The invention relates to a method for providing lane-keeping support in automobiles during the operation of a fully automatic driver assistance system according to the preamble of claim 1 designed for driver-independent vehicle guidance.
Fully automatic driver assistance systems designed for driver-independent vehicle guidance are currently being developed by many automobile manufacturers whose aim it is to unburden the driver from the driving task in certain traffic situations by fully automatically taking over the driving task. One noteworthy example is a so-called congestion assistance, which can be used in congested situations on freeways. In that case, at a predetermined threshold speed of 60 km/h, for example, both the longitudinal guidance (analogous to a distance-dependent speed control) and the lateral guidance for maintaining the vehicle within the traffic lane are performed automatically. In a special embodiment of such congestion assistants, the driver is even supposed to be permitted to remove their hands from the steering wheel at least for a certain time.
Such fully automatic driver assistance systems designed for driver-independent vehicle guidance require high levels of safety requirements, since there might be great risks both to the driver and to other participants in the traffic in the event of an error.
A method for operating such a driver assistance system is already known from DE 10 2010 021 591 A1 in which it is continuously monitored by means of a plausibility monitoring module whether a fault is present. Various situations are defined as faults, such as the vehicle traveling too fast or backwards, undershooting of a certain minimum distance to a vehicle traveling ahead, and/or the vehicle leaving the lane. If such a fault is detected, at least one driving intervention serving to bring the vehicle to a safe state is carried out. One drawback of such a system is that a fault is only detected and a counteracting intervention is only carried out once a faulty or critical state of the vehicle has already been detected.
Besides such faults, due to legal regulations it is necessary in such driver assistance systems to check the actuatorics for a fault in order to comply with a certain safety objective. For instance, the vehicle must be kept in the driving lane nonetheless even if the actuatorics controlling the lateral guidance fails. Various considerations to this end are already known.
For instance, DE 199 52 227 B4 already discloses an automobile steering system which provides a second servo drive for the automobile steering which can be used in the event of failure of the first servo drive as an emergency system. Not only is such a system associated with high costs, it also adds more weight to the vehicle.
Finally, DE 10 2010 001 068 A1 discloses a method for lane-keeping support for an automobile which comprises a torque vectoring system in which the lane-keeping support is performed through targeted asymmetrical torque distribution by means of the torque vectoring system. This, in turn, is only possible in vehicles which are equipped with such a torque vectoring system.
It is the object of the invention to provide an improved and cost-effective method for lane-keeping support for automobiles which enables the vehicle to be kept within the driving lane even in the event of failure of the steering actuatorics.
This object is achieved by a method according to claim 1. Advantageous developments follow from the dependent claims.
In principle, the invention emanates from a method for lane-keeping support for automobiles during operation of a fully automatic driver assistance system designed for driver-independent vehicle guidance. Such driver assistance systems are embodied such that, in the presence of predetermined basic conditions—at a speed that lies below the predetermined threshold speed, for example—the actuatorics of an (electrically operated) steering system and/or the actuatorics of a drive system and/or braking system are controlled by means of one or more control devices such that the vehicle is guided and maintained within the selected driving lane and with consideration of a vehicle traveling ahead and any other traffic participants. The longitudinal guidance can be performed in a manner analogous to the longitudinal guidance of a distance-dependent speed control (adaptive cruise control, ACC).
The fundamental idea of the invention is to make it possible, even in the event of failure of the steering system or the steering actuatorics, to continue to ensure that the vehicle is kept in the driving lane nonetheless, at least for a certain time. To ensure that this requirement is met, the method according to the invention is characterized in that, in the event of failure of the steering system, which can particularly be embodied as an electrically actuatable steering system, targeted braking interventions, particularly wheel-selective braking interventions, are performed to maintain the lateral guidance for lane keeping support by means of a braking system of the vehicle that is present in any case; that is, the lateral guidance of the vehicle is taken over by the braking system in the event of failure of the (electrical) steering system. This is possible because indirect steering is achieved through wheel-selective braking interventions, particularly in the direction of over-steering or understeering.
