System for driving a vehicle wheel

Abstract

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

Description

Technical Field

[0001] The present invention relates to the fields of motor vehicles and electrical engineering, and more particularly to a system for driving vehicle wheels. Background Art

[0002] An electric vehicle or a hybrid electric vehicle includes one or more electric motors that provide traction or propulsion force to the vehicle. When such a vehicle uses an electric motor whose torque is transmitted to the vehicle's wheels via a transmission chain, it is advantageous for the electric motor to have a wound rotor because this avoids the use of permanent magnets that employ rare earths, which are expensive and are a finite resource.

[0003] On the other hand, when such a vehicle directly incorporates an electric traction or propulsion motor in the vehicle's wheels, this involves motors whose rotors are external to their stators, and the rotors of these motors typically have permanent magnets. Specifically, motors with wound rotors use a ring and brush system to supply power to the wound rotor, and such a ring and brush system is not compatible with an outer rotor because such an outer rotor would cause an excessive relative speed between the ring and the brush, which would lead to premature wear of the brush. In addition, such a ring and brush system has an axial volume (i.e., in the direction of the axis of rotation of the electric motor) that is not compatible with the space available at the vehicle wheel. Finally, such a system is not compatible with the environmental conditions under which the vehicle wheel operates, especially since dust and vibrations can cause the system to malfunction or fail.

[0004] However, motors with permanent magnets in vehicle wheels are still expensive, and they generate drag currents when they are not used for vehicle traction or propulsion, which affects the efficiency of the vehicle drive system at high speeds. To prevent such drag currents, the permanent magnet rotor must be mechanically disengaged from its electric motor, but this would require a disengagement mechanism that would take up too much space on the axle of the wheel that includes these motors. Using a wound rotor motor in a vehicle wheel would avoid these no-load losses, but its ring and brush system has too many drawbacks.

[0005] Therefore, there is a need for an electric traction or propulsion motor that can be integrated into a vehicle wheel and does not have the drawbacks of the prior art. Summary of the Invention

[0006] The present invention at least partially overcomes the drawbacks of the prior art by providing a system for driving a wheel that includes a wound rotor electric motor that has good efficiency, a small axial volume, and is not dependent on the rare earth market.

[0007] To this end, the present invention proposes a drive system for driving a vehicle wheel, the drive system comprising:

[0008] - A wound stator, which is designed to be rigidly fixed to a hollow shaft that receives a wheel axle,

[0009] - A wheel rim, which is designed to be attached to the wheel axle,

[0010] - A rotor, which is rigidly fixed to the wheel rim and angularly surrounds the wound stator. The drive system is characterized in that the rotor is a wound rotor, and the drive system includes a power supply circuit for the wound rotor. The power supply circuit includes at least one electrical connection achieved by capacitive coupling. The at least one electrical connection is designed to connect at least one voltage source to at least one winding of the wound rotor. The angular direction is defined as being orthogonal to the rotation axis of the wheel and the radius of the wheel.

[0011] By means of capacitive coupling that allows the wound rotor to be electrically connected to a voltage source, it is no longer necessary to use a slip ring and brush system to supply power to the wound rotor, which allows the wound rotor to be used in a vehicle wheel without all the disadvantages of a slip ring and brush system. In particular, such capacitive coupling can be achieved with a very small axial volume while still being able to resist dust and vibration. Therefore, the drive system according to the present invention integrates a motor formed by a wound rotor and a wound stator. The motor is compact in the axial direction of the motor and does not exhibit no-load losses during high-speed driving.

[0012] In an embodiment of the present invention, the system for driving a wheel according to the present invention includes:

[0013] - A support member, which is designed to be rigidly fixed to the hollow shaft. The support member includes a cylindrical wall, and

[0014] - A cylindrical housing, which is rigidly fixed to the wheel rim and at least partially surrounds the cylindrical wall,

[0015] The at least one connection includes at least one capacitor (C1, C2). The at least one capacitor includes a conductive outer cylindrical track arranged on the inner contour of the cylindrical housing and a conductive inner cylindrical track arranged on the outer contour of the cylindrical wall. The outer cylindrical track of the at least one capacitor is arranged radially facing the inner cylindrical track of the at least one capacitor. Advantageously, the at least one capacitor includes a first capacitor and a second capacitor.

