DE102016221563A1 - Method and driver assistance system for driving a vehicle, computer program and product and control unit - Google Patents

Abstract

Method for at least partially automated guiding of a vehicle (1), comprising a front axle steering (4) and a rear axle steering (5) and at least one sensor system (S) for detecting the vehicle environment and the vehicle movements, wherein the steering systems (4, 5) and the sensors ( S) are coupled to one another via at least one control unit (SG), wherein the vehicle (1) follows a predetermined, in particular calculated, trajectory (T), characterized in that a time-shifted change of the wheel steering angle is detected when a driving situation requiring dodging is detected (δv, δh) on the front axle (4) and on the rear axle (5) takes place in order to effect at least a transverse offset of the vehicle depending on the driving situation.

Description

The invention relates to a method for at least partially automated driving a vehicle according to the preamble of claim 1. The invention further relates to a driver assistance system for carrying out the aforementioned method, a computer program product, a computer program and a control device with at least one computer for carrying out the aforementioned method according to the further independent claims.

By the DE 10 2008 013 988 A1 has become known a method for performing an evasive maneuver in a vehicle with front and rear wheel steering. By means of the same direction steering on the front and rear axles, a stable driving behavior is to be achieved, whereby, however, an increased steering effort for the driver may arise.

Furthermore, by the EP 1 251 060 B1 it is known to use the Hinterachslenkung of the vehicle in an evasive action, and in principle to track the behavior of a same direction steering movement between front and rear steering. Depending on the driving behavior of the driver is switched to evasive maneuver modes to achieve either a large steering effect or high stability.

For the partially automated or fully automated driving of a vehicle, it is important that the probability of a false triggering of the driver assistance system or the evasion assistant is largely ruled out. A vehicle should only dodge if this is actually necessary. An automatically triggered evasive maneuver on the other hand should still be safely executable even if there is an obstacle in front of the vehicle in the short term. To dodge a transverse offset of the vehicle must be effected to drive past the obstacle and to avoid a collision. For this purpose, the hitherto driven trajectory is left and the vehicle is directed to an evasion trajectory. Theoretically, dodging with the same direction steering front and rear wheels would be ideal.

Side forces on the front and rear axle or tire lateral forces on the aforementioned axles can be constructed very quickly and the driving stability is maintained, so that a vehicle can avoid it as quickly as possible. However, the actuators used for steering on the front axle and rear axle are subject to certain performance limits (actuating force, positioning speed, acceleration at the beginning or deceleration at the end of the adjusting movement). In other words, when actuated, the actuators first have to generate a wheel steering angle at the respective wheels before it is possible to build tire lateral forces and thus lateral forces on the vehicle axles. When using Hinterachslenkungen also may have a limited adjustment angle range, which is expressed in the fact that at the rear axle in comparison to the front axle significantly lower Radlenkwinkel are adjustable. By the aforementioned limitations, therefore, the theoretical advantages of the same direction steering can not be optimally played.

The invention relates to a method for at least partially automated guidance of a vehicle, which comprises a front axle steering and a rear axle steering system and at least one sensor system for detecting the vehicle surroundings and the vehicle movements. The steering and the sensors are coupled to each other at least via a control unit, wherein the vehicle follows a predetermined, in particular calculated trajectory. The method is characterized in that upon detection of a driving situation requiring evasion, a time-shifted change of the wheel steering angles takes place on the front axle and on the rear axle in order to effect at least a lateral offset of the vehicle as a function of the driving situation. Due to the time-shifted changing the wheel steering angle on the front axle and on the rear axle an optimal evasion is achieved by as fast as possible lateral forces are built up on the respective or all existing vehicle axles by the targeted construction of a necessary yaw rate. It is known that lateral or transverse forces occur at a yaw rate and that changes in the yaw rate can influence the lateral or transverse forces.

The predefined trajectory results either from the steering angle set by the driver or the trajectory is predetermined, for example, by data from a navigation system and / or calculated from data from a suitable sensor system for detecting the vehicle environment and vehicle movements and the actuator system on the respective axle sets the steering angle one. The sensor can be e.g. from a camera or LiDAR (short for light detection and ranging) or radar (short for radio detection and ranging) or a combination of such systems. Both are methods for optical distance and speed measurement as well as for the remote measurement of atmospheric parameters. Instead of the radio waves at the radar, laser beams are used at the LiDAR). There are other optical or non-contact systems conceivable.

