A multi-axis distributed vehicle auxiliary steering safety constraint calculation method

Abstract

The application provides a multi-axle distributed vehicle auxiliary steering safety constraint calculation method, sets suitable front obstacles and lane safety boundaries for collision risks, and provides stability safety boundaries for vehicle instability risks, thereby effectively improving the vehicle safety constraint calculation method. During the execution process of the method, continuous adaptive update can be realized, thereby effectively ensuring the safety during the vehicle auxiliary steering process and avoiding the risks of collision, lane deviation and instability.

Description

Technical Field

[0001] This invention belongs to the technical field of vehicle assisted steering control systems, and particularly relates to a method for calculating safety constraints of multi-axle distributed vehicle assisted steering. Background Technology

[0002] Currently, human-machine collaborative assisted control is not yet capable of completely eliminating human intervention. A driver's judgment and environmental awareness when focused are still significantly superior to a machine. When actively changing lanes or avoiding obstacles, the driver must maintain control. In many accidents involving vehicles with some degree of autonomous driving assistance, driver inattention leading to a lack of safety constraints on human-machine collaborative assistance is a significant contributing factor. Under autonomous control, vehicles are prone to deviating from their lanes or failing to steer in time to avoid surrounding obstacles, which reduces the willingness to use assisted driving functions and hinders the development of related technologies. Therefore, it is necessary to provide a more precise and reasonable calculation method for the safety constraints of assisted steering systems, based on vehicle driving safety boundaries and stability constraints. Summary of the Invention

[0003] In view of the above-mentioned technical problems existing in this field, the present invention provides a method for calculating safety constraints of multi-axle distributed vehicle assisted steering, specifically including the following steps:

[0004] S1. For a forward obstacle while driving, based on the current vehicle speed and lateral acceleration in the vehicle coordinate system, determine the limit steering trajectory that allows the vehicle to reach the lateral safe distance the fastest, and the shortest longitudinal displacement that satisfies steering stability, so as to obtain the limit avoidance trajectory of the vehicle in the current state.

[0005] S2. Determine the shortest distance and safety cost function between the vehicle and different obstacles ahead. Determine the sampling range based on the speed of the vehicle and the obstacle and the maximum and minimum time of mutual collision. Perform a bisection search within the sampling range to find the minimum turning point that satisfies the allowable error of the safety cost function. Use this minimum turning point as the starting point of the extreme avoidance trajectory to obtain the latest extreme avoidance trajectory.

[0006] S3. Set lane safety boundaries based on the actual vehicle profile and the safety distance margin from the road boundary;

[0007] S4. Set constraints on the vehicle yaw rate and center-of-gravity sideslip angle at the maximum tire performance for the stability envelope of the vehicle attitude, as stability and safety constraints.

[0008] S5. Continuously update the latest limit avoidance trajectory, lane safety boundary and stability safety constraint, and use them for vehicle-assisted steering decision-making.

[0009] Furthermore, assuming the vehicle travels along the lane at both the initial and final moments of the avoidance trajectory in step S1, then under the constraints of the current vehicle speed and lateral acceleration, the following fifth-order polynomial form of the limit steering trajectory is defined:

[0010]

[0011] In the formula, y is the lateral position coordinate of the vehicle, x is the longitudinal position coordinate of the vehicle, and y t x represents the lateral displacement of the vehicle, i.e., the lateral distance from the end of the steering trajectory to the initial moment. t This represents the longitudinal displacement of the vehicle, specifically the longitudinal distance from the end of the steering trajectory to the initial moment.

[0012] When the vehicle is turning to avoid an obstacle, the lateral displacement is chosen to be half the distance between the obstacle in front and the adjacent lane, and the shortest longitudinal displacement is calculated using the following formula.

[0013]

[0014] In the formula, v x Let a be the longitudinal velocity of the vehicle. y,max,yt For the vehicle in lateral displacement y t The maximum permissible lateral acceleration for stable steering; after obtaining the shortest longitudinal displacement using an optimization algorithm, combined with the lateral displacement y t That is, the extreme avoidance trajectory R under the current state can be determined. obs,a Furthermore, considering that the computational complexity of the optimal algorithm may be difficult to solve quickly in an embedded controller, the minimum longitudinal displacement corresponding to each lateral displacement can be calculated offline using a computer, and the corresponding table can be built and stored in the controller. During assisted steering, the controller only needs to obtain the shortest longitudinal displacement under the target lateral displacement by looking up the table, and then obtain the corresponding extreme avoidance trajectory R. obs,a .