[0016] The wound rotor is, for example, attached to the cylindrical housing and radially faces the wound stator, which is preferably attached to the support member, on the cylindrical portion of the support member. The diameter of the cylindrical portion is smaller than the diameter of the cylindrical wall on which the inner cylindrical track is arranged.

[0017] In one embodiment of the present invention, the diameter of the inner cylindrical track is greater than 235 millimeters. Thus, the inner cylindrical tracks of the first capacitor and the second capacitor have a diameter greater than 235 millimeters between two opposite inner surfaces of the inner cylindrical track, which diameter is measured orthogonally to the axis of rotation of the wound rotor. This value is chosen to allow sufficient power to be transmitted to the wound rotor so as to allow a vehicle to be towed or propelled, while limiting the radial volume.

[0018] Preferably, the distance between the inner cylindrical track and the outer cylindrical track of the at least one capacitor is between one millimeter and plus or minus twenty percent. This distance is measured in the radial direction (i.e., orthogonally to the axis of gyration of the wound rotor and passing through this axis) between two opposite inner surfaces of the inner cylindrical track and the outer cylindrical track. For a given transmitted power comparable to that of the wound rotor, this distance value provides resistance to vibrations and dust, while having a small axial volume.

[0019] More preferably, the width of the inner cylindrical track or the outer cylindrical track is between 25 millimeters 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 volume of the system for driving the wheel, while allowing sufficient supply power to be transmitted to the wound rotor.

[0020] In one embodiment of the present invention, the power supply circuit further comprises a transistor bridge, a resonant circuit and a bridge rectifier, the transistor bridge being configured to be connected to a voltage source at the input and to the resonant circuit at the output, the resonant circuit comprising at least one resonant inductor, the first capacitor and the second capacitor, and the bridge rectifier being connected to the resonant circuit at the input and to the winding of the wound rotor at the output. The resonant circuit comprises, for example, two resonant inductors and two or more resonant capacitors, which resonant capacitors include the first capacitor and the second capacitor.

[0021] Advantageously, the system for driving a wheel according to the present invention comprises control means for controlling the rotor current, which control means are capable of varying the control frequency of the transistor bridge in zero-voltage switching mode. These control means allow a supply current to be transmitted to the wound rotor so as to generate the torque requested by the vehicle driver, while minimizing the electrical losses in the stator.

[0022] Preferably, the control means comprise means for correcting the setpoint current of the wound rotor, which correcting means comprise means for estimating the rotor current. These correcting means make it possible to achieve the required torque with greater precision.

[0023] The device for estimating the rotor current includes, for example, a device for measuring the phase shift between the stator current and the stator voltage. Measuring this phase shift makes it possible to estimate the rotor current without measuring the rotor current directly.

[0024] Instead of this estimation of the rotor current by phase shift measurement, the system for driving a wheel according to the invention includes a device for measuring the rotor current in the rotating part of the power supply circuit. This drive system includes a device for sending the value of the rotor current measured by the measuring device to a control device, and this control device includes a device for receiving the measured value of the rotor current. These measuring devices make it possible to obtain an accurate estimate of the current in the wound rotor, and this accurate estimate is supplied as an input to a correction device, which allows the required torque to be precisely achieved.

