Method for calculating operating setpoints for first motor and second motor of same vehicle

Abstract

The invention relates to a method for calculating operating setpoints for a first motor (2) and a second motor (3) of the same vehicle (1), comprising: a step (SI) of calculating the thickness (eP) of an oxide film formed on the surface of the ring of the second motor; and a step (S4) of calculating the operating setpoints (RC2M1, RC2M2) of the first and second motors according to a strategy intended to cause a current to flow in the energizing means to promote regeneration of the oxide film if the thickness of the oxide film is strictly less than the threshold value.

Description

Technical Field

[0001] The present invention relates to a method for calculating drive torque set values for a first motor and a second motor of the same vehicle, the second motor being an electric motor comprising an energization device including a ring and a brush rubbing on the ring. Background Art

[0002] Certain vehicles, especially certain motor vehicles, include two drive motors: a main motor and an auxiliary motor. When low or medium torque is required, the main motor has sufficient power to drive the vehicle. For example, the power of the main motor is sufficient to keep the motor vehicle at a stable speed on a highway and / or to drive the vehicle without strong acceleration. The auxiliary motor is an electric assist motor configured to provide additional power when necessary. For example, the auxiliary motor can be enabled to help the vehicle climb a hill and / or achieve greater acceleration (e.g., when overtaking or driving the vehicle in a sport mode).

[0003] When the required drive torque is low enough to be sufficient to be transmitted by the main motor, only the main motor is enabled to achieve better energy efficiency. In this case, the auxiliary motor is thus not energized. However, the rotor of the auxiliary motor that is mechanically linked to the vehicle's wheels continues to rotate.

[0004] It is known to use a wound-rotor synchronous motor for the auxiliary motor. To enable such an electric motor, current must be supplied to its rotor. For this purpose, the wound-rotor synchronous motor includes a power device for energizing the rotor, the power device including a ring and a brush rubbing on the ring. The performance of such motors is advantageous. However, it has been observed that if the rotors of these motors rotate when not energized, these motors will be quickly damaged. Thus, when the vehicle is used for a long period of time in a manner that does not require enabling the auxiliary motor, the auxiliary motor may be damaged. Summary of the Invention

[0005] The object of the present invention is to provide a method for calculating operating set values for a first motor and a second motor of the same vehicle, which method overcomes the above disadvantages and improves the known prior art methods.

[0006] More precisely, a first subject of the present invention is a method for calculating operating set values for a first motor and a second motor of the same vehicle, which method makes it possible to prevent the second motor from being damaged.

[0007] The present invention relates to a method for calculating operating set values for a first motor and a second motor of the same vehicle, the second motor being an electric motor including a rotor and a power device for energizing the rotor, the energization device including at least one ring and at least one brush rubbing on the at least one ring, the calculation method comprising:

[0008] - A step of calculating the thickness of the oxide film formed on the surface of the at least one ring, and then

[0009] - A step of comparing the oxide film thickness with a first threshold value, and then

[0010] - If the oxide film thickness is greater than or equal to the first threshold value, a step of calculating the operating set values of the first motor and the second motor according to a first strategy aimed at optimizing the power consumption of the vehicle, and

[0011] - If the oxide film thickness is strictly less than the first threshold value, a step of calculating the operating set values of the first motor and the second motor according to a second strategy, which is different from the first strategy and is aimed at causing a current to flow through the energizing device to promote the regeneration of the oxide film.

[0012] The step of calculating the operating set values of the first motor and the second motor according to the second strategy may include calculating a torque set value of the second motor, which is equal to the minimum value between:

[0013] - The driving torque required by the vehicle,

[0014] - The maximum torque that the second electric motor can transmit, and

[0015] - The maximum torque that allows maintaining a stable vehicle path.

[0016] The oxide film thickness can be calculated iteratively based on the oxide film thickness calculated in a previous iteration of the step of calculating the oxide film thickness and on the change in the oxide film thickness itself calculated depending on the operating conditions of the second motor.

[0017] The operating conditions of the second motor may include:

[0018] - Data related to the speed of the second motor,

[0019] - Data related to the exciting current of the rotor of the second motor, and

[0020] - Data related to the ambient temperature.

[0021] The step of calculating the oxide film thickness may include:

[0022] - A sub-step of calculating the temperature at the interface between the at least one ring and the at least one brush, and / or

[0023] - A sub-step of calculating the humidity at the interface between the at least one ring and the at least one brush.

