Steer-by-wire steering system and method for operating a steer-by-wire steering system

Abstract

The invention relates to a steer-by-wire steering system (1) comprising a steering column module (2) and a steering gear module (3), wherein the steering gear module (3) has a first steering control unit (4), a second steering control unit (5), a first power electronics unit (6), a second power electronics unit (7), a first electric actuator (8) and a second electric actuator (9), wherein the first steering control unit (4), the first power electronics unit (6) and the first electric actuator (8) are supplied with electrical energy via a first power supply path (U1) and the second steering control unit (5), the second power electronics unit (7) and the second electric actuator (9) are supplied with electrical energy via a second power supply path (U2), wherein at least one auxiliary battery (25) is arranged in at least one power supply path (U1, U2), wherein the steering column module (2) has at least one force feedback actuator (18,19) with an associated control unit (20, 21), wherein the steer-by-wire steering system (1) is designed such that, in the event of a failure of the first power supply path (U1) and the second power supply path (U2), so that only the at least one auxiliary battery (25) is available for electrical power supply, the current gradient of the auxiliary battery (25) is limited by the steering control unit (4, 5) in the power supply path (U1, U2) of the auxiliary battery (25) and / or by the control unit (20, 21) of the force feedback actuator (18, 19), and a method.

Description

[0001] The invention relates to a steer-by-wire steering system and a method for operating a steer-by-wire steering system.

[0002] Steer-by-wire steering systems are characterized by the absence of a mechanical link between a steering column module and a steering gear module. The steering column module includes a steering handle and at least one angle or torque sensor, whose signals are transmitted electrically to the steering gear module, where they are then converted, for example, into a position and / or force on a rack or pushrod. Due to the lack of a mechanical link, correspondingly high demands must be placed on reliability. To this end, the steering gear module comprises a first steering control unit, a second steering control unit, a first power electronics unit, a second power electronics unit, a first electrical actuator, and a second electrical actuator.The electric actuators are designed, for example, as electric motors coupled to the rack or pushrod, whereby the rotary motion of the electric motors is converted into a translational motion of the rack or pushrod to steer the wheels. The first steering control unit, the first power electronics, and the first electric actuator are supplied with electrical energy via a first power supply path. Similarly, the second steering control unit, the second power electronics, and the second electric actuator are supplied with electrical energy via a second power supply path. The first and second power supply paths are independent of each other.

[0003] Such power supply paths are described, for example, in DE 10 2022 001 268 A1. This design includes a primary battery configured as a high-voltage battery. Independent DC / DC converters are provided, each receiving the voltage of the high-voltage battery at its input. These DC / DC converters are designed as buck converters and convert the high-voltage voltage into a suitable voltage for the steer-by-wire steering system. The first DC / DC converter forms part of the first power supply path, and the second DC / DC converter forms part of the second power supply path. It is further proposed that a backup battery be included in at least one power supply path.

[0004] The steering column module has at least one force feedback actuator with an associated control unit. Preferably, the force feedback actuator and control unit are also redundantly configured, with the force feedback actuator(s) serving to generate a counter-torque at a steering handle so that the driver has the haptic feel of a conventional steering system. Furthermore, it serves to return the steering handle to a neutral position.

[0005] In an electronic on-board network, as described in DE 10 2022 001 268 A1, a power supply is therefore also possible if the high-voltage battery is defective or if both DC / DC converters are defective.

[0006] The invention is based on the technical problem of further improving the reliability of a steer-by-wire steering system and providing a corresponding method for operating such a steer-by-wire steering system.

[0007] The solution to the technical problem is achieved by a steer-by-wire steering system with the features of claim 1 and a method with the features of claim 6. Further advantageous embodiments of the invention are set forth in the dependent claims.

[0008] The steer-by-wire steering system comprises a steering column module and a steering gear module. The steering gear module includes a first steering control unit, a first power electronics unit, and a first electric actuator, which are supplied with electrical energy from a first power supply path. The steering gear module also includes a second steering control unit, a second power electronics unit, and a second electric actuator, which are supplied with electrical energy from a second power supply path. At least one auxiliary battery is located in at least one of the power supply paths. The steering column module also includes at least one force feedback actuator with an associated control unit.The steer-by-wire steering system is designed so that if both the primary and secondary power supply paths fail, leaving only the auxiliary battery available for electrical power, the steering control unit in the auxiliary battery's power supply path and / or the force feedback actuator control unit limits the current gradient of the auxiliary battery. This prevents the auxiliary battery voltage from briefly dropping below a threshold at which the control units would shut down, rendering steering impossible. If control units for a braking system are also connected to the power supply paths, a voltage drop would also prevent braking. Limiting the current gradient prevents this.The limitation is also implemented if another backup battery or supercapacitor is placed as a buffer in the other power supply path.