[0025] Advantageously, the system for driving a wheel according to the invention includes a voltage source and an inverter, and the voltage source is connected in parallel on one hand to the input of the inverter and on the other hand to the input of the power supply circuit. The inverter is connected at its output to the wound stator. Thus, a single voltage source can be used to supply both the wound rotor and the wound stator. Description of the Drawings

[0026] Additional features and advantages of the present invention will become apparent on the one hand from the following description and on the other hand from several examples of embodiments provided by way of non-limiting illustration with reference to the schematic drawings, in which:

[0027] Figure 1 shows schematically in axial section a system for driving a vehicle wheel according to the invention, in one embodiment of the invention, the axial direction being defined by the axis of rotation of the wheel,

[0028] Figure 2 depicts the power supply circuit of the wound rotor of the system for driving Figure 1 the wheel,

[0029] Figure 3 depicts the device for controlling the rotor current flowing in the wound rotor of the drive system in Figure 1 and

[0030] Figure 4 depicts the steps in the method for estimating the rotor current flowing in the wound rotor of the drive system in Figure 1 . Detailed Description

[0031] According to one embodiment of the invention, Figure 1 ​​​​The system 1 for driving a vehicle wheel according to the invention as shown includes a fixed (i.e., non-rotating) part, which particularly includes a wound stator 3 that is rigidly fixed to the hollow shaft of the vehicle, on which the system 1 for driving the wheel according to the invention is mounted. The hollow shaft is attached to the vehicle chassis and allows the wheel shaft 20 to pass through. More specifically, the wound stator 3 is attached to a support 5 that is rigidly fixed to the hollow shaft.

[0032] The system 1 for driving the wheel also includes a rotating part, which particularly includes a wound rotor 4 that is rigidly fixed to the wheel rim 2 by means of a cylindrical intermediate part 6 (e.g., a brake drum). In Figure 1 it, for the sake of simplicity, this intermediate part is depicted in the form of a cylindrical housing 6 and is referred to as the cylindrical housing in the rest of the specification. The cylindrical housing 6 is rigidly fixed to the wheel rim 2 and the wheel shaft 20 (directly attached to the wheel rim 2 or an unshown wall of the cylindrical housing 6) by means of screws 26. When the wound rotor 4 and the wound stator 3 are supplied with electricity, the wheel shaft 20 rotates about an axis X defining the axial direction by itself. The wheel shaft 20 is rotatably mounted in the support 5 to which the stator is attached by means of bearings 22.

[0033] The wound rotor 4 includes magnet steel teeth in a known manner, and these magnet steel teeth are connected to each other, for example, by a magnet steel yoke. This yoke, which is made, for example, by stacking magnet steel sheets, is attached to the inner periphery of the cylindrical housing 6, for example, by adhesive bonding or screw connection. This inner periphery is located on a part of the cylindrical housing 6 that is axially close to the outside of the vehicle (that is, axially near the screws 26). In a variant embodiment, this inner periphery is located on a part closer to the center of the vehicle, and the wound rotor is always arranged at the same axial level as the wound stator.

[0034] Each tooth of the wound rotor 4 is surrounded by a copper wire winding 42. The wound rotor 4 is angularly (that is, in a direction orthogonal to the axial direction and the wheel radius) around the wound stator 3. In other words, the teeth of the wound rotor 4 radially extend in the direction of the air gap between the wound rotor 4 and the wound stator 3 on the side opposite to the cylindrical housing 6.

[0035] The wound stator 3 also includes magnet steel teeth in a known manner, and these magnet steel teeth are connected to each other, for example, by a magnet steel yoke. Each stator tooth is surrounded by a copper wire winding 32. The stator yoke, which is made, for example, by stacking magnet steel sheets, is attached to the outer periphery of the support 5, for example, by adhesive bonding or screw connection. This outer periphery is located on a part of the support 5 that is axially close to the outside of the vehicle (that is, axially near the screws 26) so as to face the wound rotor 4 radially.

[0036] More specifically, in this embodiment of the present invention, the support member 5 includes a cylindrical wall 52 that axially extends away from the outside of the vehicle and axially extends towards the outside of the vehicle through a cylindrical portion 56 of the support member 5. The radius of this cylindrical portion is smaller than that of the cylindrical wall 52, and the cylindrical portion 56 axially approaches the outside of the vehicle. Thus, the outer periphery to which the wound stator 5 is attached is located on this cylindrical portion 56 of the support member 5. The cylindrical portion 56 is connected to the cylindrical wall 52 through a shoulder 54, and this shoulder defines an annular ring orthogonal to the cylindrical wall 52. Alternatively, the yoke of the wound stator 3 is attached to this shoulder 54 by screws.