[0024] The first motor may be configured to drive the front wheels of the vehicle, and the second motor may be configured to drive the rear wheels of the vehicle.

[0025] After the step of calculating the operating set values of the first motor and the second motor according to the second strategy, the calculation method may include:

[0026] - After the operating period of the second motor according to the second strategy, a step of calculating the thickness of the second oxide film formed on the surface of the at least one ring,

[0027] - A step of comparing the thickness of the second oxide film with a second threshold that is strictly greater than the first threshold, and then

[0028] - If the thickness of the second oxide film is strictly greater than the second threshold, a step of calculating the operating set values of the first motor and the second motor according to the first strategy.

[0029] If the thickness of the oxide film is strictly less than the third threshold, the step of calculating the operating set values of the first motor and the second motor according to the second strategy may include calculating the energization current of the rotor and the energization current of the stator of the second motor to promote the regeneration of the oxide film at the expense of the efficiency of the second motor.

[0030] The third threshold may be equal to the first threshold, or the third threshold may be strictly less than the first threshold.

[0031] The present invention also relates to a motor vehicle, which includes a first motor and a second motor, the second motor being an electric motor, the electric motor including a rotor and power means for energizing the rotor, the energization means including at least one ring and at least one brush rubbing on the at least one ring, the vehicle further including hardware and software devices configured to implement the calculation method as defined above.

[0032] The present invention also relates to a computer program product, which includes program code instructions recorded on a computer-readable medium, and these program code instructions are used to implement the steps of the calculation method as defined above when the program runs on a computer.

[0033] The present invention also relates to a computer-readable data recording medium, on which a computer program is recorded, the computer program including program code instructions for implementing the calculation method as defined above.

[0034] The present invention also relates to a signal of a data medium, which carries the computer program product as defined above. Description of the Drawings

[0035] These objects, features and advantages of the present invention will be described in detail in the following description of a specific embodiment given without limitation with reference to the accompanying drawings, in which:

[0036] Figure 1 ​is a schematic view of a motor vehicle according to an embodiment of the present invention.

[0037] Figure 2 is a block diagram of a method for calculating operating setpoints for a first motor and a second motor of the same vehicle according to an embodiment of the present invention.

[0038] Figure 3 is an overview diagram of a method for calculating operating setpoints for a first motor and a second motor of the same vehicle according to an embodiment of the present invention. Detailed Description

[0039] Figure 1 shows schematically a sectional view of a vehicle 1 according to an embodiment of the present invention. In particular, the vehicle 1 is a motor vehicle, such as a passenger car, a commercial vehicle, a truck or even a bus. The vehicle 1 includes two motors 2, 3 which are capable of driving the rotation of the vehicle's wheels 4A, 4B so as to move the vehicle forward. In this example, the first motor 2 is coupled to the front wheels 4A of the vehicle and the second motor 3 is coupled to the rear wheels 4B of the vehicle. As a variant, this configuration can be reversed, i.e., the second motor 3 can be coupled to the front wheels and the first motor 2 can be coupled to the rear wheels. According to other variants, any other arrangement of coupling the first motor and the second motor to all or some of the vehicle's wheels can be envisaged. The first motor 2 can be referred to as the main motor and the second motor 3 can be referred to as the auxiliary motor. The second motor can be mainly intended to provide additional drive torque to the vehicle, for example to make the vehicle accelerate quickly.

[0040] The second motor 3 is an electric motor which includes a stator 5 and a rotor 6 which is mounted to be rotatable relative to the stator about a rotation axis 7. In particular, the second motor 3 is a wound-rotor synchronous motor. Thus, the rotor 6 of the second motor 3 must be energized. For this purpose, the second motor includes an electric power energizing device 8 which includes at least one ring 9 and at least one brush 10 which is fixed to the housing of the second motor 3 and rubs on the at least one ring 9. In this example, the energizing device 8 includes two rings 9 and two brushes 10 which rub on each ring respectively. In particular, the two rings 9 can be mounted on a shaft 11 which is fixed to the rotor 6 and is supported by bearings 12. The rings 9 include on their surface an oxide layer which is commonly referred to as a "patina" and which promotes the flow of current between the ring and the brush by reducing the voltage drop. Such an oxide layer can be formed in particular during the running-in phase of the second motor.

