Method for compensating braking torque when a short circuit fault occurs in a power inverter of an auxiliary motor

Abstract

A method for driving a vehicle power steering system when a short-circuit type fault is detected between the phases (U, V, W) of an auxiliary motor and the electrical wires (16) of an inverter (1) that supplies power to said auxiliary motor (2), said power steering system comprising a steering wheel and said inverter (1), characterized in that it comprises: a configuration step for determining the controllable region (ZC) and the uncontrollable region (ZNC) of the magnetic field of said auxiliary motor (2); a compensation step for compensating the spatially averaged braking torque in said controllable region.

Description

Technical Field

[0001] This invention relates to the field of power steering systems for vehicles, and more specifically to a method for driving a power steering system when a short-circuit fault occurs between the phase of the auxiliary motor and the power line of the inverter. Background Technology

[0002] The purpose of a vehicle's power steering system is to allow the driver to control the vehicle's trajectory by applying force to the steering wheel.

[0003] Generally, a steering system consists of several components, including the steering wheel connected to the steering column, a rack, and two wheels, each connected to a rod. The rack is the component that connects the steering wheel to the wheels via the steering column and rods; that is, the rack converts the force applied by the driver to the steering wheel into rotation of the vehicle's wheels.

[0004] Electric power steering systems in vehicles use an auxiliary motor driven by a steering computer to reduce the force required for the driver to turn the vehicle's wheels on the steering wheel. Based on the force applied to the steering wheel, i.e., the steering wheel torque, the auxiliary motor applies an auxiliary force, i.e., the motor torque, to the rack, thereby turning the wheels.

[0005] Subsequently, in the following description, the auxiliary motor will be considered as a three-phase synchronous motor having an excitation rotor or permanent magnet powered by three phases represented by U, V and W respectively.

[0006] The inverter comprises three power lines. Each section of the wires associated with the inverter ground is considered the "low-voltage side," while each section of the wires associated with the inverter power supply is considered the "high-voltage side." According to figures known to those skilled in the art, each wire includes a first switching unit of MOSFET type in the "low-voltage side" section, referred to as the "low-voltage side," and includes a second switching unit of MOSFET type in the "high-voltage side" section, referred to as the "high-voltage side."

[0007] Each phase of the auxiliary motor is supplied by the inverter's wiring. More specifically, each phase is connected to the wiring between the "low-voltage side" switching unit and the "high-voltage side" switching unit.

[0008] The inverter determines the rotation direction, speed, and torque of the auxiliary motor.

[0009] During the operation of the power steering system, a short-circuit fault may occur between a phase of the auxiliary motor and a wire of the inverter. This type of fault typically occurs when the switching unit malfunctions.

[0010] When a short-circuit fault is detected in the power steering system, the auxiliary motor will no longer be driven by the inverter, which is in a deactivated state (i.e., all switching units are no longer affected by voltage).

[0011] Then, during the rotation of the motor, an electric current is generated by the electrodynamic force, resulting in braking torque at the auxiliary motor level. Therefore, by increasing the force required for the driver to turn the steering wheel, the braking torque acts in the opposite direction to the steering wheel's rotation. Thus, the driver will experience a feeling similar to the steering wheel being blocked.

[0012] The supplier prevents the generation of braking torque by adding an open-circuit circuit to the phase of the auxiliary motor. This circuit primarily consists of electromechanical or static relays, which increases the cost, size, and grounding of the power steering system. Furthermore, these additional relays increase the risk of material failure, thus reducing the overall reliability of the power steering system. Summary of the Invention

[0013] The object of this invention is to remedy all or part of the aforementioned disadvantages and to provide a method for driving a vehicle power steering system when a short-circuit fault is detected between the phase of an auxiliary motor and the wiring of an inverter supplying power to the auxiliary motor, the power steering system comprising a steering wheel and an inverter, characterized in that it comprises:

[0014] The configuration steps are used to determine the controllable and uncontrollable regions of the magnetic field of the auxiliary motor.

