Procedure for assisting with a driving maneuver and driver assistance system

Abstract

Method for assisting during a driving maneuver of a vehicle (20), which includes lateral guidance and / or longitudinal guidance of the vehicle (20), wherein the vehicle (20) is guided along a trajectory (30, 32) to be determined from a current position (34) to a target position (36), wherein a coefficient of friction of the wheels of the vehicle (20) on the surface of the vehicle (20) is determined and the trajectory (30, 32) is determined as a function of the coefficient of friction, characterized in that the driving maneuver is a parking maneuver, and on inclined roadways with a low and / or very low coefficient of friction, parking spaces (22) of a certain size (40) or more are offered and / or only parking spaces are offered which are delimited on at most one side by navigation space delimitation elements (24, 26).

Description

State of the art

[0001] The invention is based on a method for assisting in a driving maneuver, which includes a lateral guidance and / or a longitudinal guidance of the vehicle, wherein the vehicle is guided along a trajectory to be determined from a current position to a target position.

[0002] The present invention also relates to a computer program and a driver assistance system which are particularly designed to carry out the method.

[0003] DE 10 2009 046 966 A1 describes a method for assisting a driver of a vehicle with electronic steering during a parking maneuver. The method first determines the path the vehicle is to follow, and then determines the steering settings of the vehicle's steerable wheels required to complete the path. In addition to the steering speed and the vehicle's speed, a friction coefficient of the tires on the ground can be taken into account to estimate the expected effort required for each steering setting.

[0004] DE 10 2008 002 699 A1 discloses a device for controlling an automatic steering system of a vehicle, comprising a signal input that receives a target direction of travel specified by an automatic vehicle control system, and an evaluation device that receives an actual direction of travel determined by a sensor of the vehicle, compares it with the specified target direction of travel, and, in the event of a deviation, determines a correction factor. The automatic steering system is switched to a mode for maintaining the corrected target direction of travel. The correction factor can be determined depending on the vehicle inclination, the road gradient, or the friction coefficient of the road being traveled.

[0005] DE 10 2005 053 666 A1 describes a method for calculating a compensation value for an error in a measured value for the lateral speed of a vehicle wheel in a parking assistance system. This method takes into account wheel slip relative to the road surface when detecting the vehicle speed.

[0006] The document DE 10 2009 047 333 A1 discloses a method for determining a trajectory of a vehicle, wherein friction coefficient information of various road areas is determined with the aid of a sensor system and a trajectory is determined as a function of the friction coefficient information.

[0007] The document DE 10 2012 203 187 A1 discloses a method for predicting and adapting movement trajectories of a motor vehicle to support the driver in his driving task and / or to prevent a collision or mitigate the consequences of an accident.

[0008] The document DE 10 2009 053 939 A1 discloses a method for controlling a vehicle during a parking process, wherein an obstacle is detected by means of sensor devices and a distance to the obstacle is determined, wherein a braking system of the vehicle is controlled and / or regulated in order to stop the vehicle in front of the obstacle and wherein the braking system is controlled and / or regulated as a function of the distance of the vehicle to the obstacle and / or as a function of a vehicle speed, a vehicle acceleration, a direction of travel, a steering angle and / or a road gradient. Disclosure of the inventionAdvantages of the invention

[0009] The method according to the invention with the features of the independent claim provides that a coefficient of friction of the vehicle's wheels on the ground is determined, and the trajectory is determined as a function of the coefficient of friction. The vehicle is guided along the determined trajectory from the current position to the target position.

[0010] In the method according to the invention, the trajectory to be followed is pre-adapted, particularly based on the various road surfaces determined. A particular advantage is that the application of the method increases the safety of driver assistance systems by counteracting slipping and / or yawing of the vehicle on the road surface by taking the coefficient of friction into account when planning the trajectory.

