DE102017215190A1 - Method and apparatus for operating an electromechanical steering assist drive - Google Patents

Abstract

The invention relates to a method for operating an electromechanical steering assist drive (7) of a steering system (1) of a motor vehicle, wherein the steering assist drive (7) comprises a multi-phase electronically commutated electric machine (12), comprising the following steps:
- Detecting a motor current in the steering assist drive (7);
- adjusting a stator magnetic field vector for operating the steering assist drive (7) depending on the motor current in the steering assist drive (7);
- Driving the steering assist drive (7) by adjusting phase voltages at phase strands of the steering assist drive (7) depending on the adjusted stator magnetic field vector.

Description

Technical area

The invention relates to steering systems with steering assistance, in particular steering systems, in which a steering assistance force or a steering assistance torque is provided by an electronically commutated position sensor.

Technical background

Modern steering systems for motor vehicles have a steering assistance, in which a steering assist drive couples a steering assist force or a steering assist torque into the steering system. The steering assist drive is operated based on a large number of functions and driven according to a desired steering assistance intervention. For example, provides a steering assist function to protect the mechanical end stops of the steering system by an increased electromechanically applied counterforce when the steering moves in the direction of the mechanical steering stops.

In certain driving situations, operating points may occur in which a high external force acting on the steering system force is introduced, so that the steering assist drive is moved against the specification of a steering assistance engagement. Such movement may bring the steering assist drive into a regenerative operating range. Such a regenerative operating range causes the induction of voltages in the excitation coils, which lead to feedback currents in the on-board power supply system supplying the steering assistance drive or the steering system. In particular, high regenerative currents can cause instabilities of the vehicle electrical system voltage, which can affect the function and integrity of other components supplied via the Borspannungsnetz. For this reason, the regenerative currents from the steering assist drive must be avoided or limited.

However, as a limiting strategy for such regenerative currents deactivation of the steering assistance drive is out of the question, since the o.a. Steering support functions are safety-relevant and must be continuously active.

In previous steering systems, the conflict of goals to reduce the regenerative currents and at the same time implement a required steering assistance intervention, achieved insufficient.

It is therefore an object of the present invention to provide a method and a device for operating a steering system, in which the regeneratively generated regenerative currents are reduced and at the same time the required steering assistance interventions can be provided.

Disclosure of the invention

This object is achieved by the method for operating an electromechanical steering assist drive in a steering system according to claim 1 and by the device and the steering system according to the independent claims.

Further embodiments are specified in the dependent claims.

• - Ermitteln eines Motorstroms in den Lenkunterstützungsantrieb;
• - Anpassen eines Statormagnetfeldvektors zum Betreiben des Lenkunterstützungsantriebs abhängig von dem Motorstrom in den Lenkunterstützungsantrieb;
• - Ansteuern des Lenkunterstützungsantriebs durch Einstellen von Phasenspannungen an Phasensträngen des Lenkunterstützungsantriebs abhängig von dem angepassten Statormagnetfeldvektor.

According to a first aspect, there is provided a method of operating an electromechanical steering assist drive of a steering system of a motor vehicle, the steering assist drive comprising an electronically commutated electric machine comprising the steps of:

• - Detecting a motor current in the steering assistance drive;
• - adjusting a stator magnetic field vector for operating the steering assist drive in response to the motor current into the steering assist drive;
• Driving the steering assist drive by adjusting phase voltages at phase strands of the steering assist drive in response to the adjusted stator magnetic field vector.

Steering support drives are usually designed as electronically commutated electrical machines. These are activated in active operation in such a way that a circulating stator magnetic field is generated, which always leads by a predetermined angle to a rotor magnetic field bound to the rotor, which can be generated, for example, by permanent magnets. To achieve a specific actuating torque, a stator magnetic field vector is specified, wherein the magnitude of the actuating torque is determined by the strength of the stator magnetic field and its direction relative to the rotor position. The stator magnetic field is generated by means of stator coils, which are connected in groups to phase strings, and are jointly energized by applying a combination of phase voltages. The current flows in the stator coils cause the stator magnetic field.