[0015] The compensation step is used to compensate for the spatial average braking torque in the controllable region.

[0016] The auxiliary motor connected to the inverter consists of three phases. A short-circuit fault can cause a phase of the auxiliary motor to come into contact with either the "low-voltage side" or "high-voltage side" portion of the inverter wiring. Therefore, the phase associated with the fault can no longer guarantee normal power supply to the auxiliary motor; that is, the phase can no longer be monitored to generate a uniform magnetic field for the auxiliary motor. However, two other phases continue to operate normally.

[0017] Therefore, short-circuit faults prevent the monitoring of the auxiliary motor's magnetic field throughout the entire electrical cycle. Controllable and uncontrollable regions can then be defined within the electrical cycle, characterized by electrical angles that depend on the short-circuit phase, the "low-voltage side" or "high-voltage side" portion of the short circuit, and the direction and speed of the auxiliary motor.

[0018] The configuration steps transmit the characteristics of the controllable and uncontrollable regions through the output signal.

[0019] In addition, braking torque is caused by a short-circuit fault due to the electromotive force generated during the rotation of the auxiliary motor.

[0020] Spatially averaged braking torque refers to the braking torque applied to the auxiliary motor on average during an electrical cycle. More generally, spatially averaged quantities are defined as the average electrical quantity of the auxiliary motor during an electrical cycle. These spatial averages are only meaningful while the auxiliary motor is rotating.

[0021] Therefore, the method includes driving an auxiliary motor with an average motor torque to provide an average motor torque in the controllable region that is significantly greater than the braking torque applied in the uncontrollable region. In the controllable region, the average motor torque is greater than or equal to the average motor torque applied under normal conditions based on the steering wheel torque, which is supplemented by an estimated spatially average braking torque. In the uncontrollable region, only braking torque is applied.

[0022] The estimated spatial average braking torque can have a fixed or variable value, depending on whether the power steering system includes open-loop or closed-loop monitoring.

[0023] In open-loop monitoring, the estimated spatial average braking torque is assumed to be a constant value; for example, it can roughly correspond to the maximum spatial average braking torque that can be applied to the auxiliary motor. In reality, when the estimated spatial average braking torque is fixed, the additional average motor torque (corresponding to the difference between the assumed constant spatial average braking torque and the actual spatial average braking torque) will be partially dissipated in the subsequent uncontrollable region through the combination of the actual spatial average braking torque and the rack force acting in the opposite direction of motion.

[0024] Under closed-loop monitoring, the estimated spatial braking torque is calculated based on the measured values ​​of phase current and electrical angle. When calculating the spatial average braking torque, the average motor torque provided in the controllable region is at least equal to the braking torque applied in the uncontrollable region.

[0025] Therefore, the motor torque, and consequently the steering wheel torque, is not uniform during the electrical cycle, but rather exhibits variations between controllable and uncontrollable regions. However, using the described method, the driver will not perceive any resistance in the steering wheel. The driver can then position the vehicle in a safe location before any maintenance is required.

[0026] According to one feature of the invention, the method includes an activation step of comparing the rotation direction of the steering wheel with the rotation direction of the auxiliary motor.

[0027] A short-circuit fault will degrade the normal operation of the auxiliary motor, preventing it from automatically transitioning from a static state to a rotating state. The auxiliary motor must be "started" by the driver turning the steering wheel or by the vehicle naturally returning to its original position, meaning it must enter a rotating state. At low speeds, the average braking torque is very low and insensitive to the driver.

[0028] The activation step confirms that the steering wheel rotation direction is the same as the auxiliary motor rotation direction in order to authorize the execution of the compensation step.

[0029] Therefore, the compensation step is only performed when the auxiliary motor is already rotating in the same direction as the steering wheel to support the driver's steering intention.

