DE102021117011B4 - Force feedback actuator for a steer-by-wire system and method for operating a force feedback actuator for a steer-by-wire system - Google Patents

Abstract

Force feedback actuator (1) for a steer-by-wire system with
an electrical machine (2) with at least a first winding (11) and a second winding (12) separate from the first winding (11), wherein the first and second windings (11, 12) each have a plurality of phase connections (U1, V1, W1, U2, V2, W2),
a switching device (3) which is electrically connected to the first and second windings (11, 12) and
a control device (4) which is configured to control the switching device (3) such that - in a normal operating mode - each phase connection of the first winding (U1, V1, W1) is electrically connected to exactly one phase connection of the second winding (U2, V2, W2) and - in a fault mode - all phase connections of the first winding (U1, V1, W1) are electrically connected to one another and the phase connections of the second winding (U2, V2, W2) are electrically separated from one another and from the phase connections of the first winding (U1, V1, W1).

Description

The invention relates to a force feedback actuator for a steer-by-wire system. The invention also relates to a method for operating a force feedback actuator for a steer-by-wire system.

Steer-by-wire systems can be used in vehicles such as passenger cars and trucks. In a steer-by-wire system, there is no mechanical coupling between the steered wheels of the vehicle and the steering wheel operated by the driver. Therefore, a force feedback actuator is typically used to give the driver feedback on the current driving dynamics. The force feedback actuator usually comprises an electric machine that is connected to the steering wheel either via a transmission and/or other mechanical components or directly. The force feedback actuator can, for example, signal to the driver that the maximum possible wheel angle is reached by a high torque applied to the steering wheel that he or she cannot turn the steering wheel any further in the desired direction.

If a fault occurs in the force feedback actuator, the driver may no longer be informed of the dynamic driving state. For example, a fault in the power electronics of the force feedback actuator can result in the electric machine no longer being powered. In such a fault, the driver no longer perceives the torque applied to the steering wheel and can inadvertently turn the steering wheel too far. This means that there is a risk, particularly at higher speeds, that the driver will make a steering request via the steering wheel that exceeds the vehicle's limits. This can make the vehicle uncontrollable.

The closest font to the application DE 10 2015 213 304 A1 discloses a force feedback actuator for a steer-by-wire system, having an electric machine with at least a first winding and a second winding separate from the first winding, wherein the first and second windings each have a plurality of phase connections and a switching device which is electrically connected to the first and second windings.

Against this background, the task is to improve the controllability of the vehicle in the event of a fault in the force feedback actuator.

The task is solved by a force feedback actuator for a steer-by-wire system with
an electrical machine with at least a first winding and a second winding separate from the first winding, wherein the first and second windings each have a plurality of phase connections,
a switching device which is electrically connected to the first and second windings and
a control device which is configured to control the switching device such that - in a normal operating mode - each phase connection of the first winding is electrically connected to exactly one phase connection of the second winding and - in a fault mode - all phase connections of the first winding are electrically connected to one another and the phase connections of the second winding are electrically separated from one another and from the phase connections of the first winding.

The object is further achieved by a method for operating a force feedback actuator for a steer-by-wire system with
an electrical machine with at least a first winding and a second winding separate from the first winding, wherein the first and second windings each have a plurality of phase connections,
a switching device which is electrically connected to the first and second windings and
a control device which controls the switching device such that - in a normal operating mode - each phase connection of the first winding is electrically connected to exactly one phase connection of the second winding and - in a fault mode - all phase connections of the first winding are electrically connected to one another and the phase connections of the second winding are electrically separated from one another and from the phase connections of the first winding.

According to the present invention, it is provided that the electrical machine has at least two separate windings. In the normal operating mode of the force feedback actuator, the separately constructed windings are electrically connected via the switching device, i.e. connected in parallel. In the normal operating mode, the electrical machine can be operated like a machine with only one winding. In the fault mode, however, the first winding of the electrical machine is short-circuited via the switching device by electrically connecting the phase connections of this winding to one another. A rotary movement of a steering wheel coupled to the force feedback actuator can induce a voltage in the electrical machine. The short-circuited winding results in a short-circuit current and thus a short-circuit torque that counteracts the rotation of the steering wheel and thus the driver's steering request. Uncontrolled steering movements, in particular jerky steering movements, can thus be braked by a noticeable counter-torque. The invention makes it possible to influence the behavior of the force feedback actuator in error mode by designing the electrical machine without changing the behavior of the force feedback actuator in normal operating mode. The short-circuit torque can thus be adjusted by selecting a suitable number of turns of the first winding in relation to the number of turns of the second winding.

