Method of controlling an axial flux motor with variators.

Abstract

The invention relates to a method for controlling an axial flux motor (10) comprising at least one rotor (3) interposed between two stators (1, 2) electrically powered by at least one electrical current regulator. The motor (10) is powered by two regulators (6, 8), the control of the motor (10) being carried out according to a desired torque value at the output of the motor (10). A lower torque limit at the output of the motor (10) is predetermined and, for a desired torque value below the lower limit, the motor (10) is powered electrically only by a first regulator of the two regulators (6, 8) while above the lower limit, the motor (10) is powered electrically simultaneously by both regulators (6, 8). Abstract figure: FIGURE 1

Description

Title of the invention: Method for controlling an axial flux motor with variators.

[0001] The present invention relates to a method for controlling an axial flux motor comprising at least one rotor interposed between two stators electrically powered by at least one electrical current regulator.

[0002] It is known to use an axial flux motor comprising at least one rotor interposed between two stators, for example for the propulsion of an electric or hybrid means of transport, in particular but not only a motor vehicle.

[0003] Such an engine is subject to high losses, which can be verified during tests during a worldwide harmonized test procedure for passenger cars and light commercial vehicles, a test procedure also known by the English acronym WLTC.

[0004] Indeed, an electric motor for a means of transport is often designed to develop a maximum torque, this maximum torque being able to be for example 240 Nm or Newton.meter, such maximum torque making strong accelerations possible.

[0005] However, the engine, when used on a varied route, can also provide much lower torques, typically between 5% and 30% of its maximum torque. This can be verified during a WLTC homologation cycle.

[0006] The motor and elements attached to it, such as inverters for an AC electric motor, then produce losses over the entire cycle. The difficulty is that the losses of a motor are often linked to the size of the motor. However, to be able to provide a significant torque, often referred to as the maximum torque of the motor, fairly large volumes of active parts are required.

[0007] A large motor therefore generally produces more losses at low torque than a small motor because this large motor will have the capacity to provide a greater maximum torque. However, the torque of an electric motor is proportional to the volume of the active parts, essentially its rotor(s) and its stator(s). The total losses are also the image of the volume of the active parts.

[0008] The problem underlying the present invention is to design a motor group comprising a motor with at least one rotor interposed between two stators and its attached elements such as stator power supply current variators which can, on the one hand, provide a high maximum torque while reducing the losses inherent thereto for torques much lower than the maximum torque.

[0009] To this end, the present invention relates to a method for controlling an axial flux motor comprising at least one rotor interposed between two electrically powered stators. electrically by at least one electrical intensity variator, characterized in that the motor is supplied by two variators, the control of the motor being carried out according to a desired torque value at the output of the motor, a lower torque limit at the output of the motor being predetermined and, for a desired torque value below the lower limit, the electrical supply of the motor is carried out only by a first variator of the two variators while above the lower limit, the electrical supply of the motor is carried out simultaneously by the two variators.

[0010] The idea behind the present invention is to propose an architecture comprising an axial flux electric motor with two stators and a rotor, the electrical supply of the stators being controlled with two variators making it possible to reduce the total losses of the system at low torque.

[0011] An axial flux motor with two stators and a single rotor allows each stator to be powered independently in parallel. For example, instead of having a single drive capable of delivering, for example, 300 Amps or 300 A in total, two drives of 150 Amps each are used.

[0012] If the operating speed of a motor is most often between 5% and 30% of the maximum torque, and this, whatever the rotation speed of the motor, then it is more advantageous to use only one variator which will supply less than two variators working in common with the axial flux motor.

[0013] The consequence is that the total losses will be reduced, in particular by supplying a single stator due to the operation of a single variator.

[0014] When the torque requirement is greater, typically between 30% and 100% of the maximum torque, then the two variators can operate simultaneously in order to provide the necessary power to the motor.

[0015] The technical effect is therefore clearly to optimize the total consumption of the electrical system, both for low speeds corresponding to low engine torque, and for high speeds, therefore high torque.

[0016] For a hybrid transportation application, this can reduce carbon dioxide emissions.