[0037] In this embodiment of the present invention, the wound rotor 4 and the wound stator 3 are powered in parallel by a voltage source 7 (in this case, the high-voltage battery of the vehicle), that is, it is intended to provide the energy required for the traction or propulsion of the vehicle. In this embodiment, the voltage source 7 is a 400 V (volt) lithium-ion battery, but alternatively, other voltage sources can be used, such as a 48 V battery with a voltage in a safer very low voltage range.

[0038] The voltage source 7 is connected at its terminals to a power supply circuit 70 for the wound rotor 4, as Figure 2 shown.

[0039] The power supply circuit 70 of the voltage source 7 connected to the voltage Vb includes a transistor bridge 8, a resonant circuit 9, a bridge rectifier 10, and the windings 42 of the wound rotor. Each winding is connected in parallel to the output terminal of the bridge rectifier 10, and all the windings 42 have a rotor current Ir flowing through them.

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

[0041] The transistors T1 to T4 of the transistor bridge 8 are, for example, HEMT (high electron mobility transistor) components made of GaN (gallium nitride) on a silicon substrate, typically having a cut-off voltage of 650 V. Of course, the control voltage of the transistors may be different from Figure 2 the control voltage; in this case, the functions of the sources and drains of the transistors T1 to T4 are interchanged.

[0042] The source of the first transistor T1 is also connected to the first terminal B1 of the first branch of the resonant circuit 9. The first branch includes a first inductor L1 of approximately 16 µH (microhenry), which is connected in series with a first capacitor C1 of approximately 400 pF (picofarad). The second terminal B3 of the first branch of the resonant circuit 9 is connected to the first input of the bridge rectifier 10, which will be described in more detail below.

[0043] Similarly, the source of the second transistor T2 is also connected to the first terminal B2 of the second branch of the resonant circuit 9. The second branch includes a second inductor L2 connected in series with a second capacitor C2. The second inductor L2 preferably has the same value as the first inductor L1, and the second capacitor C2 preferably has the same value as the first capacitor C1. The second terminal B4 of the second branch of the resonant circuit 9 is connected to the second input of the bridge rectifier 10.

[0044] The bridge rectifier 10 includes a first diode D1. The anode of the first diode is connected to the first input of the bridge rectifier 10, and the cathode of the first diode is connected to the first end of at least one winding 42 of the wound rotor 4. Similarly, the bridge rectifier 10 includes a second diode D2. The anode of the second diode is connected to the second input of the bridge rectifier 10, and the cathode of the second diode is connected to the first end of the at least one winding 42 of the wound rotor 4.

[0045] The anode of the first diode D1 is also connected to the cathode of a third diode D3. The anode of the third diode is connected to the second end of the 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. The anode of the fourth diode is connected to the second end of the at least one winding 42 of the wound rotor 4.

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

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

[0048] More specifically, in this embodiment of the present invention, this capacitive coupling is performed on the one hand between the first electrode 11 and the second electrode 12 of the first capacitor C1, and on the other hand between the first electrode 13 and the second electrode 14 of the second capacitor C2.

[0049] More specifically, the power supply circuit 70 includes: a fixed part 72 attached to a support 5, for example, rigidly fixed to a hollow shaft of a vehicle; and a rotating part 74 attached to a cylindrical housing 6 or a wheel rim 2. The fixed part 72 includes at least a transistor bridge 8, a first inductor L1 and a second inductor L2, and first electrodes 11 and 13 of a first capacitor C1 and a second capacitor C2. The rotating part 74 includes at least second electrodes 12 and 14 of the first capacitor C1 and the second capacitor C2, a bridge rectifier 10, and a winding 42 of a wound rotor 4.