Since the maintaining of the lateral guidance is taken over by the braking system immediately upon failure of the steering system, it can be ensured that the driver or other traffic participants are not subjected to an elevated safety risk even as a, result of a temporary departure from the driving lane due to defective steering on the part of the driver.
In an advantageous development of the invention, if a failure of the steering system is detected, such braking interventions can be performed that the vehicle is guided along within the driving lane on the basis of the lateral guidance requirement or lateral guidance trajectory if the steering system is working that is detected or requested by the fully automatic driver assistance system designed for driver-independent vehicle guidance. In other words, the identical lateral guidance is to be implemented independently of the actuatorics influencing the lateral guidance, and the vehicle is to be guided on the identical lateral guidance trajectory.
Alternatively, the method according to the invention can also be embodied such that, in the event of failure of the steering system, such braking interventions can be performed to maintain the lane-keeping support or the automatic lateral guidance that the vehicle is guided along a newly determined lateral guidance fallback trajectory which is determined especially for the failure situation of the steering system.
Advantageously, the lateral guidance can also be carried out in the event of failure of the steering system through a combination of the two alternatives described. For instance, immediately upon failure of the steering system, the lateral guidance can be carried out for a certain time or over a certain distance on the basis of the (originally) requested lateral guidance if the steering system is working. If the driver has then not intervened in the guidance of the vehicle, the lateral guidance is continued on the basis of a determined lateral guidance fallback trajectory.
Advantageously, the method according to the invention can also be developed such that, upon failure of the steering system, the lateral guidance is not only taken over by the braking system, but a special intervention is also made in the longitudinal guidance of the vehicle. Advantageously, such braking interventions can be made, for example, such that the vehicle, in addition to being kept within the driving lane within a predetermined first time interval or a predetermined first distance, is braked to a standstill; that is, the braking system takes over not only the lateral guidance but also ensures, through commensurate controlling of the actuatorics, that the vehicle is braked to a standstill. However, the other traffic participants, particularly a vehicle traveling ahead, must continue to be considered.
Alternatively, the longitudinal guidance can also be influenced or specifically not influenced such that, upon failure of the steering system, such braking interventions are performed if the steering system is working that the longitudinal guidance requested by the driver assistance system designed for driver-independent vehicle guidance remains nearly uninfluenced at least with respect to the deceleration request even in the event of failure of the steering system. Accordingly, the implementation with respect to an acceleration request made on the basis of the driver assistance system is also done by the corresponding actuatorics, that is, the drive unit, analogously to the fault-free case; that is, the longitudinal guidance is therefore performed identically to the original request of the driver assistance system.
In particular, this longitudinal guidance (desired on the basis of the request of the assistance system when the steering system is working) can also be carried out only for a predetermined second time interval or a predetermined second distance and/or until occurrence of a terminating condition, with a terminating condition being present, for example, if strong acceleration and/or decelerations are requested. If this is the case, in an advantageous development of the method, at the end of the second time interval and/or after the predetermined second distance and/or upon occurrence of the terminating condition, such braking interventions are performed that, in addition to the required lateral guidance for lane-keeping, the vehicle comes to a standstill or is braked to a standstill within a predetermined third time interval or a predetermined third distance.
Since a failure of the steering system can always be associated with risk to the driver despite the described fallback level, the driver should at least be informed in the event of failure of the steering system and be prompted to perform independent (lateral) guidance of the vehicle. To ensure this, a takeover prompt for takeover of the vehicle guidance is advantageously outputted to the driver either immediately upon failure of the steering system or at the end of the second time interval and/or after the predetermined second distance and/or upon occurrence of the terminating condition. If the driver does not follow this takeover prompt within a time interval, the vehicle can automatically be moved to a safe state (standstill at the edge of the road).