[0041] ​​​The vehicle 1 further includes an electronic control device 13, which is equipped with a memory 14, a microprocessor 15, and a power stage 16. The electronic control device 13 is configured to pass a current to energize the rotor 6 according to a set value calculated by the microprocessor 15. In Figure 1 , the electrical connection between the electronic control device 13 and the brush 10 is represented by a solid line 16. The mechanical link connecting the rear wheel 4B to the shaft 7 is represented by a dashed line 17 per se.

[0042] In addition, the stator 5 can also be energized by the electronic control device 13. A given balance between the rotor energizing current and the stator energizing current allows optimizing the efficiency of the second motor 3.

[0043] The first motor 2 can also be an electric motor, and even a wound-rotor synchronous motor. The first motor 2 can be similar to or even the same as the second motor 3. Like the second motor, the stator and rotor of the first motor can be energized by the electronic control device 13. The rotor of the first motor 2 is mechanically connected to the front wheel 4A.

[0044] The memory 14 of the electronic control device 13 is a data recording medium on which a computer program is recorded, and the computer program includes program code instructions for implementing a method for calculating the operating set values of the first motor 2 and the second motor 3 according to an embodiment of the present invention. The microprocessor 15 is capable of executing this computer program. Now, an embodiment of this calculation method will be described with reference to Figure 2 and Figure 3 .

[0045] The calculation method first includes a first step S1, in which the thickness of the oxide film formed on the surface of the ring 9 is calculated. The thickness of the oxide film can be iteratively calculated according to the thickness of the oxide film calculated in the previous iteration of the first step S1 and according to the usage conditions of the second motor 3. Therefore, an initial value of the oxide film thickness is required to start the method. Thus, the usage conditions of the second motor allow calculating the change in the oxide film thickness.

[0046] In a first sub-step S11, the usage conditions are acquired. These usage conditions can be provided directly or indirectly, for example, by sensors embedded in the vehicle. In particular, these usage conditions include:

[0047] - Data CU1 related to the speed of the second motor, that is, data characterizing the rotational rate of the rotor relative to the stator;

[0048] - Data CU2 related to the excitation current of the rotor 6 of the second motor 3, especially the value of the current amplitude flowing through the rotor 6; and

[0049] - Data CU3 related to the ambient temperature, such as the atmospheric temperature in the vehicle environment.

[0050] These three data, CU1, CU2, and CU3, are passed as inputs to the thermal model MT of the second motor 2. In the second sub-step S12, the thermal model MT calculates the temperature T at the interface between the ring 9 and the brush 10.

[0051] The data CU3 related to the ambient temperature is passed as an input to the humidity computer CH. In the third sub-step S13, the humidity computer CH calculates the absolute humidity H (or in other words, the humidity level) at the interface between the ring 9 and the brush 10. According to one embodiment of the present invention, this humidity level can be calculated based only on the data CU3 related to the ambient temperature. As a variant, the data transmitted by a humidity sensor and / or meteorological data CU4 obtained via a wireless communication network, for example, can be used to refine this calculation.

[0052] Then, the temperature T and the humidity H are passed as inputs to the computer CdP for the change in oxide film thickness. In the fourth sub-step S14, this computer CdP then calculates the change dP in the oxide film thickness based on the temperature T and the humidity H. If the operating conditions of the second motor 2 are favorable for the regeneration of the oxide film, the change dP in the oxide film thickness can be positive, or if the operating conditions of the second motor 2 are unfavorable for the regeneration of the oxide film, the change in the oxide film thickness can be negative. In addition, predictive navigation data (provided by a navigation system) can also be used to estimate the change in the oxide film thickness at the end of the vehicle usage period. The thermal model MT and / or the humidity computer and / or the computer CdP can include interpolation maps and / or functions in order to calculate the temperature T, the humidity H, and the change dP in the oxide film thickness, respectively.

[0053] Then, the change dP in the oxide film thickness is passed as an input to the computer CeP for the oxide film thickness. In the fifth sub-step S15, the computer CeP calculates the effective oxide film thickness eP on the surface of the ring. This calculation can be performed by adding the previously calculated change dP in the oxide film thickness to the previous value of the oxide film thickness calculated in the previous iteration of step S1. Thus, at the end of the first step S1, an estimated value of the oxide film thickness currently formed on the surface of the ring 9 is obtained.

