System for driving a vehicle wheel

Abstract

The present invention relates to a system (1) for driving a vehicle wheel, comprising: - a wound stator (3), intended to be mounted integrally with a hollow shaft receiving a wheel shaft (20); - a wheel rim (2) intended to be attached to the wheel shaft (20); and - a rotor (4) rigidly connected to the wheel rim (2), the rotor (4) radially surrounding the wound stator (3), the drive system (1) being characterised in that the rotor (4) is a wound rotor and in that the drive system (1) comprises an electric power supply circuit (70) for the wound rotor (4), the power supply circuit (70) comprising at least one electrical connection by capacitive coupling intended for connecting at least one voltage source (7) to at least one winding (42) of the wound rotor (4).

Description

[0001] DESCRIPTION

[0002] Title of the invention ■ Vehicle wheel motorization system

[0003] The present invention relates to the fields of automobiles and electrical engineering, and more specifically concerns a vehicle wheel motorization system.

[0004] Electric or hybrid electric vehicles include one or more electric machines that provide traction or propulsion for the vehicle. When such a vehicle uses an electric machine whose torque is transmitted to the vehicle's wheels via a drive chain, it is advantageous for the electric machine to have a wound rotor, since this avoids the use of permanent magnets using rare earths, which are expensive and of limited availability.

[0005] On the other hand, when such a vehicle integrates electric traction or propulsion machines directly into the vehicle's wheels, which implies machines with rotors external to their stators, it is common for the rotors of these electric machines to have permanent magnets. Indeed, an electric machine with a wound rotor uses a system of rings and brushes to electrically power the wound rotor, and this system of rings and brushes is incompatible with an external rotor due to the excessively high relative speed that such an external rotor would induce between the rings and the brushes, a speed which would cause premature wear of the brushes. In addition, this system of rings and brushes has an axial size, that is to say in the direction of the axis of rotation of the machine, which is incompatible with the space available at the vehicle's wheels.Finally, such a system is incompatible with the environmental conditions in which the vehicle's wheels operate, particularly due to dust and vibrations which would cause breakdowns or malfunction of the system.

[0006] However, permanent magnet machines in vehicle wheels remain expensive and generate a drag flux when not in use for traction or vehicle propulsion, which affects the efficiency of the vehicle's powertrain system when traveling at high speeds. To avoid this drag flux, the permanent magnet rotors would have to be mechanically disengaged from their electric machines, but this would require a disengagement mechanism that would take up too much space on the axle of the wheels containing these electric machines. Using a wound rotor machine in a vehicle wheel would avoid these no-load losses, but its system of rings and brushes has too many drawbacks.

[0007] There is therefore a need for an electric traction or propulsion machine that can be integrated into a vehicle wheel, which does not have the drawbacks of the prior art.

[0008] The present invention at least partially overcomes the drawbacks of the prior art by providing a wheel motorization system comprising a wound rotor machine having good efficiency, small axial size and independence from the rare earth market.

[0009] To this end, the invention proposes a vehicle wheel motorization system comprising:

[0010] - a wound stator, intended to be mounted securely on a hollow shaft receiving a wheel shaft,

[0011] - a wheel rim intended to be fixed to the wheel shaft,

[0012] - a rotor secured to the wheel rim, the rotor angularly surrounding the wound stator, the motorization system being characterized in that the rotor is a wound rotor and in that the motorization system comprises an electrical power supply circuit for the wound rotor, the power supply circuit comprising at least one electrical connection by capacitive coupling intended to connect at least one voltage source to at least one winding of the wound rotor. The angular direction is defined as orthogonal to the axis of rotation of the wheel and to the radius of the wheel.

[0013] Thanks to the capacitive coupling that allows the wound rotor to be electrically connected to the voltage source, the use of a ring and brush system to power the wound rotor is no longer necessary, which allows the wound rotor to be used in the wheel of a vehicle, without all the disadvantages of the ring and brush system.

[0014] In particular, this capacitive coupling can be achieved with little axial bulk, while remaining robust to dust and vibrations. The motorization system according to the invention therefore integrates an electric machine formed of the wound rotor and the wound stator, which is compact in the axial direction of the electric machine, and does not present no-load losses at high running speed.

