Method and control system for operating an electronic steering device, and steering device

Abstract

The invention relates to a method for operating a steering device (1), in particular a steer-by-wire steering device, for a motor vehicle, in which method: a steering-wheel angle can be specified by means of a steering element (2) as a measure of a requested wheel steering angle for at least one steerable wheel (7) of the motor vehicle; and an electric motor (5) for steering assistance is controlled depending on the steering-wheel angle, wherein the electric motor (5) comprises a first drive winding (11) having a plurality of electrical phases (U, V, W) and a second drive winding (12) which is redundant with respect to the first drive winding (11) and has a plurality of phases (U, V, W), wherein each phase (U, V, W) is assigned a half-bridge (HB1, HB2, HB3) of a power electronics unit (13, 14), wherein a controllable blocking switch (SU, SV, SW) is arranged between each phase (U, V, W) and the associated half-bridge (HB1, HB2, HB3), and wherein each drive winding (11, 12) is assigned a control device (15, 16) for actuating the half-bridges (HB1, HB2, HB3). The method comprises the following steps: a) monitoring the steering device (1) for malfunctions; b) if a malfunction is detected by a first of the control devices (15), opening the first blocking switches (SU, SV, SW) assigned to the first control device (15); and c) if a further malfunction is detected by a second of the control devices (16), short-circuiting the drive winding (12) assigned to the second control device (16).

Description

[0001] R. 410481

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method and control system for operating an electronic steering device, steering device

[0006] The present invention relates to a method for operating a steering device, in particular a steer-by-wire steering device, for a motor vehicle, in which a steering wheel angle can be specified by means of a steering handle as a measure for a requested wheel steering angle for at least one steerable wheel of the motor vehicle, and in which an electric motor for steering assistance is controlled depending on the steering wheel angle, wherein the electric motor has at least one drive winding with several electrical phases which are operated by means of controllable half-bridges of a power electronics.

[0007] Furthermore, the invention relates to a control system for a steering device as described above, with power electronics comprising a half-bridge for each phase of the at least one drive winding.

[0008] Furthermore, the present invention relates to a steering device with such a control system.

[0009] State of the art

[0010] Methods, control systems, and steering devices of the type mentioned above are already known from the prior art. For example, German patent application DE 10 2012 105 143 A1 discloses a method for operating an electronic power steering system. This method provides that, upon detection of a serious fault in the electronic power steering system, the electric motor is switched off within a predetermined time period (R. 410481).

[0011] - 2 - is switched off, and that when the power steering assist is switched off, the electric motor is at least temporarily short-circuited. This is intended to bring the power steering system into a safe state if a malfunction occurs.

[0012] Disclosure of the invention

[0013] The inventive method with the features of claim 1 has the advantage that, firstly, the electric motor is redundantly constructed by having two drive windings, each with several phases, which are each controlled by power electronics. Each drive winding, together with the associated power electronics, forms a sub-machine of the electric motor. Each of these machines, or each of the drive windings, is assigned a control unit, thus ensuring redundant operation of the steering system in a compact installation space. The individual control units are either structurally separate units or a control unit with a common housing in which the individual control units are integrated, for example, in the form of subsystems of the control unit, which may be configured, for instance, on a common circuit board within the housing or on separate circuit boards.If one of the control units, drive windings, or sub-machines fails, steering assistance can still be provided by the remaining part of the steering system. According to the invention, a controllable interlock switch, in particular a phase isolator, is interposed between each phase of the respective drive winding and the respective half-bridge. This switch can electrically connect the phase to the half-bridge (interlock switch closed) or disconnect it (interlock switch open). To carry out the method, in a first step, a) the steering system is monitored for malfunctions. Specifically, the control units and / or the power electronics are monitored for malfunctions.If, in a subsequent step b), a malfunction of one of the sub-machines, in particular of a first of the control units, is detected, the interlock switches assigned to this control unit or sub-machine are opened. By opening the interlock switches between the affected part of R. 410481.