Furthermore, the sensor system can have at least one yaw rate sensor for detecting the yaw rate of the vehicle, with yaw rate sensors measuring the angular speed along an axis of rotation measure up. Integration can be used to deduce the angle at which a body has rotated within a certain time. The yaw of a vehicle is understood as the rotation of the vehicle about the vertical axis in the center of gravity. Furthermore, the sensors may include sensors for detecting vehicle speeds or accelerations (vehicle movements) as well as the steering angle of the vehicle on the front axle and the rear axle. Other inertial sensors such as acceleration sensors can be used. In addition, sensors for detecting the vehicle environment (temperatures of the tires and the road surface and the environment) or weather conditions (moisture, rain, snow, ice) or vehicle data (wheel speed, drive torque, tire pressure, etc.) can be used. The sensors mentioned here are only a selection.

The sensors can be accommodated in one or more control units, which each contain an evaluation unit or are shared by a separate evaluation unit. The sensors may additionally consist of individual sensors, which are housed in suitable locations in the vehicle. Control devices and sensors are wirelessly or wired coupled to each other and preferably connected to each other via a bus system such as CAN bus or the like. An algorithm may be stored in the at least one control device in order to evaluate the signals of the sensors and / or to make calculations, which may be e.g. affect the time offset and the change in wheel steering angle.

The at least one control unit can be provided with further data about the vehicle environment, which result from the possibilities of C2C and / or C2X communication. In C2C and C2X is information from outside the vehicle, wherein in a C2C communication of an understanding of vehicles with each other and in C2X communication of an understanding of the vehicle with data suppliers outside the vehicle, eg. B. at the roadside or satellite-based as information units for the vehicle environment is to go out. These may include information about ambient temperatures, weather (wet, ice), and the like. A vehicle in front can thus, for example, send data to the following vehicle.

A driving situation that requires evasion is, for example, the detection of an obstacle on an intended or calculated trajectory. This may be a vehicle driving ahead, suddenly slowing down, or else an obstacle, which as a rule is not present on the trajectory, such as, for example, a vehicle entering the trajectory. The change in the wheel steering angles at the front axle and at the rear axle must be made to the extent that the vehicle safely bypasses the obstacle, so that a collision is avoided. For this purpose, it is necessary to determine the so-called transverse offset of the vehicle, which is required so that there is no collision.

In the time-shifted changing the wheel steering angle on the front axle and on the rear axle, the adjustment of the Radlenkwinkel according to the invention is offset in time. Theoretically, a change in the wheel steering angle at the rear axle is delayed in time only made when the change was initiated at the wheel steering angle on the front axle at least. However, this does not necessarily mean that, for example, the actuator of the rear-axle steering is only activated when a wheel steering angle has already been set on the front axle or the change in the wheel steering angle has been completed there. Rather, a dynamic interaction of the actuators is meant in dependence on their performance at the front axle and at the rear axle, so that, for example, at the rear axle, an opposing or smaller wheel steering angle in the same direction with respect to the wheel steering angle set or adjusted at the front axle is set after the change started at the front axle. Time-displaced to change the wheel steering angle on the front axle can be set on the rear axle and a co-directional or lesser opposite wheel steering angle. The time offset is calculated specifically and as a function of certain parameters inside and outside the vehicle for the required change in the wheel steering angle and implemented by means of the steering actuators on the front and rear axles. The parameters to be considered will be discussed in detail later. As a result, a targeted, in particular short-term yaw rate build-up and dismantling is to be achieved in order to achieve the minimization of the time required for evasion. In other words, the time offset achieves a faster build-up of lateral forces, which enables a responsive short-term avoidance of the vehicle. Advantageously, this can be used to counteract the aforementioned limitations on the performance of the steering actuators.

In a dynamic steering operation during evasion, the wheel steering angle changes permanently. For the present consideration, therefore, the wheel steering angle at a specific time or its change within a time interval must be taken into account.

Preferably, the time-shifted steering takes place on the front axle and on the rear axle at least as a function of the driving speed of the vehicle and / or the coefficient of friction and / or the wheel steering angle applied to the front and / or rear axle and / or a yaw rate of the vehicle and / or at least one characteristic of at least one steering actuator and / or data on the vehicle environment and Vehicle movements and a required transverse offset. The coefficient of friction is of particular importance here.

In motor vehicles, the contact between the vehicle and the roadway is mediated only by the tire contact patch. The transmission of the lateral force with respect to the respective vehicle axle or the tire lateral forces to be transmitted by the tires depend on or are limited by the wheel load and the possible coefficient of adhesion between the tire and the roadway. In this case, the condition of the road surface plays a special role, since the coefficient of friction or coefficient of adhesion between the tire and the roadway depends very much on the nature of the roadway (dry, moist, wet, snow, ice, gravel, etc.). In addition, other influences on the tire, such. B. braking or accelerating. Delaying or accelerating is known to have a direct impact on the cornering force or lateral force of the tire. A tire can transmit maximum cornering force only if it turns. Therefore, for example, during deceleration / braking, it should be noted that tires or wheels do not lock. However, a tire can also transmit lateral forces if it does not turn (sliding friction of the tire with the road).

