Method for operating a steer-by-wire steering system of a vehicle

Abstract

A method for operating a vehicle's steer-by-wire steering system, wherein the steer-by-wire steering system operates in a redundancy and / or fallback level upon detection of a fault, and wherein the vehicle speed is limited to a maximum vehicle speed, characterized in that the maximum vehicle speed is limited in the redundancy level depending on the driving situation, wherein the driving situation-dependent limitation of the vehicle speed is carried out in the following steps: - Acquiring current and / or future driving situation data via at least one sensor and / or via ticket data; - Determining the probability of occurrence of future driving maneuvers based on the driving situation data; - Comparing the determined probability of occurrence with the current and / or future remaining steering performance of the steer-by-wire steering system;- Calculating a maximum vehicle speed adapted to the driving situation.

Description

The invention relates to a method for operating a steer-by-wire steering system of a vehicle according to the preamble of claim 1.So-called steer-by-wire steering systems of vehicles are already known from the prior art in different ways. Such a steering system differs from the conventional steering systems in that the steering of the wheels is completely decoupled from the mechanical steering movement of the driver or takes place only by a purely electronic transmission. The conventional mechanical transmission devices are omitted; instead, the driver generates data on the so-called steering handle or on the steering wheel by means of his steering movement, with which data an electronic control unit is fed. This control module evaluates the data and converts it into corresponding steering commands. The steering gear or the actuator is thus controlled to set a wheel steering angle which carries out the desired steering movement.The requirements for the reliability of such a steering system are particularly high. Thus, in any possible malfunction, the steerability of the vehicle must be ensured. Redundancies and fallback levels are provided for this purpose.For example, it is known to provide redundancy in the actuator system of the steered wheels of the vehicle. The operation of the steering system is referred to as a redundancy level with a redundancy mentioned. If a disturbance or a so-called first fault then occurs in the actuator system, then a steering angle requested by the driver or vehicle can furthermore be implemented at the wheels of the vehicle via the redundancy level.If such a steering system is operated in a redundancy level, then usually only a reduced steering power, for example in the form of a reduced steering angle speed, is available. With a limited steering power, it is possible that certain driving maneuvers can no longer be carried out.If an error or a disturbance then additionally occurs in the redundancy level, the required steering angle can no longer be carried out at all by the steer-by-wire steering system.In order to reduce the effects of such a reduced steering power and the risk of a possible total failure of the actuator system for setting the wheel steering angle to a safety-non-critical level, in the present state of the art, the speed of the vehicle is limited to a uniform maximum speed in the range of 10-30 km / h when the steer-by-wire steering system is operated in a redundancy plane. The driver of the vehicle is thus greatly restricted in his executable driving maneuvers and flexibility.DE 10 2015 223 612 A1 shows, by way of example, how certain vehicle consumers are restricted or degraded in the event of a system in the vehicle being disturbed.It is therefore an object of the invention to provide a method for operating a steer-by-wire steering system which enables lower restrictions and higher flexibility for the driver in a fallback or redundancy level of the steering system.The object is achieved by a method having the features of claim 1.A method for operating a steer-by-wire steering system of a vehicle is proposed, which is operated in a redundancy or a fallback level when a fault is detected in the system.Such a steer-by-wire steering system describes a steering system in which the actuation by the vehicle driver and the actual wheel steering are energy-decoupled from one another.In order to ensure the safety requirements, for example in the event of a failure or a malfunction of a component or in the case of parts of the regulating or control circuit, the steer-by-wire steering system comprises a so-called redundancy of components or functions or a level of fallback.Redundancy is the additional presence of functionally identical or comparable resources of a technical system if these are not normally required in the case of fault-free operation. Resources can be, for example, redundant information, motors, assemblies, complete devices, control lines and power reserves.As a rule, these additional resources serve to increase the reliability, functional and operational reliability.Redundancy therefore also means within the meaning of the invention that the module under consideration or one of the aforementioned resources, which is subject to a fault or a failure, is supplemented by one or more modules, in particular in a parallel arrangement. Such redundant implementations can be identical or different from the failed or the disturbed module, for example.Particularly preferably, the steering actuator system on the steered wheels of the vehicle is designed to be redundant. After the occurrence of a fault or a fault, a steering angle requested by the driver or by the vehicle can then preferably still be implemented at the vehicle wheels by a steering actuator in a so-called redundancy level.Such a redundancy level describes a special form of a fallback level. A fallback level represents a secondary system which, in the event of failure of a primary system, offers protection against a risk or prevents the total failure of the overall system, frequently while maintaining a reduced operating quality.Thus, as an alternative to a redundancy level mentioned, a further fallback level is also possible, in which the system is operated in the event of a fault or a failure.If the steering system is operated in such a redundancy level or fallback level, it is preferably provided that the steering power of the system is reduced. For example, the response of the steering system to steering commands made by the driver is slower or the steering system can no longer set the entire required steering angle or the steering angle acceleration is reduced.Furthermore, it is provided that the vehicle speed is limited to a maximum vehicle speed during operation of the steering system in the redundancy level mentioned.A safety risk, which may exist