[0014] - 3 -

[0015] The power electronics and the associated phases ensure that the affected drive winding is completely disconnected from the first control unit. This prevents the counter-torque that would otherwise be generated by induction during the electric motor's rotation, thus guaranteeing continued operation of the electric motor. In particular, the continued operation of the electric motor, which is then controlled by the second control unit, is not dampened or slowed by the short circuit of the first power electronics. Therefore, in the first case, if the first control unit fails according to step b), continued operation of the steering system is ensured. If a malfunction is also detected by a second control unit, the drive winding assigned to the second control unit is short-circuited in step c). Furthermore, in this case, the second interlock switches assigned to the second control unit are closed.Short-circuiting the second drive winding ensures that the electric motor cannot rotate freely, but is instead dampened or braked by the second drive winding of the second sub-machine. This has the advantage that the entire steering system operates in a damped or braked manner in the event of a control unit failure, thus exerting a counter-torque on the steerable wheels. This allows the vehicle to remain steerable and be brought to a safe state. If all the interlock switches were open, the electric motor would not be able to exert any counter-torque on the steering system, meaning the associated steerable wheels would be freely pivoting while driving. This would prevent precise longitudinal steering of the vehicle. In particular, it would prevent the vehicle from being steered using the braking system.However, if, as provided in the present invention, the electric motor generates a counter-torque through the short-circuited drive winding, a yaw moment can be generated by selectively applying a braking torque to one of the wheels, in particular to one of the steerable wheels. This yaw moment acts on the motor vehicle and thereby causes the steerable wheels to pivot in a controlled manner, thus enabling the motor vehicle to be steered in a controlled manner. This allows the motor vehicle, for example, to be safely steered to the side of the road and brought to a standstill even if the control units have failed. R. 410481.

[0016] - 4 -

[0017] According to a preferred embodiment of the invention, the drive winding associated with the second control unit is short-circuited by energizing the associated half-bridges and closing at least the second blocking switches associated with the second control unit. In particular, the short-circuiting is effected by closing the second blocking switches and the low-side switches of the half-bridges of the second drive winding.

[0018] Preferably, a first protection module is assigned to the first control unit and a second protection module to the second control unit. In step b), activation of the second protection module is enabled. This module is configured to short-circuit the second drive winding and close the second interlock switches upon activation. Only in step c) is the second protection module then activated and the second drive winding short-circuited accordingly. Step b) is performed by the control units, and step c) is performed using the described protection modules. The protection modules thus act as degradation means by which the actual function of the steering system is degraded step by step to ensure the safety of the vehicle. The protection modules are already enabled in step b), meaning they are allowed or released for activation, and the actual activation only takes place in step c).

[0019] Preferably, the control units are interconnected via a communication link to monitor the status of each other. Thus, the steering system is monitored for malfunctions, in part, by the control units monitoring each other. If the second control unit detects a malfunction in the first, it activates the second protection module, enabling its activation. Only when a malfunction is detected in the first control unit is the first protection module, which was previously enabled, activated, thereby deactivating the entire steering system and switching it to the safe state as described in step c). R. 410481

[0020] - 5 -

[0021] Preferably, the functionality of the protection modules is checked by the control units, in particular the functionality of the first protection module is checked by the first control unit and that of the second protection module by the second control unit.

[0022] The control system according to the invention, with the features of claim 5, is characterized in that it is specifically designed to execute the method according to the invention, as described above, when used as intended. This results in the advantages already mentioned above. In particular, the control system comprises the first protection module assigned to the first control unit and the second protection module assigned to the second control unit. This results in the advantages already mentioned above.

[0023] It is particularly advantageous for the first and second control units to be connected to each other via at least one communication link, especially a CAN bus. This makes mutual monitoring of the control units possible.

[0024] Furthermore, it is preferably provided that the protection modules each have a release input for releasing or enabling activation, wherein the first control unit is connected to the release input of the first protection module and the second control unit is connected to the release input of the second protection module in order to activate it upon detection of a further malfunction and to switch the steering device to the safe state according to step c).

[0025] Preferably, the power electronics have a B6 bridge circuit for each of the drive windings.