[0050] The transistor bridge 8 is switched at a frequency that allows a quasi-sinusoidal current to be generated in the resonant circuit 9, and this quasi-sinusoidal current is converted into a direct current by the bridge rectifier 10 to supply a direct current to the wound rotor 4. By utilizing the resonance generated by the resonant circuit 9 and switching the transistors T1 to T4 at a frequency close to the resonance frequency, satisfactory power transfer can be achieved between the first electrodes 11 and 13 and the second electrodes 12 and 14 of the first capacitor C1 and the second capacitor C2. The switching of the transistors T1 to T4 is preferably completed in a zero-voltage switching mode to limit the electrical losses during switching. Generally, the drain and source stray capacitances inherent in the transistors are sufficient to ensure ZVS.

[0051] Therefore, the sizes of the first capacitor C1 and the second capacitor C2 are determined to allow sufficient energy transfer to power the wound rotor 4. For this purpose, the electrodes of the first capacitor C1 and the second capacitor C2 are in the form of cylindrical copper tracks with a large diameter, which have a rotation axis parallel to the rotation axis X of the wheel and can be easily integrated into the vehicle wheel. Of course, alternatively, these electrodes can also use materials other than copper, such as aluminum.

[0052] More specifically, as can be seen in Figure 1 the first electrodes 11 and 13 of the first capacitor C1 and the second capacitor C2 are in the form of cylindrical tracks that are axially spaced apart from each other and axially surround a cylindrical wall 52 over their width l. The first electrodes 11 and 13 of the first capacitor C1 and the second capacitor C2 are attached to the cylindrical wall 52 in such a way that these first electrodes each radially face the second electrodes 12 and 14 of the first capacitor C1 and the second capacitor C2, and these second electrodes 12 and 14 are in the form of cylindrical tracks located radially outside the cylindrical tracks of the first electrodes, so the first electrodes are called inner cylindrical tracks. The outer cylindrical tracks 12 and 14 are attached to the inner profile of a part of the cylindrical housing 6 that is axially far from the outside of the vehicle at a certain axial distance from each other. The outer cylindrical tracks 12 and 14 (that is, the second electrodes 12 and 14) face the inner cylindrical tracks 11 and 13 over their entire width l (that is, in their axial dimension).

[0053] In this embodiment of the invention, the inner cylindrical tracks forming the first electrodes 11 and 13 each have a width l of approximately 30 millimeters (i.e., with a tolerance of 1%), which width is measured axially (and thus parallel to the axis of rotation of the vehicle wheel). Alternatively, the width l is, for example, between 10 millimeters and 40 millimeters, depending on the size of the wheel and the power transmitted through the capacitors C1 and C2.

[0054] Furthermore, in this embodiment of the invention, the inner cylindrical tracks forming the second electrodes 11 and 13 each have a diameter D of approximately 240 millimeters, which diameter is measured radially between two surfaces of the inner profile of each second electrode. Alternatively, the diameter D is, for example, between 200 millimeters and 300 millimeters, depending on the size of the wheel and the power transmitted through the capacitors C1 and C2.

[0055] Moreover, in this embodiment of the invention, the distance d in the radial direction between the first electrode 11 of the first capacitor C1 and the second electrode 12 is approximately one millimeter. Similarly, the distance d in the radial direction between the first electrode 13 of the second capacitor C2 and the second electrode 14 is approximately one millimeter. Since this distance d is large enough, it allows the drive system 1 to withstand shocks when the vehicle is moving, and since the distance is small enough, it does not require the width of the cylindrical tracks forming the electrodes to be too large at equal operating power. Specifically, the axial and radial dimensions of the cylindrical tracks forming the electrodes of the first capacitor C1 and the second capacitor C2 are chosen such that C1 and C2 have values large enough to allow power transmission between the voltage source 7 and the wound rotor 4, and the power is large enough to allow the vehicle to be propelled. These capacitors also have a volume that allows the wound rotor 4, the wound stator 3, and the power supply circuit 70 to be integrated in the vehicle wheel.

