STEER-BY-WIRE-LENKSYSTEM

Description

Technical area

[0001] The invention relates to steer-by-wire steering systems for motor vehicles, and in particular to an architecture for the components of the steer-by-wire steering system with which the requirements regarding functional safety can be met. Technical background

[0002] Future steering systems will be designed as steer-by-wire steering systems. Steer-by-wire steering systems eliminate the need for an intermediate steering shaft, which provides a mechanical connection between a steering handle (steering wheel) and a rack mechanically coupled to the joint to the wheels. Such a steering system has a steering wheel unit that communicates with a steering unit. A steering angle is detected in the steering wheel unit and transmitted to the steering unit, which converts the corresponding steering wheel angle into a steering angle for the steered wheels. The steering wheel unit has a feedback actuator connected directly or via a gear to the steering handle to provide the driver with force feedback, ensuring a pleasant steering feel and reliable steering operation.

[0003] Due to the lack of a mechanical connection between the steering wheel unit and the steering unit, there are high safety requirements to reliably record the steering angle information and transmit it to the steering unit.

[0004] From the publication IN 2019 21007278A, a system for dynamically changing the steering ratio of a motorized vehicle to control the angle of the drive wheels is known. The system comprises a steering control unit, two steering angle generator units, a steering control mechanism, at least one pair of steering motors, and a torque feedback unit. The steering angle generator unit, which is operatively connected to the steering control mechanism, collects data from sensors provided within the vehicle. A steering angle signal is then generated to control the steering control unit. The system is provided with a first steering angle generator unit and a second steering angle generator unit, each of the steering angle generator units operating independently of one another to generate the steering angle for the movement of the wheels. The steering control unit is configured to check the plausibility of the steering angle.

[0005] The document DE 10 2019 007 715 A1 discloses a steer-by-wire system for a vehicle, comprising a first subsystem and a second subsystem, which are independent of one another and are each designed to detect a steering handle angle of a steering handle of the vehicle by means of a steering handle angle sensor and to steer the vehicle by adjusting a wheel angle of at least one wheel of the vehicle as a function of the detected steering handle angle by means of a steering actuator unit, wherein a third subsystem which is independent of the two subsystems and is designed to detect the steering handle angle of the steering handle of the vehicle by means of a third steering handle angle sensor and to steer the vehicle as a function of the detected steering handle angle by means of at least one lateral guidance influencing system which is independent of the first subsystem and second subsystem.

[0006] Document WO 02 / 32742 A1 discloses a method for operating a control unit for a steer-by-wire steering system of a vehicle, wherein the input signals steering wheel angle, steering angle, restoring torque acting on the steered wheels from a feedback actuator, and torque transmitted to a steering handle are detected. The detected input signals are monitored by plausibility checks and / or analytical redundancy, and wherein at least one steering actuator acting on the steered wheels of the vehicle is controlled as a function of the steering wheel angle. At least one feedback actuator acting on a steering wheel is controlled as a function of the restoring torque. The functions of the control unit and the availability of a fallback level, as well as a device for activating the fallback level, are monitored, and switching from the steer-by-wire steering system to the fallback level occurs when a fault occurs in the steer-by-wire steering system.

[0007] The document DE 102 48 343 A1 discloses a method for controlling an actuating force simulator of a vehicle steering system, which actuating force simulator is assigned to a steering actuating device that can be actuated by a driver, comprising the steps of: determining at least one first input variable that describes a driving dynamics state of the vehicle (driving dynamics variable), determining at least one second input variable that describes a force acting on the steerable wheels of the vehicle ordescribes a torque acting on the steerable wheels of the vehicle connected or connectable actuating means (actuating torque), determining at least one third input variable which describes the angle of pivoting of the steerable wheels of the vehicle (actuating angle), determining at least one output variable on the basis of the at least three input variables, which output variable describes a torque acting on the steering actuating device (actuating torque), and controlling the actuating force simulator in accordance with the determined actuating torque in order to apply a specific actuating torque or actuating force to the steering actuating device.

[0008] Other conventional solutions for redundantly designing a control unit in the steering wheel unit are technically complex, and therefore it is the object of the present invention to provide an improved steer-by-wire steering system having a signal processing architecture that is cost-effective and can meet the requirements with regard to functional safety. Disclosure of the invention

[0009] This object is achieved by the steer-by-wire steering system according to claim 1.

[0010] Further embodiments are specified in the dependent claims.