[0026] The steering device according to the invention, with the features of claim 10, is characterized by the control system according to the invention. This results in the advantages already mentioned above. Further advantages and preferred features and combinations of features become apparent in particular from the foregoing and from the claims. R. 410481

[0027] - 6 -

[0028] The invention will now be explained in more detail with reference to the drawings. To this end, we show...

[0029] Figure 1 shows a steering device for a motor vehicle,

[0030] Figure 2 shows a simplified representation of the steering system's control system.

[0031] Figure 3 shows a simplified detail view of the control system from Figure 2.

[0032] Figure 4 shows an operating procedure for operating the tax system, and

[0033] Figure 5 shows another detailed view of the control system.

[0034] Figure 1 shows a simplified representation of an advantageous steering device 1 for a motor vehicle, designed as a so-called steer-by-wire steering device. The steering device 1 includes a steering handle 2, which in this case is designed as a steering wheel. The steering handle 2 is connected via a bearing shaft 3 to a sensor device 4, which detects the steering wheel angle set by the user on the steering wheel 2 as well as the steering torque applied to the steering handle 2. Furthermore, the steering device 1 includes an electric motor 5, which is connected via a steering gear 6 to steerable wheels 7 of the motor vehicle in order to set a desired wheel steering angle. The actuator 5 is connected to the sensor 4 via an advantageous control system 8 in order to pivot the wheels 7 by a desired wheel steering angle depending on the detected steering wheel angle and, optionally, the applied steering torque.The steering gear 6 includes, in particular, a rack 9 which is operatively connected to the actuator 5 via a transmission 10. The transmission 10 is, for example, a belt drive or a gear drive.

[0035] Figure 2 shows a simplified representation of the control system 8. The electric motor 5 is designed as a redundant actuator, having two drive windings 11, 12 which can be controlled independently of each other. R. 410481

[0036] - 7 - are used to operate the electric motor 5. Each of the drive windings 11, 12 is assigned a power electronics unit 13, 14, by means of which the respective assigned drive winding 11, 12 with its respective phases U, V, W can be operated. Each power electronics unit 13, 14 is assigned a control unit 15, 16, which controls the corresponding drive winding depending on the sensor values ​​detected by the sensor device 4.

[0037] Figure 3 shows a simplified detail view of the electric motor 5 with the power electronics 13, 14. Each drive winding 11, 12 has several phases U, V, W, although only three phases are shown here as an example. Naturally, each drive winding 11, 12 can also have more phases. For each of the phases U, V, W, the respective power electronics 13, 14 has a half-bridge HB1 to HB3, each of which has two semiconductor switches connected in series, which can be controlled by the respective control unit 15, 16. Each of the half-bridges HB1 to HB3 is connected to the respective phase U, V, W by a blocking switch Su, Sv, Sw, in particular a phase isolator. Opening the blocking switches Su, Sv, Sw disconnects the half-bridges HB1 to HB3 from the drive winding 11, 12, and closing the blocking switches Su, Sv, Sw connects the phases U, V, W to the respective half-bridge.

[0038] As shown in Figure 2, each power electronics unit 13, 14 is further assigned a protection module 17, 18, which serves to bring the steering device 1 into a safe state if necessary. For this purpose, the control system 8 executes the procedure described below.

[0039] Figure 4 shows an example flowchart to simplify the explanation of the procedure.

[0040] Upon commissioning of the steering device 1, the steering device 1 is initially operated in a normal operating mode N, so that, depending on a steering wheel angle, the actuator 5 is controlled to set a wheel steering angle at the wheels 7. R. 410481

[0041] - 8 -

[0042] After commissioning, the control units 15 and 16 also begin to monitor each other for functionality in step a). For this purpose, they are linked to each other by at least one communication connection 19. The communication connection 19 is, for example, a CAN bus connection of the vehicle.

[0043] For example, if control unit 15 detects a malfunction F1 in the other control unit 16, the functioning control unit 15 or 16 controls the protection module 17 or 18 assigned to it in step b) to enable or unlock its activation in a first safety level.

[0044] The protection modules 17, 18 are designed to close the blocking switches Su, Sv, Sw of the associated power electronics 13 on the one hand and to control the switches of the half-bridges of the respective associated drive winding 12,13 on the other hand in order to short-circuit the respective associated drive winding 12,13.