[0056] Preferably, the drive system 1 further includes a voltage source 7 and an inverter 30, which is configured to supply a three-phase current, or more generally a polyphase current, to the wound stator 3. The voltage source 7 is connected in parallel to the input of the inverter 30 and the input of the transistor bridge 8. The inverter 30 and the fixed part 72 of the power supply circuit 70 (except for the first electrodes 11 and 13 of the first capacitor C1 and the second capacitor C2) are integrated in the vehicle wheel by being attached (opposite to the wound stator 3) against the shoulder 54 of the support 5.

[0057] The connection of the first inductor L1 and the second inductor L2 to the respective electrodes 11 and 13 of the first capacitor C1 and the second capacitor C2 is achieved through holes in the cylindrical wall 52 of the support 5.

[0058] The connections 66, 68 of the second electrodes 12, 14 to the bridge rectifier 10 and the connections 62, 64 of the bridge rectifier 10 to the windings 42 of the wound rotor 4 are realized, for example, by means of grooves axially extending on the inner surface of the cylindrical housing 6. These grooves particularly allow conductors to pass radially between the second electrodes 12 and 14 and the inner surface of the cylindrical housing 6, and these conductors are surrounded by electrical insulation. Alternatively, the capacitors C1 and C2 are cylindrical tracks that are not completely closed by themselves, and the openings in these tracks allow conductors to pass through.

[0059] The connection of the bridge rectifier 10 to the windings 42 of the wound rotor 4 is preferably realized by means of two rings 16 and 18, which are arranged orthogonally to the rotational axis X in their maximum dimension and are arranged on the inner contour of the cylindrical wall 6, near the windings 42 of the wound rotor 4. The first end of each winding 42 is connected to the ring 16, thereby bringing current into the winding 42, and the second end of each winding 42 is connected to the ring 18 for outputting current from the winding 42.

[0060] Similarly, the connection of the inverter 30 to the windings 32 of the wound stator 3 is realized via the annular buses U, V, W, and each annular bus is dedicated to one supply phase of the wound rotor. These annular buses are arranged orthogonally to the rotational axis X in their maximum dimension and are attached, for example, to the shoulder 54 of the support 5 on the same side as the windings 32 of the wound stator 3. When the stator windings are connected in a star configuration, the first end of each winding 32 of the wound stator 3 is connected, for example, to the annular buses U, V, or W, and the second end of each winding 32 of the wound stator 3 is connected to the neutral annular bus N. The neutral annular bus N is also arranged orthogonally to the rotational axis X in its maximum dimension and is attached to the shoulder 54 of the support 5 on the same side as the windings 32 of the wound stator 3. The connection between the output phases of the inverter 30 and the corresponding annular buses U, V, W passes through the holes in the shoulder 54 of the support 5.

[0061] In order to protect the active part of the electric motor, including the wound rotor 4 and the wound stator 3, from dust coming from under the vehicle, the annular lip seal 24 ensures the sealing of the free space left between the support 5 and the cylindrical housing 6. This lip seal 24 is attached to the end of the cylindrical housing 6 located away from the outside of the vehicle, and this lip seal extends radially as far as the cylindrical wall 52.

[0062] Finally, the drive system 1 according to the invention comprises control means 100 for controlling, for example, an inverter 30 and a power supply circuit 70 located in an electronic module of a vehicle. The control means 100 receives a motor torque setpoint for a vehicle wheel, which torque setpoint is converted by the control means 100 into a current setpoint Ir* in the wound rotor. This setpoint is obtained by reading a map which gives the rotor current setpoint for a given torque setpoint.

[0063] Once the control means 100 has determined the current setpoint Ir* in the wound rotor 4, these means control the switching frequency of transistors T1 to T4 to reach this current setpoint Ir*. In order to ensure that this current setpoint Ir* is reached in the wound rotor 4, the control means 100 implements an adjustment of the switching frequency f of transistors T1 to T4.