[0011] According to a first aspect, a steer-by-wire steering system for steering a motor vehicle is provided, comprising: a steering wheel unit comprising: ∘ a steering handle; ∘ a plurality of steering wheel angle sensors for redundantly detecting steering wheel angle information, ∘ a feedback unit configured to exert haptic feedback on the steering handle; o a control unit connected to a steering unit via a first or a private data bus system in order to receive an indication of a feedback torque and to control the feedback unit so that it exerts the haptic feedback on the steering handle; a steering unit comprising: ∘ a steering actuator connected to steered wheels via a steering mechanism in order to adjust the steering angle of the steered wheels; ∘ a steering control unit configured to receive a plurality of steering wheel angle information items from the plurality of steering wheel angle sensors, to verify the plausibility of the information, and to control the steering actuator depending on the verified steering wheel angle; whereby the steering wheel angle sensors transmit the respective steering wheel angle information to the steering unit via separate communication connections.

[0012] The safety requirements for steer-by-wire steering systems are high. In particular, safety targets for steering systems in motor vehicles are defined according to ISO 26262. In this regard, it is stipulated that the steering wheel angle information must be available in the steering unit that controls the steering actuators in accordance with the ASIL D safety standard. The haptic feedback function, in contrast, only needs to meet the less restrictive ASIL B safety standard. Due to the high safety requirements regarding its availability, the steering unit must be designed with complete redundancy.

[0013] The system architecture of a steer-by-wire steering system proposed above proposes implementing a redundant steering wheel angle sensor in the steering wheel unit and connecting it separately to a control unit of the steering unit, so that the plausibility check of the steering wheel angle can take place in the steering unit. This has the advantage that, on the one hand, the control unit of the steering wheel unit can be designed very simply, especially with a single channel, since the haptic feedback only needs to be ASIL B-compliant, whereas the control unit of the steering unit must be dual-channel anyway, i.e., designed to process two redundant steering wheel angles, and redundant. Therefore, the technical requirements for the higher safety level (ASIL D) for angle plausibility check are already met here.

[0014] The protection of the steering wheel angle information corresponds to a safety level ASIL B and can be provided as plausibility-checked steering wheel angle information according to the safety level ASIL D in the control unit of the steering unit.

[0015] Furthermore, the components of the steering unit can be designed redundantly to ensure a high level of reliability.

[0016] It can be provided that the steering wheel angle sensors are supplied with electrical power from different power grids via separate power supplies. This allows the steering wheel angle sensors to be supplied with electrical power independently, providing increased reliability in the event of a power supply failure.

[0017] By way of example only, it is mentioned that the separate communication connections may comprise a separate signal connection between each of the plurality of steering wheel angle sensors and the steering unit, wherein the signal connection comprises an electrical signal line for transmitting sensor signals. This ensures independence from digital data bus systems.

[0018] Also as an example, it can alternatively be provided that the separate communication connections comprise a respective data bus system for transmitting the steering wheel angle information from each of the plurality of steering wheel angle sensors and the steering unit, wherein in particular one of the data bus systems corresponds to the first data bus system via which the steering unit transmits the feedback torque to the control unit of the steering wheel unit.

[0019] Accordingly, the steering angle sensors can be connected to the steering control unit of the steering unit via separate communication connections. This can be achieved by connecting directly to the steering unit's control unit via a signal line or by using separate bus systems, such as CAN, FlexRay, Ethernet, or another bus system.

[0020] According to the invention, a first of the steering wheel angle sensors is directly connected to the feedback unit to provide the steering wheel angle information in the control unit, wherein the control unit is connected to the steering unit to transmit the corresponding steering wheel angle information from the control unit to the steering unit via the first or the private data bus system, wherein a second of the steering wheel angle sensors is connected to the steering unit via a second data bus system.

[0021] Furthermore, the steering wheel unit's feedback unit can be designed non-redundantly. This saves effort and meets the requirements for the functional safety of this component.

[0022] It can be provided that the first or the second data bus system is in communication connection with another vehicle system.

[0023] According to a further aspect, a method for operating the above steer-by-wire steering system is provided, comprising the following steps: Transmitting the steering wheel angle information from the steering wheel unit to the steering unit via separate communication connections, verifying the plausibility of the steering wheel angle information to obtain a plausibility-based and secured steering wheel angle; and controlling the steering actuator depending on the secured steering wheel angle. Brief description of the drawings

[0024] Embodiments are explained in more detail below with reference to the attached drawings. They show: Figure 1 shows a schematic representation of an exemplary steer-by-wire steering system; Figure 2 shows a schematic representation of another exemplary steer-by-wire steering system; and Figure 3 shows a schematic representation of a steer-by-wire steering system according to an embodiment. Description of embodiments

[0025] Figure 1 shows a schematic representation of an exemplary steer-by-wire steering system 1. The steer-by-wire steering system 1 has a steering wheel unit 2 and a steering unit 3.

