Method for controlling a steer-by-wire steering system, control unit and motor vehicle

Abstract

The invention relates to a method for controlling a steer-by-wire steering system for a motor vehicle (1) in normal operation, wherein the motor vehicle (1) comprises a front axle (10) with front wheels (FL, FR) and a rear axle (20) with rear wheels (RL, RR) and at least two actuators (5, 6, 7, 8) for changing the vehicle trajectory of the motor vehicle (1), which are connected to a control unit (9), comprising the following steps: * determining the desired vehicle trajectory, * determining the respective power reserve of the actuators (5, 6, 7, 8) by comparison of the actually consumed power with the maximum available power of the respective actuator (5, 6, 7, 8), * transferring the respective power reserve to the control unit (9), and * actuating the actuator (5, 6, 7, 8) with the higher power reserve for changing the vehicle trajectory by a control signal of the control unit (9).

Description

[0001] Method for controlling a steer-by-wire steering system, control unit and motor vehicle

[0002] The invention relates to a method for controlling a steer-by-wire steering system, a control unit and a motor vehicle.

[0003] In a steer-by-wire steering system, the steered wheels and the steering wheel are not mechanically but electrically coupled. The steered wheels are controlled by steering signals. The respective steering wheel position is detected by a steering angle sensor. The corresponding steering signal causes a steering actuator to change the position of the steered wheels. The desired vehicle trajectory can also be achieved through wheel-specific torque distribution, in which the vehicle drive and / or braking system are controlled accordingly (torque vectoring). The vehicle drive and / or braking system are mechanically and control-wise adapted for this functionality.

[0004] During normal operation, the proper functioning of the steer-by-wire steering system is continuously monitored. Steering wheel movements detected by sensors are transmitted to a central control unit. The control unit processes the inputs and makes decisions about how the wheels should be steered.

[0005] A system for automated vehicle control in a motor vehicle is known from DE 10 2021 202 301 A1, which originates from the applicant. The system aims to optimize the vehicle's performance, efficiency, and stability by coordinating the various actuators (brakes, drive, steering) based on a reference motion, a cost function, and a dynamic model. Although the known system already functions very well, there is room for improvement with regard to the interaction of multiple actuators for steering the vehicle.

[0006] The invention is based on the object of improving the method known from the aforementioned prior art such that multiple actuators can be used to effect steering movements of the vehicle during normal operation, while avoiding interactions between the actuators that impair driving behavior. The invention is further based on the object of specifying a control unit and a motor vehicle. According to the invention, the object is achieved with regard to the method by the subject matter of claim 1, with regard to the control unit by the subject matter of claim 8, and with regard to the motor vehicle by the subject matter of claim 9.

[0007] Specifically, the problem is solved by a method for controlling a steer-by-wire steering system for a motor vehicle during normal operation, wherein the motor vehicle comprises a front axle with front wheels and a rear axle with rear wheels, and at least two actuators for changing the vehicle trajectory of the motor vehicle, which actuators are connected to a control unit. The method comprises the following steps:

[0008] Determine the desired vehicle trajectory

[0009] Determine the respective power reserve of the actuators by comparing the actually consumed power with the maximum available power of the respective actuator

[0010] Transmitting the respective power reserve to the control unit and

[0011] Controlling the actuator with the higher power reserve to change the vehicle trajectory by a control signal from the control unit.

[0012] The proposed method is, in particular, a method for operating a steer-by-wire steering system in a motor vehicle. Furthermore, the proposed method is advantageously implemented within the framework of a method for operating a motor vehicle with a steer-by-wire steering system.