[0015] In one embodiment of the invention, the wheel motorization system according to the invention comprises: - a support intended to be secured to the hollow shaft, the support comprising a cylindrical wall, and

[0016] - a cylindrical enclosure secured to the wheel rim, surrounding the cylindrical wall at least in part, said at least one connection comprising at least one capacitor (C1, C2) comprising an external conductive cylindrical track arranged on an internal contour of the cylindrical enclosure, and an internal conductive cylindrical track arranged on an external contour of the cylindrical wall, the external cylindrical track of said at least one capacitor being arranged radially opposite the internal cylindrical track of said at least one capacitor. Advantageously, said at least one capacitor comprises a first capacitor and a second capacitor.

[0017] The wound rotor is for example fixed on the cylindrical enclosure and faces radially the wound stator which is preferably fixed to the support, on a cylindrical portion of the support of smaller diameter than the cylindrical wall on which the internal cylindrical tracks are arranged.

[0018] In one embodiment of the invention, the diameter of the internal cylindrical track is greater than 235 millimeters. The internal cylindrical tracks of the first and second capacitors therefore have a diameter, measured orthogonally to the axis of rotation of the wound rotor, between two opposite internal surfaces of the internal cylindrical tracks, greater than 235 millimeters. This value is chosen so as to allow sufficient power transmission to the wound rotor, allowing traction or propulsion of the vehicle, while limiting the radial size.

[0019] Preferably, the distance between the inner cylindrical track and the outer cylindrical track of said at least one capacitor is one millimeter to within plus or minus twenty percent. This distance is measured between two facing inner surfaces of the inner and outer cylindrical tracks, in a radial direction, i.e. orthogonal to the axis of revolution of the wound rotor, and passing through this axis. This distance value provides robustness to vibrations and dust while having a small axial size, for the same transfer power compared to the wound rotor.

[0020] More preferably, the width of the internal or external cylindrical track is between 25 and 35 millimeters. This width is measured in the axial direction of the rotor, i.e. parallel to the axis of rotation of the wheel. Such a width value also makes it possible to limit the axial size of the wheel motorization system, while allowing sufficient supply power to be transferred to the wound rotor.

[0021] In one embodiment of the invention, the power supply circuit further comprises a transistor bridge, a resonant circuit and a rectifier bridge, the transistor bridge being configured to be connected at the input to the voltage source, and being connected at the output to the resonant circuit, the resonant circuit comprising at least one resonance inductor, the first capacitor and the second capacitor, and the rectifier bridge being connected at the input to the resonant circuit and at the output to the winding of the wound rotor. The resonant circuit comprises for example two resonance inductors, and two or more resonance capacitors comprising the first capacitor and the second capacitor.

[0022] Advantageously, the wheel motorization system according to the invention comprises means for controlling a rotor current, the control means being capable of varying the control frequency of the transistor bridge in zero voltage switching mode. These control means make it possible to transfer a supply current to the wound rotor so as to produce the torque requested by a driver of the vehicle, while minimizing electrical losses in the stator.

[0023] Preferably, the control means comprise means for correcting a setpoint current of the wound rotor, the correction means comprising means for estimating the rotor current. These correction means make it possible to achieve the required torque with greater precision.

[0024] The means for estimating the rotor current include, for example, means for measuring a phase shift between a stator current and a stator voltage. Measuring this phase shift makes it possible to estimate the rotor current without measuring it.

[0025] Alternatively to this estimation of the rotor current by a phase shift measurement, the wheel motorization system according to the invention comprises means for measuring the rotor current in a rotating part of the power supply circuit, the motorization system comprising means for sending a measured value of the rotor current by the measurement means to the control means, the control means comprising means for receiving the measured value of the rotor current. These measurement means make it possible to have an exact estimation of the current in the wound rotor, supplied as input to the correction means, which makes it possible to achieve the required torque with precision. Advantageously, the wheel motorization system according to the invention comprises the voltage source, an inverter, and the voltage source is connected in parallel to the inputs of the inverter on the one hand, and to the inputs of the power supply circuit on the other hand. The inverter is connected at the output to the wound stator.Thus a single voltage source is used to power both the wound rotor and the wound stator.