[0026] The steering wheel unit 2 serves to specify a steering wheel angle and comprises a steering handle 21, in particular in the form of a steering wheel, which is coupled to a first steering wheel angle sensor 22 and a second steering wheel angle sensor 23 in order to achieve redundant detection of the current steering wheel angle. For example, the first steering wheel angle sensor 22 and the second steering wheel angle sensor 23 can be arranged on a steering wheel shaft 24 that is firmly connected to the steering wheel 21. The steering wheel angle sensors 22, 23 can be contactless sensors and, in particular, can be based on a magnetic or optical measuring principle in a manner known per se.

[0027] Furthermore, the steering wheel 21 is provided with a feedback unit 25, via which a steering torque can be applied to the steering wheel 21 via the steering wheel shaft 24, enabling so-called force feedback. Force feedback corresponds to haptic feedback intended to provide the vehicle driver with a realistic steering feel. The haptic feedback can, for example, be a feedback torque acting counteracting a manual steering torque. For this purpose, lateral forces acting on the steered wheels are appropriately transmitted to the steering wheel 21 in the form of a counter-torque to the manual steering torque. This allows the driver to haptically perceive road surface characteristics.

[0028] The feedback unit 25 typically includes a feedback actuator 26 and a steering torque sensor 27. The feedback actuator 26 is configured to adjust a haptic feedback in a manner known per se depending on lateral forces or steering torques acting externally on the steered wheels.

[0029] A control unit 28, for example in the form of a microcontroller, is provided to obtain information about the steering torque acting on the steering wheel shaft 24 and detected by the steering torque sensor 27, and to control a power driver circuit 29 accordingly. For this purpose, the feedback unit 25 is connected to the steering unit 3 and, if applicable, other vehicle systems via a first CAN A data bus system, such as CAN, FlexRay, Ethernet, or the like. A private CAN data bus system can also be used between the steering unit 3 and the steering wheel unit 2 to transmit the restoring torque.

[0030] In the example shown, the steering wheel angle sensors 22, 23 can be powered via separate power supplies 5 from two independent power supply networks 6 (12V main, 12V backup) in order to ensure redundant operational reliability of the steering wheel angle sensors 22, 23 with regard to power failure.

[0031] Furthermore, the steering wheel angle sensors 22, 23 can be connected by their outputs to the steering unit 3 via separate communication connections 7. The communication connection 7 between the first steering wheel angle sensor 22 and the steering unit 3 can be established via the first data bus system CAN A, and the communication connection 7 between the second steering wheel angle sensor 23 and the steering unit 3 can be established via a second data bus system CAN B. The first data bus system CAN A and the second data bus system CAN B can, if necessary, be connected to other vehicle systems 10.

[0032] The steering unit 3 has a steering control unit 31, which can be configured with a microcontroller 31. Furthermore, the steering unit 3 has a power driver circuit 32 and a steering actuator 33 controlled via the power driver circuit 32. The steering actuator 33 is preferably configured as an electric motor and is connected to a rack 8 via a steering mechanism 34. The rack 8 is arranged for translational movement and is mechanically coupled to steered wheels 9 in order to bring them into a steering position.

[0033] The steering control unit 31 is configured to assume the function of steering the steered wheels 9. The steering angle of the steered wheels 9 can be adjusted by adjusting the steering actuator 33. The steering angle of the steered wheels 9 is adjusted according to a secured steering wheel angle, which results from first steering wheel angle information and second steering wheel angle information. The first steering wheel angle information and the second steering wheel angle information are provided by the first and second steering wheel angle sensors 22, 23 via the respective communication connection 7. The received steering wheel angle information is validated in the steering control unit 31 of the steering unit 3 in order to secure the steering wheel angle. In this way, the steering wheel angle secured with a high level of security is available in the steering unit 3.

[0034] The steering angle information from the first and second steering wheel angle sensors 22, 23 is transmitted via two separate data bus systems 7, the first data bus system CAN A and the second data bus system CAN B, respectively. Each of the data bus systems 7 can also be configured to transmit additional data. For example, the first data bus system 7 CAN A can transmit the steering angle information from the first steering wheel angle sensor 22 to the steering unit 3 and can also be used to transmit the feedback torque from the steering unit 3 to the control unit 28.

[0035] In the example of Figure 2The steering wheel angle sensors 22, 23 are not connected to the steering unit 32 via a respective data bus system 7. Instead, the steering wheel angle sensors 22, 23 are connected directly to corresponding signal inputs 36 of the steering unit 3 via signal lines 7'. This represents a simplification that allows for faster communication, more stable timing, and higher signal resolution regarding the steering wheel angle information transmitted to the steering unit 3. The signal lines 7' can comprise electrical connecting lines for transmitting a digital or analog sensor signal.

[0036] The design of the Figure 3 shows a steer-by-wire steering system in which the second steering wheel angle sensor 23 is connected directly to the steering unit 3 via the second data bus system 7 or the second signal line 7'.