[0013] The method according to the invention has the advantage that, by selecting the actuator with the higher power reserve compared to the other actuators, it is avoided that actuators with full power influence each other. On the other hand, driving safety during steering is improved because the risk of an actuator with a low power reserve failing during the steering process is reduced. Selecting the actuator with the higher power reserve compared to the other actuators protects the other actuators. The method according to the invention for controlling a steer-by-wire steering system relates to normal operation. The above advantages have the effect of reducing the risk of failure of the steer-by-wire steering system or of the control method, and avoiding a switch to fail-safe mode. If, for example, the actuator for controlling steered front wheels (front axle steering actuator) has a larger orhigher power reserve than the other actuators for changing the vehicle trajectory of the motor vehicle, this actuator is selected and actuated for steering. If another actuator, e.g. the drive device or the braking device, has a higher power reserve than the other actuators for changing the vehicle trajectory of the motor vehicle, this actuator is selected and actuated for steering. The control of a steer-by-wire steering system therefore also includes, in particular, the control of actuators that are not, or at least not exclusively, assigned to the steering system, but with which the motor vehicle can also be steered by appropriate control, in particular a control of the drive device and / or the braking device or of actuators assigned to these devices.

[0014] It is also possible to combine multiple actuators simultaneously according to the inventive principle. For example, the actuator for controlling steered front wheels (front-axle steering actuator) can be actuated, and to support it, another actuator intended to change the vehicle trajectory can be activated. This actuator will be selected from the group comprising a drive device, a braking device, and a rear-axle steering actuator. The selection criterion is the respective individual power reserve of the actuators, with the actuator with the higher power reserve for changing the vehicle trajectory compared to the other actuators being controlled by a control signal from the control unit.

[0015] The term "control" is not understood in the strict sense of control technology, but also encompasses closed-loop control. The invention therefore also relates to a method for controlling a steer-by-wire steering system and a corresponding control unit.

[0016] Within the scope of the invention, each actuator is assigned an individual power reserve, which results from a power supply, such as an electric battery, which is provided in the vehicle in a conventional manner. The maximum power or nominal power of the respective actuator results, for example, from the power of the battery. The actually consumed power is determined, for example, via the actual charge state of the battery. Other methods for determining the individual power reserve of the actuators are possible. It is emphasized that the calculation of the available power reserve in the various actuators is carried out in such a way that the current degradation is taken into account. The actuator does not perform any check regarding its power grid connection and consumption in relation to one another.Instead, it evaluates the performance of its electricity consumption from the grid, taking into account degradation, and compares this with the power delivered.

[0017] An example of precise determination of the degradation of the steering actuator depending on the driving condition of the vehicle is shown in W02023002583A1, which is attributed to the applicant, and is therefore not described in detail.

[0018] The power reserve corresponds to the difference between the maximum available power and the actual power consumed by an actuator. This value is transmitted to the control unit. To influence the vehicle's trajectory, the control unit selects the actuator with the greatest power reserve. The power reserve of the selected actuator is greater than the power reserve of the other actuators intended to change the vehicle's trajectory. This ensures optimal use of the available power and reliable maintenance of normal operation to achieve the desired vehicle movement.

[0019] A control unit is provided to control the actuators. This is part of the steer-by-wire steering system or a vehicle motion control system, which includes various components to control the movement and behavior of the vehicle. The system preferably uses a variety of sensors to collect data about the vehicle's movement, road conditions, and environment. Based on this data, the system actively controls the various vehicle components to achieve the desired vehicle movement. The general operating principle of the steer-by-wire steering system or vehicle motion system is known and will not be explained in detail.

[0020] The selected actuator with the greatest power reserve is controlled by a control signal from the control unit. The actuator implements the steering movements accordingly to achieve the desired vehicle trajectory. Continuous execution of this process results in efficient and reliable control of the steer-by-wire steering system during normal vehicle operation, enabling a safe and comfortable ride for the driver and passengers. Precise coordination and optimal integration of the actuators prevent uncontrolled steering.

[0021] The advantages mentioned in connection with the method also apply correspondingly to the control unit according to the invention. The method steps described in connection with the method are also disclosed in connection with the control unit, specifically in such a way that the control unit is configured or adapted to perform these method steps.

[0022] Preferred embodiments of the invention are specified in the subclaims.

[0023] The actuators for changing the vehicle trajectory of the motor vehicle are preferably selected from a group comprising a drive device, a braking device, a front-axle steering actuator, and a rear-axle steering actuator. The above-mentioned group is not exhaustive. Other actuators for changing the vehicle trajectory of the motor vehicle can be considered, if available. This embodiment has the advantage of using existing actuators.

