METHOD FOR OPERATING A STEER-BY-WIRE STEERING SYSTEM OF A MOTOR VEHICLE, CONTROL DEVICE, COMPUTER PROGRAM, AND STEER-BY-WIRE STEERING SYSTEM

Abstract

A method is disclosed for a steer-by-wire steering system of a motor vehicle, the system having at least one steering function that requests one or more steering angle changes as target steering angles for at least at one vehicle axle. An arbitration unit (AE) weights the steering angle changes as target steering angles (SLw_i) and, taking into account at least one target steering angle (SLw_i), determines an overall target steering angle (G_SLw). Before the overall target steering angle (G_SLw) is set by an actuator of the steer-by-wire steering system, a check is carried out to see whether a gradient of the overall target steering angle (G_SLw) is smaller than or equal to the gradient of the at least one target steering angle (SLw_i).

Claims

1-12. (canceled)

13. A method for operating a steer-by-wire steering system of a motor vehicle having at least one steering function, an arbitration unit, and an actuator, the method comprising: requesting, by a steering function, one or more steering angle changes for at least one vehicle axle; weighting, by an arbitration unit (AE), the one or more steering angle changes as target steering angles (SLw_i); determining an overall target steering angle (G_SLw) taking into account at least one of the target steering angles (SLw_i); checking whether a gradient of the overall target steering angle (G_SLw) is smaller than or equal to a gradient of the at least one target steering angles (SLw_i); and setting, by an actuator of the steer-by-wire steering system, an overall target steering angle (G_SLw).

14. The method according to claim 13, wherein requesting the one or more steering angle change is performed as a function of a driving situation (Fzg_S) of the motor vehicle.

15. The method according to claim 14, further comprising determining the driving situation (Fzg_S) of the motor vehicle using at least one parameter selected from a driving mode, a steering wheel position, a steering wheel angle speed, a steering-wheel angle acceleration, a speed of the vehicle, a yaw angle speed, a transverse acceleration, a longitudinal acceleration, and a wheel steering angle of at least one wheel on an axle to be steered.

16. The method according to claim 15, wherein determining the driving situation (Fzg_S) of the motor vehicle includes the arbitration unit taking into account signals from at least one control unit that is distinct from the steer-by-wire steering system, the said signals being read in at an interval from 5 to 40 ms.

17. The method according to claim 16, wherein the interval is 10 ms.

18. The method according to claim 13, further comprising determining a safety factor (v_safe) as a function of a speed of the vehicle, wherein determining the safety factor (v_safe) is performed prior to checking whether the gradient of the overall target steering angle (G_SLw) is smaller than or equal to the gradient of the at least one target steering angles (SLw_i).

19. The method according to claim 18, wherein the safety factor (v_safe) decreases as the speed of the vehicle increases.

20. The method according to claim 18, further comprising debouncing a result of the checking in order to determine whether G_SLw≤SLw_i or G_SLw≤SLw≤SLw_i+v_safe.

21. The method according to claim 13, wherein checking is performed on a continuous basis.

22. The method according to claim 13, wherein checking is performed periodically at an interval from 1 to 20 ms.

23. The method according to claim 22, wherein the interval is 4 ms.

24. The method according to claim 13, wherein when determining the overall target steering angle (G_SLw), the arbitration unit (AE) carries out a superimposition (B), having regard to a first target steering angle (S_Lw1) and at least one further target steering angle (S_Lw2).

25. The method according to claim 24, wherein the superimposition (B) is a function of a driving situation (Fzg_S) of the motor vehicle.

26. The method according to claim 13, further comprising providing a control unit configured with the at least one steering function, the control unit distinct from the control unit of the steer-by-wire steering system and wherein the at least one steering function is selected from a corridor function, a parking function, a fallback function, and a driver assistance function.

27. A steer-by-wire steering system comprising a control unit configured to carry out the method of claim 13.

28. The steer-by-wire steering system according to claim 27, wherein the steer-by-wire steering system is configured as a rear-axle steering system of a motor vehicle.