[0011] The coefficient of friction of the wheels on the ground used in the invention can also be referred to as the coefficient of friction of the road surface. Within the scope of the invention, the coefficient of friction of the vehicle's wheels on the ground can, for example, be a measure of the frictional force in relation to the contact force between the vehicle and the ground. When contacting bodies move relative to one another, friction acts as a mechanical resistance against the kinetic force. This resistance force can be referred to as frictional force. As long as the external force is smaller than the frictional force and the body remains at rest, static friction exists. Static friction is generally greater than dynamic friction. If static friction is overcome and the body begins to move, Coulomb's law of dynamic friction applies to the frictional force: FR=μ×FN

[0012] The coefficient of friction, also called the friction number, is abbreviated as µ or sometimes f, as in the formula mentioned, and indicates a system and / or material property. Friction values ​​depend, among other things, on the material pairing, temperature, surface condition, sliding speed, ambient medium, and an intermediate substance, such as a lubricant. Friction values ​​can fluctuate between limit values ​​and are preferably determined experimentally. The friction value of the wheels depends particularly on the surface—whether it is dry, wet, icy, or smeared—and also on other factors such as the tire material and the ambient temperature.

[0013] The method according to the invention has the advantage that the coefficient of friction, which may already be available on a data bus, such as a CAN bus, can be used to determine the vehicle trajectory. In principle, the coefficient of friction of the wheels on the ground can be determined in any desired way, e.g., by determining the braking distance. The determination of the coefficient of friction is known to those skilled in the art, for example, from ESP or ABS systems. In particular, the coefficient of friction can alternatively or additionally be determined or verified for plausibility by evaluating image information from one or more image sensors, in particular front cameras, rear cameras, BSD cameras (blind spot detection) cameras, SVA cameras (side view assistant) cameras, and / or SVS cameras (surround view system) cameras, which can be used, for example, by other driver assistance systems for other purposes.

[0014] The measures listed in the dependent claims enable advantageous further developments and improvements of the method specified in the independent claim.

[0015] Advantageously, the determined coefficient of friction is classified into at least three classes comprising value ranges for high, normal (i.e., medium), and low coefficients of friction, preferably into four classes comprising value ranges for very low, low, medium, and high. The determined coefficient of friction can be assigned to one of these classes.

[0016] A typical value for dry sliding friction between rubber and asphalt is µ = 0.8. For example, a locked car wheel on pavement has a coefficient of friction of 0.5 on dry pavement and 0.2 on wet pavement.

[0017] When classifying the coefficient of friction, for example, three classes can be provided: a first class below 0.5, a second class between 0.5 and 0.8, and a third class above 0.8. The first class, for example, can be assigned an attribute of a low coefficient of friction, the second class an attribute of a medium coefficient of friction, and the third class an attribute of a high coefficient of friction. However, even more classes can also be provided, for example a class with a very low coefficient of friction below µ = 0.2, a class with a low coefficient of friction between 0.2 and 0.5, a class with a medium coefficient of friction between 0.5 and 0.8, and a class with a high coefficient of friction above 0.8. It is clear that a multitude of class subdivisions with different numerical values ​​are possible, and an optimal class division will be the result of practical tests.

[0018] The friction coefficient information can be used, for example, as described in the table below: Friction coefficient information Friction class Parking space measurement Path planning trajectory Path planning parameters asphalt Normal Normal Normal Normal Snow Low Enlargement of minimum parking space Planning a flatter trajectory Increasing safety distances Ice Very low Only parking spaces without rear barrier Planning a flatter trajectory Increasing safety distances

[0019] It is particularly advantageous to determine a flatter trajectory at low and / or very low friction coefficients than at normal or high friction coefficients. The flatter trajectory requires less lateral acceleration during steering, which can help prevent skidding.

[0020] Advantageously, at low and / or very low friction coefficients, a trajectory is determined with a greater distance to the navigation space boundary elements than at normal or high friction coefficients. This establishes a safety distance. The safety distance can be, for example, 10 cm to 2 m, preferably 50 cm to 1 m. This advantageously counteracts the risk of collision with the navigation space boundary elements due to possible slipping or yawing of the vehicle during braking maneuvers, especially when stopping the vehicle.