[0030] According to a feature of the invention, the activation step compares the steering wheel torque and / or the speed of the auxiliary motor with a predetermined threshold.

[0031] This method induces variations in motor torque and, consequently, steering wheel torque between controllable and uncontrollable regions. However, at high steering wheel torque and / or high speeds of the auxiliary motor, i.e., above a predetermined threshold, the variation in steering wheel torque feel is reduced. In fact, the frequency of variation in steering wheel torque feel is directly proportional to the speed of the auxiliary motor.

[0032] Furthermore, variations in the perceived steering wheel torque are reduced through the power steering system's reduction gear and the inherent torsion of certain components. Increasing the number of pole pairs in the auxiliary motor, reducing the stiffness of the power steering system, or increasing the reduction ratio are advantageous parameters for improving the uniformity of the steering wheel torque feel.

[0033] Therefore, by considering a short circuit between one phase of the auxiliary motor and the inverter's wiring, while other phases and other wiring operate normally, this method ensures that the perceived steering wheel torque is substantially uniform. The perceived steering wheel torque is even more uniform when the estimated spatial braking torque is variable.

[0034] According to the features of the present invention, the configuration step determines two phases of the auxiliary motor that are unaffected by faults.

[0035] Therefore, in the case of short-circuit faults, the method adopts the same strategy, but uses different configuration parameters according to the characteristics of the fault, namely the fault phase and the wire section.

[0036] According to the features of the present invention, the compensation step includes:

[0037] The stage of detecting the relative electrical position of the auxiliary motor with respect to the controllable area.

[0038] The stage of determining the spatial average motor torque based on the measured steering wheel torque.

[0039] The stage of converting spatially averaged motor torque into instantaneous motor torque.

[0040] The stage of controlling the phase current of the auxiliary motor.

[0041] The detection phase receives the measured electrical angle, the measured rotational speed of the auxiliary motor, and data relative to the controllable and uncontrollable regions determined by the configuration step as input.

[0042] Preferably, the detection phase determines the unsigned electrical position of the auxiliary motor relative to the entrance of the controllable area.

[0043] During the testing phase, the direction of the steering wheel torque is also defined based on the rotation direction of the auxiliary motor. This direction of the steering wheel torque can be used to switch the inverter to be used.

[0044] We refer to the inverter switches as a set of positions for the inverter's six switching units. A switching unit can be in an open or closed position.

[0045] The determination phase allows the space-average motor torque to be applied to the auxiliary motor to be estimated based on the measured steering torque.

[0046] The conversion phase receives the spatial average motor torque and the relative electrical position of the auxiliary motor as inputs in order to determine the instantaneous motor torque to be applied to the auxiliary motor.

[0047] Finally, the control phase receives the instantaneous motor torque, the direction of the auxiliary torque, and the phase of the auxiliary motor that has not degraded due to the fault, thereby controlling the auxiliary motor via two functional phases. The role of the control phase is to reproduce the distribution of the instantaneous motor torque in the controllable region by vector monitoring of the current in the Park / Clarke reference marker, as is known to those skilled in the art.

[0048] According to one feature of the invention, the detection phase triggers the implementation of a phase for determining the spatial average motor torque.

[0049] Therefore, the detection phase allows for the execution of specific steps each time the auxiliary motor enters the controllable area.

[0050] According to one feature of the invention, the conversion stage realizes a setpoint curve representing the instantaneous motor torque based on the relative electrical position of the auxiliary motor relative to the controllable region.

[0051] Therefore, the instantaneous motor torque has a distribution that depends on the relative electrical position of the auxiliary motor with respect to the controllable region. This distribution can follow, for example, a niche curve or a half-sine curve centered on the controllable region.

[0052] The setpoint curve is adjustable so that the instantaneous motor torque integrated in the controllable region is equal to the spatial average motor torque.

[0053] According to one feature of the invention, the control phase successively uses a switch called a "deactivated inverter switch", a first switch group and a second switch group to perform vector monitoring of the phase current.