[0026] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0027] [fig 1] schematically represents in axial section, a vehicle wheel motorization system according to the invention, in one embodiment of the invention, the axial direction being defined by the axis of rotation of the wheel,

[0028] [fig 2] represents a power supply circuit of a wound rotor of the wheel motorization system of figure 1,

[0029] [fig 3] represents means for controlling the rotor current flowing in the wound rotor of the motorization system of figure 1, and

[0030] [fig 4] ] represents steps of a method for estimating a rotor current flowing in the wound rotor of the motorization system of figure 1.

[0031] According to one embodiment of the invention, a vehicle wheel motorization system 1 according to the invention shown in FIG. 1, comprises a fixed (i.e. non-rotating) part, which notably comprises a wound stator 3, secured to a hollow shaft of a vehicle on which the wheel motorization system 1 according to the invention is mounted. The hollow shaft is fixed to the chassis of the vehicle and allows the passage of a wheel shaft 20. More precisely, the wound stator 3 is fixed to a support 5 secured to the hollow shaft.

[0032] The wheel motorization system 1 also comprises a rotating part, which notably comprises a wound rotor 4, secured to a wheel rim 2 by means of a cylindrical intermediate part 6, for example a brake drum. In Figure 1, to simplify, this intermediate part is shown in the form of a cylindrical enclosure 6 and named as such in the remainder of the description. The cylindrical enclosure 6 is fixed integrally to the wheel rim 2, and to the wheel shaft 20 by means of screws 26 (fixed directly to the wheel rim 2 or to a wall (not shown) of the cylindrical enclosure 6). When the wound rotor 4 and the wound stator 3 are powered, the wheel shaft 20 rotates on itself about an axis X defining an axial direction. The wheel shaft 20 is rotatably mounted in the support 5 on which the stator is fixed, by means of bearings 22.

[0033] The wound rotor 4 comprises, in a known manner, magnetic steel teeth, for example connected to each other by a magnetic steel yoke. This yoke, produced for example by stacking magnetic steel sheets, is fixed for example by gluing or screwing onto an internal periphery of the cylindrical enclosure 6. This internal periphery is located on a portion of the cylindrical enclosure 6 which is axially proximal to the outside of the vehicle, that is to say axially located near the screws 26. In an alternative embodiment, this internal periphery is located on a portion closer to the center of the vehicle, the wound rotor always being arranged axially at the same level as the wound stator.

[0034] The teeth of the wound rotor 4 are each surrounded by a winding 42 of copper wire. The wound rotor 4 surrounds the wound stator 3 angularly, that is to say in a direction orthogonal to the axial direction and to a radius of the wheel. In other words, the teeth of the wound rotor 4 extend radially, on the side opposite the cylindrical enclosure 6, in the direction of an air gap between the wound rotor 4 and the wound stator 3.

[0035] The wound stator 3 also comprises, in a known manner, magnetic steel teeth, for example connected to each other by a magnetic steel yoke. The stator teeth are each surrounded by a copper wire winding 32. The stator yoke, made for example by stacking magnetic steel sheets, is fixed for example by gluing or screwing to an external periphery of the support 5. This external periphery is located on a portion of the support 5 which is axially proximal to the outside of the vehicle, that is to say axially located near the screws 26, so as to be radially facing the wound rotor 4.

[0036] More specifically, in this embodiment of the invention, the support 5 comprises a cylindrical wall 52 axially distal to the outside of the vehicle and extended axially towards the outside of the vehicle by a cylindrical portion 56 of the support 5, of smaller radius than the cylindrical wall 52, this cylindrical portion 56 being axially proximal to the outside of the vehicle. The external periphery on which the wound stator 5 is fixed is therefore located on this cylindrical portion 56 of the support 5. The cylindrical portion 56 is connected to the cylindrical wall 52 by a shoulder 54 defining an annular crown orthogonal to the cylindrical wall 52. Alternatively, the yoke of the wound stator 3 is fixed by screws to this shoulder 54.