[0017] For a purely electric means of transport application, this makes it possible to gain autonomy in the means of transport.

[0018] Advantageously, each variator electrically supplies a respective stator with, below the lower terminal, one of the two stators remaining not electrically supplied.

[0019] This represents the preferred embodiment of the present invention with a variator dedicated to each stator and suspending the electrical supply of one of the two stators.

[0020] These measures make it possible to no longer power a stator, hence a reduction in the active parts of which the stator is part, then not powered in the motor, and a reduction in losses.

[0021] It is the stopping of the electrical supply to one of the stators which is most conducive to a reduction in losses due to low torque. However, within the framework of the present invention, it is possible to envisage only significantly reducing the electrical supply to one of the two stators, which is not, however, preferred.

[0022] Advantageously, the lower limit is between 1 and 50% of the maximum torque of the motor, this corresponds to low torques conducive to an increase in losses, the motor being designed to be able to deliver significantly higher torques.

[0023] Advantageously, the lower limit is set between 5 and 30% of the maximum torque of the motor. As an example, for a motor with a maximum torque of 240 Nm when a torque of 40 Nm is required, this torque represents 17% of the maximum torque of the motor.

[0024] Advantageously, the two variators are of equal power while delivering the same maximum current value. This allows for symmetry of electrical power supply to the two stators.

[0025] The invention also relates to an axial flux motor group implementing such a control method, the motor group comprising an axial flux motor comprising at least one rotor interposed between two stators electrically powered by at least one electrical current variator, characterized in that the motor is powered by two variators, the control of the motor as a function of a desired torque value at the output of the motor being determined by a control unit of the variators also comprising memories for storing the maximum torque of the motor and a calculator of the lower terminal as a function of the maximum torque, the control unit managing the electrical power supplied by the variators to the motor with means for interrupting the electrical power supply of one of the two variators.

[0026] Advantageously, the motor is supplied with alternating current, each variator being integrated into an inverter associated respectively with a stator.

[0027] Advantageously, the stators comprise concentric windings comprising a series of pins with windings wound around each pin, the pins being secured to each other.

[0028] Advantageously, said at least one rotor of the motor comprises one or more magnet structures, the or each magnet structure being composed of a plurality of unit magnets in the form of pads extending along a thickness of the rotor, the or each magnet structure being arranged concentrically to the rotor.

[0029] The topology of an axial flux motor comprising two stators and a single highly pixelated rotor is particularly well suited for this type of architecture.

[0030] For an axial flux motor, one or more rotors of the prior art could comprise from 1 to 10 large magnets forming magnet poles whereas the present invention provides many more small magnets grouped in one or more magnet structures each forming a magnet pole.

[0031] It is important not to confuse a magnet pole, a rotor being able to carry for example five to ten or even more, with unit magnets which are significantly more numerous, a rotor being able to carry for example several hundred.

[0032] This provides a rotor which, among other advantages, can rotate at high speed and which does not include iron, which limits rotor losses. It has also been discovered that a plurality of unit magnets provides a magnet structure which is more resistant to overall rotor bending while producing very little heat due to the low losses generated, the heat dissipated by the unit magnets being less than the heat dissipated by a corresponding larger single-piece magnet.

[0033] Advantageously, each magnet structure forms a magnet pole comprising more than twenty unit magnets bonded by a resin electrically insulating them from each other or each inserted into a respective housing delimited by one of the meshes of a mesh.

[0034] Advantageously, each magnet structure is individually coated in a layer of composite.

[0035] This measure further enhances the mechanical strength of the magnet structure taken as a whole. The magnet pole-forming magnet structure can then be coated as a whole in a non-conductive composite layer in addition to the individual magnets being coated in a composite layer.

[0036] The invention finally relates to an electric or hybrid means of transport, characterized in that it comprises a motor unit as previously described.

