DE102016204957A1 - Automated lane change in dynamic traffic based on driving dynamics restrictions - Google Patents

Abstract

Method for decision-making and planning of the driving trajectory of an automated lane change of a land vehicle in dynamic traffic 2 , consisting of
a) a method for deciding whether the surrounding traffic and the driving dynamics restrictions by the vehicle as well as the road conditions allows a lane change and proposes a lane change time for it
and
b) a method for planning the lane change which predetermines the trajectory for the subsequent automated lane change and allows it - to change the predetermined trajectory during the lane change - in accordance with changed conditions of traffic, the environment and the vehicle.

Description

The invention relates to a method for automated decision and specifications for the execution of an automated comfort-oriented lane change of a road vehicle.

• a) Trajektorien-Entscheidungsmodul (TEM) das die Entscheidung für einen Fahrstreifenwechsel durchführt
• b) Trajektorien Planung Algorithmus (TPA), der eine Soll-Trajektorie plant, die nachfolgend von einem Automatisierungssystem des Fahrzeugs ausgeführt wird

The invention is divided into a

• a) Trajectory decision module (TEM) which makes the decision for a lane change
• b) trajectory planning algorithm (TPA), which plans a target trajectory, which is subsequently executed by an automation system of the vehicle

The object of the invention is part of an automated guidance of a road vehicle.

The 1 summarizes the automation levels as defined by SAE (Society of Automotive Engineers, USA) and is described below.

The complete definitions of the individual stages as well as of the italics are given in Report SAE J3016 , The levels are to be understood as more technically descriptive than legal normative. At the same time, the contents of the individual cells represent rather minimal and maximum requirements for the respective stage. The term "system" accordingly stands either for driver assistance system, combination of driver assistance systems or autonomous drive system. The degree of automation is becoming increasingly complex, starting with systems that inform or warn the driver (level 0), continue with systems that take only the longitudinal or lateral guidance of the vehicle, the driver always has the responsibility to observe the environment or as a fallback solution (Level 1). A further increase is determined by level 2 systems which already take over the longitudinal and lateral guidance of the vehicle, the observation of the environment and the fallback level remain with the driver (level 2). Level 3 assistance systems automate the vehicle without the driver having to monitor the environment, but still need to act as a fallback level. In Level 4, the system is already fully responsible for vehicle guidance and must provide appropriate system-related fallback solutions in the event of failure. Level 4 only differs from 4 in that automated driving needs to work in all conditions, while Level 4 is limited to selected situations.

The invention relates to an automated lane change that can be applied under different levels of automation. In particular, systems from level 3, where the driver no longer has to observe the environment are relevant here, but it is also an application below Level 2 conceivable.

In the following, the prior art will be described to the two major innovations of the trajectory decision module (TEM) and the trajectory planning as a target specification (TPA) for the control system according to.

• a) Stand der Technik Trajektorien-Entscheidungsmodul (TEM)

In US 20140074356 / WO 2012/160591 The prior art for "Lane Change Assist" systems will be described in detail. The claims relate to the entire system for automated lane change and in particular the design of the man-machine interface, information for an automated decision to change lanes and trajectory planning for it is not included. In US 20050256630 A "Lane Change Assist" system is described. The decision module described differs in that simple kinematic relationships are used for the decision, driving dynamics limits, road conditions and the dynamics of the traffic are not considered in detail, a trajectory planning is not described, as it is in US 20030025597 and EP0890470 , Outside the patent literature there are numerous publications on the trajectory decision module (TEM) and trajectory planning algorithm (TPA):

• a) Prior Art Trajectory Decision Module (TEM)

In the last thirty years various researches have been working on lane change, such as [1]. In [2] the characteristics of a lane change, such as the duration and the necessary distance as well as the starting position of the vehicle were examined on the basis of 16 drivers. It has also been shown that the age of the driver and the orientation of the lane change have no effect on these characteristics. Another study that used a driving simulator to record steering angles during lane changes shows that the type of front vehicle does not affect the duration of the maneuver and the steering wheel's maximum steering angle. On the other hand, the speed of the front vehicle very well influences the mentioned characteristics [3]. In [4] became one developed another lane change model based on "cellular automaton" (CA). It focuses on some system limits of the vehicle, such as maximum acceleration and maximum deceleration. The laws used here were used in another study [5] for the traffic simulation of the two- and three-lane highways to show that the developed model also allows realistic simulations.