[0021] In systems with longitudinal control, for example, in semi-autonomous or autonomous systems in which a control unit controls the brake, a reduced maximum speed is preferably provided at low and / or very low friction coefficients. For example, at low and / or very low friction coefficients, the reduction can be 10% to 80%, in particular 20% to 50%, of a speed that would be assumed at a medium or high friction coefficient of the road surface. This counteracts the risk of collision with the navigation space boundary elements due to possible slipping or yawing when the vehicle stops.

[0022] In semi-autonomous or autonomous systems where a control unit controls the brakes, if a low and / or very low friction coefficient is detected, the driver can also be informed that the semi-autonomous or autonomous vehicle control function, such as automatic longitudinal guidance, is not possible. In this case, the corresponding control unit of the semi-autonomous or autonomous system can also be configured to stop executing the maneuver and instead return control of the vehicle to the driver.

[0023] According to the invention, the driving maneuver, which involves lateral and / or longitudinal guidance of the vehicle, is a parking maneuver, a parking exit maneuver, or a passage through a dangerous or narrow spot. The method can be applied, for example, to a semi-autonomous or autonomous parking assistant. By applying the method according to the invention to the parking assistant, situations with low and / or very low friction coefficients, such as parking into an icy parking space, can be mastered.

[0024] According to the invention, on inclined roadways with a low and / or very low coefficient of friction, parking spaces of a certain size and / or only parking spaces are offered that are limited on at most one side by navigation space boundary elements.

[0025] Alternatively or additionally, the method may also be used in the context of other driver assistance systems in which the vehicle is guided along a trajectory to be determined from a current position to a target position, for example in an ACC system (“adaptive cruise control” system) or in a collision avoidance system which involves automatic longitudinal and lateral guidance.

[0026] According to the invention, a computer program is further proposed, according to which one of the methods described herein is carried out when the computer program is executed on a programmable computer device. The computer program can be, for example, a module for implementing a driver assistance system or a subsystem thereof in a vehicle or an application for driver assistance functions that can be executed on a smartphone. The computer program can be stored on a machine-readable storage medium, such as a permanent or rewritable storage medium or in association with a computer device or on a removable CD-ROM, DVD, or USB stick. Additionally or alternatively, the computer program can be made available for download on a computer device, such as a server or a cloud computing system, e.g.over a data network such as the Internet or a communications connection such as a telephone line or a wireless connection.

[0027] According to the invention, a driver assistance system with the features of the further independent claim is also provided, which is particularly suitable for carrying out one of the methods described above. Short description of the drawings

[0028] Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

[0029] It shows Fig. 1 a schematic representation of functional components of a driver assistance system and Fig. 2 a top view of a situation with a vehicle and a parking space. Embodiments of the invention

[0030] Fig.Figure 1 shows a schematic representation of functional components of a driver assistance system 1 according to the present invention. The driver assistance system 1 is designed to determine a coefficient of friction of a road surface and to determine a trajectory depending on the coefficient of friction.

[0031] For this purpose, the driver assistance system 1 comprises at least one environment detection device 2, which may include, for example, ultrasonic sensors, radar sensors, infrared sensors, lidar sensors, and / or a camera system. Weather sensors, such as temperature sensors or rain sensors, may also be associated with the environment detection device 2. Furthermore, the environment detection device 2 may also have means for detecting the vehicle's inclination angle. The inclination angle of the road may be determined, for example, using a GPS system and existing map material. The driver assistance system 1 may further comprise communication interfaces, GPS devices, and an odometry system (not shown). The signals from the environment detection device 2 are received in an input circuit 3. The input circuit 3 is connected to a bus system 4 for data exchange with a data processing device 5.

[0032] The data processing device 5 comprises a friction coefficient determination unit 6, which further processes, for example, data from a control system from an ESP program or an ABS program, which determines a friction coefficient of the wheels of a vehicle on a surface. The friction coefficient of the vehicle's wheels on the surface can be provided by such a control system, for example, on a data bus, such as a CAN bus. Alternatively or additionally, the friction coefficient determination unit 6 can determine the friction coefficient itself and / or further process data from a camera system. For this purpose, the friction coefficient determination unit 6 can have known image processing tools and can detect, for example, puddles, snow, and ice surfaces in environmental images. It can be provided that the friction coefficient determination unit 6 processes further data, in particular, for example, weather data provided by rain sensors and / or thermometers.After evaluating the available data, the friction coefficient determination unit 6 determines the friction coefficient of the vehicle on the ground, weighting the data against each other and checking their plausibility.