In contrast to straight-ahead driving, side forces result when cornering and thus when dodging. Due to the profile and structure elasticities in the tire transverse direction, the power transmission can take place only with simultaneous elastic deformation of the tire. This manifests itself in the form of a transverse slip, which is also referred to as slip angle. When cornering, the wheel runs under the influence of the lateral force by an angle α deviating obliquely to the vehicle longitudinal direction or wheel-rolling direction. The behavior of a vehicle can be described as neutral if, when cornering, the slip angles α at the front and rear axles are approximately the same. If the slip angle at the front axle is greater than at the rear axle, the vehicle is understeering. If the slip angle at the rear axle is greater than at the front axle, the vehicle oversteers.

The slip angle β finally describes the angle between the vehicle longitudinal axis and the driving speed in the center of gravity of the vehicle. Put simply, the slip angle is a measure of the driving behavior of a car. If the slip angle is very large when cornering or when dodging with a curve-like trajectory, the vehicle tends to break out at the rear axle (oversteer). The slip angle is the angle between the direction of movement of the vehicle and the longitudinal axis in the center of gravity. The yaw rate of a vehicle is also determined around the center of gravity. Yawing is the turning of a vehicle around its vertical axis. Since the yaw of the vehicle has a direct influence with regard to the development of lateral forces, the yaw rate in addition to the slip angle is a significant factor for the driving stability size. From the yaw rate finally the yaw angle can be determined.

• - Einstellbare Stellwinkel (Stellweg)
• - Stellwinkelgeschwindigkeit
• - Beschleunigung des Aktuators
• - Stellkraft
• - Stellmoment
• - Umgebungstemperatur.

Another important factor is the wheel steering angle immediately before the avoidance process on the front axle and / or the rear axle. If the evasive action is started starting from the straight-ahead travel of a vehicle, then a wheel steering angle of 0 degrees at the front and / or rear axle must be assumed, so that there should be no yaw rate. In normal cornering (with a constant radius), a wheel steering angle should be present at least on the front axle and there is a constant yaw rate. Depending on the driving situation, however, a wheel steering angle may also be present in the case of a steered rear axle, for example if the rear axle is directed in the same direction as the front axle in an overtaking operation to increase the stability. As already mentioned, the properties or performance data or even limitations of the steering actuator or actuators are a decisive factor and can be summarized as a parameter of a steering actuator. By way of example, but not exhaustively, the following influencing variables may be mentioned at this point, which may be incorporated into the formation of a parameter for a steering actuator:

• - Adjustable adjustment angle (travel)
• - angular velocity
• - acceleration of the actuator
• - Force
• - Setting torque
• - Ambient temperature.

As already stated above, data on the vehicle environment and vehicle movements for the time-delayed steering are also to be considered. Environment data can provide information about temperatures and road conditions, with vehicle movements primarily the vehicle speed and / or accelerations with respect to the trajectory and possibly further such as vehicle lateral movements, for example, in deviation from the trajectory concern.

To achieve the fastest possible structure of a, in particular maximum possible, lateral force at the front and the rear axle of the vehicle, a required yaw rate change of the vehicle is calculated in the at least one control unit. This calculation takes into account the flotation angle of the vehicle and the slip angles at the front and rear axles which, as previously stated, have an influence on the power transmission of the tires. To generate tire lateral forces, the required wheel steering angle changes are finally calculated as a function of the required yaw rate change of the vehicle and finally the time offset of the change in the wheel steering angle at the front and the rear axle. This is not a one-time process of calculation just before dodging. Rather, the temporal offset of the change in the wheel steering angle is calculated and adjusted permanently and dynamically over the entire avoidance process. During the evasive change conditions, such as changes in the coefficient of friction with a view of the road or its condition is thus taken into account.

For an optimal evasion or an optimized avoidance strategy, in particular with regard to a short reaction time in the event of a sudden danger or obstacle situation, three different driving situations and associated behaviors can be assumed, depending on the coefficient of friction, the required transverse offset and the forward speed prevailing before the evasive action , The three aforementioned influencing factors do not exclusively determine the temporal sequence of the yaw rate change and its proportion. The aim of all driving strategies is the realization of a fast and maximum possible lateral force build-up to achieve tire lateral forces in order to minimize the time needed for evasion.

For a dry, undamaged road surface, a high coefficient of friction must be assumed. Under such conditions, the highest side forces and lateral tire forces can be achieved. Especially with these conditions, the maximum available lateral force potential of the tires can not be exhausted due to the above-mentioned limitation by the performance of the steering actuators. In other words, higher side forces could be achieved if the steering actuators, for example, would work without delay, with unlimited speed and with a very large adjustment angle. Because of the limitations, therefore, a strategy is proposed below.