[0054] When the auxiliary motor enters the non-control area, the inverter switching unit enters the state corresponding to the inverter deactivation switch, that is, all switching units are in the off state.

[0055] When the auxiliary motor enters the controllable region, depending on the fault condition, the inverter's switching unit sequentially enters one of two possible states.

[0056] According to one feature of the invention, the driving method includes the step of estimating the spatially average braking torque caused by a fault in an uncontrollable region.

[0057] The space-average braking torque caused by a fault in an uncontrollable region is the actual space-average braking torque.

[0058] Therefore, under closed-loop monitoring, the estimated spatial average braking torque is calculated based on the current, electrical angle, and auxiliary motor speed of the available phases. The estimated spatial average braking torque is variable and is essentially equal to the actual spatial average braking torque.

[0059] According to one feature of the invention, the determination phase uses the space-average braking torque estimated during the estimation step to determine the space-average motor torque.

[0060] Then, in the compensation step, the spatially averaged braking torque estimated during the estimation step is compensated by electrical cycle averaging within the controllable region. Attached Figure Description

[0061] The invention will be better understood through the following description, which relates to embodiments of the invention, given by way of non-limiting examples and explained with reference to the accompanying schematic diagrams, wherein:

[0062] Figure 1 This is a schematic diagram of the method according to the present invention;

[0063] Figure 2 It is an equivalent diagram of a driveless inverter connected to an auxiliary motor with a short-circuit fault;

[0064] Figure 3 It is a schematic diagram of the controllable and uncontrollable regions of the auxiliary motor based on short-circuit faults and the direction of auxiliary torque;

[0065] Figure 4 It is a schematic diagram of the setpoint curve representing the instantaneous motor torque based on the relative electrical position of the auxiliary motor relative to the controllable area;

[0066] Figure 5 This indicates the on / off status of the inverter. Detailed Implementation

[0067] Figure 2 The diagram shown is an electrical diagram connecting inverter 1 to auxiliary motor 2 in the vehicle's electric power steering system.

[0068] Inverter 1 is an electronic device powered by a DC generator 11, which includes a grounding part 12 and a power supply part 13, so that it can provide three-phase AC power.

[0069] Inverter 1 includes three wires 14, 15, and 16 arranged in parallel between the grounding portion 12 and the power supply portion 13 of generator 11. Each wire 14, 15, and 16 includes "low-voltage side" switching units 117, 118, and 119, i.e., switching units connected to the grounding portion 12 of generator 11, and "high-voltage side" switching units 17, 18, and 19, i.e., switching units connected to the power supply portion 13 of generator 11. Switching units 17, 18, 19, 117, 118, and 119 are MOSFET type. Therefore, inverter 1 includes three "low-voltage side" switching units 117, 118, and 119 and three "high-voltage side" switching units 17, 18, and 19.

[0070] Each wire 14, 15, 16 includes phase lines U, V, and W between the "low-voltage side" switch units 117, 118, 119 and the "high-voltage side" switch units 17, 18, 19. Therefore, there are three phase lines U, V, and W.

[0071] Each phase line U, V, and W supplies power to coils 28, 27, and 29 of auxiliary motor 2.

[0072] During normal operation, the current flowing in the phase lines U, V, and W generates a rotating magnetic field, which determines the rotation direction, speed, and torque of the rotor 200 of the auxiliary motor 2.

[0073] The positive and negative directions can be arbitrarily defined. In the remainder of the instruction manual, the positive direction corresponds to the triangular direction.

[0074] exist Figure 2 In the inverter 1, a faulty "low-voltage side" switch unit 119 connected to phase line U causes a short-circuit fault between phase line U of generator 11 and grounding portion 12. The short-circuit switch unit is in the closed position. Phase lines V and W still function, but phase line U does not.

[0075] In the event of a short-circuit fault, an electromotive force is generated by the rotation of rotor 200, thereby generating a braking torque at the level of auxiliary motor 2.