[0037] In this embodiment of the invention, the wound rotor 4 and the wound stator 3 are powered in parallel by a voltage source 7, here a high-voltage electric battery of the vehicle, i.e. intended to provide the energy necessary for traction or propulsion of the vehicle. The voltage source 7 is in this embodiment a 400V (Volts) Lithium Ion battery but alternatively other voltage sources can be used, for example a 48V battery with a voltage in the safer range of very low voltage.

[0038] The voltage source 7 is connected at its terminals to a supply circuit 70 of the wound rotor 4, shown in figure 2.

[0039] The power supply circuit 70, connected to the voltage source 7 of voltage Vb, comprises a transistor bridge 8, a resonant circuit 9, a rectifier bridge 10 and the windings 42 of the wound rotor, each connected in parallel to an output of the rectifier bridge 10, all of the windings 42 being crossed by a rotor current Ir.

[0040] The transistor bridge 8 is connected at the input to the voltage source 7 and at the output to a resonant circuit 9. The transistor bridge 8 comprises a first transistor T1 and a second transistor T2 whose drains are connected to a positive terminal of the voltage source 7. The source of the first transistor T1 is connected to the drain of a third transistor T3 of the transistor bridge 8, the source of the third transistor T3 being connected to a negative terminal of the voltage source 7. Similarly, the source of the second transistor T2 is connected to the drain of a fourth transistor T4 of the transistor bridge 8, the source of the fourth transistor T4 being connected to the negative terminal of the voltage source 7.

[0041] Transistors T1 to T4 of transistor bridge 8 are for example HEMT (High Electron Mobility Transistor) components made of GaN (Galium Nitride) on silicon substrate, typically having a blocking voltage of 650V. Of course, the control voltage of the transistors can be different from that of Figure 2; in this case, the role of the sources and drains of transistors T1 to T4 is reversed.

[0042] The source of the first transistor T1 is also connected to a first terminal B1 of a first branch of the resonant circuit 9, this first branch comprising a first inductance L1 of approximately 16 nI (microHenry) connected in series with a first capacitance Cl of approximately 400 pF (picoFarad). A second terminal B3 of the first branch of the resonant circuit 9 is connected to a first input of a rectifier bridge 10 detailed later.

[0043] Likewise, the source of the second transistor T2 is also connected to a first terminal B2 of a second branch of the resonant circuit 9, this second branch comprising a second inductance L2 connected in series with a second capacitor C2, the second inductance L2 preferably being of the same value as the first inductance L1 and the second capacitor C2 preferably being of the same value as the first capacitor C1. A second terminal B4 of the second branch of the resonant circuit 9 is connected to a second input of the rectifier bridge 10.

[0044] The rectifier bridge 10 comprises a first diode DI whose anode is connected to the first input of the rectifier bridge 10 and whose cathode is connected to a first end of at least one winding 42 of the wound rotor 4. Similarly, the rectifier bridge 10 comprises a second diode D2 whose anode is connected to the second input of the rectifier bridge 10 and whose cathode is connected to the first end of said at least one winding 42 of the wound rotor 4.

[0045] The anode of the first diode DI is also connected to the cathode of a third diode D3 whose anode is connected to a second end of said at least one winding 42 of the wound rotor 4. Similarly, the anode of the second diode D2 is also connected to the cathode of a fourth diode D4 whose anode is connected to the second end of said at least one winding 42 of the wound rotor 4.

[0046] A smoothing capacitor C is connected in parallel to said at least one winding 42 of the wound rotor 4, i.e. to the cathode of the second diode D2 and to the anode of the fourth diode D4.

[0047] According to the invention, in this power supply circuit 70, the electrical connection between the voltage source 7 and the windings 42 of the wound rotor 4 is made by capacitive coupling.