To initiate evasion, a wheel steering angle in the opposite direction to the rear axle is set in dependence on the wheel steering angle to be set on the front axle in order to temporarily achieve the required yaw rate change of the vehicle as quickly as possible. In the aforementioned conditions, a maximum possible yaw rate change can take place without oversteering or understeering of the vehicle, while at the same time maximum lateral force build-up can be achieved. With a view to a short reaction time or the required late evasion and a false triggering that can be avoided, the initiation of evasion can take place here very quickly, since a very fast lateral force build-up is made possible by means of the temporal offset.

In less good conditions with a comparatively average coefficient of friction (wet to wet road, road dirt, etc.) can already be worked with a reduced yaw rate or a reduced yaw rate change, since the tire force potential is such that the tire lateral forces at least temporarily reach a maximum. In other words, due to the environmental or road conditions, only limited lateral force can be transmitted. At even higher yaw rate, the vehicle would slip because the tires can transmit less lateral forces without cornering force. In order to initiate the evasion as a function of the front axle steering angle to be set, in particular with a time offset, a steering angle at the rear axle which is in the same direction, in particular, is set to achieve the temporarily required yaw rate change of the vehicle. In effect, the phase distortion of the tire lateral forces and thus the phase delay or skew of the adjustment angle at the front axle or rear axle (wheels) is smaller and the Radlenkwinkelgeschwindigkeit is also lower. In contrast to conditions with a high coefficient of friction even opposing steering at the beginning of the maneuver may no longer be necessary.

In conditions with a slippery road through snow or ice, a much lower coefficient of friction is to be assumed, so that the power of the steering actuators can be sufficient to exploit or achieve the maximum, albeit comparatively even, lower tire force potential. The limitation of the properties or performance of the steering actuators has a smaller effect here, in particular in the case of changes in the wheel steering angle. However, an optimization due to the time offset is also possible here in an advantageous manner, since any changes, e.g. the road conditions can be sensed and included.

In the above examples, it should be noted that a roadway only consistently has the same conditions theoretically. Thus, during the evasion and in particular when initiating the evasion, a first roadway section may have conditions with high coefficients of friction, while an adjoining section has smoothness, ie a roadway with a lower coefficient of friction.

In conclusion, it can be said that the time lag of the steering angle changes at the rear axle decreases in comparison to the front axle, the lower the coefficient of friction.

Dynamic changes in the steering angle are preferably made after initiation during the entire evasive maneuver, wherein the steering angle is changed at the rear axle with a time offset to the steering angle at the front axle to at least maintain or change the yaw rate to specifically lateral force on the front and / or Build rear axle. Depending on the prevailing conditions, the avoidance process can thus be optimally designed.

Starting from the previously described, at least temporary, d. H. short-term increase in the yaw rate is preferred after the initiation of avoidance quickly, especially as quickly as possible adjusted at the rear axle a same direction change the wheel angle to cause an increase in the lateral force. In doing so, the yaw rate is reduced in order to reduce it as much as necessary. The initial increase in the yaw rate when initiating evasion to build up a side force as quickly as possible is converted into a stable state by this step by changing the wheel steering angle on the rear axle in the same direction as the wheel steering angle on the front axle.

The method steps mentioned so far extend from the initiation of evasion into the evasive action. Preferably, to complete the evasion, time-shifted wheel angle changes are made approximately in opposite directions to the changes on the introduction to the front and / or rear axle. In this case, the avoidance can be regarded as completed when the vehicle is located by the amount of the transverse offset next to the obstacle. It can be braked there and, if necessary, stopped until it stops or the journey can continue from there, in particular at the same speed.

In one embodiment, it may be provided that after completion of the avoidance, the wheel steering angle on the wheels or the steering angle are at least one axis approximately inversely to the evasion delayed offset, such that the original trajectory can be taken before evading again. In effect, after passing the obstacle, the journey on the originally planned or pre-calculated trajectory should be continued. It should be borne in mind here that with regard to driving comfort, the fastest possible return to the trajectory may not be necessary or desirable. In particular, in semi-automated guiding is also conceivable that after passing the obstacle or stopping the avoidance process, the driver takes control and continues the vehicle on the imaginary of him trajectory.

In partially automated driving of the vehicle, the driver has predetermined the desired trajectory and / or the vehicle is automatically steered (at least in a section of the intended trajectory), at least in a partial area of the trajectory. This may require the attention of the driver. In automated driving, the driver is relieved to the extent that the vehicle meets all tasks and decisions while driving. The avoidance can be automated in both cases, without the driver having to intervene in the evasive action.

In further advantageous embodiments, in addition to the actuators for a front and rear axle steering further actuators can be used for the evasion. Also can be connected to e.g. a rear axle more than one actuator can be used for steering.

