Driver assistance system

Abstract

Method for operating a driver assistance system for vehicles, comprising the following steps: - determining (S1) a section of road ahead which the vehicle will travel in the immediate future; - estimating (S2) a predictive wheel friction coefficient of the motor vehicle for the road section ahead; - Estimation (S3) of a permissible steering torque with which the vehicle can travel the section of road ahead; - Determining (S4) an actual steering torque of the vehicle; - Determining and executing (S5) a control command which sets the permissible steering torque if it is determined that the actual steering torque deviates from the permissible steering torque, wherein the estimated predictive wheel friction value is checked for plausibility by means of a current or past wheel friction value.

Description

The present invention relates to a method for operating a driver assistance system and to a driver assistance system.DE 10 2012 112 725 A1 discloses a method for estimating a predictive wheel coefficient of friction.DE 10 2013 016 434 A1 discloses a method for operating a driver assistance system for vehicles, which has the following steps: ascertaining a route section ahead which will be traveled by the vehicle in the immediate future; estimating a predictive wheel coefficient of friction of the motor vehicle for the route section ahead; estimating an admissible steering torque with which the vehicle can travel the route section ahead; ascertaining an actual steering torque of the vehicle; ascertaining and executing a control command which sets the admissible steering torque if it is ascertained that the actual steering torque deviates from the admissible steering torque.Against this background, the object of the invention is to specify a driver assistance system or a method for operating a driver assistance system, by means of which the reliability of a predicted wheel coefficient of friction is improved.According to the invention, this object is achieved by a method for operating a driver assistance system having the features of patent claim 1 and / or by a driver assistance system having the features of patent claim 10.Vehicles within the meaning of this patent application are motor-driven land vehicles. Rail vehicles are also included.A steering torque describes the steering effect of a steering force on a body. A permissible steering torque is a steering torque by means of which a route section can be traveled on by a vehicle without an accident. An actual steering torque of a vehicle is the steering torque that acts on the vehicle due to a certain steering setting.Driver assistance is the support or replacement of a driver by electronic auxiliary devices in motor vehicles. In this case, safety aspects are often of primary importance, but also the increase in driving comfort or the friends in driving. Another aspect is the improvement of the economic efficiency.A forward route section of a vehicle extends in front of a vehicle in the direction of travel and can have any length.The wheel coefficient of friction, also called the coefficient of friction, is a dimensionless measure of the frictional force in relation to the contact pressure force between a wheel and a road surface. A predictive wheel coefficient of friction is a prediction of a wheel coefficient of friction for a section of road lying ahead. A measured wheel coefficient of friction is a current or past wheel coefficient of friction, which was measured or calculated by a sensor system.A sensor, also referred to as a detector, (measurement variable or measurement) pick-up or (measurement) sensor, is a technical component that can record specific physical, chemical properties or states, e.g. temperature, humidity, pressure, speed, brightness, acceleration, pH value, ionic strength, electrochemical potential and / or the material nature of its environment qualitatively or quantitatively as a measurement variable. These variables are detected by means of physical or chemical effects and transformed as sensor data into an electrical signal that can be processed further.Radar is the name for various detection and positioning methods and devices based on electromagnetic waves in the radio frequency range (radio waves). A radar device is a device that emits electromagnetic waves in a bundled fashion, receives and evaluates the echoes reflected by objects. Information about the objects can thus be obtained. The following information can be obtained from the received waves reflected by the object: the angle and the distance to the object, the relative movement between transmitter and object, the distance and the absolute speed of the object, contours or images of the object.Lidar, also called ladar, is a radar-related method for optical distance and speed measurement as well as for remote measurement of atmospheric parameters. Instead of the radio waves as in the radar, laser beams are used.Position data is, for example, GPS data.Road data is all data relating to a road, for example data relating to the course of the road, curve radii, data relating to the surface condition, data relating to the width of the road and the like.A deceleration command is a command for decelerating single or plural movable elements of a movable body. Accordingly, a deceleration command may be directed to a change in direction of a body and / or to a braking of the body. For example, a change in direction of a vehicle can be brought about by delaying wheels selectively, that is to say, for example, at the rear right.In contrast, in this patent application, a vehicle brake is understood to mean a reduction in the speed of the entire vehicle.A steering command is directed to a change in direction of a vehicle. Steering forces can be transmitted to the wheels of the vehicle via a steering axle of a mechanical steering system and / or via actuators of an electronic steering system.A lane change assistant is configured to actively assist a driver in a steering maneuver, for example a lane change, by the lane change assistant ascertaining suitable steering commands.An interface is a device between at least two functional units, at which an exchange of logical variables, e.g. data, or physical variables, e.g. electrical signals, takes place, either only unidirectionally or bidirectionally. The exchange can be analog or digital. The exchange can furthermore take place in a wired or wireless manner.The basic idea of the invention is to support a sport driving style as a function of an estimated predictive wheel coefficient of friction. Too low a wheel coefficient of friction may lead, for example, to oversteering or understeering of the vehicle during cornering. This causes many accidents.The concept of the invention is to intervene in a driving maneuver if it is determined that a wheel coefficient of friction is not sufficient for safe execution of the driving maneuver.According to the invention, the estimated predictive wheel coefficient of friction is checked for plausibility by means of a current or past wheel coefficient of friction. Accordingly, it may be provided that an estimated predictive wheel coefficient of friction is corrected on the basis of a difference between a previous predictive wheel coefficient of friction and a previous actual wheel coefficient of friction.Thus, errors even if they are unknown cause can be reduced.Advantageous embodiments and refinements emerge from the further dependent claims and from the description with reference to the figures of