[0037] The attached drawings illustrate the invention:

[0038] [Fig. 1] represents a schematic view of a motor group comprising an axial flux motor with a rotor interposed between two rotors, two variators and a control unit, such a motor group implementing a control method according to the present invention,

[0039] [Fig.2] represents a perspective view of an axial flux motor which may be part of a motor group according to the present invention, the rotor of the motor comprising magnet structures forming magnet poles and composed of unit magnets,

[0040] In [Fig.2], only one winding is referenced 5 but what is stated for this referenced winding is stated for all the windings. The same applies to a pin 4 on each stator, a unit magnet 15, a magnet structure 12 and a branch 14 of the rotor.

[0041] [Fig. 1] shows an axial flux motor group comprising an axial flux motor 10 comprising at least one rotor 3 interposed between two stators 1, 2 electrically powered by two electrical current variators 6, 8. The control of the motor 10 as a function of a desired torque value at the output of the motor 10 is determined by a control unit 9 of the variators 6, 8.

[0042] A lower output torque limit of the motor 10 is predetermined. This can be done by experience and depends on the type of motor 10. This lower limit corresponds to low output torques which result in losses, the motor 10 being oversized to operate at such low torques.

[0043] For a desired torque value below the lower limit, the motor 10 is supplied with power only by a first variator of the two variators 6, 8. This makes it possible to minimize losses.

[0044] Above the lower limit and until the maximum torque is obtained if desired, the electrical power supply to the motor 10 is carried out simultaneously by the two variators 6, 8 so that the motor 10 has its full power.

[0045] It is more judicious to allocate a variator 6, 8 to a respective stator 1, 2. In this case, each variator can electrically supply a respective stator. Below the lower limit, one of the two stators 1, 2 then remains not electrically supplied and therefore the volume of active parts of the motor 10 decreases as well as the losses at relatively low torque.

[0046] The lower limit can be between 1 and 50% of the maximum torque of the motor 10. This depends on the size of the motor 10. The larger the volume of the active parts of the motor 10, the more the lower limit will have to be raised to minimize losses at low torque.

[0047] Without this being limiting, the lower limit can be set between 10 and 30% of the maximum torque of the engine 10. The value of the lower limit can be determined during tests of the engine 10 on a bench.

[0048] For example, for the sake of argument and without this being limiting, for a motor 10 delivering a maximum torque of 240 Nm, it has been determined that under a low torque of 40 Nm it may be advantageous to stop the electrical supply to one of the two stators 1, 2 which gives a lower limit equal to 17% of the maximum torque of the motor 10.

[0049] The two variators 6, 8 can be of equal power while delivering the same maximum current value.

[0050] When the two variators 6, 8 are not of equal power, it is preferred that it is the variator of the lowest power which no longer supplies power.

[0051] In this particular case, it is also possible just below the lower limit that the lowest power variator no longer electrically supplies the motor 10. However, for even lower torques, the highest power drive can be switched off and replaced in the power supply by the lowest power drive, which will be sufficient to ensure such low torque.

[0052] As previously mentioned, the control of the motor 10 as a function of a desired torque value at the output of the motor 10 is determined by a control unit 9 of the variators 6, 8.

[0053] This control unit 9 comprises memories for storing the maximum torque of the engine 10 recorded during preliminary tests of the engine 10 and a calculator or means for calculating the lower limit as a function of the maximum torque still during preliminary tests on the engine 10.

[0054] The control unit 9 manages the electrical power supplied by the variators 6, 8 to the motor 10 with means for interrupting the electrical power supply from one of the two variators 6, 8 to the motor 10, advantageously and preferably to a dedicated stator, this at relatively low torque.

[0055] When the axial flux motor 10 is supplied with alternating current, each variator 6, 8 can be integrated into an inverter associated respectively with a stator 1, 2.

[0056] As visible in [Fig.2], the stators 1, 2 can comprise concentric windings 5 ​​by comprising a series of pins 4 with windings 5 ​​wound around each pin, the pins 4 being secured to each other.

[0057] The rotor 3 of the motor 10 may comprise one or more magnet structures 12.

[0058] The or each magnet structure 12 may be composed of a plurality of unit magnets 15 in the form of pads extending along a thickness of the rotor 3, the or each magnet structure 12 being arranged concentrically to the rotor 3.

[0059] Each magnet structure 12 can form a magnet pole by comprising more than twenty unit magnets 15 bonded by a resin electrically insulating them from each other or each inserted into a respective housing delimited by one of the meshes of a mesh.