A driving maneuver is interpreted in [6] with a predictive control model (MPC) with the ability to control and stabilize a double lane change maneuver using ISO standardized fuzzy control. The same procedure was used in another project [7] to control the speed of the vehicle together with the lane change. The experiments carried out in the two-lane directional traffic showed a suitable longitudinal and lateral vehicle guidance with regard to the prevailing traffic.

In [8] some models for lane changes in cars and trucks were presented. By incorporating the behavior of tracking another vehicle and applying the dynamic system boundaries, a new model was developed in which a speed change during the maneuver is possible [9]. This model is simple and closer to the real behavior of a driver when changing lanes. The investigation of the parameters influencing a lane change has shown that the type, the size and the duration of the maneuver are not dependent on the preceding vehicle but only on the starting point of the lane change [10]. Furthermore, in this work a simple mathematical model based on the optimized maneuver fuel consumption was derived.

Innovation of the Invention at TEM

• (1) Einbeziehung der Effekte der lateralen Verschiebung und der Reifenreibung,
• (2) Beachtung der Fahrdynamik und
• (3) die Echtzeit-Fähigkeit.
• (4) Weiterhin, sollte sich die Verkehrssituation während des Manövers ändern, wird der ursprünglich geplante Fahrschlauch dynamisch geändert. Diese Flexibilität beim Entscheidungsprozess ist der nächste große Vorteil des Algorithmus. Dadurch, dass die Algorithmus Parameter durch plötzlich strengere Anforderungen geändert werden, wird auch die Sicherheit des Manövers erhöht.

The advantages and innovative parts of the algorithm presented below are:

• (1) incorporating the effects of lateral displacement and tire friction,
• (2) consideration of driving dynamics and
• (3) the real-time capability.
• (4) Furthermore, if the traffic situation changes during the maneuver, the originally planned route is changed dynamically. This flexibility in the decision making process is the next big advantage of the algorithm. The fact that the algorithm parameters are changed by suddenly stricter requirements also increases the safety of the maneuver.

b) Prior Art Trajectory Planning Algorithm (TPA)

In [11] the possible change of the driving distance is calculated taking into account the dynamics for the obvious time window. Thereafter, the lane change lane is planned to avoid collisions during the maneuver. Chen uses the Piecewice Quadratic Bezier curves for route planning [12]. The low need for computing power is the main advantage of the method. The adherence to the dynamic limits as well as the comfort of the passengers are examined by the calculation of the maximum line curvature and the yaw rate. In another study, some models were developed based on driving dynamics and also driver strategies during the lane change maneuver. Experimental evaluations using real driving tests show that the presented models are better and more accurate compared to those using polynomial lane change planning [13, 14]. Further, risk maps were used to plan the lane change [15]. Experiments show that this method can be used in various maneuvers, such. B. Planning the shortest route when changing lanes without risking collisions. The so-called celldecomposition is another method for the selection and construction of the route [16]. Here, the road is divided into smaller cells and then applied an optimized search method to find the route to the target position without colliding. Intelligent control technologies, such as For example, fuzzy control [17], neural networks [18] and swarm intelligence [19] are also used for trajectory planning. In a study by Feng, an algorithm was devised whereby the lane change by jerk reduction, i. comfort gain was also realized [20]. This model uses fuzzy neural networks and genetic algorithms to provide a robust steering control on the track. The simulation results show that the controller produces smooth and accurate route change maneuvers.