the drawing.According to a preferred development of the invention, the predictive wheel coefficient of friction is estimated by means of sensor data. This sensor data is, for example, camera data, radar data and / or lidar data. Accordingly, it may be provided that an imminent route section is detected by means of an optical sensor, i.e. a camera, a radar sensor and / or a lidar sensor, and a wheel coefficient of friction of the imminent route section is deduced on the basis of the optical sensor data relating to the imminent route section. For example, when road conditions are wet, reflections on the road surface often occur, which can be optically detected. Snow or ice on a roadway can also be detected optically. In addition, the wheel coefficient of friction is frequently also adversely affected by a poor road surface condition, which is optically detectable.According to a preferred development of the invention, the predictive wheel coefficient of friction is estimated by means of position data of the vehicle and known road data. Accordingly, it can be provided, for example, that a curve radius or a curve curvature of a section of track is known and the wheel coefficient of friction is estimated on the basis thereof for the section of track. It is understood that further influencing factors, such as the weather conditions, can also be taken into account for this purpose.According to a preferred development of the invention, the control command comprises a deceleration command and / or a steering command. A driver can thus be supported in a wide variety of ways.It can be provided to assist the driver merely with a steering command or a deceleration command for selectively decelerating a wheel. This option is to be preferred over vehicle braking, since less intervention is thus made in the individual driving style of the driver and the driver can accordingly experience a sport driving style, provided that the imminent route section can be traveled on safely by these means.Accordingly, it may be provided to determine whether the permissible steering torque is adjustable without vehicle braking being initiated. This is particularly advantageous for driver assistance systems of sports cars, since sporting driver assistance systems intentionally intervene as little as possible in the driving style of a driver.It may also be expedient to brake the vehicle if it is determined that the permissible steering torque cannot be set at a current speed of the vehicle. Accordingly, it may be provided that it is determined that a route section ahead cannot be traveled at a current speed of the vehicle. Thus, accidents can be avoided even if a vehicle braking seems unavoidable.According to a preferred development of the invention, further control commands are determined by a lane change assistant on the basis of the estimated permissible steering torque. Accordingly, it may be provided that the method as described above interacts with a lane change assistant. Even if only small steering torques are generally required for lane change maneuvers, it occasionally happens that, for example, unfavorable weather conditions such as strong aquaplaning or snow residue on roads adversely affect a wheel coefficient of friction to such an extent that additional deceleration commands and / or steering commands are required even for a lane change.Thus, for example, especially in the medium European winter, it occasionally happens that the major part of roads are very well cleared, so that no adverse effects on the coefficient of friction of the wheels result.As a result, these lanes are driven at normal speed. Nevertheless, snow remains often on deceleration strips, for example, which often overseeze a driver.The method as described above makes it possible to enter into such situations in such a way that a driving style is only taken into account if it is foreseeable that an imminent route section cannot be driven in a safe manner.According to a preferred development of the invention, it is determined whether a counter-roadway can be traveled on without risk and the permissible steering torque is determined on the basis thereof. For example, some curves can be traveled at a higher speed when these curves are cut, i.e. when at least partial sections of a curve are partially traveled on the opposite roadway. The cutting of curves is generally a intentionally initiated driving maneuver and is based on an intentional decision of a driver. Accordingly, drivers may feel annoying if a driver assistance system would prevent safe cutting of a curve.In contrast, this further development of the invention provides an additional safety margin if, for example, careless curves are cut. For example, it frequently occurs that a driver is surprised in a cut curve by oncoming traffic and cannot safely avoid this because the wheel coefficient of friction would not be sufficient for a lane change back to the own lane.In such cases, it can be provided that sensors detect an unintentional curve and prevent a vehicle from cutting a curve and / or brake a vehicle in such a way that a possible avoidance maneuver back to the own lane is possible at all times without risk.Alternatively, it can also be provided that the driver is warned by the driver assistance system or that attention is drawn to the fact that the occurrence of oncoming traffic within the range of vision of the driver would result in an accident.The present invention is explained in more detail below with reference to the exemplary embodiments indicated in the schematic figures of the drawings. The following are shown: FIG. 1 is a schematic block diagram of an embodiment of the invention; FIG. 2 is a schematic block diagram of an embodiment of the invention.FIG. 1 shows a block diagram of a driver assistance method according to an embodiment of the invention. In step S 1, a route section ahead is ascertained, which will be traveled by the vehicle in the immediate future.In step S 2, a predictive wheel coefficient of friction of a motor vehicle is estimated for the section of road ahead. In step S 3, an allowable steering torque with which the vehicle can travel the route section ahead is estimated.In step S 4, an actual steering torque of the vehicle is determined. In step S 5, a control command that sets the allowable steering torque is determined and executed when it is determined that the actual steering torque deviates from the allowable steering torque.FIG. 2 shows a block diagram of a driver assistance system according to an embodiment of the invention. The driver assistance system 10 comprises a first interface 12 to means 14 for ascertaining a route section lying ahead, which will be traveled on by the vehicle in the immediate future.In addition, it comprises a second interface 16 to means 18 for estimating a predictive wheel coefficient of friction of the motor vehicle for the section of road lying ahead. Furthermore, it has a determination unit 20 for determining an actual steering torque of the vehicle. Furthermore, it comprises a computing unit 22 for estimating an admissible steering torque with which the vehicle can travel on the route section lying ahead, and for ascertaining a control command which sets the admissible steering torque.Reference numerals denote reference numerals10 Driver assistance system 12 Interface 14 Means for ascertaining a route section 16 lying ahead Interface 18 Means for estimating a predictive wheel coefficient of friction 20 Ascertainment unit 22 Arithmetic unit S 1-S 5 Method steps