for the driver of the vehicle or for the vehicle occupants and for other road users after a disturbance in the steering system, is strongly dependent on the current and imminent driving situations.For example, a loss of steerability of the vehicle when travelling on a straight road structurally delimited from the opposite roadway is substantially less critical than during cornering or during travel in the urban area.For this reason, it is provided that the aforementioned maximum vehicle speed, to which the vehicle is limited during operation of the steering system in a redundancy or a fallback level, is set or limited depending on the driving situation.Thus, when limiting the maximum vehicle speed, a distinction or differentiation is made between the respective current or future driving situation in which the vehicle is located. The maximum possible vehicle speed is then limited as a function of the current or future driving situation in which the vehicle is located.The limiting of the maximum vehicle speed as a function of the driving situation takes place with the following steps:In a first step, it is provided that the current or future driving situation is detected via a detection of current or future driving situation data.Such a detection of the driving situation data can be carried out by suitable sensor systems, for example vehicle sensors or by driving map data.In this case, it is preferably provided to record the current driving situation as well as the future driving situation or the imminent driving situation. For example, the current vehicle acceleration, the current steering angle and further current vehicle data can be detected by means of acceleration sensors, yaw rate sensors and steering angle sensors. Using map data, for example data of an active navigation system, the route of the vehicle to be traveled in the immediate future can be ascertained. On the basis of these, environment and vehicle data, such as the route, can be ascertained. For example, a flat or uneven roadway, an asphalt road or a ballast road, a freeway or a land road, a city trip and, for example, a curved trip or a straight roadway, can be ascertained. In addition, current weather conditions and further environmental data, such as the traffic situation, can also be determined via vehicle sensor systems or else via driving map data or satellite data.The probability of occurrence of future driving situations is then determined on the basis of the driving situation data. By means of this acquired driving situation data, it is therefore possible in particular to determine the quantity of driving maneuvers that may still possibly occur (with a high probability) or are necessary.For example, it can be detected that the vehicle is on a straight freeway trip for the next 20 minutes, the weather conditions are good and there is less traffic volume on the current route and route which is being traveled in the future. From this, the probability of the occurrence of a possible driving maneuver, i.e., for example, a journey of the vehicle on the freeway at constant speed with a low traffic volume, can be ascertained. High steering power and the effects of the steering power reduced in the redundancy level are hardly pronounced in such an exemplary driving maneuver.After the probability of occurrence of the possible driving maneuvers has been determined, it is furthermore provided in a next step to compare this probability of occurrence with the current or future still present steering performance of the steer-by-wire steering system (which is operated in the redundancy level). With such a comparison, it is then possible, in particular with the inclusion of suitable safety criteria, to determine which of the determined driving maneuvers can still be carried out in the safety-non-critical range with the steering power of the steering system still present.Subsequently or simultaneously, a maximum vehicle speed can be determined, at which maximum vehicle speed these driving maneuvers can be supplied.The maximum vehicle speed can thus preferably be determined in a manner adapted to the driving situation.The maximum speed of the vehicle permitted after a fault in the steering system does not have to be uniformly limited in every case to a value that is not critical for all driving situations. Instead, the present invention enables a maximum vehicle speed to be increased in less critical driving situations. This provides the vehicle driver and the vehicle occupant with an apparent added value in terms of ride comfort and flexibility. This is because the restrictions of the driver of the vehicle in the further use of the vehicle, in which the steering system is operated in a redundancy level, can be significantly reduced.It is furthermore preferably provided that the availability of at least one further vehicle actuator is included in the calculation or determination of the situation-dependent maximum vehicle speed. For example, a braking intervention (for example, of an electrohydraulic brake system of the vehicle) can take place on only one wheel of the vehicle or on only one side (viewed from the longitudinal central axis of the vehicle to the left or right). Such a braking intervention enables additional steering of the vehicle.Furthermore, in addition to a method for operating a steer-by-wire steering system, a steer-by-wire steering system suitable for carrying out the method is claimed.In such a steer-by-wire steering system, the steering of the wheels is completely decoupled from the mechanical steering movement of the driver, wherein only a purely electronic transmission of the steering data takes place. In this case, the vehicle driver preferably generates data (for example a setpoint steering angle) by a steering movement on a steering handle, which data are evaluated by a control unit and then the corresponding steering commands vehicle wheel are converted into a wheel rotational movement or steering movement of the vehicle wheels.The control unit is likewise preferably capable of matching the driving situation data with the steering power and of calculating the probability of occurrence of the possible driving maneuvers. Furthermore, it is preferably provided that the control unit then calculates a maximum vehicle speed adapted to the driving situation.Furthermore, a computer program or a computer program product is claimed, which is configured to execute a method according to one of Claims 1 to 8 on an electronic computing and / or control unit.These and further features are also evident from the claims and the description, wherein the individual features can each be realized individually or in multiple forms in the form of sub-combinations in an embodiment of the invention and can represent advantageous embodiments which are protectable per se and for which protection is claimed here.