The phase strands are energized by a power driver circuit as appropriate according to a commutation scheme by applying a respective phase voltage to each phase string. The lead of the stator magnetic field with respect to the rotor magnetic field caused by the rotor is usually about 90 ° electrical rotor position (360 ° / pole pair number) to cause a maximum actuating torque by the steering assist drive.

For characterizing the stator magnetic field vector with respect to the rotor magnetic field, a rotor-fixed coordinate system is selected, wherein a d-direction indicates a direction of the rotor magnetic field and a q-direction indicates a 90 ° electrical rotor position angle offset direction. Thus, while a q-component (with respect to the rotor-fixed coordinate system) of the stator magnetic field causes a control torque, the d-component of the stator magnetic field is torque-neutral and does not lead to a first approximation to influence the engine torque.

The stator magnetic field in the desired orientation to the rotor position and the desired strength is predetermined by the stator magnetic field vector and effected by suitable commutation of the phase strands by the power drive circuit. In doing so, phase voltages or phase currents are suitably provided to provide the appropriate magnitude and orientation of the resulting stator magnetic field, i. to adjust the stator magnetic field vector with respect to the current rotor position.

If the rotor of the steering assist drive is moved counter to the direction of rotation intended by the motor commutation by the action of external forces or moments, stresses are induced in the stator coils by the movement of the rotor magnetic field.

These can result in a respective phase voltage, which can be higher than the supply voltage of the on-board voltage network, by which the steering assistance drive is supplied. Due to the power driver circuit, in particular by the body diodes of the power semiconductors used therein, these regenerative phase voltages lead to a coupling of resulting phase currents in the on-board voltage network in the form of a conventional motor current opposite feedback current. This regenerative current can lead to an increase in the vehicle electrical system voltage in the vehicle electrical system. This effect is undesirable and can lead to instabilities of other components connected to the electrical system.

The above method therefore provides for detecting a regenerative current in the vehicle electrical system (negative motor current) regenerated by the steering assist drive, and for generating a particularly significant regenerative current generating or increasing a d-component of the stator magnetic field (by corresponding modification or adaptation of the stator magnetic field vector ) to effect. The height of the d-component of the stator magnetic field vector should depend on the magnitude of the recovery current.

The d-component of the stator magnetic field is achieved by specifying a stator magnetic field vector and a corresponding commutation of the power driver circuit, which leads to an additional current component of the phase currents through the phase strands. However, this additional current component in the phase currents has an effect on the motor torque and instead only results in the occurrence of ohmic losses in the stator coils. As a result, the electric power generated by the regenerative operation of the steering assist drive in the steering assist drive itself can be at least partially converted into ohmic power loss (heat) or consumed.

By adjusting the amounts of the additional d-component of the stator magnetic field causing phase currents to the amount of the determined recovery current this can be significantly reduced or eliminated, so that a risk of other vehicle components can be excluded by an excessive vehicle electrical system voltage. In addition, variation of the d-component of the stator magnetic field does not affect the steering assisting engagement to be provided by the steering assist drive, so that the higher-level steering assisting functions can remain active. For this purpose, only the amplitude of the d-component must be limited so that in view of predetermined stator current limits, the specification of the steering assistance function with the q-component can still be set.

It may be provided that the stator magnetic field vector is adapted only if the motor current indicates a regenerative current in a vehicle power supply system supplying the steering assistance drive.

Furthermore, if it is determined that the motor current indicates a regenerative current in an on-board voltage supply system supplying the steering assistance drive and exceeds a predetermined current threshold in terms of amount, the stator magnetic field vector can be adapted.

In particular, the stator magnetic field vector may be adjusted depending on the rotor position of a rotor of the steering assist drive, a steering assisting engagement to be provided, and a predetermined offset stator magnetic field vector.

In one embodiment, the offset stator magnetic field vector may have an orientation corresponding to a momentary orientation of the rotor magnetic field to bias a d-component of the stator magnetic field through the offset stator magnetic field vector.