[0076] Based on the defective phase line U, the speed and rotation direction of the auxiliary motor 2, and the grounding 12 or power supply 13 of the short-circuit inverter 11, the electrical cycle, controllable region ZC, and uncontrollable region ZNC of the auxiliary motor 2 can be determined.

[0077] The uncontrollable region ZNC corresponds to the electric angle at which the electromotive force generates braking torque.

[0078] The controllable region ZC corresponds to the electrical angle of one electrical cycle minus the uncontrollable region ZNC. The angular position Z relative to the controllable region ZC is defined by the specific coils 27, 28, and 29. c The corresponding controllable region ZC has input angle position and output angle position Z. c .exist Figure 3 In this context, the angular position is determined relative to the coil 27 powered by phase line U. Preferably, the angular position is determined relative to the coil powered by the defective phase line.

[0079] As in Figure 3 As can be seen, there is a first uncontrollable region 25, which corresponds to the short circuit between phase line U and grounding part 12 when the auxiliary motor 2 is assisting in the positive direction, and corresponds to the short circuit between phase line U and power supply part 13 when the auxiliary motor 2 is assisting in the negative direction.

[0080] There is a second uncontrollable region 22, which corresponds to the short circuit between phase line U and grounding part 12 when the auxiliary motor 2 is assisting in the negative direction, and corresponds to the short circuit between phase line U and power supply part 13 when the auxiliary motor 2 is assisting in the positive direction.

[0081] There is a third uncontrollable region 24, which corresponds to the short circuit between phase line V and grounding part 12 when the auxiliary motor 2 is assisting in the positive direction, and corresponds to the short circuit between phase line V and power supply part 13 when the auxiliary motor 2 is assisting in the negative direction.

[0082] There is a fourth uncontrollable region 21, which corresponds to the short circuit between phase line V and grounding part 12 when the auxiliary motor 2 is assisting in the negative direction, and corresponds to the short circuit between phase line V and power supply part 13 when the auxiliary motor 2 is assisting in the positive direction.

[0083] There is a fifth uncontrollable region 26, which corresponds to the short circuit between phase line W and grounding part 12 when the auxiliary motor 2 is assisting in the positive direction, and corresponds to the short circuit between phase line W and power supply part 13 when the auxiliary motor 2 is assisting in the negative direction.

[0084] Finally, there is a sixth uncontrollable region 23, which corresponds to the short circuit between phase line W and grounding portion 12 when the auxiliary motor 2 is assisting in the negative direction, and corresponds to the short circuit between phase line W and power supply portion 13 when the auxiliary motor 2 is assisting in the positive direction.

[0085] When the speed of the auxiliary motor 2 is zero, the angles of the uncontrollable regions 21, 22, 23, 24, 25, and 26 are equal to an electrical angle of 60°. Therefore, the controllable region ZC corresponds to one electrical cycle of the auxiliary motor 2 minus the angle corresponding to the uncontrollable region ZNC, which is 300°.

[0086] As the speed of auxiliary motor 2 increases, the angle of the uncontrollable region ZNC increases.

[0087] The total value of the braking torque generated in the uncontrollable region ZNC and its distribution in the uncontrollable region ZNC depend on the speed of the auxiliary motor 2.

[0088] Therefore, when the auxiliary motor 2 is short-circuited between phase U and grounding part 12, and under closed-loop monitoring, such as Figure 1 The method shown according to the invention allows for defining configuration parameters Z specific to phase line U and short-circuit portion 12 during the configuration step. c φ. Configuration parameter Z c φ, especially the controllable region ZC and the input and output angle positions Z of the two functional phase lines φ. c .

[0089] In closed-loop monitoring, the estimation step receives the rotational speed V of auxiliary motor 2. m Measurement of the electric angle α of the motor m And information related to the phase current available on each functional phase line V, W as input.