Innovation of the Invention at TPA

The invention provides an algorithm that incorporates dynamics of the surrounding traffic in the design of the lane change trajectory. If the traffic conditions change during the lane change so that the originally generated lane is no longer safe, it will be changed to suit the new conditions. During development, a combination of polynomial and trigonometric functions was used to generate the alternate route. The parameters and coefficients of the path function were derived from the physical relationships and system boundaries. Simulation results confirm a satisfactory performance of the algorithm when initiating and changing the trajectory. In addition, the changeover to the changed trajectory is carried out continuously and smoothly, without violation of the system boundaries.

Description of the invention

a) Description Trajectories Decision Module (TEM)

The decision for a lane change must be made with the presence of other vehicles and in a dynamic traffic situation. In 2 For example, the ego vehicle (lane-changing vehicle) is marked with E, the vehicle traveling in the same lane with A, the leading and the rear-driving vehicle on the target strip with B and D. Furthermore, the dashed line drawn vehicle in the second image is the E vehicle during the maneuver. It is shown that if the following four conditions are met, safe lane change is possible:
During the maneuver, the lateral distance between the right front corner E of the vehicle and the right rear corner B of the vehicle must be at least C ₁ ( 2-a ).

At the end of the maneuver movement, the distance to B must be at least C ₂ ( 2 B ).

During the maneuver, the lateral distance between the right rear corner E of the vehicle and the left front corner D of the vehicle must be at least C ₃ . Furthermore, after the maneuver, the longitudinal distance between E and D must be at least C ₄ ( 2-c ).

The given lateral speed of the ego vehicle must be achievable during the maneuver and taking into account the potentially prevalent tire friction.

The method described examines the possibilities for generating a trajectory taking into account all the enumerated conditions. If the trajectory is feasible, the maneuver is allowed within the predefined time; otherwise the ego vehicle is kept in the same lane until the appropriate situation for a lane change exists. The decision algorithm uses time as the main decision feature. First, the duration of the most critical trajectory is determined taking into account constraints. Thereafter, the duration of the other trajectories is calculated and compared with each other to decide on the feasibility of a lane change. Subsequently, the method of calculating the critical trajectories is explained based on individual conditions.

Case 1: Vehicle driving ahead on the same lane, Figs. 2-a and Fig. 3

Taking into account the safety distance C ₁ between the vehicles, the lateral distance between vehicles A and E is calculated:

By means of numerical methods one can solve the equation (1) and calculate the time duration t _{1 of} the maneuver while maintaining the distance C ₁ .

Case 2: A preceding vehicle and another vehicle on the target lane, Fig. 2-b

In such a situation, the safety distance C ₂ is determined as follows:

By substituting all necessary parameters in (2) one can calculate C ₂ and further the maneuver time, denoted by t ₂ .

Case 3: An overhauled vehicle on the target lane, Figs. 2-c and Fig. 4

x_E – x_D = 2v_xD + l_Er + l_Df (4) This case represents a combination of the first two cases. To determine the duration of the lane change, first the appropriate maneuver time is calculated based on the safe lateral distance and using equation (3). Then, another appropriate maneuver time is calculated based on the safe longitudinal distance at the end of the maneuver and using equation (4). Finally, the longer of the two times is selected and designated as t ₃ :

x _E - x _D = 2v _xD + 1 _Er + 1 _Df (4)

Case 4: The most aggressive lane change

The generated trajectory must be feasible taking into account the driving dynamics. It must be ensured that the determined lateral acceleration is achievable during the maneuver regarding tire-road contact and while maintaining the stability of the vehicle. To ensure this, the duration of the most violent maneuver is calculated and then the trajectory is generated. 5 shows the 3-D diagram for a maneuver time depending on mass, speed and maximum traction between the tire and the road surface. The displayed area divides the room into two areas. The upper room area represents the permissible maneuver times.

The lower room area are the inadmissible times, since they do not fulfill the stability criteria explained earlier. The points of the displayed surface represent the minimum of the permissible times. The results of the individual simulations are approximated by (5), whereby the minimum maneuvering time t _{m is} determined by tire friction coefficient μ and vehicle speed v _x .