In addition to the front and rear axle steering, acceleration or deceleration may be accelerated on at least one wheel, or a first wheel accelerated and at least two wheels decelerated, or at least two wheels accelerated or decelerated to additionally affect the yaw rate. As a result, the time offset of the changes in the wheel steering angle can be reduced. In other words, the amount of time spent on evading can be minimized to the same extent or in addition. Also, in case of failure or malfunction (e.g., reduced power) of a steering actuator, especially at the rear axle, compensation can be achieved. Preferably, the deceleration can be effected by braking, which can be achieved by actuators for braking. Alternatively or additionally, the deceleration and / or the acceleration can be effected on at least one axis by means of torque vectoring or preferably by an electric wheel or axle drive. Torque vectoring is an active differential in which a torque or torque can be applied to the respective axle side by means of a clutch or brake integrated in the differential.

The invention further relates to a driver assistance system for at least partially automated driving of a vehicle, for carrying out the aforementioned method with at least one sensor system and at least one control device, the sensor system comprising at least one optical detection device and / or radar and / or LiDAR and / or the sensor system and / or or the at least one control device has at least one device for communication with mobile or stationary devices outside the vehicle. The mobile device outside the vehicle may be other vehicles that are also equipped with such a device for communication. Thus, for example, environment data on weather and road conditions can be evaluated by a vehicle in front via the trajectory intended by the vehicle with the driver assistance system and possibly used for avoidance (C2C communication). The stationary devices outside the vehicle may be, for example, devices set up at the edge of the roadway, which can transmit weather or road condition data to the vehicle. Also conceivable is the use of satellite-based information systems that can be evaluated while driving along the trajectory (C2X communication).

The invention further relates to a computer program product comprising a computer-usable medium, in particular a storage medium, with computer-readable program code which implements the aforesaid method when the program is executed on a computer.

The invention also relates to a computer program having a program code for implementing the aforementioned method when the program is executed on a computer. The program code may include an algorithm that is particularly suitable for evaluating the potential provided by the sensor or stored in the at least one control unit data to control the aforementioned different actuators, in particular with regard to the time offset, so that the time required for evasion is minimized ,

Finally, the invention relates to at least one control device having at least one computer (computer or computing unit), which can execute a computer program for carrying out a method as mentioned above, wherein the control device is equipped with at least one sensor system arranged in the vehicle, preferably via a vehicle bus system, such as e.g. CAN bus, is coupled and can communicate, wherein the controller has at least one communication device for communication with outside of the vehicle located mobile (C2C) or fixed (C2X) communication devices, as already mentioned above, to account for vehicle environment data.

• 1 eine schematische Darstellung eines Kraftfahrzeuges mit gelenkter Vorder- sowie Hinterachse,
• 2 eine schematische Darstellung eines Ausweichvorganges eines Fahrzeuges,
• 3 eine graphische Gegenüberstellung von ausgesuchten Fahrwerkswerten bei einem Ausweichvorgang (hoher Reibwert),
• 4 eine Darstellung analog 3 mit mittlerem Reibwert,
• 5 eine Darstellung analog 3 oder 4 mit niedrigem Reibwert.

The invention will be described below with reference to preferred embodiments with reference to the drawing. In the figure show:

• 1 a schematic representation of a motor vehicle with steered front and rear axle,
• 2 a schematic representation of an evasive action of a vehicle,
• 3 a graphical comparison of selected chassis values during an evasive action (high coefficient of friction),
• 4 a representation analog 3 with average coefficient of friction,
• 5 a representation analog 3 or 4 with low coefficient of friction.

1 schematically shows a vehicle 1 with a steerable front axle 21 and a steerable rear axle 31 , To steer the wheels 2 at the front axle 21 is a steering device 4 provided, which these via a steering linkage 41 the wheel steering angle in front δ _v can set or change. This angle δ _v is on the right wheel 2 in the 1 drawn by way of example. At the rear axle 31 provides a steering device 5 via a steering linkage 51 for adjusting or changing the wheel steering angle δ _h at the rear wheels 3 , In the embodiment shown, the front axle steering 4 and the rear axle steering 5 via a control unit SG electrically connected or coupled. One in the focus S _G measured yaw rate R _G is via a suitable sensor in the center of gravity of the vehicle 1 determined (rate of rotation sensor) and by an electronic stability control ESC recorded or evaluated. At the outer ends of the vehicle 1 are sensors S arranged, which are assigned a sensor and which are used for vehicle environment detection. These may be temperature sensors, optical sensors which comprise, for example, a camera, or else LiDAR or radar, which are suitable for temperature, distance or also optical detection, for example the roadway. It can thus weather conditions such as humidity or the temperature on the road, etc. recorded and the control unit SG be supplied. The vehicle follows a trajectory T , which is also shown schematically in the figure at the front end of the vehicle in the direction of travel.