[0090] Therefore, the estimation step determines the estimated spatial average braking torque C applied by the electromotive force to the uncontrollable region ZNC. fm In other words, the estimation step calculates the minimum torque provided in the subsequent controllable region ZC based on the rotational speed to counteract the braking torque applied in the subsequent uncontrollable region ZNC.

[0091] According to the method of the present invention, the activation step is performed by receiving the rotational speed V of the auxiliary motor 2. m and the measured steering wheel torque C vm As input.

[0092] When the measured steering wheel torque C vm and the rotational speed V of auxiliary motor 2 m Greater than a predetermined value, for example, the measured steering wheel torque C. vm The speed V of auxiliary motor 2 is 5 N·m. m When the speed is 50 rpm and they are in the same direction, the activation step allows the activation of the step to compensate for the space-average braking torque. For this purpose, the activation step will send an activation signal. When the condition is not met, that is, when no activation signal is issued, the activation step no longer drives inverter 1, which then enters a deactivated state, referred to as a deactivated inverter switch. The activation step can also receive the phase current available on each functional phase line V, W.

[0093] The compensation process includes the detection phase, determination phase, conversion phase, and control phase.

[0094] The detection phase receives the measured electrical angle α of the auxiliary motor 2, which was determined during the configuration step. m And the input and output angle positions Z of the rotational speed Vm and the controllable range ZC. c As input.

[0095] The detection phase determines the relative electrical position α of motor 2 with respect to the input relative to the controllable region ZC. r (Unsigned), and the direction of the auxiliary torque R of the functional phase lines V and W is also defined according to the rotation direction of the auxiliary motor 2.

[0096] Finally, the detection phase activates the determination phase at each electrical cycle by activating the activation signal e.

[0097] The determination phase receives the activation signal e from the detection phase and measures the steering wheel torque C. vm and the estimated space-average braking torque C fm As input.

[0098] The determination phase calculates the average motor torque Cmm to be applied over the controllable region ZC to maintain an acceptable steering torque for the driver. The determination phase also incorporates the steering wheel torque C measured under fault-free conditions. vm Taking into account and compensating for the estimated space-average braking torque C fm .

[0099] During the conversion phase, the relative electrical position α of the auxiliary motor 2 is used as a reference. r The average motor torque C to be applied to the controllable region ZC mm Converted into instantaneous motor torque C mi Average motor torque C mm Equal to the instantaneous motor torque C in the controllable region ZC mi The integral. According to Figure 4 The setpoint curve shown represents the average motor torque C. mm The distribution is within the controllable region ZC (0° to 300° in our case). The uncontrollable region ZNC corresponds to the electric angle in the range of 300° to 360°.

[0100] The control phase receives the direction of the auxiliary torque R from the auxiliary motor, the two functional phase lines V and W, and the instantaneous torque C of the motor. mi In order to be based on Figure 5 The switch indicates that the inverter 1 controls the two functional phase lines V and W of the auxiliary motor 2.

[0101] Depending on the activation signal and fault switch unit, the inverter may have 21 types of switches.

[0102] The switches determine the position of each switching unit in the inverter.

[0103] For example, switch C31 limits the "low-voltage side" switch unit of phase line U to the closed position and the "high-voltage side" switch unit of phase line U to the open position. That is, the switch unit of phase line V on the "low-voltage side" is in the closed position and the "high-voltage side" switch unit of phase line V is in the open position. The "low-voltage side" switch unit of phase line W is in the closed position and the "high-voltage side" switch unit of phase line W is in the open position.

[0104] A deactivated switching inverter is a passive switch C0, in which six switching units are in the open position. In the uncontrolled region, the inverter is in a deactivated switching inverter state.

[0105] In the controllable region, the inverter is continuously located in two possible active switches.