[0054] Next, in the second step S2, the previously calculated oxide film thickness eP is compared with a first threshold Se1. The first threshold Se1 is preferably a predefined value recorded in the memory 14 of the electronic control device 13. This first threshold can be set during a previous calibration phase of the vehicle. Next, according to the comparison result between the oxide film thickness eP and the first threshold Se1, two results may occur.

[0055] According to the first result, if the thickness eP of the oxide film is greater than or equal to the first threshold Se1 (or in other words, if it is judged that the thickness of the oxide film is large enough without the risk of damaging the second motor 3), then in the third step S3, the operating set values of the first motor and the second motor are calculated according to the first strategy aimed at optimizing the power consumption of the vehicle 1. This first strategy can be consistent with the conventional management strategy of a vehicle equipped with two motors. In particular, if the torque request is less than or equal to the capacity of the first motor (i.e., the maximum torque of the first motor), then this strategy only enables the first motor 2. In this case, the second motor is therefore not enabled, and in particular, no current flows through the energizing device 8. However, the rotor 6 of the second motor is driven to rotate due to its mechanical connection to the wheel 4B of the vehicle. Therefore, the brush 10 rubs against the ring 9 without current flowing through this interface. This operating mode tends to increase the temperature at the interface between the ring 9 and the brush 10, thus deteriorating the oxide film, in particular reducing the thickness of the oxide film. However, this is not disadvantageous because the thickness eP of the oxide film is sufficient to withstand this operating mode at least until the next iteration of the method. Of course, according to this first strategy, if the torque request exceeds the capacity of the first motor 2, the second motor 3 can be enabled.

[0056] According to the second result, if the thickness eP of the oxide film is strictly less than the first threshold Se1, then in the fourth step S4, the operating set values of the first motor and the second motor are calculated according to a second strategy different from the first strategy, and this second strategy is aimed at making current flow through the energizing device to promote the regeneration of the oxide film. Therefore, this operating strategy is not aimed at optimizing the power consumption of the vehicle. On the contrary, this operating strategy has lower energy efficiency than the first strategy, but its advantage is that it allows the regeneration of the oxide film (i.e., restoring the oxide film to the surface of the ring 9). In particular, according to this second strategy, even if the torque request is less than or equal to the capacity of the first motor 2, the second motor 3 is forced to start. Therefore, the required torque can be transmitted jointly by the first motor 2 and the second motor 3, or even only by the second motor 3. Therefore, current flows through the energizing device 8, thus allowing the regeneration of the oxide film.

[0057] The third step S3 and the fourth step S4 control the operation of the first motor 2 and the second motor 3. In particular, steps S3 and S4 may include calculating the torque request for each of the motors 2 and 3. In Figure 2 , for the first strategy, these torque requests for the first motor and the second motor are represented by the reference numerals RC1_M1 and RC1_M2 respectively. For the second strategy, the torque requests are represented by the reference numerals RC2_M1 and RC2_M2 respectively. Alternatively, these steps may also include calculating any quantity related to the torque request, such as calculating the magnitude and / or voltage of the control current of the motors 2 and 3.

[0058] For both the first and second strategies, the control commands sent to motors 2 and 3 can be weighted according to the dynamic stability requirements of the vehicle. In particular, if the torque request is too high relative to the adhesion conditions between the vehicle and the road, the torque request can be limited in any case to avoid vehicle out of control.

[0059] If the oxide film thickness is strictly less than the first threshold Se1, the torque setpoint RC2_M2 of the second electric motor can be equal to the minimum between:

[0060] - the drive torque required by the vehicle, in particular the torque setpoint expressed by the vehicle's driver by depressing the accelerator pedal,

[0061] - the maximum torque that the second electric motor can transmit, and

[0062] - the maximum torque that allows the vehicle path to be maintained stably.

[0063] Thus, if the required torque is less than or equal to the maximum torque that the second electric motor 3 can transmit, only the second motor is enabled to generate the required torque, provided that the adhesion conditions between the vehicle and the ground are met to ensure a stable path. If the required torque is strictly greater than the maximum torque that the second electric motor 3 can transmit, the second motor is enabled at its maximum power, and then the torque difference between the required torque and the maximum torque of the second motor is transmitted by the first motor.