[0024] The control unit can weight the control signal based on the respective power reserve to prioritize the actuator with the comparatively higher power reserve. This results in the desired selection. Here, too, the selection can include several simultaneously operated actuators whose individual power reserves are higher than the individual power reserves of the other actuators.

[0025] In a further embodiment, the control unit continuously checks the respective power reserve of the actuators, prioritizes the respective actuators according to the respective power reserve, and controls them to generate the desired vehicle trajectory according to the prioritization during normal operation. Here, too, individual selection or various simultaneous combinations are possible.

[0026] The braking system can have individual wheel brake actuators, whereby the individual wheel brake actuators control the braking force applied to the wheels of the motor vehicle on a wheel-by-wheel basis. The resulting torque distribution at the wheels affects the yaw angle and thus the vehicle trajectory. Alternatively or additionally, the drive system can be adapted and controlled for wheel-by-wheel torque distribution.

[0027] The braking device and / or the drive device can be part of a torque vectoring system that distributes torque to individual wheels, so that the front and rear wheels, i.e., the respective left and right wheels, are each subjected to different torques. This influences the yaw angle and yaw rate in a conventional manner. The torques are drive torques and / or braking torques.

[0028] Preferably, the front axle steering actuator and / or the rear axle steering actuator are signal-controlled and thus part of the steer-by-wire system.

[0029] Preferably, the drive actuator device has a first drive and a second drive, with the first drive located on the front axle and the second drive located on the rear axle. By controlling the drives on the front and rear axles separately, driving dynamics and stability can be optimized. The vehicle can be more agile and responsive, making the overall handling more precise and safer.

[0030] Furthermore, the front and / or rear drive on the front and rear axles preferably each have an open differential gear. An open differential gear is not equipped with a locking device.

[0031] The brake actuator device preferably comprises individual wheel brake actuators, wherein the individual wheel brake actuators control the braking force applied to the wheels of the motor vehicle. This has the advantage that torque distribution is achieved by different braking torques or braking pressures on the left and right individual wheels. If the steer-by-wire steering system detects a driving situation requiring asymmetrical braking force distribution, the individual wheel brake actuators can act precisely and independently of one another to keep the vehicle stable.

[0032] An individual wheel brake or an individual wheel brake actuator is understood to be a brake that applies a braking torque to each wheel individually, which is independent of the braking torque of the other wheel on the same axle. Preferably, the front axle steering actuator is arranged on the front steering rod and / or the rear axle steering actuator is arranged on the rear steering rod, with the two steering actuators adjusting the respective steering rod and transmitting it to the wheels. This has the advantage that the invention has a simple design and can be applied to standard steering systems. Front-wheel steering is understood to mean wheel steering in which the front wheels are actively steered, i.e. with a driven steering rod. The invention is therefore applicable to conventional drive concepts.

[0033] The invention is explained in more detail below using an embodiment with reference to the attached schematic figures.

[0034] Show

[0035] Fig. 1 is a schematic representation of a steer-by-wire steering system, and

[0036] Fig. 2 shows a vehicle with a steerable front axle and a steerable rear axle, in which an embodiment of the method for controlling the steer-by-wire steering system according to the invention is implemented.

[0037] Fig. 1 shows a steer-by-wire steering system 3, which is installed in the chassis of a motor vehicle 1, in particular a passenger car, shown in a top view and in an abstract manner in Fig. 2. An exemplary embodiment of the method for controlling the steer-by-wire steering system 3 according to the invention is implemented in the motor vehicle 1.

[0038] As shown in Fig. 2, the motor vehicle 1 has a front axle 10 with a left front wheel FL and a right front wheel FR, as well as a rear axle 20 with a left rear wheel RL and a right rear wheel RR. The two front wheels FL, FR are mechanically connected by a front steering rod 2a. The two rear wheels HL, HR are mechanically connected by a rear steering rod 2b.

