of the invention illustrated in [Fig. 1 1], the fluid channels 40 extend over the innermost radial ends of the notches 26, as close as possible to the air gap 42 formed between the rotor 8 and the stator 10.

[0100] Each fluid channel 40 is located as close as possible to the notch 26 through which the electrical windings 28 pass, which are heat sources.

[0101] By passing the heat transfer fluid as close as possible to the electrical windings 28 or coils, it is possible to cool them more effectively. When the heat transfer fluid has a relatively low viscosity, it is possible to increase the flow rate of this heat transfer fluid within the rotating electrical machine 2 by increasing the cross-sectional area through which the heat transfer fluid passes. This increase in fluid flow rate can advantageously be achieved without increasing pressure losses.

[0102] In the example of [Fig.2], only the outer radial end of the notches 26 opens onto a fluid channel 40.

[0103] In this example of [Fig.2], the notches 26 are closed radially towards the air gap 42 between the rotor 8 and the stator 10.

[0104] In the variant illustrated in [Fig. 4], the slots 26 are open radially towards the air gap 42 between the rotor 8 and the stator 10. In this case, the slots 26 are formed between two non-contiguous tooth roots 52. These two consecutive tooth roots 52 form an axial slot 54 between them.

[0105] The fluid channels 40 have a neck 66, at the junctions with the notches 26.

[0106] In another embodiment of the invention illustrated in [Fig. 10], the fluid channels are formed each within the respective notch, by a space 60 left free in the absence of a conductive pin 38 in the row of conductive pins 38. In this case, the fluid channel 40 is located within the notch 26 itself, and the fluid channel 40 is also said to be adjacent to the notch 26. In this example of [Fig. 10], the notches 26 are closed at each radial end.

[0107] In one variant (not shown), at least one of the radial ends of the notch or notches 26 is open towards the air gap.

[0108] In the examples in Figures 2 to 4, and 10 to 12, the fluid channels on the stator body 36 are all identical.

[0109] Alternatively, with reference to [Fig. 9], the fluid channels on the stator body 36 are of different shapes. In the example described, the fluid channels 40 are of two different types, for example, two different shapes. The fluid channels 40 of different shapes are, for example, arranged alternately.

[0110] In general, the cross-sectional shape of the fluid channels 40 can be substantially rectangular (see figures 3, 4, 7, 9 to 10, 11, 12), rounded (see figures 2, 6) or trapezoidal (see figures 5, 8, 9)

[0111] As illustrated in Figures 7 and 8, the fluid channels 40 extending over the radial end, in particular the outermost end, of the notches 26 may have non-symmetrical shapes with respect to a plane containing the axis of rotation X. For example, the fluid channels 40 may have an L-shaped shape directed to the right (see [Fig.7]) or a parallelogram shape inclined to the right (see [Fig.8]).

[0112] In an example of an embodiment illustrated in [Fig. 12], the stator body 36 comprises a plurality of additional fluid channels 40b separated from the fluid channels 40 adjacent to the notches 26. In this example of [Fig. 12], the fluid channels 40, adjacent to the notches 26, extend axially parallel to the notches.

Claims

Demands

1. Rotating electrical machine (2) having an axis of rotation (X), comprising: - at least one rotor (8), - at least one stator (10) comprising: o a stator body (36) comprising slots (26), o a plurality of electrical windings (28) passing in the slots (26), in particular the electrical windings (28) being formed by conductive pins (38) housed partially in the slots (26) of the stator body (36) and electrically connected two by two via their ends to form electrical phases, o a fluid channel (40) configured for a flow of heat transfer fluid, in particular a dielectric fluid, the channel (40) extending axially within the stator body (36), the fluid channel (40) being adjacent to at least one of the slots (26) and being radially aligned with the slot (26).

2. Rotating electric machine (2) according to claim 1, wherein the stator body (36) comprises at least one fluid channel (40) per notch (26), and the fluid channel (40) extends axially parallel to the notch (26).

3. Rotating electric machine (2) any one of the preceding claims, wherein the fluid channel (40) is inscribed in the same angular sector (50) as the notch (26).

4. Rotating electric machine (2) according to any one of the preceding claims, wherein the fluid channel (40) opens onto two opposite axial end faces of the stator body (36).

5. Rotating electric machine (2) according to any one of the preceding claims, wherein the fluid channel (40) extends over the outermost radial end of the notch (26).

6. Rotating electrical machine (2) according to any one of claims 1 to 4, wherein the fluid channel (40) extends over the innermost radial end of the notch (26)

7. Rotating electric machine (2) according to any one of the preceding claims, the fluid channel (40) has a symmetrical shape with respect to a plane containing the axis of rotation (X).

8. Rotating electric machine (2) according to any one of claims 1 to 6, the fluid channel (40) has a non-symmetrical shape with respect to a plane containing the axis of rotation (X).

9. Rotating electrical machine (2) according to any one of the preceding claims, wherein the fluid channel (40) has a radial dimension, in the direction of a geometric radius of the stator (10), which is at most 50%, or at most 30% or 20%, of a radial dimension of the slot (26)

10. Rotating electric machine (2) according to any one of the preceding claims, wherein the stator body (36) comprises at least one additional fluid channel (40b) separate from the fluid channel (40) adjacent to the notch (26).

11. Rotating electrical machine (2) according to any one of the preceding claims, wherein at least one of the fluid channels (40) is formed within the notch by a space (60) left free by the absence of electrical winding).

12. Rotating electric machine (2) according to any one of the preceding claims, wherein the notch (26) is open radially towards the air gap between the rotor (8) and the stator (10).

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