[0009] In one embodiment, the steering control unit is designed to control the associated electric actuator with reduced dynamics. For example, the electric actuator is controlled in such a way that the gear or pushrod speed and / or acceleration is set lower than specified by the input at the steering handle.

[0010] The resulting temporary geometric offset between steering wheel angle and steering angle can then be compensated for by the steering gear module with a certain time delay.

[0011] In another embodiment, the associated control unit of the force feedback actuator is designed to generate an increased counter-torque at a steering handle of the steering column module. This increased counter-torque prevents rapid changes in the steering handle's angle of rotation. As a result, the steering gear module receives instructions from the steering column module that do not require high dynamics from the electric actuator, so that the current gradients are indirectly limited by the steering handle.

[0012] The two measures can also be implemented simultaneously. Furthermore, it can be stipulated that an increased counter-torque is first applied to the steering handle, whereby, if this measure alone is insufficient, the steering control unit additionally limits the dynamics for the electric actuator in order to reduce the current gradient of the auxiliary battery.

[0013] In another embodiment, the steering column module comprises a first force feedback actuator, a second force feedback actuator, a first control unit and a second control unit, wherein the first force feedback actuator and the first control unit are connected to the first power supply path and the second force feedback actuator and the second control unit are connected to the second power supply path.

[0014] In another embodiment, the first power supply path includes a first DC / DC converter and the second power supply path includes a second DC / DC converter, both connected to a high-voltage battery at their inputs. The two DC / DC converters can be of different designs, thus reducing the risk of simultaneous failure due to the same fault. Alternatively, they can be identical in design, for example, featuring two independent windings on a common core as the secondary windings of a galvanically isolated DC / DC converter.

[0015] Regarding the procedural details, reference is made to the preceding explanations.

[0016] The invention is explained in more detail below with reference to a preferred embodiment. The single figure shows a schematic block diagram of a steer-by-wire steering system. In the Fig.Figure 1 schematically depicts a steer-by-wire steering system 1 comprising a steering column module 2 and a steering gear module 3. The steering gear module 3 includes a first steering control unit 4 and a second steering control unit 5, which are interconnected for data communication, as indicated by the double arrow. Furthermore, the steering gear module 3 includes a first power electronics unit 6 and a second power electronics unit 7. The steering gear module 3 also includes a first electric actuator 8 and a second electric actuator 9. The first electric actuator 8 has first stator windings 10, and the second electric actuator 9 has second stator windings 11, which are wound on a common stator. The two stator windings 10 and 11 drive a common rotor 12, the rotor shaft 13 of which is coupled to a rack 14. The coupling can, for example, be a gearbox.

[0017] The steering column module 2 comprises a steering handle 15 and a steering column 16, on which at least one rotation angle sensor 17 is arranged. Furthermore, the steering column module 2 comprises a first force feedback actuator 18 and a second force feedback actuator 19, as well as a first control unit 20 and a second control unit 21. The first control unit 20 and the second control unit 21 have a data connection, which is indicated by a double arrow. The first control unit 20 and the second control unit 21 are connected to the rotation angle sensor 17 via data transmission. The steering column module 2 is redundantly connected to the steering gear module 3 via two bus systems 22, 23. The first steering control unit 4, the first power electronics 6, and the first electrical actuator 8 are connected to a first power supply path U1, which includes a first DC / DC converter 24 and a backup battery 25.The auxiliary battery 25, for example, has a nominal voltage of 12 V, 24 V, or 48 V. On the input side, a high-voltage battery (not shown) is connected to the DC / DC converter 24. The first force feedback actuator 18 and the first control unit 20 are also connected to the first power supply path U1. The second steering control unit 5, the second power electronics 7, the second electric actuator 9, the second force feedback actuator 19, and the second control unit 21 are connected to a second power supply path U2, which includes a second DC / DC converter 26. The input side of the second DC / DC converter 26 is connected to the same high-voltage battery as the first DC / DC converter 24.

[0018] In the event of a double fault, for example, if both DC / DC converters 24, 26 are defective or if the high-voltage battery has failed, the auxiliary battery 25 is the only remaining electrical energy source available for performing an emergency maneuver. It must be ensured that excessive current gradients do not cause the voltage of the auxiliary battery 25 to fall below a shutdown threshold for the first steering control unit 4. Several options exist for limiting the current gradient of the auxiliary battery 25. In a first embodiment, the first control unit 20 detects that the second power supply path U2 is no longer available and that the first DC / DC converter 24 is no longer available (e.g., via a status signal from the DC / DC converter 24 on the first bus system 22).

[0019] The first control unit 20 then controls the first force feedback actuator 18 in such a way that it generates an increased counter-torque at the steering handle 15. This increased counter-torque does require energy from the auxiliary battery 25, but this is not critical because the currents are not very high. Due to the increased counter-torques, the driver can no longer generate high angular velocities at the steering handle 15, thus reducing the dynamic demands on the first steering control unit 4.