[0039] Furthermore, Fig. 1 and Fig. 2 show that the motor vehicle 1 comprises a steer-by-wire steering system 3 and at least two actuators of a vehicle motion control system 4, which comprises a drive device or drive actuator device 5, a brake device or brake actuator device 6, a front axle steering actuator 7 and a rear axle steering actuator 8, which influence the change in the vehicle trajectory of the motor vehicle 1 and are connected to and controllable by a control unit 9.

[0040] In a narrower sense, the front axle steering actuator 7 and the rear axle steering actuator 8 belong to the steer-by-wire steering system 3. The drive device or drive actuator device 5 and the brake device or brake actuator device 6 belong, in a narrower sense, to the torque vectoring system. Since both systems influence the vehicle trajectory, they can be understood as part of a general vehicle motion control system 4 and are explained together below from this perspective.

[0041] The method for controlling the steer-by-wire steering system is explained in more detail with reference to Fig. 2. First, the steering movement of the motor vehicle 1 is detected by suitable sensors, e.g., steering angle sensors (not shown). These sensors measure the angle by which the steering wheel is turned and thus detect the driver's desired steering movement. The data from the steering angle sensors is transmitted to the control unit 9 of the steer-by-wire steering system. The control unit 9 processes the measured steering angles and calculates the required steering movements to achieve the desired steering angles at the wheels. In other words, the control unit 9 generates electronic signals that are forwarded to the steering actuators 7, 8, in particular to the front-axle steering actuator 7 and rear-axle steering actuator 8. The steering actuators 7, 8 have the task of changing the wheel steering angle of the wheels FL, FR, RL, RR and thus influencing the vehicle trajectory.

[0042] The steering actuators 7, 8 are equipped with sensors that measure the actual power consumption. This data is transmitted to the control unit 9, which also knows the maximum available power of each actuator 5, 6, 7, 8.

[0043] The control unit 9 compares the actual power consumed by each actuator with the maximum available power to determine the individual power reserve of each actuator 5, 6, 7, 8. The power reserve indicates how much power an actuator 5, 6, 7, 8 can still deliver before its maximum capacity is reached.

[0044] The control unit 9 selects the actuator 5, 6, 7, 8 with the greatest power reserve. This actuator 5, 6, 7, 8 is capable of efficiently implementing the desired control commands. The control unit 9 sends corresponding control signals to the selected actuator 5, 6, 7, 8 to perform the steering or change the vehicle trajectory. The selected actuator 5, 6, 7, 8 efficiently executes the adjustments and thus influences the vehicle trajectory of the motor vehicle 1 according to the specifications.

[0045] In the embodiment according to Fig. 1 and Fig. 2, the motor vehicle 1 comprises a feedback actuator 11.

[0046] In Fig. 1 and Fig. 2, the control unit 9 is equipped with a data processing device and forms the central element of the steering and movement system. It receives and processes various data to ensure optimal steering and vehicle movement.

[0047] Furthermore, Figures 1 and 2 show the drive actuator device 5 and the brake actuator device 6. These actuators determine the steering, speed and braking operations of the motor vehicle 1.

[0048] In the exemplary embodiment shown in Fig. 2, the drive actuator device 5 has a first drive 12 and a second drive 13, each of which is arranged on different axles 10, 20 of the vehicle. The first drive 12 is arranged on the front axle 10, while the second drive 13 is arranged on the rear axle 20.

[0049] Furthermore, Fig. 2 shows that the brake actuator device 6 comprises individual wheel brake actuators 14, 15. The individual wheel brake actuators 14, 15 are arranged on the front and rear wheels and are connected to the control unit 7 and controllable by the control unit 9.

[0050] In the embodiment according to Fig. 2, the front axle steering actuator 7 and the rear axle steering actuator 8 are each arranged on the steering rods 2a, 2b of the motor vehicle 1. The two front wheels FL, FR are mechanically connected by a front steering rod 2a and the two rear wheels RL, RR by a rear steering rod 2b. Both the front wheels FL, FR and the rear wheels RL, RR are steerable. For this purpose, the respective steering rod 2a, 2b is moved to the right or left in a known manner. For the front wheel steering, a front axle steering actuator 7 is mechanically connected to the front steering rod 2a, which provides the drive force required for steering. The rear axle steering actuator 8 is mechanically connected to the rear steering rod 16 for the rear wheel steering and provides the required drive force.The front-axle steering actuator 7 and the rear-axle steering actuator 8 are electronically controlled as part of the steer-by-wire steering system and are not mechanically connected to the steering wheel. The steering actuators 7 and 8 receive their control signals from the steering angle sensors, which output a steering signal corresponding to the respective steering wheel position.