Claims

Method for operating a driver assistance system for vehicles, which has the following steps: - determining (S1) a route section ahead which will be traveled by the vehicle in the immediate future; - estimating (S2) a predictive wheel coefficient of friction of the motor vehicle for the route section ahead; - estimating (S3) a permissible steering torque with which the vehicle can travel the route section ahead; - determining (S4) an actual steering torque of the vehicle; - determining and executing (S5) a control command which sets the permissible steering torque if it is determined that the actual steering torque deviates from the permissible steering torque, wherein the estimated predictive wheel coefficient of friction is checked for plausibility by means of a current or previous wheel coefficient of friction.Method for operating a driver assistance system according to Claim 1, wherein the predictive wheel coefficient of friction is estimated by means of sensor data.Method for operating a driver assistance system according to one of the preceding claims, wherein the predictive wheel coefficient of friction is estimated by means of position data of the vehicle and known road data.Method for operating a driver assistance system according to one of the preceding claims, wherein the control command comprises a deceleration command and / or a steering command.The method of operating a driver assistance system of claim 4, wherein wheels of the vehicle are selectively decelerated.Method for operating a driver assistance system according to one of the preceding claims, wherein it is furthermore determined whether the permissible steering torque is adjustable without vehicle braking being initiated.Method for operating a driver assistance system according to Claim 6, wherein the vehicle is braked if it is determined that the permissible steering torque cannot be set at a current speed of the vehicle.Method for operating a driver assistance system according to one of the preceding claims, wherein further control commands are determined by a lane change assistant on the basis of the estimated permissible steering torque.Method for operating a driver assistance system according to one of the preceding claims, wherein it is determined whether a counter-lane can be traveled on without risk and the permissible steering torque is determined on the basis thereof.Driver assistance system (10) for a vehicle for carrying out a method according to one of the preceding claims, having a first interface (12) to means (14) for determining a route section ahead which will be traveled by the vehicle in the immediate future, having a second interface (16) to means (18) for estimating a predictive wheel coefficient of friction of the motor vehicle for the route section ahead, having a determination unit (20) for determining an actual steering torque of the vehicle and having a computing unit (22) for estimating an admissible steering torque with which the vehicle can travel on the route section ahead, and for determining a control command which sets the admissible steering torque.

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