[0064] For ease of reference, the switching frequency f is approximately 2 MHz (megahertz), which makes it possible to generate a voltage of 2000 V between the electrodes of each of the capacitors C1 and C2 in the resonant circuit 9 when the voltage Vb at the terminals of the voltage source 7 is 400 V. Transistors T1 to T4 (especially when selected from HEMT components) are capable of switching a voltage of 400 V at 2 MHz with ZVS. This configuration makes it possible to supply a current of approximately 10 amperes to the wound rotor 4.

[0065] As Figure 3 shown, this adjustment uses a controller 104 which receives as input the difference ε between the current setpoint Ir* in the wound rotor 4 and the estimated current Îr in the wound rotor 4. Thus, the controller 104 is analogous to means for correcting the current setpoint Ir* in the wound rotor 4. The controller 104 is, for example, a PID (Proportional Integral Derivative) controller which provides at its output a switching frequency correction Δfc which is added to the setpoint f* of the switching frequency of transistors T1 to T4 to obtain the switching frequency f to be applied to transistors T1 to T4. The setpoint f* of the switching frequency of transistors T1 to T4 is derived from a map 102 in which the current setpoint Ir* in the wound rotor and the voltage Vb of the voltage source 7 are read as inputs.

[0066] The estimated current Îr in the wound rotor 4 is obtained, for example, by steps of a method for estimating the current in the wound rotor 4 implemented by the control means 100 ( Figure 4 shown).

[0067] The first step in this method is to measure the current (for example the current If flowing in the second branch of the resonant circuit 9) in the fixed part 72 of the power supply circuit 70, in the form of a current signal varying with time.

[0068] The second step in this method is to apply an absolute value operator to the previously measured current If signal and thus deliver a rectified signal of the current If flowing in the second branch of the resonant circuit 9.

[0069] The third step in this method is to apply a low-pass filter to the previously obtained rectified signal, which filter provides an estimated value Îr of the current in the wound rotor 4.

[0070] As a variant, a second more accurate estimated value Îr of the current in the wound rotor 4 is obtained by measuring the phase shift between the stator voltage and the stator current, and this estimated value is used to calculate the difference ε at the input of the controller 104. This phase shift corresponds to the magnetization of the synchronous motor (the higher the rotor current, the more the motor will be magnetized; typically, the rotor current is regulated so that the stator current and voltage are in phase, and thus, due to the absence of reactive power exchange, the Joule losses in the stator are minimized). The difference between the measured phase shift and the theoretical phase shift obtained using the current setpoint Ir* in the wound rotor 4 enables the estimated value Îr of the current in the wound rotor 4 to be obtained.

[0071] In another variant embodiment of the present invention, in order to obtain an estimated value Îr of the current in the wound rotor 4, the drive system 1 includes means for measuring the rotor current Ir at the level of the wound rotor 4. For example, these measuring means are Hall effect sensors. In this variant, the drive system 1 includes means for sending the rotor current Ir measured by the measuring means, and these sending means are, for example, wireless communication means attached to the cylindrical housing 6. The means for receiving the measurement result of the rotor current Ir sent by the sending means are, for example, located in an electronic module. These receiving means themselves are adapted to receive this measurement result in the format used by the sending means. Alternatively, the sending means are used to encode the measurement result of the rotor current Ir provided by the measuring means in the form of an electrical signal having a frequency very different from the switching frequency f, and this sending means applies this electrical signal to the terminals of the electrodes 12 and 14 so that the electrical signal can be decoded by the receiving means connected to the fixed part 72 of the power supply circuit 70. In this variant and its alternatives, the receiving means and the sending means form part of the drive system 1 according to the present invention.

[0072] Optionally, as a variant, in order to refine the open-loop estimation of the current setpoint Ir* in the wound rotor and knowing the voltage at the terminals of the wound rotor 4, the control device 100 uses the rotor resistance value provided by a table, which value is given as a function of the temperature of the rotor, and this temperature is estimated elsewhere (for example, via a temperature sensor at the stator and a thermal model for estimating the rotor temperature based on the temperature measured at the stator). Alternatively, the temperature of the rotor is sent to the control device 100 by a temperature sensor that is positioned in contact with the rotor winding 42 and communicates wirelessly with the electronic module.