[0048] More specifically, in this embodiment of the invention, this capacitive coupling is carried out on the one hand between a first electrode 11 of the first capacitor C1 and a second electrode 12 of this first capacitor C1, and on the other hand between a first electrode 13 of the second capacitor C2 and a second electrode 14 of this second capacitor C2. Indeed, the power supply circuit 70 comprises a fixed part 72 fixed for example to the support 5 secured to the hollow shaft of the vehicle, and a rotating part 74 fixed to the cylindrical enclosure 6 or to the wheel rim 2. The fixed part 72 comprises at least the transistor bridge 8, the first and second inductances L1 and L2 as well as the first electrodes 11 and 13 of the first and second capacitors C1 and C2. The rotating part 74 comprises at least the second electrodes 12 and 14 of the first and second capacitors C1 and C2, as well as the rectifier bridge 10 and the windings 42 of the wound rotor 4.

[0049] The transistor bridge 8 is switched at a frequency making it possible to produce at the level of the resonant circuit 9, a quasi-sinusoidal current, transformed by the rectifier bridge 10 into direct current to supply the wound rotor 4 with direct current. The exploitation of the resonance created by the resonant circuit 9, by switching the transistors T1 to T4 at a frequency close to the resonance frequency, allows a satisfactory transfer of electrical power between the first electrodes 11 and 13 and the second electrodes 12 and 14 of the first and second capacitors C1 and C2. The switching of the transistors T1 to T4 is preferably carried out in zero voltage switching mode to limit electrical losses during switching. In general, the parasitic drain and source capacitances inherent in the transistor are sufficient to ensure ZVS switching.

[0050] The first and second capacitors Cl and C2 are therefore sized to allow sufficient energy transfer to power the wound rotor 4. For this, the electrodes of the first and second capacitors Cl and C2 take the form of cylindrical copper tracks of substantial diameter, with an axis of revolution parallel to the axis of rotation X of the wheel and which can be easily integrated into the wheel of the vehicle. Of course, as a variant, materials other than copper can be used for these electrodes, for example aluminum.

[0051] More precisely, as can be seen in Figure 1, the first electrodes 11 and 13 of the first and second capacitors C1 and C2 take the form of cylindrical tracks axially spaced from one another and axially encircling the cylindrical wall 52 over their width 1. The first electrodes 11 and 13 of the first and second capacitors C1 and C2 are fixed to the cylindrical wall 52 so as to each radially face respectively the second electrodes 12 and 14 of the first and second capacitors C1 and C2, these second electrodes 12 and 14 taking the form of cylindrical tracks radially external to the cylindrical tracks of the first electrodes, thus called internal cylindrical tracks. The external cylindrical tracks 12 and 14 are fixed axially spaced from one another on an internal contour of a portion of the cylindrical enclosure 6 which is axially distal to the outside of the vehicle.The external cylindrical tracks 12 and 14, that is to say the second electrodes 12 and 14, face over their entire width 1, that is to say in their axial dimension, respectively the internal cylindrical tracks 11 and 13.

[0052] In this embodiment of the invention, the internal cylindrical tracks forming the first electrodes 11 and 13 each have a width 1 of approximately 30 millimeters, that is to say with a tolerance of 1%, measured axially, therefore parallel to the axis of rotation of the vehicle wheel. As a variant, this width 1 is for example between 10 and 40 millimeters, depending in particular on the dimensions of the wheel and the power transferred through the capacitors C1 and C2.

[0053] Furthermore, in this embodiment of the invention, the internal cylindrical tracks forming the second electrodes 11 and 13 each have a diameter D, measured radially between two surfaces of an internal contour of each second electrode, of approximately 240 millimeters. Alternatively, this diameter D is for example between 200 and 300 millimeters, depending in particular on the dimensions of the wheel and the power transferred through the capacitors C1 and C2.