For the purposes of the present invention, an electrical machine with separate windings is understood to mean an electrical machine that has several, in particular multi-phase windings, wherein the electrical machine can be operated with one of the windings without a further winding being required to operate the machine. The first winding and the second winding are preferably designed as a multi-phase winding, i.e. as a winding with several winding strands. The first winding and the second winding are particularly preferably designed as a three-phase winding, i.e. as a winding with exactly three winding strands.

Preferably, the first winding comprises a first turn and the second winding comprises a second turn, wherein the first and the second turn are arranged around a common tooth of the electrical machine.

The switching device preferably comprises a plurality of semiconductor switches, in particular power semiconductor switches, for example MOSFETs, IGBTs or thyristors.

According to an advantageous embodiment of the invention, the force feedback actuator comprises at least one resistor, which is arranged between a phase connection of the first winding and the switching device. The force feedback actuator particularly preferably comprises a plurality of resistors, each of which is arranged between a phase connection of the first winding and the switching device. In principle, the short-circuit torque resulting in the fault mode depends on the design of the electrical machine. As the speed increases, the short-circuit torque increases to a maximum and then drops. The short-circuit characteristic can be changed by the one resistor or the multiple resistors. The maximum of the short-circuit torque can be shifted to higher speeds by the resistor. By suitably selecting the number of turns of the first winding, in particular in relation to the turns of the second winding, in combination with the selection of one or more suitable resistors, a particularly flexible setting of the short-circuit characteristic curve can be achieved.

According to an advantageous embodiment of the invention, it is provided that the control device is configured to detect an error in the force feedback actuator and, if an error is detected, to switch from the normal operating mode to the error mode. In the method according to the invention, it can be provided that the control device detects an error in the force feedback actuator and, if an error is detected, switches from the normal operating mode to the error mode. To detect the error, a sensor connected to the control device can be provided in the force feedback actuator, for example a current sensor or a voltage sensor.

According to an advantageous embodiment of the invention, the force feedback actuator comprises power electronics that are electrically connected to the switching device. The electric machine can be controlled via the power electronics in order to generate a force feedback torque on a steering wheel coupled to the electric machine. The power electronics preferably comprise an inverter.

According to an advantageous embodiment of the invention, the power electronics are configured to control the first and second windings in parallel in the normal operating mode. In the method according to the invention, it can be provided that the power electronics control the first and second windings in parallel in the normal operating mode and only control the second winding in the fault mode.

Another object of the invention is a steering wheel with a force feedback actuator as described above.

The same advantages can be achieved that have already been explained in connection with the force feedback actuator.

• 1 ein Ausführungsbeispiel eines erfindungsgemäßen Force-Feedback-Aktuators in einer schematischen Darstellung in einem Normalbetriebsmodus;
• 2 der Force-Feedback-Aktuator gemäß 1 in einem Fehlermodus;
• 3 eine Detaildarstellung der elektrischen Maschine des Force-Feedback-Aktuators gemäß 1; und
• 4 eine Darstellung des Drehmoments des Force-Feedback-Aktuators gemäß 1 in Abhängigkeit von der Drehzahl im Vergleich zu bekannten Force-Feedback-Aktuatoren.

Further details and advantages of the invention will be explained below with reference to the embodiment shown in the drawings.

• 1 an embodiment of a force feedback actuator according to the invention in a schematic representation in a normal operating mode;
• 2 the force feedback actuator according to 1 in a failure mode;
• 3 a detailed representation of the electric machine of the force feedback actuator according to 1 ; and
• 4 a representation of the torque of the force feedback actuator according to 1 depending on the speed compared to known force feedback actuators.

In the 1 and 2 a force feedback actuator 1 according to an embodiment of the invention is shown, wherein in the illustration according to 1 in a normal operating mode and in the display according to 2 is in a fault mode. The force feedback actuator 1 according to the embodiment is designed as part of a steer-by-wire system, wherein the electric machine of the force feedback actuator 1, in particular a rotor of the electric machine 2, is coupled to a steering wheel of the steer-by-wire system, so that the electric machine 2 can apply a force feedback torque to the steering wheel.

The electric machine 1 comprises a first multi-phase, here three-phase, winding and a second multi-phase, here three-phase, winding, which are designed separately from one another. The first winding comprises three phase connections U1, V1, W2 and the second winding comprises three phase connections U2, V2, W2. As shown in 3 can be seen, the first winding comprises first turns 11 and the second winding comprises second turns 12, which are arranged such that both the first turns 11 and the second turns 12 are arranged around a common tooth 10 of the electrical machine 2. In this respect, the electrical machine 2 can therefore be operated with only one of the two windings, without the other of the windings being required to operate the electrical machine 2.