[0045] For example, due to a detected malfunction of the control unit 16, in step b) the locking switches Su, Sv, Sw of the associated power electronics 14 are also opened and the protection module 17 is unlocked or enabled for activation. This results in a first safety state S1 of the steering device 1, which makes it possible for the steering device 1 to continue operating in a step S3 with only the control unit 15 and the remaining drive winding 11, without the drive winding 12 generating a counter-torque through back-induction.

[0046] However, the functionality of control units 15 and 16 continues to be monitored according to step a). If it is detected that the remaining control unit 15 has also failed or exhibits a critical malfunction F2, a second safety state S2 is initiated by step c).

[0047] The second protection module 17, which has already been enabled, is activated, causing it to close the associated locking switches Su, Sv, Sw and short-circuit the associated drive winding 11. This ensures that the steerable wheels 7 are not affected by the current flowing into the drive winding 11. R. 410481

[0048] - 9 - The induced counter-torque of the electric motor 5 during an adjustment of the wheel steering angle is damped in its freedom of movement, and consequently, a wheel steering angle can be set in a controlled manner. By short-circuiting the drive windings 11 and closing the locking switches Su, Sv, Sw of the drive windings 11, it is ensured that a counter-torque is induced in the electric motor 5 when a wheel steering angle is changed, so that only a damped change of the wheel steering angle is possible. This advantageously enables safe continuation of driving or bringing the entire vehicle into a safe state, since a wheel steering angle can be adjusted by applying a targeted braking torque to at least one of the vehicle's wheels.

[0049] By applying a targeted braking torque, the vehicle is subjected to a yaw moment, which leads to an adjustment of the wheel steering angle. While the performance capabilities of such emergency steering are limited, they are sufficient to, for example, safely guide the vehicle onto a shoulder and bring it to a standstill. The advantageous control of the control system 8 thus ensures that, in the event of a failure of both control units, the targeted damping of the electric motor 5 is used to achieve a steering maneuver using braking torques.

[0050] Figure 5 shows a simplified detail view of the control system 8 with the two sub-machines 5_1 and 5_2 according to an exemplary embodiment. The control units 15, 16 are each connected to gate drivers 21, 22 of the respective power electronics 13, 14 to operate the power electronics 13, 14. The interlock switches Su, Sv, Sw are connected downstream of these. As mentioned previously, the control units 15, 16 are connected to each other, in particular by a CAN bus 20, to enable mutual monitoring.

[0051] The control units 15, 16 each include a microcontroller M15, M16, which, depending on a predefined steering wheel rotation angle, can determine the wheel steering angle and control the associated power electronics 13, 14 accordingly. Each microcontroller M15, M16 is associated with a feedforward control 23, 24, which controls the operation of the respective microcontroller R. 410481

[0052] - 10 -

[0053] M15, M16 are also monitored, so that the failure of the second control unit 16,15 can also be reliably detected. The pre-controls 23, 24 and the microcontrollers M15, M16 are each connected to an activation input 25,26 of the respective protection module 17, 18.

[0054] As soon as one of the protection modules 17, 18 is enabled or allowed to be activated, it reports the activated state back to the associated microcontroller M15, M16, as shown by a dashed arrow in Figure 4. A standard B6 test or lockout switch test can then be used to verify whether the respective sub-machine 5_1 and 5_2 of the electric motor 5 has been safely deactivated.

[0055] The advantageous steering device 1 ensures that a safe emergency steering system in two stages is provided with minimal installation space, which in any case guarantees that the motor vehicle is brought to a safe state.