Decision for the lane change

The decision for a lane change can be made by the time calculations of t ₁ , t ₂ , and t ₃ and by inserting min (t _m ) = t ₄ . Table 1 shows the possible cases for a lane maneuver along with the allowable maneuver times or time intervals. Table 1: Possible cases for a lane change No. case Possible time (area) No. case Possible time (area) 1 t ₁ > t ₂ > t ₄ > t ₃ [t ₂ t ₄ ] 8th t ₂ > t ₁ = t ₃ > t ₄ t ₁ 2 t ₁ > t ₂ > t ₃ > t ₄ [t ₂ t ₃ ] 9 t ₁ > t ₂ = t ₄ > t ₃ t ₂ 3 t ₂ > t ₁ > t ₄ > t ₃ [t ₁ t ₄ ] 10 t ₁ > t ₂ = t ₃ > t ₄ t ₂ 4 t ₂ > t ₁ > t ₃ > t ₄ [t ₁ t ₃ ] 11 t ₂ > t ₁ > t ₄ = t ₃ [t ₁ t ₃ ] 5 t ₁ = t ₂ > t ₄ > t ₃ [t ₁ t ₄ ] 12 t ₁ > t ₂ > t ₄ = t ₃ [t ₂ t ₃ ]

By way of example, case 2 will be explained from Table 1 as an example. T ₁ > t ₂ > t ₃ > t ₄ , as in 6 shown. The trajectory between the tracks 1 and 2 can not be chosen because the conditions for the trajectory 2, z. B. C ₂ , is not felt. Furthermore, all trajectories between 3 and 4 violate the condition C ₄ . Therefore, the safe lane change trajectories in this example can only be those between 2 and 4.

b) Description Trajectory Planning (TPA)

The most important advantage of the invention is the conception of an algorithm that incorporates the environmental conditions and traffic dynamics in planning the lane change into the bill. In the event of a change in the traffic situation during the course of the maneuver so that the originally generated trajectory becomes critical, the model can change the trajectory. The change to the newly constructed trajectory is implemented continuously and smoothly, so that the driving dynamics and comfort conditions remain met.

The solution to the problem described above is to assume a constant longitudinal velocity by the following equation for generating the trajectory: y (t) = αsin (bt + e) + ct ³ + dt ² + gt + h (6)

• (A) die ursprüngliche Form der Trajektorie am Manöveranfang (Start bei t₁ in der 2) oder
• (B) die geänderte Trajektorie während des Manövers (Start bei t₂ in der 2) ist.

The parameters a, b, c, d, e, g, h are determined by the following method:
In compliance with the constraints described below, which may vary depending on whether the destination is either

• (A) the original shape of the trajectory at the beginning of the maneuver (start at t ₁ in the 2 ) or
• (B) the changed trajectory during the maneuver (start at t ₂ in the 2 ).

• A) Hier ist die laterale Geschwindigkeit und die Beschleunigung am Anfang und am Ende des Manövers als Null angenommen. Gleichzeitig wird auch die laterale Position am Anfang des Manövers als Null angenommen.

The two cases will be closer in the 7 explained.

• A) Here the lateral speed and the acceleration at the beginning and at the end of the maneuver are assumed to be zero. At the same time, the lateral position at the beginning of the maneuver is assumed to be zero.

• B) Hierbei muss die Kontinuität der lateralen Position, die Geschwindigkeit und die Beschleunigung des Fahrzeugs bei der Umplanung der Trajektorie berücksichtigt werden. Die Variationen der aufgezählten Faktoren müssen homogenisiert und ohne etwaigen Sprüngen bei den jeweiligen Werten verlaufen. Daraus kann man folgende fünf mathematische Bedingungen herleiten:
  

Altogether there are the following five conditions:

• B) The continuity of the lateral position, the speed and the acceleration of the vehicle must be taken into account when planning the trajectory. The variations of the listed factors must be homogenized and without any jumps in the respective values. From this one can derive the following five mathematical conditions:
  

In both cases, five coefficients for trajectory equation are obtained from the five conditions. The other two parameters, b and e, are derived to minimize the following cost function: f = (a (b, e) sin (bt _f + e) + c (b, e) t 3 / f + d (b, e) t 2 / f + g (b, e) t _f + h ( b, e) - 3.75) ² (9)