2 schematically shows a vehicle 1 , which is a trajectory T follows and on an obstacle H is heading, which may be a vehicle or another, especially suddenly, occurring obstacle, such as a lying on a road trailer or a vehicle entering from a side street, etc. Right of the obstacle H runs the original trajectory T of the vehicle 1 , Shown dashed is the position of the vehicle 1 ". Based on the position of the vehicle 1 should this mean that following the intended or calculated trajectory T the vehicle 1 to the position 1 "would arrive, in the event that no obstacle H is present on the route or roadway. Due to the obstacle H is the vehicle 1 but forced to dodge and the avoidance trajectory Ta to follow, so that the evasion leads at least to the dash-dotted line position of the vehicle 1 '. Also shown is an evasion trajectory Ta 'when the vehicle is traveling from position 1' and following the avoidance trajectory Ta ' back to the original trajectory T in order to continue his journey from position 1 ", where the evasive action shall proceed as follows:

In the position 1 becomes the obstacle H detected, which is on the trajectory T which is either intended by the driver (semi-automated guided driving), or in a fully automated guided vehicle of the calculated trajectory T equivalent. After recognizing the obstacle H an efficient evasive maneuver is initiated using the front axle steering and the rear axle steering, wherein the wheel steering angle at the front axle and at the rear axle are changed with a time delay, so that lateral forces are built on the vehicle axles and the vehicle as quickly as possible 1 the intended trajectory T leaves as soon as possible and the evasion trajectory Ta follows. After reaching or passing the obstacle in the position 1 ', the avoidance process can be approximately inverted, so that after passing the obstacle, avoidance following the evasion trajectory Ta ' again with time-delayed steering of the rear axle relative to the front axle, to finally bring the vehicle to the position according to Fig. 1 "to drive on the intended trajectory T continue.

The 3 . 4 and 5 show a graphical comparison of the case of an avoidance operation to achieve the transverse offset q resulting or to be set values along a time axis t. On the representation of the transverse offset q follow in a second diagram the representation of the yaw angle Ψ and the slip angle β , The diagram below shows the wheel steering angles at the front axle δ _v and on the rear axle δ _h shown. In the following fourth diagram, the wheel steering angular velocities at the front axle are δ̇̇̇ _v and at the rear axle δ̇ _h shown. In the last or lowest fifth diagram of the 3 to 5 the sides or transverse tire forces are plotted on the front axle (F _{q, v} ) and on the rear axle (F _{q, h} ). In each of the 3 to 5 Moreover, certain times t0 to t4 are drawn, which will be discussed in the following.

3 shows a situation with a high coefficient of friction. These conditions are found, for example, on dry roads with a good undamaged pavement. It can be seen that the tire force limit is not reached during the evasive maneuver. In particular, the performance or dynamics of the actuators (also called actuator) is not sufficient here to exploit the maximum lateral force potential. Starting from the time t0, which corresponds to the initiation of the avoidance process, a positive wheel steering angle δ _v is at the front axle and at the rear axle a negative wheel steering angle δ _h set. This corresponds to an opposite direction steering the two steered axles to each other. From time t1, the wheel steering angle on the rear axle also changes 31 such that from this point on to the wheel steering angles δ _v at the front axle 21 same wheel steering angle δ _{h is} set. Regarding the present yaw rate R _G In this situation, at the beginning of the evasive maneuver, additional yawing (increasing the existing yaw rate) is thus produced by the short-term counter-directional steering between the front and rear axles. This is in the graph at the increase of the yaw angle Ψ seen. The structure of the yaw rate R _G supports the fast lateral force build-up on the front axle 21 and rear axle 31 , so that lateral forces can be built up as quickly as possible. It can be seen that between the times t0 and t1, the lateral or tire transverse forces F _{q, h} at the rear axle 31 opposite to the forces F _{q, v} at the front axle 21 increase more. Based on the graphs of the wheel steering angle velocities δ̇̇ _v , δ̇̇ _h at the front axle 21 and rear axle 31 it can be seen that the wheel steering angle δ _v , δ _h at the front axle 21 and rear axle 31 be set with a phase delay or delayed. At the time t2, the wheel steering angle δ _v reaches a maximum at the front axle, while the wheel steering angle δ _h at the rear axle 31 still rising. Only at time t3 reaches the wheel steering angle δ _h at the rear axle 31 its maximum, while the wheel steering angle δ _v already clearly decreases at the front axle. At this time t3 also has the yaw angle Ψ already go through its maximum and continue to decrease. This is accompanied by the yaw rate R _G negative and the yaw angle Ψ decreases, while at this time the intended lateral offset q of the vehicle 1 already reached about halfway. At this time, the slip angle is increasing β a little bit too far. The sides or tire lateral forces on the front axle (F _{q, v} ) and on the rear axle (F _{q, h} ) continue to increase in magnitude to or become negative, since the dodge is quasi braked or terminated.