[0054] Furthermore, in this embodiment of the invention, the distance d in the radial direction between the first and second electrodes 11 and 12 of the first capacitor C1 is approximately one millimeter. Similarly, the distance d in the radial direction between the first and second electrodes 13 and 14 of the second capacitor C2 is approximately one millimeter. This distance d allows the motorization system 1 to be robust to impacts during the rolling of the vehicle, by being sufficiently large, and not to require too large a width of the cylindrical tracks forming the electrodes, at equal operating power, while remaining sufficiently small.Indeed, the axial and radial dimensions of the cylindrical tracks forming the electrodes of the first and second capacitors C1 and C2 are chosen so that C1 and C2 are of a sufficiently large value to allow a transfer of power between the voltage source 7 and the wound rotor 4, which is sufficiently large to allow the propulsion of the vehicle. These capacitors have at the same time a size allowing the integration of the wound rotor 4, the wound stator 3 and the power supply circuit 70 in the wheel of the vehicle. Preferably, the motorization system 1 also comprises the voltage source 7 and an inverter 30 configured to supply the wound stator 3 with three-phase current, or more generally polyphase current. The voltage source 7 is connected in parallel to the inputs of the inverter 30 and to the inputs of the transistor bridge 8.The inverter 30 as well as the fixed part 72 of the power supply circuit 70, with the exception of the first electrodes 11 and 13 of the first and second capacitors C1 and C2, are integrated into the wheel of the vehicle by being fixed against the shoulder 54 of the support 5, opposite the wound stator 3.

[0055] The connections of the first and second inductances L1 and L2 to the respective electrodes 11 and 13 of the first and second capacitors C1 and C2 are made through holes in the cylindrical wall 52 of the support 5.

[0056] The respective connections 66, 68 of the second electrodes 12, 14 to the rectifier bridge 10 and the connections 62, 64 of the rectifier bridge 10 to the windings 42 of the wound rotor 4 are made for example by means of grooves extending axially on an internal surface of the cylindrical enclosure 6. These grooves allow in particular conductors to pass radially between the second electrodes 12 and 14 and the internal surface of the cylindrical enclosure 6, these conductors being surrounded by electrical insulation. As a variant, the capacitors C1 and C2 are cylindrical tracks not completely closed on themselves, an opening in these tracks allowing the passage of conductors.

[0057] The connections of the rectifier bridge 10 to the windings 42 of the wound rotor 4 are preferably made by means of two rings 16 and 18 arranged in their largest dimension orthogonally to the axis of rotation X, and arranged on an internal contour of the cylindrical wall 6 near the windings 42 of the wound rotor 4. A first end of each winding 42 is connected to the ring 16 bringing the current into the windings 42, and a second end of each winding 42 is connected to the ring 18 for outputting the current from the windings 42.

[0058] Similarly, the connections of the inverter 30 to the windings 32 of the wound stator 3 are made via circular buses U, V, W each dedicated to a power supply phase of the wound rotor. These circular buses are arranged in their largest dimension orthogonal to the axis of rotation X and are for example fixed to the shoulder 54 of the support 5 on the side of the windings 32 of the wound stator 3. A first end of each winding 32 of the wound stator 3 is for example connected to a circular bus U, V or W, and a second end of each winding 32 of the wound stator 3 is connected to a circular neutral bus N, when the stator windings are connected in star. The circular neutral bus N is also arranged in its largest dimension orthogonally to the axis of rotation X and fixed to the shoulder 54 of the support 5 on the side of the windings 32 of the wound stator 3.The connections between the output phases of the inverter 30 and the corresponding circular buses U, V, W pass through drillings in the shoulder 54 of the support 5.

[0059] In order to protect the active parts of the electric motor comprising the wound rotor 4 and the wound stator 3 from dust coming from underneath the vehicle, an annular lip seal 24 ensures the sealing of the space left free between the support 5 and the cylindrical enclosure 6. This lip seal 24 is fixed to one end of the cylindrical enclosure 6, distal relative to the exterior of the vehicle, this lip seal extending radially to the cylindrical wall 52.

[0060] Finally, the motorization system 1 according to the invention comprises control means 100 for the inverter 30 and the power supply circuit 70, located for example in an electronic module of the vehicle. The control means 100 receive a motor torque setpoint on the wheel of the vehicle, this torque setpoint being converted by the control means 100 into a current setpoint Ir* in the wound rotor. This setpoint is obtained by reading a map giving, for a given torque setpoint, a rotor current setpoint.