[0073] Of course, the present invention is not limited to the examples just described and many adjustments can be made to these examples without departing from the scope of the present invention.

Claims

1. A drive system (1) for driving a vehicle wheel, the drive system comprising: - A wound stator (3) intended to be rigidly fixed to a hollow shaft receiving a wheel axle (20), - A wheel rim (2) intended to be attached to the wheel axle (20), - A rotor (4) rigidly fixed to the wheel rim (2), the rotor (4) angularly surrounding the wound stator (3), The drive system (1) is characterized in that the rotor (4) is a wound rotor and the drive system (1) comprises a power supply circuit (70) for the wound rotor (4), the power supply circuit (70) comprising at least one electrical connection realized by capacitive coupling, the at least one electrical connection being intended to connect at least one voltage source (7) to at least one winding (42) of the wound rotor (4).

2. The wheel drive system (1) according to claim 1, comprising: - A support (5) intended to be rigidly fixed to the hollow shaft, the support (5) comprising a cylindrical wall (52), and - A cylindrical housing (6) rigidly fixed to the wheel rim (2), the cylindrical housing at least partially surrounding the cylindrical wall (52), The at least one connection comprises at least one capacitor (C1, C2), the at least one capacitor comprising conductive outer cylindrical tracks (11, 13) arranged on the inner profile of the cylindrical housing (6) and conductive inner cylindrical tracks (12, 14) arranged on the outer profile of the cylindrical wall (52), the outer cylindrical track (11) of the at least one capacitor (C1, C2) being arranged radially facing the inner cylindrical track (12) of the at least one capacitor (C1).

3. The wheel drive system (1) according to claim 2, wherein, The at least one capacitor comprises a first capacitor (C1) and a second capacitor (C2).

4. The wheel drive system (1) according to claim 2 or 3, wherein, The diameter (D) of the inner cylindrical tracks (12, 14) is greater than 235 mm.

5. The wheel drive system (1) according to any one of claims 2 to 4, wherein, The distance (d) between the inner cylindrical tracks (12, 14) and the outer cylindrical tracks (11, 13) of the at least one capacitor is from one millimeter to within plus or minus twenty percent.

6. The wheel drive system (1) according to any one of claims 2 to 5, wherein, The width (l) of the inner cylindrical tracks (12, 14) or the outer cylindrical tracks (11, 13) is between 25 mm and 35 mm.

7. The wheel drive 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 bridge rectifier, the transistor bridge (8) being configured to be connected to the voltage source (7) at an input and to the resonant circuit (9) at an output, the resonant circuit (9) comprising at least one resonant inductor (L1, L2), the first capacitor (C1) and the second capacitor (C2), and the bridge rectifier being connected to the resonant circuit (9) at an input and to the winding (42) of the wound rotor (4) at an output.

8. The wheel drive system (1) according to claim 7, comprising control means (100) for controlling the rotor current (I r ), said control means (100) being capable of changing the control frequency (f) of the transistor bridge (8) in a zero voltage switching mode.

9. The wheel drive system (1) according to claim 8, wherein, The control device (100) includes means for correcting a setpoint current (I* r ) of the wound rotor (4), and the correction means includes means for estimating the rotor current (I r ).

10. The wheel drive system (1) according to claim 9, wherein, The device for estimating the rotor current (I r ) includes a device for measuring the phase shift between the stator current and the stator voltage.

11. The wheel drive system (1) according to claim 9, comprising means for measuring a rotor current (I r ) in a rotating part (74) of the power supply circuit (70), the drive system (1) comprising means for sending a value of the rotor current (I r ) measured by the measuring means to the control means, the control means comprising means for receiving a measured value of the rotor current (I r ).

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