29. . A non-transitory computer-readable storage medium containing machine-readable code that is configured to perform the method of claim 13 when executed by a steer-by-wire steering system of a motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Below, the invention is described with reference to preferred embodiments relating to the drawing, which shows:

[0048] FIG. 1: A vehicle with a steer-by-wire steering system

[0049] FIG. 2: A flow chart of a method according to the prior art

[0050] FIG. 3: A flow chart of a method according to the invention

DETAILED DESCRIPTION

[0051] FIG. 1 shows schematically a vehicle 1 with a steerable front axle 21 and a steerable rear axle 31. For steering the wheels 2 on the front axle 21 a steering system 4 is provided, which can set or change the wheel steering angle δ, at the wheels 2 by means of a steering rod 41. In this example the said angle δ, is indicated for the right-hand wheel 2 in FIG. 1. At the rear axle 31 a steer-by-wire steering system 5 provides for the setting or changing of the wheel steering angle δ.sub.h of the rear wheels 3 by means of a steering rod 51. In the embodiment shown, the wheels controlled by the front axle steering system 4 and the wheels controlled by the rear axle steering system 5 are steered in opposite directions so that at low speeds, for example of less than 50 km/h, the turning circle is smaller and the parking possibilities are better compared with vehicles which have only one steered axle. Moreover, with two steered axles automated journeys can advantageously be carried out in a better way. The steering angle at the front axle is set by the driver, in this case basically by means of a steering wheel 14, the steering angle Lw being detected by a sensor unit, and the steering angle being relayed via a signal line to the steer-by-wire steering system 4, which sets it. The sensor unit for transmitting the steering angle Lw is connected electrically to the control unit of the steer-by-wire steering system 5 by way of a bus system. The bus system is for example a CAN bus or a FlexRay bus. Via the bus system steering functions for a driver assistance system ADAS for autonomous driving, correction functions Korr for limiting the maximum steering angle, a parking assistance function PAS for automated parking and an electronic stability control ESC are connected electrically to the control unit SG of the steer-by-wire steering system of the rear axle. This control unit SG is provided with an arbitration unit AE which continually checks the gradients of the target steering angles dSLw_i/dt against the gradient dG_SLw/dt of the overall target steering angle G_SLw determined by the arbitration unit. In FIG. 1, to that end the control unit SG is shown spaced apart along the broken line, in order to indicate that the arbitration unit AE is part of the control unit SG or the rear steer-by-wire steering system 5.

[0052] A yaw rate RG measured at the center of gravity SG is determined by a suitable sensor (rotation rate sensor) at the center of gravity of the vehicle 1 and received and evaluated by the electronic stability control ESC. At the outer corners of the vehicle 1 sensors S are arranged, which are associated with a sensor system and serve to recognize the surroundings of the vehicle. These can be temperature sensors, optical sensors that may for example include a camera, or even a LiDAR or radar, which are suitable for temperature, distance or even visual observation of the road, for example. Thus, weather conditions such as humidity or the temperature on the road, etc., can be determined and sent to the control unit SG. The vehicle follows a trajectory T, which in the figure is likewise represented schematically at the front end of the vehicle in its travel direction.

[0053] FIG. 2 shows the signal path from the steering device or steering wheel 14 until the actual change of the steering angle or the setting of the overall target steering angle G_SLw by the steer-by-wire steering system STEER-BY-WIRE system according to the prior art. Following the steering movement by the driver at the steering wheel 14, a steering angle Lw is detected by the sensor unit. Along the signal path the target steering angle SLw is relayed via a vehicle bus system such as the CAN bus to a control unit SG SBWL of the steer-by-wire system. The control unit SG SBWL of the steer-by-wire system takes into account the corridor function Korr running in it so that a maximum steering angle is not exceeded. Thus, among other things the steered wheel is prevented from colliding with parts of the chassis or the vehicle body. The control unit SG SBWL then determines the overall target steering angle G_SLw and sends it to the steer-by-wire steering system SBWL which, by means of the actuator built into it, carries out the change of the wheel steering angle. The arrangement described and the method that can be carried out with it does not enable other steering functions to be incorporated.