[0060] Each magnet structure 12 may be individually coated in a layer of composite.

[0061] The or each rotor 3, in figures 1 and 2 a single rotor 3, may comprise magnet structures 12 forming magnet poles, each magnet structure 12 being composed of a plurality of unit magnets 15.

[0062] This means that there are magnet structures 12 forming distinct magnet poles but that each magnet structure 12 comprises a plurality of unit magnets 15, including a unit magnet referenced 15 in [Fig.2], this reference 15 being taken to qualify any unit magnet.

[0063] There may therefore be several magnet structures 12 but these magnet structures 12 cannot be assimilated to the plurality of unit magnets 15 which compose them in the meaning of the present invention.

[0064] In [Fig.2], an assembly of a rotor 3 and two stators 1, 2 is visible. On a first stator, threads 7 are visible for fixing each pin 4 to a disc-shaped support.

[0065] The winding 5 can be mounted on the pin 4 before assembly, before bringing the pins 4 into contact by their lateral edges and holding them by fixing means of the screw type passing through the threads 7 or by gluing or welding the first faces and / or respectively the second faces together, opposite the first faces and not visible in [Fig.2].

[0066] Without this being limiting, the rotor 3 is surrounded by an armature 18 comprising branches, only one of which is referenced 14, connecting a hub 19 to a hoop 13.

[0067] The presence of branches 14 on the rotor 3 is not an essential characteristic in the context of the present invention and a rotor 3 without branches can also be used.

[0068] The invention finally relates to an electric or hybrid means of transport comprising a motor unit as previously described. This means of transport can be of any kind, although an electric or hybrid motor vehicle is a preferred application for the present motor unit.

Claims

Claims

1. Motor group comprising an axial flux motor (10) comprising at least one rotor (3) interposed between two stators (1, 2) electrically powered by two electrical current variators (6, 8), a control of the motor (10) as a function of a desired torque value at the output of the motor (10) being determined by a control unit (9) of the variators (6, 8) also comprising memories for storing a maximum torque of the motor (10) and a calculator of a lower limit as a function of the maximum torque, the control unit (9) managing the electrical power supplied by the variators (6, 8) to the motor (10) with means for interrupting the electrical power supply of one of the two variators (6, 8) for a desired torque value below the lower limit while above the lower limit, the electrical power supply of the motor (10) is carried out simultaneously by the two variators (6, 8),characterized in that said at least one rotor (3) of the motor (10) comprises one or more magnet structures (12), the or each magnet structure (12) being composed of a plurality of unit magnets (15) in the form of pads extending along a thickness of the rotor (3), the or each magnet structure (15) being arranged concentrically to the rotor (3).,

2. Motor group according to the preceding claim, in which each variator electrically supplies a respective stator with, below the lower terminal, one of the two stators (1, 2) remaining not electrically supplied.

3. A power unit according to any preceding claim, wherein the lower limit is between 1 and 50% of the maximum torque of the motor (10).

4. Engine group according to the preceding claim, in which the lower limit is set between 5 and 30% of the maximum torque of the engine (10).

5. Motor group according to any one of the preceding claims, in which the two variators (6, 8) are of equal power while delivering the same maximum current value.

6. Motor group according to the preceding claim, in which the motor (10) is supplied with alternating current, each variator (6, 8) being integrated into an inverter associated respectively with a stator (1, 2).

7. Motor group according to any one of the preceding claims, in which the stators (1, 2) comprise concentric windings (5) in comprising a series of pins (4) with coils (5) wound around each pin, the pins (4) being secured to each other.

8. Motor group according to any one of the preceding claims, in which each magnet structure (15) forms a magnet pole by comprising more than twenty unit magnets (15) bonded by a resin electrically insulating them from each other or each inserted in a respective housing delimited by one of the meshes of a mesh.

9. A motor unit according to any preceding claim, wherein each magnet structure (12) is individually coated in a layer of composite.

10. Electric or hybrid means of transport, characterized in that it comprises a motor unit according to any one of the preceding claims.

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