[0106] For example Figure 2 The fault shown is that caused by a short circuit between phase line U and grounding part 12, which closes the "low-voltage side" switch unit of phase line U. Therefore, one of the active switches C31, C34, C35, C36, C205, C206, C209, and C210 can be used to control the inverter, i.e., the active switch with phase line U's "low-voltage side" switch unit 119 in the closed position.

[0107] In addition, when phase line U is short-circuited with power supply section 13, there may be "active" switches C32, C33, C37, C38, C207, C208, C211, and C212 corresponding to available switches.

[0108] When phase line U is short-circuited with grounding part 12, there may be "active" switches C31, C32, C36, C37, C201, C202, C210, and C212 corresponding to available switches.

[0109] When phase line V is short-circuited with power supply section 13, there may be "active" switches C33, C34, C35, C38, C203, C204, C209, and C211 corresponding to available switches.

[0110] In addition, when phase line W is short-circuited with grounding part 12, there may be "active" switches C31, C32, C33, C34, C201, C203, C205, and C207 corresponding to available switches.

[0111] In addition, when phase line W is short-circuited with power supply section 13, there may be "active" switches C35, C36, C37, C38, C202, C204, C206, and C208 corresponding to available switches.

[0112] During each electrical cycle when the activation signal is issued, the inverter will sequentially use all or some of the eight control switches to go through the monitoring phase in the controllable area and the passive phase in the uncontrollable area corresponding to switch C0.

[0113] Of course, the present invention is not limited to the embodiments described and illustrated in the accompanying drawings. Modifications can still be made, particularly from the perspective of the composition of various elements or by means of alternative technical equivalents, without departing from the scope of protection of the present invention.

Claims

1. A method for driving a vehicle power steering system when a short-circuit fault is detected between a phase (U, V, W) of an auxiliary motor (2) and wires (14, 15, 16) of an inverter (1) supplying power to the auxiliary motor (2), the power steering system comprising a steering wheel and the inverter (1), characterized in that the method comprises: The configuration step is used to determine the controllable region (ZC) and uncontrollable region (ZNC) of the magnetic field of the auxiliary motor (2), wherein the controllable region (ZC) and the uncontrollable region (ZNC) are defined by electrical angle and the rotation direction and speed of the auxiliary motor. A compensation step is used to compensate for the spatially average braking torque in the controllable region, the compensation step including: Detecting the relative electrical position (α) of the auxiliary motor with respect to the controllable region (ZC). r (stage) The phase of determining the spatially averaged motor torque (C mm ) from the measured steering wheel torque (C vm ), a phase of converting the space-averaged motor torque (C mm ) into an instantaneous motor torque (C mi ) The stage of controlling the phase current of the auxiliary motor (2).

2. The driving method according to claim 1, comprising an activation step for comparing the rotation direction of the steering wheel with the rotation direction of the auxiliary motor (2).

3. The driving method according to claim 2, wherein the activation step applies steering wheel torque (C) vm ) and / or the speed of the auxiliary motor (V) m ) is compared with a predetermined threshold.

4. The driving method according to any one of the preceding claims, wherein the configuration step determines two phases (φ) of the auxiliary motor (2) that are unaffected by faults.

5. The driving method according to any one of claims 1 to 3, wherein the detection phase triggers the determination of the spatial average motor torque (C). mm The implementation of the phase ).

6. The driving method according to any one of claims 1 to 3, wherein the conversion phase is implemented based on the relative electrical position (α) of the auxiliary motor relative to the controllable region (ZC). r ) represents the instantaneous motor torque (C) mi The setpoint curve.

7. The driving method according to any one of claims 1 to 3, wherein the control phase successively uses a switch (CO) called a "deactivated inverter switch", a first switch group and a second switch group to perform vector monitoring of the phase current.

8. The driving method according to any one of claims 1 to 3, comprising the step of estimating the spatially average braking torque caused by a fault in the uncontrollable region.

9. The driving method of claim 8, wherein the determining phase uses the spatially average braking torque (C) estimated during the estimation step. fm To determine the space-average motor torque (C) mm ).

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