As shown in 1 and 2 As shown further, the electrical machine 2 is connected to a switching device 3. The switching device 3 contacts in particular the first and second windings of the electrical machine 2 via their phase connections U1, V1, W1, U2, V2, W2. The switching device comprises several semiconductor switches, in particular power semiconductor switches, for example MOSFETs, IGBTs or thyristors. In the exemplary embodiment, a total of five semiconductor switches S1, S2, S3, S4, S5 are provided as part of the switching device 3. The semiconductor switches S1, S2, S3, S4, S5 can optionally be put into an electrically conductive state or into an electrically non-conductive state. For example, the illustration in 1 the semiconductor switches S1 and S2 in an electrically non-conductive state and the semiconductor switches S3, S4, S5 in an electrically conductive state. The representation in 2 shows the semiconductor switches S1 and S2 in an electrically conductive state and the semiconductor switches S3, S4, S5 in an electrically non-conductive state.

A first semiconductor switch S1 is arranged between a first phase connection of the first winding U1 and a second phase connection of the first winding V1. A second semiconductor switch S2 is arranged between the second phase connection of the first winding U1 and a third phase connection of the first winding W1. A third semiconductor switch S3 is arranged between the first phase connection of the first winding U1 and a first phase connection of the second winding U2. A fourth semiconductor switch S4 is arranged between the second phase connection of the first winding V1 and a second phase connection of the second winding V2. A fifth semiconductor switch S5 is arranged between the third phase connection of the first winding W1 and a third phase connection of the second winding W2.

To control the switching device 3, in particular the semiconductor switches S1, S2, S3, S4, S5, the force feedback actuator 1 further comprises a control device 4. The control device can be designed, for example, as a programmable microcontroller. According to the invention, the control device is configured to control the switching device 3 in such a way that - in a 1 shown normal operating mode - each phase connection of the first winding U1, V1, W1 is electrically connected to exactly one phase connection of the second winding U2, V2, W2. In this respect, the first winding of the electrical machine 2 is connected in parallel to the second winding of the electrical machine 2. In this normal operating mode, the electrical machine 2 can be controlled via power electronics 5, for example comprising an inverter. For this purpose, the first phase connections of the windings U1, U2 are connected to a first phase connection U of the power electronics 5 and the second phase connections of the windings V1, V2 to a second phase connection V of the power electronics 5 and the third phase connections of the windings W1, W2 to a third phase connection W of the power electronics 5.

The control device 4 is further configured according to the invention to - in a 2 shown fault mode - to electrically connect all phase connections of the first winding U1, V1, W1 and to disconnect the phase connections of the second winding U2, V2, W2 are to be electrically separated from each other and from the phase connections of the first winding U1, V1, W1. In this respect, the first winding of the electrical machine 2 is short-circuited and the second winding remains open.

The control device 4 is also configured to detect an error in the force feedback actuator 1, for example based on a signal from a sensor not shown in the drawings. The sensor can be designed as a current sensor or a voltage sensor. The error can be, for example, an error in the power electronics 5, in particular a failure of the power electronics 5. The control device 4 is also configured to switch from the normal operating mode to the error mode when an error is detected. In the error mode, the short-circuited winding can generate a short-circuit current and thus a short-circuit torque, which counteracts the rotational movement of the steering wheel and thus the driver's steering request. Uncontrolled steering movements, in particular jerky steering movements, can thus be braked by a noticeable counter-torque.

The power electronics 5 are electrically connected to the switching device 3. In the normal operating mode, the power electronics 5 controls the first and second windings in parallel in order to generate a torque with the electric machine 2.

Optionally, the force feedback actuator can be 1 and 2 a resistor can be provided between a phase connection of the first winding U1, V1, W1 and the switching device 3. Alternatively, a resistor can be provided between several, in particular all, phase connections of the first winding U1, V1, W1 and the switching device 3. The short-circuit characteristic can be changed by the resistor or several resistors. The maximum of the short-circuit torque can be shifted to higher speeds by the resistor. By appropriately selecting the number of turns of the first winding, in particular in relation to the turns of the second winding, in combination with the selection of one or more suitable resistors, a particularly flexible setting of the short-circuit characteristic curve can be achieved.