[0064] Similarly, if the oxide film thickness is greater than or equal to the first threshold Se1, the torque setpoint RC1_M1 of the first electric motor can be equal to the minimum between:

[0065] - the drive torque required by the vehicle, in particular the torque setpoint expressed by the vehicle's driver by depressing the accelerator pedal,

[0066] - the maximum torque that the first electric motor can transmit, and

[0067] - the maximum torque that allows the vehicle path to be maintained stably.

[0068] If the required torque is strictly greater than the maximum torque that the first electric motor 2 can transmit, the first motor is enabled at its maximum power, and then the torque difference between the required torque and the maximum torque of the first motor is transmitted by the second motor.

[0069] When the first and second motors control different axles (as is the case in the presented embodiment), choosing one strategy or the other causes the drive function of the vehicle to move from one axle to the other. For the user of the vehicle, this movement may be imperceptible or only slightly perceptible. Advantageously, in order to avoid changing strategies too frequently, the method may include a hysteresis loop. More precisely, following step S4, the method may include a fifth step S5 of calculating a second oxide film thickness eP2 formed on the surface of the at least one ring following the operating period of the second motor according to the second strategy. This calculation may be carried out in particular by an oxide film thickness computer CeP2, which is identical or similar to the oxide film thickness computer CeP described above. In particular, the calculation of the second oxide film thickness eP2 may be based on the torque setpoint RC2_M2 previously transmitted to the second motor. Next, in a sixth step S6, the second oxide film thickness eP2 is compared with a second threshold Se2 that is strictly greater than the first threshold Se1. If the oxide film thickness is strictly greater than the second threshold Se2 (i.e., if the oxide film on the surface of the ring 9 is sufficiently regenerated), then the operating setpoints of the first and second motors may be calculated according to the first strategy in accordance with the third step S3. Conversely, if the oxide film thickness is less than or equal to the second threshold Se2 (i.e., if the oxide film regeneration on the surface of the ring 9 is insufficient), then the operating setpoints of the first and second motors may be calculated according to the second strategy in accordance with the third step S3.

[0070] According to another improvement of the invention, the fourth step S4 may include a sub-step E41 in which the energization currents of the rotor and the stator of the second motor are calculated to promote the regeneration of the oxide film at the expense of the efficiency of the second motor. In other words, it is a matter of defining the energization currents of the rotor and the stator, the aim of which is not the optimal power consumption or the optimal efficiency of the second motor 3, but rather the operation of the second motor that allows the oxide film to be regenerated further accelerated. Specifically, the operation of the second motor 3 is controlled via the energization currents of the rotor and the stator. These energization currents are typically set via a map specific to the second motor to achieve a certain balance so that the second motor operates with the best possible efficiency. This map includes a set of parameters, the values of which are preset during the commissioning phase of the motor. The improvement to the invention proposed here involves generating a second map for the second motor that is different from the first map, the aim of which is not to target the best efficiency but rather to target better regeneration of the oxide film. This can be obtained, for example, by modifying the balance between the energization current of the rotor and the energization current of the stator. The advantage of this improvement is that it allows the oxide film to be regenerated even more effectively; however, this improvement requires a second commissioning of the motor and sufficient computing and memory resources to implement the improvement.

[0071] When the previously calculated oxide film thickness eP is strictly less than the third threshold, sub-step S41 can be implemented. According to the first option, this third threshold can be equal to the first threshold Se1. Thus, once the oxide film thickness is strictly less than the first threshold Se1, sub-step S41 is systematically implemented. Therefore, the calculation method remains quite simple to implement. Alternatively, according to the second option, this third threshold can be strictly less than the first threshold Se1. Thus, sub-step S41 is implemented only when the rotor energization current and the stator energization current for the purpose of optimal power consumption to actuate the second motor are not sufficient to regenerate the oxide film. Therefore, this second option, which would reduce the efficiency of the second motor, is implemented only as a last resort.

[0072] Finally, with the aid of the present invention, it is ensured that the oxide film thickness of the second motor never becomes too small, because too small an oxide film thickness may cause damage to the second motor. Thus, the reliability of the second motor is improved. Although the vehicle sometimes operates in an operating mode different from the operating mode allowing optimal efficiency, the overall efficiency is improved because the lifespan of the vehicle is extended. In addition, the proposed calculation method is easy to implement and requires limited computing resources. The present invention can be advantageously applied to any transport vehicle including two motors, at least one of which is a wound-rotor synchronous electric motor.