[0020] In an alternative embodiment, the first steering control unit 4 limits the dynamics of the first electric actuator 8 independently of the inputs at the steering handle 15. For this purpose, empirically determined values ​​can be stored that must not be exceeded in order to prevent the voltage at the auxiliary battery 25 from falling below the cut-off threshold. This leads briefly to an asynchrony between the angular position of the steering handle 15 and the steering angle of the wheels, which is acceptable for safely executing the emergency maneuver. In essence, the first steering control unit 4 applies a lower rack speed and acceleration than requested by the driver via an input at the steering handle 15, although the desired rack position is reached after a certain time. The first steering control unit 4 can also be configured to monitor parameters of the auxiliary battery 25 in order to adjust the dynamics.Finally, the two measures can also be combined.

[0021] The first force feedback actuator 18 generates an increased counter-torque at the steering handle 15, preventing the driver from setting a high steering angular velocity. This reduces the dynamic demands on the first steering control unit, thus limiting the current gradient of the auxiliary battery 25. The steering angle at the wheels, set by the steering gear module 3, follows the driver's input at the steering handle 15. Should the driver nevertheless make inputs that would result in an excessively high current gradient at the auxiliary battery 25, the steering control unit 4 limits these inputs to prevent the current gradient from falling below a critical threshold. This ensures that the voltage of the auxiliary battery 25 does not drop below a shutdown threshold for the control units. Reference symbol list 1 Steer-by-wire steering system 2 Steering column module 3 Steering gear module 4 first steering control unit 5 second steering control unit 6 first power electronics 7 second power electronics 8 first electric actuator 9 second electric actuator 10 first stator winding 11 second stator winding 12 Rotor 13 Rotor shaft 14 Rack and pinion 15 Steering handle 16 Steering column 17 Rotation angle sensor 18 first force feedback actuator 19 Second force feedback actuator 20 first control unit 21 second control unit 22 first bus system 23 second bus system 24 first DC / DC converter 25 backup batteries 26 second DC / DC converter U1 first power supply path U2 second power supply path QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 001 268 A1 [0003, 0005]

Claims

[1] Steer-by-wire steering system (1) comprising a steering column module (2) and a steering gear module (3), wherein the steering gear module (3) comprises a first steering control unit (4), a second steering control unit (5), a first power electronics unit (6), a second power electronics unit (7), a first electric actuator (8) and a second electric actuator (9), wherein the first steering control unit (4), the first power electronics unit (6) and the first electric actuator (8) are supplied with electrical energy via a first power supply path (U1) and the second steering control unit (5), the second power electronics unit (7) and the second electric actuator (9) are supplied with electrical energy via a second power supply path (U2), wherein at least one backup battery (25) is arranged in at least one power supply path (U1, U2), wherein the steering column module (2) comprises at least one force feedback actuator (18, 19) with an associated control unit (20, 21) shows,wherein the steer-by-wire steering system (1) is designed such that in the event of a failure of the first power supply path (U1) and the second power supply path (U2), so that only the at least one auxiliary battery (25) is available for electrical power supply, the current gradient of the auxiliary battery (25) is limited by the steering control unit (4, 5) in the power supply path (U1, U2) of the auxiliary battery (25) and / or by the control unit (20, 21) of the force feedback actuator (18, 19). [2] Steer-by-wire steering system according to claim 1, characterized by , that the steering control unit (4, 5) is designed to control the associated electrical actuator (8, 9) with reduced dynamics. [3] Steer-by-wire steering system according to claim 1 or 2, characterized by, that the associated control unit (20, 21) of the force feedback actuator (18, 19) is designed to generate an increased counter-torque at a steering handle (15) of the steering column module (2). [4] Steer-by-wire steering system according to any of the preceding claims, characterized by , that the steering column module (2) comprises a first force feedback actuator (18), a second force feedback actuator (19), a first control unit (20) and a second control unit (21), wherein the first force feedback actuator (18) and the first control unit (20) are connected to the first power supply path (U1) and the second force feedback actuator (19) and the second control unit (U2) are connected to the second power supply path (U2). [5] Steer-by-wire steering system according to any of the preceding claims, characterized by, that the first power supply path (U1) has a first DC / DC converter (24) and the second power supply path (U2) has a second DC / DC converter (26) which are connected on the input side to a high-voltage battery. [6] Method for operating a steer-by-wire steering system (1) according to claim 1, characterized by , that in the event of a failure of the first power supply path (U1) and the second power supply path (U2), so that only the at least one backup battery (25) is available for electrical power supply, the current gradient of the backup battery (25) is limited by the steering control unit (4, 5) in the power supply path (U1, U2) of the backup battery (25) and / or by the control unit (20, 21) of the force feedback actuator (18, 19), so that an emergency maneuver can be carried out without the voltage of the backup battery (25) dropping below a critical shutdown threshold.

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