In particular, the offset stator magnetic field vector may have a strength that is iteratively adjusted by addition and subtraction of a respective predetermined increment depending on the motor current, in particular whether the motor current indicates a regenerative current, the amount exceeds a predetermined current threshold.

Furthermore, the increment amount can be selected depending on a driving situation.

According to a further embodiment, the offset stator magnetic field vector may have a magnitude that is determined as a function of the motor current. In particular, the offset stator magnetic field vector can have a strength which is dependent on the q component of the stator magnetic field vector required in the current operating point and the maximum possible or permitted phase current amplitude.

In particular, the offset stator magnetic field vector can be selected depending on a driving situation.

• - einen Motorstrom in den Lenkunterstützungsantrieb zu ermitteln;
• - einen Statormagnetfeldvektor zum Betreiben des Lenkunterstützungsantriebs abhängig von dem Motorstrom in den Lenkunterstützungsantrieb anzupassen;
• - den Lenkunterstützungsantrieb durch Einstellen von Phasenspannungen an Phasensträngen des Lenkunterstützungsantriebs abhängig von dem angepassten Statormagnetfeldvektor anzusteuern.

In another aspect, there is provided an apparatus for operating an electromechanical steering assist drive of a steering system of a motor vehicle, the steering assist drive comprising a polyphase electronically commutated electric machine, the apparatus being configured to:

• to detect a motor current in the steering assist drive;
• to adapt a stator magnetic field vector for operating the steering assist drive to the steering assist drive depending on the motor current;
• - To control the steering assist drive by adjusting phase voltages to phase strands of the steering assist drive depending on the adjusted stator magnetic field vector.

• - einen Lenkunterstützungsantrieb mit einer eine mehrphasige elektronisch kommutierten elektrischen Maschine und einer Leistungstreiberschaltung, und
• - die obige Vorrichtung.

In another aspect, a steering system of a motor vehicle includes:

• a power steering drive having a multi-phase electronically commutated electric machine and a power drive circuit, and
• - The above device.

list of figures

• 1 eine schematische Darstellung eines Lenksystems;
• 2 eine schematische Darstellung eines Lenkunterstützungsantriebs; und
• 3 ein Flussdiagramm zur Veranschaulichung eines Verfahrens zum Stellen einer d-Komponente des Erregermagnetfelds.

Embodiments are explained below with reference to the accompanying drawings. Show it:

• 1 a schematic representation of a steering system;
• 2 a schematic representation of a steering assistance drive; and
• 3 a flowchart illustrating a method for setting a d-component of the exciting magnetic field.

Description of embodiments

1 shows a schematic representation of a steering system 1 of a motor vehicle. The steering system 1 includes a steering column 2 that with a steering wheel 3 is coupled, allowing a steering movement from a driver to the steering wheel 3 is exercised as a manual steering torque on the steering column 2 acts. The steering column 2 transfers the hand moment to a pinion 4 , with a, in particular as a rack running, handlebar 5 is coupled.

The handlebar 5 is between two steered wheels 6 of the motor vehicle. The wheels 6 are held so that they are in a linear motion of the handlebar 5 be pivoted about a steering angle.

The steering column 2 or the handlebar 5 continue to be with a steerable steering assist drive 7 coupled to provide a steering assistance in the form of a steering assistance engagement. The steering assist engagement may be a steering assist torque applied to the steering column 2 acts, or a steering assist force on the handlebar 5 correspond.