[0033] In the illustrated embodiment, the driver assistance system 1 further comprises a classification module 7, which is configured to classify the determined friction coefficient. The classification module 7 is configured to receive and further process the data from the friction coefficient determination unit 6. For this purpose, the determined friction coefficient is provided by the friction coefficient determination unit 6 as a numerical value. The numerical value is compared with defined values, preferably determined experimentally, which define friction coefficient classes. A first class corresponds, for example, to a very low friction coefficient, another class to a low friction coefficient, a third class to a medium friction coefficient, and another class to a high friction coefficient. The determined friction coefficient is assigned to one of the defined classes.The result can then be made available to other modules for processing periodically at intervals of a few milliseconds to a few seconds.

[0034] The data processing device 5 comprises a module 8 for determining trajectories, which is configured to receive and further process data from the environment detection device 2, the friction coefficient determination unit 6, and / or the classification module 7. The friction coefficient determination unit 6, the classification module 7, and the module 8 for determining trajectories can, for example, be subunits of a parking assistant or a maneuvering assistant of a vehicle. Based on the entered target position and the detected environment, the module 8 for determining the trajectories determines, for example, in a first step, all possible single-move and multi-move trajectories leading from a current position of the vehicle to the target position, and in a further step, selects the trajectory that promises the safest and shortest route into the parking space while maintaining the minimum distances.The minimum distances can be increased for low and very low friction coefficients. Module 8 for determining the trajectories is preferably also configured to offer parking spaces of a certain size or larger when the friction coefficient is low and / or to offer only parking spaces that are bordered on at most one side by navigation space boundary elements. If the control unit for parking maneuver control also specifies a maximum speed, module 8 for determining the trajectories can reduce this speed according to the road surface friction coefficient.

[0035] The data processing device 5 is connected to a further 10 or the same 4 bus system with an output circuit 11, via which display elements 12, a longitudinal guidance actuator 13 and / or a lateral guidance actuator 14 can be controlled by the maneuvering assistance system, for example a parking assistant.

[0036] Fig.Figure 2 shows a top view of a situation involving a vehicle 20 and a parking space 22. In the position shown here, the parking space 22 is bounded at the rear by a first vehicle 24 and at the front by a second vehicle 26. The two vehicles 24, 26 form navigation space boundary elements for a planned parking maneuver.

[0037] As the motor vehicle 20 passes by, the surroundings of the motor vehicle 20 are detected using suitable sensors 21 of an environment detection device. Suitable sensors for the environment detection device include, in particular, the ultrasonic sensors shown, but also infrared sensors, radar sensors, lidar sensors, or optical sensors, for example, cameras.

[0038] If the distance 40 between the two vehicles 24, 26 is sufficiently large, a suitable parking space is assumed. Whether the distance 40 between the two vehicles 24, 26 is sufficient can depend, according to the invention, on the determined coefficient of friction of the vehicle 20 on the ground. Thus, the same parking space can be identified by the system as a possible parking space in summer, for example, but not in winter when the road is icy. A minimum distance 38 to be maintained in the parked position, shown here as an example with reference to the first vehicle 24, can also depend on the determined coefficient of friction of the vehicle 20 on the ground.

[0039] Within the scope of the invention, parking spaces that are only bounded on one side are understood to be those that are bounded either only by the rear of the first vehicle 24 or by the front of the second vehicle 26. The same applies analogously to perpendicular parking spaces. Once the suitable parking space 22 has been detected, a map of the surroundings is created based on the surrounding data, and a trajectory 28, 30, 32 with a target position 36 is calculated, along which the motor vehicle 20 can park in the parking space 22. After the trajectory 28, 30, 32 has been determined, the motor vehicle 20 is guided automatically or semi-automatically from its current position 34 along the trajectory 28, 30, 32 to the target position 36 in the parking space 22.