At the end of the evasion, ie reaching the transverse offset q , the wheel steering angles at the front axle δ _v and at the rear axle δ _h set so that the evasion trajectory Ta approximately parallel to the originally intended trajectory T runs. It is the graph in this 3 but also in the 4 and 5 clearly discernible that over the period of the evasive maneuver, the above values change dynamically.

4 shows a middle friction scenario. The road or road can here z. B. be wet or wet. In any case, it has a lower coefficient of friction compared to the situation according to 3 on. Using the wheel steering angle diagram δ _v , δ _h can clearly be seen at time t1 that here first a change of the wheel steering angle takes place at the rear axle δ _h , while at this time the wheel steering angle at the front axle δ _v already changed. The time offset of the change of the wheel steering angle at the rear axle is again clearly visible in the diagram for the wheel steering wheel speeds. From the second diagram, it can be seen that a reduced yaw rate build-up is used in this scenario. Compared to in 3 In the low friction situation shown in FIG 4 a significantly lower maximum yaw angle Ψ reached. The times t2 and t3 also show a time offset of the change in the wheel steering angle δ _v . δ _h because the maximum of the wheel steering angle at the front axle δ _v is reached much earlier than the maximum value of the wheel steering angle reached at time t3 δ _h at the rear axle. Due to the lower coefficient of friction is, as in the last diagram for 4 can be seen, at times already reached or exhausted a maximum tire force potential. In this scenario, therefore, with a reduced yaw rate construction compared to the scenario in 3 to go out with a high coefficient of friction. The reduced yaw rate build-up can also be recognized from the fact that the wheel steering angle velocity stagnates when the maximum tire lateral forces F _{q, v} , F _{q, h} are reached. Compared to the situation with a comparatively high coefficient of friction, in 4 Under certain circumstances, the performance of the steering actuators already sufficient to achieve the maximum but lower tire force potential and thus the lateral force build-up already presented scenario with lower coefficient of friction. In any case, the effect is that the phase delay or time offset of the tire lateral forces and thus also the time offset of the change of the wheel steering angle become smaller, whereby the wheel steering angle speed δ̇ _v , δ̇ _{h is also} smaller. From the diagram to the wheel steering angles δ _v . δ _h It can be seen that in the scenario shown here an opposing steering on the rear axle 31 at the beginning of the evasive maneuver is no longer necessary. The wheel steering angle δ _v . δ _h are delayed but already adjusted with the same sense of direction. Under the given boundary conditions, this represents the optimum ratio between yawing and steering in the same direction.

In 5 is a scenario in which the coefficient of friction is further reduced - for example, on slippery roads due to snow or ice. The coefficient of friction is in this case reduced to the extent that it can be assumed that the power of the steering actuators is sufficient and the characteristic of the steering actuator (s) only play a minor role with regard to a limitation. It is obvious that the maximum tire force potential with ice slipperiness is very low. In other words, only very small transverse tire forces can be transmitted at a very low coefficient of friction. This can be clearly seen in the graph of tire lateral forces, where the maximum of the tire lateral forces available is reached very quickly over long periods of time and stagnates over a long period of time. It is noticeable that when changing the wheel steering angles at the front axle and at the rear axle in the period t2 to t3, the tire lateral forces also undergo a clear change of direction (positive tire lateral forces change into negative tire lateral forces). The transitions of the tire lateral forces shown could be graphically steeper and therefore faster to run due to an increased power of the steering actuators. It shows here the very strong dependence on the coefficient of friction, whereby the phase delay or time offset of the Radwinkeländerung on the front axle 21 and on the rear axle 31 is very low. Over the entire course, the yaw angle changes Ψ and thus also the yaw rate R _G of the vehicle hardly. However, it can be seen that, despite the adverse conditions (due to the very low coefficient of friction), a very stable driving behavior can be achieved.