Claims

R. 410481 - 11 - Claims 1. Method for operating a steering device (1), in particular a steer-by-wire steering device, for a motor vehicle, in which a steering wheel angle can be specified by means of a steering handle (2) as a measure for a requested wheel steering angle for at least one steerable wheel (7) of the motor vehicle, and in which an electric motor (5) is controlled for steering assistance depending on the steering wheel angle, wherein the electric motor (5) has a first drive winding (11) with several electrical phases (U,V,W) and a second drive winding (12) redundant to the first drive winding (11) with several phases (U,V,W), wherein each phase (U,V,W) is assigned a half-bridge (HB1, HB2, HB3) of a power electronics (13, 14), wherein a controllable interlock switch (Su, Sv, Sw) is interposed between each phase (U,V,W) and the respective half-bridge (HB1, HB2, HB3), and wherein each Drive winding (11, 12) each with a control unit (15,16) for controlling the associated half-bridges (HB1, HB2, HB3) and locking switches (Su, Sv, Sw) with the following steps: a) Monitoring the steering system for malfunctions, b) Upon detection of a malfunction by one of the first control units (15), opening the first locking switches (Su, Sv, Sw) assigned to the first control unit (15), c) Upon detection of an additional malfunction by a second of the control units (16), short-circuiting the drive winding (12) assigned to the second control unit (16).

2. Method according to claim 1, characterized in that the drive winding (12) assigned to the second control unit is short-circuited by activating the assigned half-bridges and closing at least the second locking switches (Su,Sv,Sw) assigned to the second control unit. R. 410481 - 12 - 3. Method according to claim 1, characterized in that a first protection module (17) is assigned to the first control unit (15) and a second protection module (18) is assigned to the second control unit (16), wherein in step b) activation of the first protection module (17) is enabled, and that in step c) the first protection module (17) is activated, which is configured to short-circuit the drive winding (11).

4. Method according to one of the preceding claims, characterized in that the control units (15, 16) each monitor the status of the other control unit (16, 15) via a communication link (19).

5. Method according to one of the preceding claims, characterized in that the functionality of the first protection module (17) and / or the second protection module (18) is checked by the control units (15, 16).

6. Control system (8) for a steering device (1) for a motor vehicle, in which a steering wheel angle can be specified by means of a steering handle (2) as a measure for a requested wheel steering angle for at least one steerable wheel (7) of the motor vehicle, and in which an electric motor (5) is controlled for steering assistance depending on the steering wheel angle, wherein the electric motor (5) has a first drive winding (11) with several first electrical phases (U, V, W) and a second drive winding (12) redundant to the first drive winding (11) with several second electrical phases (U, V, W), with power electronics (13, 14) which has a half-bridge (HB1, HB2, HB3) for each phase (U, V, W), wherein a controllable interlock switch (Su, Sv, Sw) is interposed between each phase and the respective half-bridge (HB1, HB2, HB3), and wherein a control unit is connected to each drive winding (11, 12). (15,16) to control the half-bridges (HB1,HB2,HB3) is assigned, characterized in that the control system (8) is specifically designed to execute a method according to one of claims 1 to 4 when used as intended. R. 410481 - 13 - 7. Control system according to claim 5, characterized in that the first control unit (15) and the second control unit (16) are connected to each other by a communication link (19), in particular CAN bus.

8. Control system according to one of claims 5 or 6, characterized in that a first protection module (17) is assigned to the first control unit (15) and a second protection module (18) is assigned to the second control unit (16), wherein the first protection module (17) is configured to short-circuit the first drive winding (11), and that the second protection module (18) is configured to short-circuit the second drive winding (12).

9. Control system according to one of the preceding claims, characterized in that the protection modules (17, 18) each have an enable input (25, 26), wherein the first control unit (15) is connected to the enable input (25, 26) of the first protection module (17) and the second control unit (16) is connected to the enable input (25, 26) of the second protection module (18).

10. Control system according to one of the preceding claims, characterized in that the respective power electronics (13,14) for the respective associated drive windings (11,12) each has a B6 bridge circuit.

11. Steering device (1) for a motor vehicle, in which a steering wheel angle can be specified by means of a steering handle (2) as a measure for a requested wheel steering angle for at least one steerable wheel (27) of the motor vehicle, and in which an electric motor (5) is controlled for steering assistance depending on the steering wheel angle, wherein the electric motor (5) has a first drive winding (11, 12) with several first electrical phases (U, V, W) and a second drive winding (12) redundant to the first drive winding (11) with several second electrical phases (U, V, W), characterized by a control system (8) according to one of claims 5 to 9.

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