[0061] Once the current setpoint Ir* in the wound rotor 4 has been determined by the control means 100, they control the frequency of the switching of the transistors T1 to T4 to achieve this setpoint current Ir*. In order to ensure that this setpoint current Ir* is achieved in the wound rotor 4, a regulation of the switching frequency f of the transistors T1 to T4 is implemented by the control means 100.

[0062] As an indication, the switching frequency f is of the order of 2MHz (MegaHertz), which allows, with the voltage Vb of 400V at the terminals of the voltage source 7, to generate a voltage of 2000V between the electrodes of each of the capacitors Cl and C2 of the resonant circuit 9. The transistors Tl to T4, in particular when they are chosen from HEMT components, are capable of switching a voltage of 400V at 2 MHz (provided they have ZVS switching). Such a configuration makes it possible to supply a current of the order of 10 amperes to the wound rotor 4. As shown in Figure 3, this regulation uses a regulator 104 receiving as input a difference 8 between the setpoint current Ir* in the wound rotor 4 and an estimate ïr of the current in the wound rotor 4. The regulator 104 is therefore similar to means for correcting the setpoint current Ir* in the wound rotor 4.The regulator 104 is for example a PID (Proportional Integral Derivative) regulator providing at output a switching frequency correction Afc to be added to a switching frequency setpoint f* of the transistors T1 to T4, to obtain the switching frequency f to be applied to the transistors T1 to T4. The switching frequency setpoint f* of the transistors T1 to T4 is deduced by a map 102, in which the setpoint current Ir* in the wound rotor and the voltage Vb of the voltage source 7 are read at input.

[0063] The estimation ïr of the current in the wound rotor 4 is for example obtained by the steps shown in FIG. 4, of a method for estimating the current in the wound rotor 4, implemented by the control means 100.

[0064] The first step of this method is the measurement of a current in the fixed part 72 of the supply circuit 70, for example of a current If flowing in the second branch of the resonant circuit 9, in the form of a current signal as a function of time.

[0065] The second step of this process is the application to the current signal If measured previously, of an operator giving its absolute value and therefore delivering a rectified current signal If circulating in the second branch of the resonant circuit 9.

[0066] The third step of this process is the application of a low-pass filter to the rectified signal obtained previously, this filter providing an estimate ïr of the current in the wound rotor 4.

[0067] Alternatively, a second, more precise estimate ïr of the current in the wound rotor 4, used to calculate the difference 8 at the input of the regulator 104, is obtained by measuring the phase shift between the stator voltage and the stator current. This phase shift corresponds to the magnetization of the synchronous machine (the higher the rotor current, the more the machine will be magnetized; usually the rotor current is regulated so as to have the stator current and voltage in phase and therefore the minimum of joule losses in the stator because there is no exchange of reactive power). The difference between this measured phase shift and the theoretical phase shift that would be obtained with the setpoint Ir* of current in the wound rotor 4 makes it possible to obtain an estimate ïr of the current in the wound rotor 4.

[0068] In another alternative embodiment of the invention, to obtain an estimate ïr of the current in the wound rotor 4, the motorization system 1 comprises means for measuring the rotor current Ir at the wound rotor 4, for example these measuring means are a Hall effect sensor. In this alternative, the motorization system 1 comprises means for sending the rotor current Ir measured by the measuring means, these sending means being for example wireless communication means fixed to the cylindrical enclosure 6. Means for receiving the rotor current measurement Ir sent by the sending means are located for example in the electronic module. These receiving means are of course adapted to receive this measurement in the format used by the sending means.Alternatively, the sending means are means for coding the rotor current measurement Ir supplied by the measuring means, in the form of an electrical signal at a frequency very different from the switching frequency f, this electrical signal being applied by the sending means to the terminals of the electrodes 12 and 14 so that it can be decoded by receiving means connected to the fixed part 72 of the power supply circuit 70. The receiving means and the sending means in this variant and its alternative, are part of the motorization system 1 according to the invention.