LIST OF REFERENCE NUMBERS

1.

vehicle

Second

front

Third

rear wheel

4th

front axle

5th

rear axle

21st

Front

31st

rear axle

41st

steering linkage

51st

steering linkage

ESC

Electronic stability control

R _G

yaw rate

SG

control unit

S _G

main emphasis

S

sensors

T

trajectory

Ta

evasion

Ta '

evasion

H

Obstacle (vehicle)

q

transverse offset

Ψ

yaw

β

float angle

δ _v

Wheel steering angle front

δ _h

Wheel steering angle rear

δ̇̇ _v

Radlenkwinkelgeschwindigkeit front

δ̇ _h

Radlenkwinkelgeschwindigkeit behind

Fq, v

Side force, front tire force

Fq, h

Lateral force, lateral tire force behind

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008013988 A1 [0002]
• EP 1251060 B1 [0003]

Claims (15)

Method for at least partially automated guiding of a vehicle (1), comprising a front axle steering (4) and a rear axle steering (5) and at least one sensor system (S) for detecting the vehicle surroundings and the vehicle movements, wherein the steering systems (4, 5) and the sensors ( S) are coupled to one another via at least one control unit (SG), wherein the vehicle (1) follows a predetermined, in particular calculated, trajectory (T), characterized in that a time-shifted change in the wheel steering angle is detected when a driving situation requiring dodging is detected (δv, δh) on the front axle (4) and on the rear axle (5) takes place in order to effect at least a transverse offset of the vehicle (1) as a function of the driving situation. Method according to Claim 1 , characterized in that the staggered steering at least in dependence on vehicle speed and / or coefficient of friction and / or on the front and / or rear axle (4, 5) adjacent Radlenkwinkeln (δv, δh) and / or a yaw rate (R _G ) of the Vehicle and / or at least one characteristic of at least one Lenkungsaktuators and / or data on vehicle environment and vehicle movements and a required transverse offset (q) takes place. Method according to Claim 1 or 2 , characterized in that to achieve the fastest possible structure of a, in particular maximum possible, lateral force (Fq, v; Fq, h) on the front and rear axles (21, 31) of the vehicle (1) a required yaw rate change of the vehicle in the at least one control unit (SG) is calculated, and in dependence thereon the required change in the wheel steering angle (δv, δh) and the time offset of the change of the wheel steering angle at the front and rear axle (21, 31) is calculated. Method according to one of the preceding claims, characterized in that in order to initiate evasion as a function of the wheel steering angle (δv) to be initially set on the front axle, a counter-steering wheel angle (δh) is set at the rear axle to temporarily determine the required yaw rate change of the vehicle (1 ) to reach. Method according to one of claims 1 to 3, characterized in that for initiating the evasion as a function of the front axle steering angle (δv) to be set, a steering angle (δh), which is the same direction, in particular less, is set at the rear axle in order temporarily to obtain the required one Yaw rate change of the vehicle (1) to achieve. Method according to Claim 4 or 5 characterized in that after initiation of the swerving dynamic changes in the steering angles (δv, δh) are made, wherein the steering angle (δh) is changed at the rear axle with a time offset to the steering angle at the front axle (δv) to at least maintain the yaw rate or to change in order to deliberately build lateral force (Fq, v; Fq, h) on the front and / or rear axle (21, 31). Method according to one of the preceding claims from 4 to 6, characterized in that after initiating the evasion quickly, in particular as quickly as possible, a same-direction change of Radlenkwinkel (δh) is set to cause an increase in the lateral force. Method according to one of the preceding claims from 6 to 7, characterized in that to complete the evasion time-shifted changes to the Radlenkwinkeln (δv, δh) approximately in the opposite direction to the changes of the wheel steering angle (δv, δh) when introduced to the front and / or Rear axle (21, 31) are made. Method according to one of the preceding claims from 3 to 8, characterized in that after completion of the avoidance, the wheel steering angle (δv, δh) are changed offset in time approximately at least one axis approximately inversely to the deflection, such that the original trajectory (T) before evading can be taken again. Method according to one of the preceding claims, characterized in that in addition to the front and rear axle steering (4, 5) on at least one wheel acceleration or deceleration or at least two wheels accelerates a first wheel and a second wheel is decelerated or accelerates at least two wheels or delayed. Method according to Claim 10 , characterized in that the deceleration is caused by braking and / or that the deceleration or the acceleration is effected on at least one axis by torque vectoring or a preferably electric wheel or axle drive. Driver assistance system for at least partially automated driving a vehicle (1), for carrying out a method according to one of claims 1 to 11, with at least one sensor (S) and at least one control unit (SG), wherein the sensor system (S) at least one optical detection device and Radar and / or LiDAR, wherein the sensor system (S) and / or the at least one control device (SG) at least one device for Communication with mobile or stationary devices outside the vehicle has. A computer program product comprising a computer usable medium having computer readable program code which implements the method of any one of claims 1 to 11 when the program is executed on a computer, particularly on a controller. Computer program with a program code for implementing the method according to one of Claims 1 to 11 if the program is running on a computer. Control unit with at least one computer that runs a computer program Claim 14 for carrying out a method according to one of the preceding claims from 1 to 11, wherein the control device (SG) with at least one sensor arranged in the vehicle (S), preferably via a vehicle bus system, can communicate, wherein the control device (SG) at least one communication device for communicating with mobile or stationary communication devices located outside the vehicle, in order to be able to take vehicle environment data into account.

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