[0054] FIG. 3 shows a schematic flow chart of an arrangement and method according to the invention. Shown approximately in the middle is a bus system in the vehicle, which can be a CAN bus or a FlexRay bus or similar bus for the relaying of signals. To the left of the bus various steering functions are indicated. The functions driver steering angle Lw, corridor function Korr, parking assistance PAS, driver assistance system for autonomous driving ADAS and the electronic stability control ESC, already described earlier in connection with FIG. 1, each request a target steering angle SLw_1 to SLw_5 when necessary and these are sent to the bus. For example, the further steering function Lx is indicated, which requests a target steering angle SLw_x and stands for further steering functions not mentioned here and the target steering angles requested by them. The designation Fzg_S indicates that the driving situation is also sent to the bus as a signal and can be read in from it by the arbitration unit AE. All the target steering angles SLw_1 to SLw_5 are read in as separate signals by the arbitration unit AE, which contains a superimposition function B. The arbitration unit AE weights the individual target steering angles (SLw_1 to SLw_x) and prioritizes a target steering angle SLw_i. In other words, the arbitration unit decides in favor of a source that corresponds to one of the aforesaid steering functions. It is also possible that, at least temporarily, the information from two sources is mixed with one another. Ultimately, however, taking into account the current driving situation Fzg_S, the arbitration unit AE determines a target steering angle SLw_i and from it determines an overall target steering angle G_SLw, which is calculated continually.

[0055] To avoid sudden steering movements, by means of the superimposition function associated with it the arbitration unit can change gradually from a first determined target steering angle to a target steering angle determined subsequently. This also takes place continually.

[0056] In a further step, a check is carried out continually at intervals of 4 ms to see whether the gradient of the overall target steering angle G_SLw in question is smaller than or equal to the gradient of the target steering angle SLw_i determined, plus a safety factor v_safe added in each case. The result of the said checking is stored in each case and by comparison with the next-calculated value it is checked whether the same result occurs repeatedly. For example, if the condition occurs five times in succession (True?=yes), then at the steer-by-wire steering system the overall target steering angle G_SLw is set. The actuator of the steer-by-wire steering system then sets this overall target steering angle G_SLw. If the check shows repeatedly, for example five times in succession within 20 ms, that the condition is not fulfilled (True?=no), then the steer-by-wire steering system is set to an error mode or safety mode SLw_safe. In that case, depending on the driving situation the steer-by-wire steering system freezes the current steering angle or, depending on the driving situation, gradually approaches a steering angle of 0° which corresponds to driving straight ahead. This ensures that if an error occurs in the calculation of the overall target steering angle G_SLw, no situation that cannot be controlled by a normal driver will occur. Thus, a steer-by-wire steering system or a method for operating a steer-by-wire steering system is advantageously obtained, which satisfies the strict safety requirements specified by ASIL.

INDEXES

[0057] 1 vehicle [0058] 2 Front wheel [0059] 3 Rear wheel [0060] 4 Front axle steering [0061] 5 Rear axle steering [0062] 14 Steering wheel [0063] 21 Front axle [0064] 31 Rear axle [0065] 41 Steering rod [0066] 51 Steering rod [0067] AE Arbitration unit [0068] ADAS Driver assistance system for autonomous driving [0069] B Superimposition function [0070] BUS Bus system (CAN, Flexray) [0071] ESC Electronic stability control [0072] Korr Corridor function [0073] PAS Parking assistance function [0074] RG Yaw rate [0075] SG Control unit [0076] SG Center of gravity [0077] S Sensor system [0078] T Trajectory [0079] δ.sub.v Wheel steering angle, front [0080] δ.sub.h Wheel steering angle, rear [0081] Fzg_S Driving situation [0082] Lw Steering angle set by driver [0083] Lx Further steering function [0084] SLw(_1 to _5) Target steering angle [0085] SLw_x Further target steering angle [0086] SLw_i Target steering angle (determined by AE) [0087] SG SBWL Control unit of the steer-by-wire steering system [0088] G_SLw Overall target steering angle [0089] SBWL Steer-by-wire steering system [0090] dG_SLw/dt Gradient of the overall target steering angle [0091] dSLw_i/dt Gradient of the target steering angle [0092] SLw_safe Safety mode of the steer-by-wire steering system [0093] v_safe Safety factor