The steering assistance drive 7 can be designed as an electric motor or electromechanical positioner, and to provide the steering assistance with the steering column 2 or the handlebar 5 be coupled in a suitable manner. In the present, in 1 In the embodiment shown, the steering assistance drive acts 7 on the handlebar 5 ,

It is also a steering control unit 10 intended to control the steering system 1 is trained. Using a manual steering torque sensor 8th on the steering column 2 can one over the steering wheel 3 on the steering column 2 applied hand steering torque determines and a corresponding manual steering torque specification HM to the steering control unit 10 be transmitted. Accordingly, the steering column 2 with a steering angle sensor 9 Be provided, the rotation angle of the steering column 2 recorded and a corresponding steering angle LW to the steering control unit 10 provides. Instead of or in addition to the steering angle sensor 9 For example, a position angle sensor may be provided which has an exact rotor position of the steering assistance drive 7 determines, so that a detected by the attitude angle sensor size can be provided as a steering angle indication. Alternatively, a handlebar position sensor may also be provided which has a position of the handlebar 5 can provide as an indication of a steering angle. The steering angle information LW and the manual steering torque specification HM serve to perform one or more steering assistance functions in the steering control device 10 ,

A steering assistance drive 7 is usually designed as an electronically commutated electric machine, in particular as a permanent-magnet electric machine. The construction of a steering assistance drive 7 is schematic in 2 shown. The steering assistance drive 7 includes a power driver circuit 11 and an electric machine 12 ,

The electric machine 12 is shown in cross section. One recognizes a stator arrangement 121 with an interior recess 123 surrounding stator teeth 122 passing through stator coils 124 are wound. The stator coils 124 can be interconnected in groups with each other serially and / or in parallel and as different phase strands P _U . P _V . P _W be energized separately, so a certain direction of a resulting magnetic field in the inner cavity 123 pretend. In the present case, the respective opposite stator coils 124 energized as a phase strand together.

In the interior recess 123 there is a rotor 126 having one or more permanent magnets to provide a rotor magnetic field. The illustrated rotor 126 has a pole pair, however, in other embodiments, rotors having more than one pole pair may be formed to form a plurality of overlapping rotor magnetic fields.

At different orientations of the stator magnetic field to the rotor magnetic field acts on the rotor 126 a force affecting the electric machine 12 drives. As a rule, depending on the rotor position, the stator magnetic field is generated in such a way that it leads in the direction of rotation by 90 ° electrical position angle. The electrical position angle corresponds to the mechanical position angle divided by the number of pole pairs of the rotor 126 ,

For simplified calculation of the necessary phase currents with which the stator coils 124 are energized, a rotor-fixed coordinate system is specified, which includes a d-axis and a q-axis. The d-axis points in the direction of the rotor 126 emitted rotor magnetic field through the q-axis in a direction offset by 90 ° electrical rotor position angle direction, so that the d-axis and q-axis of the coordinate system with the rotor 126 rotate. Since the stator magnetic field by superposition of the stator coils 124 generated individual magnetic fields is generated, one speaks of a d-component or a q-component of the resulting stator magnetic field or a stator magnetic field vector.

The stator coils 124 the electric machine 12 are via a power driver circuit 11 , in particular as H-bridge or as in 2 shown as B6 bridge circuit may be formed, driven. The power driver circuit 11 has circuit breaker 111 on that for each phase strand P _U . P _V , P _W form an inverter that has a high supply potential V _H and a low supply potential V _L a voltage board network 13 connected. The circuit breakers 111 are preferably formed as a semiconductor switch, in particular as a power MOSFET. Between the circuit breakers 111 becomes a respective phase voltage U _U . U _V . U _W provided to the corresponding phase strands P _U . P _V . P _W be connected.

The circuit breakers 111 be through a control unit 14 controlled in accordance with an actuating torque specification, the one to be asked by the steering control unit 10 provided steering assistance torque LM equivalent. The circuit breakers 111 be according to a respective commutation signal from the controller 14 open or closed. Therefore, the phase strands P _U . P _V . P _W either with a high or low supply potential VH . VL occupied or de-energized, with a certain phase current or a specific phase voltage by pulse width modulation in the control of the corresponding circuit breaker 111 is achieved in a conventional manner.

An indication of an orientation of the stator magnetic field currently to be applied, ie the direction of a corresponding stator magnetic field vector, is determined from the instantaneous rotor position. The set strength and direction of the currently to be created or set Stator magnetic field vector results from the desired steering assistance engagement, ie the steering assist torque and the steering assist force, respectively.