[0040] The trajectory 28, 30, 32 describes, for example, the path traveled by the center point 42 of the rear axle of the motor vehicle 20. Depending on the position of the motor vehicle 20 and the geometry of the detected parking space 22, the driving maneuver can be performed in a single or multiple movement. In a multiple movement maneuver, forward and reverse movements alternate. A single movement maneuver is shown. The area swept over by the vehicle 20 or the space traveled through is also known as the driving path and can be used in addition to or alternatively to the trajectory to describe the path into the parking space 22. The driving path is not shown for the sake of clarity.

[0041] The dashed trajectory 28 represents, by way of example, a trajectory determined according to the prior art, which, for example, is a possible route into the parking space 22 while maintaining the minimum distances to the other vehicles 24, 26. The trajectories 30, 32 determined according to the invention differ from trajectory 28 in that they are flatter. This means, for example, that a steering angle change rate is limited and / or that the wheel steering angle is limited. The wheel steering angle can, for example, be limited to less than 40°, less than 30°, or less than 20°. The steering angle change rate can be limited with respect to the location traveled and / or limited with respect to time. If the system limits the steering angle change rate with respect to time, it can be provided that a trajectory can only be traveled at a certain maximum speed specified by the system.This is particularly advantageous in systems with automatic longitudinal control. Furthermore, the trajectories 30, 32 end at the minimum distance 38 from the first vehicle 24, which is increased compared to the distance 44 of the trajectory 28 according to the prior art.

[0042] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of expert practice.

Claims

[1] Method for assisting in a driving maneuver of a vehicle (20), which includes a transverse guidance and / or a longitudinal guidance of the vehicle (20), wherein the vehicle (20) is guided along a trajectory (30, 32) to be determined from a current position (34) to a target position (36), wherein a coefficient of friction of the wheels of the vehicle (20) on the surface of the vehicle (20) is determined and the trajectory (30, 32) is determined as a function of the coefficient of friction, characterized by that the driving maneuver is a parking maneuver, and on inclined roadways with a low and / or very low coefficient of friction, parking spaces (22) of a certain size (40) or more are offered and / or only parking spaces are offered which are delimited on at most one side by navigation space delimitation elements (24, 26). [2] Method according to claim 1, characterized by that the coefficient of friction is classified into at least three classes comprising value ranges for high, normal and low friction values. [3] Method according to claim 2, characterized by that at low and / or very low friction coefficients a flatter trajectory (30, 32) is determined than at normal or high friction coefficients. [4] Method according to one of claims 2 or 3, characterized by that at a low and / or very low coefficient of friction, a trajectory (30, 32) with a greater distance (38) to navigation space boundary elements (24, 26) is determined than at a normal or high coefficient of friction. [5] Method according to one of claims 2 to 4, characterized by that in semi-autonomous or autonomous systems in which a control unit controls the brake, if a low and / or very low coefficient of friction is detected, the driver is informed that the function of the semi-autonomous or autonomous vehicle control is not possible. [6] Method according to one of the preceding claims, characterized bythat in systems with longitudinal control at low and / or very low friction coefficients a reduced maximum speed is provided. [7] A computer program which, when run on a computer, carries out one of the methods according to any one of claims 1 to 6. [8] Driver assistance system (1) for assisting in a driving maneuver, which includes a lateral guidance and / or a longitudinal guidance of the vehicle (20), wherein the vehicle (20) is guided along a trajectory (30, 32) to be determined from a current position (34) to a target position (36), with a friction coefficient determination unit (6) which is set up to determine a friction coefficient of a road surface and with a module (8) for determining trajectories (30, 32), which is set up to determine the trajectory (30, 32) as a function of the friction coefficient, characterized bythat the driving maneuver is a parking maneuver, and on inclined roadways with a low and / or very low coefficient of friction, parking spaces (22) of a certain size (40) or more are offered and / or only parking spaces are offered which are delimited on at most one side by navigation space delimitation elements (24, 26).

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