In the case of the force feedback actuator 1 according to the exemplary embodiment, it is possible to influence its behavior in the fault mode by designing the electrical machine 2 without changing the behavior of the force feedback actuator 1 in the normal operating mode. The short-circuit torque can thus be set by selecting a suitable number of turns of the first winding 11. Furthermore, the torque characteristic of the force feedback actuator can be flexibly set in the fault mode. This will be explained below using the illustration in 4 explained. The 4 shows a curve 20 of the torque M of the force feedback actuator 1 according to 1 depending on the speed n.

For comparison, curves 21, 22 of force feedback actuators known from the prior art are shown. Curve 21 comes from a force feedback actuator whose electric machine 2 has a common three-phase winding with three phase connections. It can be seen that the maximum torque M according to curve 21 has a larger value than in the force feedback actuator 1 according to the invention. In this respect, a less fluctuating course of the torque over the speed can be achieved in the force feedback actuator 1 according to the invention.

Curve 22 comes from a force feedback actuator whose electric machine 2 also has a common three-phase winding with three phase connections. In addition, a resistor is provided between the phase connections of the electric machine in the force feedback actuator. This resistor shifts the maximum of the torque characteristic curve in the direction of higher speeds n compared to curve 21. It can be seen that the maximum of the torque M according to curve 22 has a larger value than in the force feedback actuator 1 according to the invention. In this respect, a less fluctuating course of the torque M over the speed n can be achieved in the force feedback actuator 1 according to the invention.

list of reference symbols

1

force feedback actuator

2

electric machine

3

switching device

4

control device

5

power electronics

S1-S5

semiconductor switches

U1, V1, W1

phase connection of the first winding

U2, V2, W2

phase connection of the second winding

U, V, W

phase connection of the power electronics

10

Tooth

11

first winding

12

second winding

M

torque

N

speed

Claims (10)

Force feedback actuator (1) for a steer-by-wire system with an electric machine (2) with at least a first winding (11) and a second winding (12) separate from the first winding (11), the first and second windings (11, 12) each having a plurality of phase connections (U1, V1, W1, U2, V2, W2), a switching device (3) which is electrically connected to the first and second windings (11, 12) and a control device (4) which is configured to control the switching device (3) such that - in a normal operating mode - each phase connection of the first winding (U1, V1, W1) is electrically connected to exactly one phase connection of the second winding (U2, V2, W2) and - in a fault mode - all phase connections of the first winding (U1, V1, W1) are electrically connected to one another and the phase connections of the second winding (U2, V2, W2) are electrically separated from each other and from the phase connections of the first winding (U1, V1, W1). Force feedback actuator (1) according to claim 1 , characterized by at least one resistor which is arranged between a phase connection of the first winding (U1, V1, W1) and the switching device (3). Force feedback actuator (1) according to one of the preceding claims, characterized in that the control device (4) is configured to detect an error in the force feedback actuator (1) and, when an error is detected, to switch from the normal operating mode to the error mode. Force feedback actuator (1) according to one of the preceding claims, characterized by power electronics (5) which are electrically connected to the switching device (3). Force feedback actuator (1) according to claim 4 , characterized in that the power electronics (5) are configured to control the first and the second winding (11, 12) in parallel in the normal operating mode. with a steering wheel and a force feedback actuator (1) according to one of the preceding claims. Method for operating a force feedback actuator (1) for a steer-by-wire system with an electric machine (2) with at least a first winding (11) and a second winding (12) separate from the first winding (11), the first and second windings (11, 12) each having a plurality of phase connections (U1, V1, W1, U2, V2, W2), a switching device (3) which is electrically connected to the first and second windings (11, 12) and a control device (4) which controls the switching device (3) such that - in a normal operating mode - each phase connection of the first winding (U1, V1, W1) is electrically connected to exactly one phase connection of the second winding (U2, V2, W2) and - in a fault mode - all phase connections of the first winding (U1, V1, W1) are electrically connected to one another and the phase connections of the second winding (U2, V2, W2) are electrically separated from each other and from the phase connections of the first winding (U1, V1, W1). procedure according to claim 7 , characterized in that at least one resistor is arranged between a phase connection of the first winding (U1, V1, W1) and the switching device (3). Method according to one of the Claims 7 or 8 , characterized in that the control device (4) detects an error in the force feedback actuator (1) and, when an error is detected, changes from the normal operating mode to the error mode. Method according to one of the Claims 7 until 9 , characterized in that the force feedback actuator (1) comprises power electronics (5) which is electrically connected to the switching device (3).

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