Claims

Method for operating a steer-by-wire steering system of a vehicle, wherein the steer-by-wire steering system is operated in a redundancy and / or a fallback level when a fault is detected, and wherein the vehicle speed is limited to a maximum vehicle speed, characterized in that the maximum vehicle speed is limited during the operation of the steer-by-wire steering system in the redundancy level as a function of the driving situation, wherein the driving situation-dependent limitation of the vehicle speed is carried out with the following steps: - acquiring current and / or future driving situation data via at least one sensor system and / or via driving map data; - determining the probability of occurrence of future driving maneuvers on the basis of the driving situation data; matching the determined probability of occurrence with a current and / or future still present steering performance of the steer-by-wire steering system; calculating a maximum vehicle speed adapted to the driving situation.Method according to claim 1, wherein the steer-by-wire steering system is operated at a reduced steering power in the redundancy and / or fallback level.Method according to Claim 1 or 2, wherein current and / or future route sections of the vehicle to be traveled on a freeway and / or in a urban area and / or on a highway are detected via the ticket data.Method according to one of the preceding claims, wherein the current steering angle and / or the current vehicle acceleration and / or the current yaw rate of the vehicle are detected via at least one sensor system.Method according to one of the preceding claims, wherein the availability of at least one further vehicle actuator is included in the calculation of the maximum vehicle speed.Method according to one of the preceding claims, wherein in the event of a fault in at least one steering actuator in the vehicle, the steering actuator is operated redundantly.Steer-by-wire steering system for carrying out a method according to one of the preceding Claims 1 to 6, comprising at least one electronic computing and / or control unit which is configured to restrict the maximum vehicle speed as a function of the driving situation.Computer program or computer program product, which is configured to execute a method according to one of Claims 1-6 on an electronic computing and / or control unit.