The current rotor position can be determined by a position sensor 113 measured or sensorless by evaluating gradients of the phase currents or phase voltages can be determined in a conventional manner. From the indications of the strength and the orientation of the currently to be applied stator magnetic field vector results in a necessary commutation of the power driver circuit 11 , by which the magnitudes of the phase voltages for the individual phase strands P _U . P _V . P _W the electric machine 12 be determined.

Does it come with a movement of the rotor 126 contrary to an intended direction of rotation, so can by the power driver circuit 11 a regenerative current in the supplying on-board voltage network 13 flow. The regenerative current corresponds to a negative motor current in the steering assist drive 7 , The regenerative current in the on-board voltage network 13 can lead to voltage fluctuations of the vehicle electrical system voltage, the other with the on-board voltage network 13 damage connected components or impair their function.

In order to avoid such regenerative currents or to reduce or limit the regenerative currents, a method for operating the steering assistance drive is provided, as described with reference to the flow chart of the 3 is explained in more detail.

In step S1 becomes with active steering assistance drive 7 a motor current I _mot measured. If the motor current is negative (with respect to a motor current in the backup mode), this is a regenerative current in the on-board voltage network 13 , This motor current or this regenerative current can be achieved by a corresponding current measuring device 15 between the on-board voltage network 13 and the power driver circuit 11 be determined. Alternatively, the regenerative current can also be achieved by a current summation balance of the individual inverter currents of the power driver circuit 11 be determined. The determination of the motor current can also be based on the power balance of the power driver circuit 11 using the measured phase currents, the set voltages, the rotor position angle (for transformation) and the current supply voltage of the power driver circuit 11 be carried out in a conventional manner.

In step S2 a strength and orientation of the stator magnetic field vector to be set is determined as a function of the predetermined steering assist torque to be set and the instantaneous rotor position. The orientation of the stator magnetic field vector is determined for the rotor-fixed coordinate system.

In step S3 it checks if the motor current has a certain current threshold I _S falls below, for example, from -5A. Alternatively, it is checked whether the amount of the regenerative current (negative motor current) exceeds a corresponding current threshold. If this is the case (alternative: yes), then the procedure with step S4 otherwise, the process continues with step S6 continued.

Results from the review of the step S3 in that a regenerative current is above a current threshold I _S certain amount of electricity is present, so in step S4 depending on the current rotor position an amount of d-component of the stator magnetic field in the rotor-fixed coordinate system increases. The increase can be iterative by a certain incremental amount, so that the regenerative current decreases in a row. The incremental amount by which the d-component of the stator magnetic field is increased may depend on the amount of current of the regenerative current and, in particular, may be selected depending on a driving condition. Thus, the increment amount may be selected depending on a traveling direction (forward, backward), a vehicle speed, and / or a road condition.

The adjustability of the incremental amount determined by the thereby predetermined gradient of increasing the d-component of the stator magnetic field to a maximum allowable feedback. This depends on the basic stability of the vehicle electrical system and can theoretically be specified individually by the customer.

In step S5 a commutation is determined based on the strength and orientation of the stator magnetic field vector to be provided. This causes correspondingly increased phase currents in the phase strands. The d-component of the stator magnetic field does not contribute to a torque generation of the electric machine 12 at and therefore leads only to the occurrence of ohmic losses. In this way, generator-generated power in the steering support drive 7 Ohmic losses in the stator coils 124 be absorbed and consumed. The process is step by step S1 cyclically performed.

Results from the review of the step S3 in that an amount of the recovery current is smaller than the current threshold value I _S can be specified in step S6 the d-component of the stator magnetic field can be reduced by a certain incremental amount. The particular incremental amount by which the d-component of the stator magnetic field is reduced may depend on the amount of current of the regenerative current and in particular may be selected depending on driving maneuvers. Subsequently, the method with step S5 continued.

Alternatively, instead of the steps S4 and S6 the d-component of the stator magnetic field to be set can be determined directly from the measured regenerative current, for example by a predetermined linear relationship between the regenerative current and the d-component of the stator magnetic field to be set.