Claims

1. A method for calculating operating setpoints of a first motor (2) and a second motor (3) of the same vehicle (1), the second motor (3) being an electric motor comprising a rotor (6) and power means (8) for energizing the rotor, the energizing means comprising at least one ring (9) and at least one brush (10) rubbing on the at least one ring, the calculation method comprising: - a step (S1) of calculating the thickness (eP) of an oxide film formed on the surface of the at least one ring, and then - a step (S2) of comparing the oxide film thickness with a first threshold (Se1), and then - if the oxide film thickness is greater than or equal to the first threshold, a step (S3) of calculating the operating setpoints (RC1_M1, RC1_M2) of the first motor and the second motor according to a first strategy aimed at optimizing the power consumption of the vehicle, and - if the oxide film thickness is strictly less than the first threshold, a step (S4) of calculating the operating setpoints (RC2_M1, RC2_M2) of the first motor and the second motor according to a second strategy, the second strategy being different from the first strategy and aimed at passing a current through the energizing means to promote the regeneration of the oxide film.

2. The calculation method according to the previous claim, characterized in that, The step (S4) of calculating the operating setpoints of the first motor and the second motor according to the second strategy comprises calculating a torque setpoint of the second motor (3), the torque setpoint being equal to the minimum of: - the driving torque required by the vehicle, - the maximum torque that the second electric motor can transmit, and - the maximum torque that allows the vehicle path to be maintained stably.

3. The calculation method according to any one of the preceding claims, characterized in that, The oxide film thickness (eP) is calculated iteratively based on the oxide film thickness calculated in a previous iteration of the step of calculating the oxide film thickness and on the variation (deP) of the oxide film thickness itself calculated depending on the operating conditions (CU1, CU2, CU3, CU4) of the second motor (3).

4. The calculation method according to the previous claim, characterized in that, The said operating conditions of the second motor (3) include: - data (CU1) related to the speed of the second motor, - data (CU2) related to the excitation current of the rotor of the second motor, and - data (CU3) related to the ambient temperature.

5. The calculation method according to any one of the preceding claims, characterized in that, The step (S1) of calculating the oxide film thickness comprises: - a sub-step (S12) of calculating the temperature (T) at the interface between the at least one ring (9) and the at least one brush (10), and / or - a sub-step (S13) of calculating the humidity (H) at the interface between the at least one ring (9) and the at least one brush (10).

6. The calculation method according to any one of the preceding claims, characterized in that, The first motor (2) is configured to drive the front wheels (4A) of the vehicle, and the second motor (3) is configured to drive the rear wheels (4B) of the vehicle.

7. The calculation method according to any one of the preceding claims, characterized in that Following the step (S4) of calculating the operating setpoints of the first motor and the second motor according to the second strategy, the calculation method comprises: - a step (S5) of calculating a second oxide film thickness (eP2) formed on the surface of the at least one ring (9) following the operating period of the second motor (3) according to the second strategy, - Step (S6) of comparing the second oxide film thickness with a second threshold (Se2) that is strictly greater than the first threshold (Se1), and then - If the second oxide film thickness (eP2) is strictly greater than the second threshold, step (S3) of calculating the operating set values of the first motor and the second motor according to the first strategy.

8. The calculation method according to any one of the preceding claims, characterized in that, If the oxide film thickness (eP) is strictly less than a third threshold, the step (S4) of calculating the operating set values of the first motor and the second motor according to the second strategy includes calculating the energization current of the rotor (6) and the energization current of the stator (5) of the second motor to promote the regeneration of the oxide film at the expense of the efficiency of the second motor.

9. The calculation method according to the previous claim, characterized in that The third threshold is equal to the first threshold (Se1), or the third threshold is strictly less than the first threshold (Se1).

10. A motor vehicle (1) comprising a first motor (2) and a second motor (3), the second motor being an electric motor comprising a rotor (6) and power means (8) for energizing the rotor, the energizing means comprising at least one ring (9) and at least one brush (10) rubbing on the at least one ring, the vehicle further comprising hardware and software means (13, 14, 15, 16) configured to implement the calculation method according to any one of the preceding claims.

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