[0051] List of reference symbols

[0052] I Motor vehicle

[0053] 2a front handlebar

[0054] 2b rear handlebar

[0055] 3 Steering system

[0056] 4 Vehicle motion control system

[0057] 5 Drive actuator device

[0058] 6 Brake actuator device

[0059] 7 Front axle steering actuator

[0060] 8 Rear axle steering actuator

[0061] 9 Control unit

[0062] 10 front axle

[0063] 20 rear axle

[0064] II Feedback actuator

[0065] 12 first drive

[0066] 13 second drive

[0067] 14, 15 Single wheel brake actuators

[0068] FL front wheel left

[0069] FR front wheel right

[0070] RL rear wheel left

[0071] RR rear wheel right

Claims

Claims 1. A method for controlling a steer-by-wire steering system for a motor vehicle (1) during normal operation, wherein the motor vehicle (1) comprises a front axle (10) with front wheels (FL, FR) and a rear axle (20) with rear wheels (RL, RR) and at least two actuators (5, 6, 7, 8) for changing the vehicle trajectory of the motor vehicle (1), which actuators are connected to a control unit (9), comprising the following steps: Determining the desired vehicle trajectory, Determining the respective power reserve of the actuators (5, 6, 7, 8) by comparing the actually consumed power with the maximum available power of the respective actuator (5, 6, 7, 8); Transmitting the respective power reserve to the control unit (9) and - Controlling the actuator (5, 6, 7, 8) with the higher power reserve to change the vehicle trajectory by a control signal from the control unit (9).

2. Method according to claim 1, characterized in that the actuators (5, 6, 7, 8) for changing the vehicle trajectory of the motor vehicle (1) are selected from a group comprising a drive device (5), a braking device (6), a front axle steering actuator (7) and a rear axle steering actuator (8).

3. Method according to claim 1 or 2, characterized in that the control unit (9) weights the control signal based on the respective power reserve in order to prioritize the actuator (5, 6, 7, 8) with the comparatively higher power reserve.

4. Method according to one of the preceding claims, characterized in that the control unit (9) continuously checks the respective power reserve of the actuators (5, 6, 7, 8), prioritizes the respective actuators (5, 6, 7, 8) according to the respective power reserve and controls them in normal operation to generate the desired vehicle trajectory according to the prioritization.

5. Method according to one of claims 2 to 4, characterized in that the braking device (6) has individual wheel brake actuators (14, 15), wherein a braking force applied to the wheels (FL, FR, RL, RR) of the motor vehicle (1) is controlled individually for each wheel by the individual wheel brake actuators (14, 15).

6. Method according to one of claims 2 to 5, characterized in that the drive device (5) is adapted and controlled for wheel-individual torque distribution.

7. Method according to one of claims 2 to 6, characterized in that the front axle steering actuator (7) and / or the rear axle steering actuator (8) are signal-controlled.

8. Control unit for controlling a steer-by-wire steering system for a motor vehicle (1) during normal operation, wherein the motor vehicle (1) comprises a front axle (10) with front wheels (FL, FR) and a rear axle (20) with rear wheels (RL, RR) and at least two actuators (5, 6, 7, 8) for changing the vehicle trajectory of the motor vehicle (1), which actuators are connected to the control unit (9) which is adapted to carry out the following steps: Determining the desired vehicle trajectory, Determining the respective power reserve of the actuators (5, 6, 7, 8) by comparing the actually consumed power with the maximum available power of the respective actuator (5, 6, 7, 8); Transmitting the respective power reserve to the control unit (9) and - Controlling the actuator (5, 6, 7, 8) with the higher power reserve to change the vehicle trajectory by a control signal from the control unit (9). 9 . Motor vehicle with a control unit according to claim 8.

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