Equations 10 and 11 set the working range of the algorithm for safe planning of the changed trajectory:

In the equations, (t _f2 ) _max and (t _f2 ) _{min represent} maximum and minimum times that the algorithm can use as the end time for the changed trajectory. The coefficients k _p and k _s are derived by means of dynamic driving simulations and are shown in equations (12) and (13):

In equations (12) and (13), p _t according to equation (14) stands for the "movement friction" of the trajectory, specifically at time t _s2 , where the changed trajectory begins. In the 8th k _p and k _{s are shown} as a function of p _t . If the points are in the shaded area, these are the possible states for t _f2 . In that case it is possible for the algorithm to construct a changed trajectory between t _s2 and t _f2 . Based on the 8th the following conclusions can be drawn about the described algorithm:
The successful construction of the new trajectory is more likely in the earlier maneuver phases. The probability of a successful restructuring of the trajectory coincides with the maneuver time course.

If the modified trajectory is prone to longer maneuver times (t _f2 > t _f1 ), the starting point must be less than 45% of the total maneuver time. On the other hand, if the faster lane change maneuver is desired (t _f2 > t _f1 ), the starting point must be before the time of 85% of the total maneuver time.

bibliography

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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

• US 20140074356 [0008]
• WO 2012/160591 [0008]
• US 20050256630 [0008]
• US 20030025597 [0008]
• EP 0890470 [0008]

Cited non-patent literature

• Report SAE J3016 [0005]

Claims (11)

 A trajectory decision module (TEM) for an automated lane change, characterized in that the following features are considered: • inclusion of the effects of lateral dynamics • tire-roadway traction, • Observing the limits of vehicle dynamics • Real-time capability of the algorithm • Flexibility in decision logic. • Dynamics of the traffic situation: Should the traffic situation change during the maneuver, the method presented can, based on the aforementioned properties, modify the lane change trajectory. This integrates the dynamics of the process into the algorithm. A trajectory decision module (TEM) for an automated lane change according to claim 1, characterized in that in the case of a preceding vehicle, the time for the lane change t _{1 is determined} according to equation (1). A trajectory decision module (TEM) for an automated lane change according to claim 1, characterized in that in the case of a preceding vehicle and another vehicle on the target lane the time for the lane change t ₂ according to equation ( 2 ) is determined. A trajectory decision module (TEM) for automated lane change according to claim 1, characterized in that in the case of an outdated vehicle on the target lane the time for the lane change t ₃ according to equation (3) and (4) is determined. A trajectory decision module (TEM) for an automated lane change according to claim 1, characterized in that in the case of an aggressive lane change, the minimum time for the lane change t _m = t _{4 is determined} according to equation (5). A trajectory decision module (TEM) for an automated lane change according to claim 1-5, characterized in that the permissible time for the lane change is determined by comparing the maneuver times t ₁ , t ₂ , t ₃ and t ₄ according to Table 1. A trajectory planning (TPA) for an automated lane change characterized in that it allows a constant re-planning of the trajectory according to the restrictions of the dynamic traffic and the vehicle dynamics taking into account the tire / road contact. A trajectory planning (TPA) for an automated lane change according to claim 7, characterized in that the planning of the driving trajectory according to equation (6) takes place with the assumption of constant longitudinal velocity. A trajectory planning (TPA) for an automated lane change according to claim 7-8 characterized in that the determination of the parameters b and e from equation (6) by optimizing the cost function according to equation (9). A trajectory planning (TPA) for an automated lane change according to claim 7-9, characterized in that the determination of the parameters a, c, d, g, h from equation (6) - in the event that the trajectory during the maneuver need not be rescheduled - determined according to equations (7). A trajectory planning (TPA) for an automated lane change according to claim 7-9 characterized in that the determination of the parameters a, c, d, g, h of equation (6) - in the event that the trajectory must be rescheduled during the maneuver - is determined according to equations (8).

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