[0037] The first steering wheel angle sensor 22, however, is read via the control unit 28 of the steering wheel unit 2. Thus, the steering wheel angle information from the first steering wheel angle sensor 22 is available in the control unit 28 of the steering wheel unit 2. As described above, the control unit 28 is connected to the steering unit 3 via the first data bus system 7 and uses the first data bus system CAN A, with which the steering wheel unit 2 is already connected to the steering unit 3, to transmit the restoring torque from the steering unit 3 to the steering wheel unit 2. Thus, the first data bus system CAN A or the private data bus privateCAN between the steering wheel unit 2 and the steering unit 3 can be used additionally to transmit the redundant steering wheel angle information.

[0038] Thus, the steering wheel angle information can be transmitted via various routes to the steering unit 3, where the plausibility check of the steering angle information can be performed to obtain the plausibility-checked steering wheel angle. In this way, due to the lower safety level, the feedback unit 25 of the steering wheel unit 2 only needs to be designed with a single channel or non-redundantly, since it only needs to comply with the ASIL B safety level. The required plausibility check of the steering angle information, however, takes place in a unit with a high safety level. This unit corresponds to the steering unit 3, which is already designed according to the high required safety level of ASIL D.

[0039] In a further embodiment, the plausibility check of the steering wheel angle information can also be carried out in a control unit in the vehicle that is separate from the steering unit 3 and has a corresponding safety integrity and redundancy in accordance with the required safety level. List of reference symbols

[0040] 1Steer-by-wire steering system 2Steering wheel unit 21Steering handle 22First steering wheel angle sensor 23Second steering wheel angle sensor 24Steering wheel shaft 25Feedback unit 26Feedback actuator 27Steering torque sensor 28Control unit 29Power driver circuit 3Steering unit 31Steering control unit 32Power driver circuit 33Steering actuator 34Steering mechanism 5Power supplies 6Supply power network 7Communication connections 8Steering rack 9Steered wheels CAN AFirst data bus system CAN BSecond data bus system privateCANPrivate data bus system 36Signal inputs

Claims

1. Steer-by-wire steering system (1) for steering a motor vehicle, comprising: - a steering wheel unit (2) which has: ∘ a steering handle (21); ∘ a plurality of steering wheel angle sensors (22, 23) for redundant detection of steering wheel angle information; ∘ a non-redundant feedback unit (25) which is designed to apply haptic feedback or a feedback torque to the steering handle (21); ∘ a control unit (28) which is connected to a steering unit (3) via a first or a private data bus system (CAN A, privateCAN) in order to receive information about the haptic feedback or the feedback torque and to control the feedback unit (25) in such a way that it applies the haptic feedback or the feedback torque to the steering handle (21); - the steering unit (3), which has: ∘ a steering actuator (33) which is connected to steered wheels (9) via a steering mechanism (34) in order to adjust the steering angle of the steered wheels (9); ∘ a steering control device (31) which is designed to receive a plurality of items of steering wheel angle information from the plurality of steering wheel angle sensors (22, 23), to check the plausibility of said information, and to control the steering actuator (33) depending on the steering wheel angle which has been checked for plausibility and safety; wherein the steering wheel angle sensors (22, 23) transmit the respective items of steering wheel angle information to the steering unit (3) via separate communication connections (7), wherein a first of the steering wheel angle sensors (22) is connected directly to the feedback unit (25) in order to provide the steering wheel angle information in the control unit (28), wherein the control unit (28) is connected to the steering unit (3) in order to transmit the corresponding steering wheel angle information from the control unit (28) to the steering unit (3) via the first or the private data bus system (CAN A, privateCAN), wherein a second of the steering wheel angle sensors (23) is connected to the steering unit (3) via a second data bus system (CAN B).

2. Steer-by-wire steering system (1) according to claim 1, wherein the components of the steering unit (3) are designed to be redundant, in order to ensure a high level of reliability.

3. Steer-by-wire steering system (1) according to claim 1 or 2, wherein the steering wheel angle sensors (22, 23) are supplied with electrical energy from different power supply networks via separate power supplies (6).

4. Steer-by-wire steering system (1) according to one of claims 1 to 3, wherein the first or the second data bus system (CAN A, CAN B) is in communicative connection with another vehicle system.

5. Method for operating a steer-by-wire steering system (1) according to any of claims 1 to 4, comprising the following steps: - transmitting the items of steering wheel angle information from the steering wheel unit (2) to the steering unit (3) via separate communication connections (7, 7'), - checking the plausibility of the items of steering wheel angle information in order to obtain a steering wheel angle which has been checked for plausibility and safety; - controlling the steering actuator (33) depending on the steering wheel angle which has been checked for safety.