Furthermore, the d-component of the stator magnetic field can be determined as a function of a required in the current operating point q-component and a predetermined maximum possible stator magnetic field, the predetermined maximum possible stator magnetic field can correspond to a maximum permissible phase current amplitude.

By this method, it is possible that the implementation of the steering assistance intervention remains unaffected by the measure for reducing a regenerative current and at the same time the on-board voltage network 13 can be protected against overvoltages.

LIST OF REFERENCE NUMBERS

1

steering system

2

steering column

3

steering wheel

4

pinion

5

handlebars

6

bikes

7

Power steering drive

8th

Manual steering torque sensor

9

Steering angle sensor

10

Steering control unit

11

Power driver circuit

111

breakers

113

position sensor

12

electric machine

121

stator

123

inner recess

122

stator teeth

124

stator coils

126

rotor

13

Voltage network

15

Current measurement device

LM

Steering assist torque

VH, VL

supply potential

Claims (12)

Method for operating an electromechanical steering assist drive (7) of a steering system (1) of a motor vehicle, wherein the steering assist drive (7) comprises a multiphase electronically commutated electric machine (12), comprising the following steps: - Detecting a motor current in the steering assist drive (7); - adjusting a stator magnetic field vector for operating the steering assist drive (7) depending on the motor current in the steering assist drive (7); - Driving the steering assist drive (7) by adjusting phase voltages at phase strands of the steering assist drive (7) depending on the adjusted stator magnetic field vector. Method according to Claim 1 wherein the stator magnetic field vector is adjusted only when the motor current indicates a regenerative current in an on-board voltage network (13) supplying the steering assist drive (7). Method according to Claim 1 or 2 wherein, when it is determined that the motor current is indicative of a regenerative current in an on-board voltage network (13) supplying the steering assist drive (7) and exceeds a predetermined current threshold in magnitude, the stator magnetic field vector is adjusted. Method according to Claim 3 wherein the stator magnetic field vector is adjusted depending on the rotor position of a rotor (126) of the steering assist drive (7), a steering assistance engagement to be provided, and a predetermined offset stator magnetic field vector. Method according to Claim 3 or 4 wherein the offset stator magnetic field vector has an orientation corresponding to a momentary orientation of the rotor magnetic field for biasing a d-component of the stator magnetic field with respect to a rotor-fixed coordinate system through the offset stator magnetic field vector. Method according to Claim 5 wherein the offset stator magnetic field vector has a magnitude which is iteratively adjusted by adding and subtracting a respective predetermined incremental amount depending on the motor current, in particular whether the motor current indicates a regenerative current amount exceeds a predetermined current threshold. Method according to Claim 6 , wherein the incremental amount is selected depending on a driving situation, in particular depending on a driving direction, a vehicle speed and / or on a road surface. Method according to Claim 5 wherein the offset stator magnetic field vector has a magnitude that is determined, in particular not iteratively, as a function of the motor current. Method according to one of Claims 4 to 8th wherein the offset stator magnetic field vector is limited depending on the required in the current operating point q-component of the stator magnetic field vector and a predetermined maximum possible or allowed phase current amplitude. Method according to Claim 8 or 9 , wherein the offset stator magnetic field vector is selected depending on a driving situation, in particular depending on a driving direction, a vehicle speed and / or on a road surface. A device for operating an electromechanical steering assist drive (7) of a steering system (1) of a motor vehicle, the steering assist drive (7) comprising a polyphase electronically commutated electric machine (12), the device being configured to: to detect a motor current in the steering assist drive (7); to adapt a stator magnetic field vector for operating the steering assist drive (7) to the steering assist drive (7) depending on the motor current; - To control the steering assist drive (7) by adjusting phase voltages to phase strands of the steering assist drive (7) depending on the adjusted stator magnetic field vector. A steering system (1) of a motor vehicle, comprising: - a steering assist drive (7) having a multi-phase electronically commutated electric machine (12) and a power driver circuit (11), and - an apparatus according to Claim 11 ,

Images