[0069] Optionally, as a variant, to refine the open-loop estimation of the current setpoint Ir* in the wound rotor, and knowing the voltage across the wound rotor 4, the control means 100 use a rotor resistance value provided by tables giving this resistance value as a function of the rotor temperature, the latter being estimated elsewhere, for example via a temperature sensor at the stator and a thermal model estimating the rotor temperature as a function of the temperature measured at the stator. As a variant, the rotor temperature is fed back to the control means 100 by a temperature sensor located in contact with the rotor windings 42 and communicating wirelessly with the electronic module.

[0070] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

Claims

CLAIMS 1- Vehicle wheel motorization system (1) comprising: - a wound stator (3), intended to be mounted securely to a hollow shaft receiving a wheel shaft (20), - a wheel rim (2) intended to be fixed to the wheel shaft (20), - a rotor (4) secured to the wheel rim (2), the rotor (4) angularly surrounding the wound stator (3), the motorization system (1) being characterized in that the rotor (4) is a wound rotor and in that the motorization system (1) comprises an electrical power supply circuit (70) for the wound rotor (4), the power supply circuit (70) comprising at least one electrical connection by capacitive coupling intended to connect at least one voltage source (7) to at least one winding (42) of the wound rotor (4). 2- Wheel motorization system (1) according to claim 1, comprising: - a support (5) intended to be secured to the hollow shaft, the support (5) comprising a cylindrical wall (52), and - a cylindrical enclosure (6) secured to the wheel rim (2), surrounding the cylindrical wall (52) at least in part, said at least one connection comprising at least one capacitor (Cl, C2) comprising an external cylindrical conductive track (11, 13) arranged on an internal contour of the cylindrical enclosure (6), and an internal cylindrical conductive track (12, 14) arranged on an external contour of the cylindrical wall (52), the external cylindrical track (11) of said at least one capacitor (Cl, C2) being arranged radially opposite the internal cylindrical track (12) of said at least one capacitor (Cl). 3- Wheel motorization system (1) according to claim 2, wherein said at least one capacity comprises a first capacity (Cl) and a second capacity (C2). 4- Wheel motorization system (1) according to claim 2 or 3, in which the diameter (D) of the internal cylindrical track (12, 14) is greater than 235 millimeters. 5- Wheel motorization system (1) according to any one of claims 2 to 4, in which the distance (d) between the internal cylindrical track (12, 14) and the external cylindrical track (11, 13) of said at least one capacity is one millimeter to within plus or minus twenty percent. 6- Wheel motorization system (1) according to any one of claims 2 to 5, in which the width (1) of the internal (12, 14) or external (11, 13) cylindrical track is between 25 and 35 millimeters. 7- Wheel motorization system (1) according to any one of claims 3 to 6, wherein the power supply circuit (70) further comprises a transistor bridge (8), a resonant circuit (9) and a rectifier bridge, the transistor bridge (8) being configured to be connected at the input to the voltage source (7), and being connected at the output to the resonant circuit (9), the resonant circuit (9) comprising at least one resonance inductance (LI, L2), the first capacitor (Cl) and the second capacitor (C2), and the rectifier bridge being connected at the input to the resonant circuit (9) and at the output to the winding (42) of the wound rotor (4). 8- Wheel motorization system (1) according to claim 7, comprising means (100) for controlling a rotor current (I r ), the control means (100) being capable of varying the control frequency (f) of the transistor bridge (8) in zero voltage switching mode. 9- Wheel motorization system (1) according to claim 8, in which the control means (100) comprise means for correcting a reference current (I* r ) of the wound rotor (4), the correction means comprising means for estimating the rotor current (I r ). 10- Wheel motorization system (1) according to claim 9, in which the means for estimating the rotor current (I r ) include means for measuring a phase shift between a stator current and a stator voltage. 11- Wheel motorization system (1) according to claim 9, comprising means for measuring the rotor current (I r ) in a rotating part (74) of the power supply circuit (70), the motorization system (1) comprising means for sending a measured value of the rotor current (I r) by the measuring means, to the control means, the control means comprising means for receiving the measured value of the rotor current (I r ) .

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