[0015] Furthermore, in step S2, the shortest distance between the vehicle and different obstacles ahead is calculated using the following formula:

[0016]

[0017] In the formula, x ego,i y ego,i x tar,i y tar,i , where are the coordinates of reference points on the vehicle and the obstacle, respectively; n and m are the number of reference points on the vehicle and the obstacle ahead, respectively. The vehicle is considered safe when the shortest distance is greater than the sum of the safety radii of the two reference points; otherwise, a collision occurs. To account for control and calculation errors, a safety margin is added, and the safety boundary L′ between the vehicle and the obstacle is defined. min Specifically, it is expressed as follows:

[0018]

[0019] In the formula, R ego With R obs These are the radii of the decomposed circles representing the reference points on the vehicle and the obstacle, respectively, and Ψ is the set safety margin;

[0020] The security cost function is specifically defined as follows:

[0021]

[0022] Based on the vehicle's speed and the obstacle ahead, and the maximum time τ when they collide. max and minimum time τ min Determine the sampling range F for the bisection search as follows. s :

[0023] F s ∈[F s,min ,F s,max ]

[0024]

[0025] In the formula, v tar The longitudinal velocity of the obstacle ahead;

[0026] The specific termination condition for the binary search is:

[0027] L safe,max ≥J safe ≥L safe,min

[0028] In the formula, L safe,max L safe,min These represent the maximum and minimum allowable errors for the search, respectively.

[0029] Once the termination condition is met, the midpoint of the search interval is taken as the minimum turning point coordinate D. st And use this coordinate point as the extreme avoidance trajectory R obs,a The starting point is thus used to obtain the latest extreme avoidance trajectory.

[0030] Furthermore, in step S3, the lane safety boundary D b Specifically, it is determined by the following formula:

[0031]

[0032] In the formula, D ego,w D is the longest distance from each reference point on the vehicle to the vehicle's outline. safe This refers to the safe distance margin between vehicles and road boundaries.

[0033] Furthermore, the vehicle yaw rate ω mentioned in step S4 r The specific settings for the centroid sideslip angle β constraint are as follows:

[0034]

[0035]

[0036] In the formula, μ is the adhesion coefficient of the road surface, and α max,i α min,i Let g be the tire slip angle of the i-th axle of the vehicle, g be the acceleration due to gravity, and l be the speed of motion. i Let be the distance from the i-th axis of the vehicle to the vehicle's center of mass.

[0037] In step S5, the latest limit avoidance trajectory, lane safety boundary and stability safety constraint obtained in the previous steps are sequentially superimposed and applied to the driving assistance strategy, and adaptive updates are performed within the cycle. This allows the controller to intervene in the turning input when it touches the safety envelope boundary, thereby ensuring that the vehicle drives within the safe area and has a certain safety margin.

[0038] The multi-axis distributed vehicle assisted steering safety constraint calculation method provided by this invention sets appropriate forward obstacle and lane safety boundaries for collision risks, and provides stability safety boundaries for vehicle instability risks, thereby effectively improving the vehicle safety constraint calculation method. The method can continuously and adaptively update during execution, thus effectively ensuring safety during vehicle assisted steering and avoiding the risks of collisions, lane departures, and instability. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall process of the method provided by the present invention;

[0040] Figure 2 Let ω be the yaw rate of the vehicle. r A schematic diagram of the parallelogram envelope curve constraint with the centroid side deflection angle β;

[0041] Figure 3 This is a schematic diagram of the adaptive update process of the method provided by the present invention. Detailed Implementation

[0042] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The multi-axle distributed vehicle assisted steering safety constraint calculation method provided by this invention, such as... Figure 1 As shown, the specific steps include:

[0044] S1. For a forward obstacle while driving, based on the current vehicle speed and lateral acceleration in the vehicle coordinate system, determine the limit steering trajectory that allows the vehicle to reach the lateral safe distance the fastest, and the shortest longitudinal displacement that satisfies steering stability, so as to obtain the limit avoidance trajectory of the vehicle in the current state.

[0045] S2. Determine the shortest distance and safety cost function between the vehicle and different obstacles ahead. Determine the sampling range based on the speed of the vehicle and the obstacle and the maximum and minimum time of mutual collision. Perform a bisection search within the sampling range to find the minimum turning point that satisfies the allowable error of the safety cost function. Use this minimum turning point as the starting point of the extreme avoidance trajectory to obtain the latest extreme avoidance trajectory.

[0046] S3. Set lane safety boundaries based on the actual vehicle profile and the safety distance margin from the road boundary;

[0047] S4. Set constraints on the vehicle yaw rate and center-of-gravity sideslip angle at the maximum tire performance for the stability envelope of the vehicle attitude, as stability and safety constraints.

[0048] S5. Continuously update the latest limit avoidance trajectory, lane safety boundary and stability safety constraint, and use them for vehicle-assisted steering decision-making.

[0049] In a preferred embodiment of the present invention, step S1 assumes that the vehicle is traveling along the lane at both the initial and final moments of the avoidance trajectory. Then, under the constraints of the current vehicle speed and lateral acceleration, the following fifth-order polynomial form of the limiting steering trajectory is defined:

[0050]

[0051] In the formula, y is the lateral position coordinate of the vehicle, x is the longitudinal position coordinate of the vehicle, and y t x represents the lateral displacement of the vehicle, i.e., the lateral distance from the end of the steering trajectory to the initial moment. t This represents the longitudinal displacement of the vehicle, specifically the longitudinal distance from the end of the steering trajectory to the initial moment.

[0052] When the vehicle is turning to avoid an obstacle, the lateral displacement is chosen to be half the distance between the obstacle in front and the adjacent lane, and the shortest longitudinal displacement is calculated using the following formula.

[0053]

[0054] In the formula, v xLet a be the longitudinal velocity of the vehicle. y,max,yt For the vehicle in lateral displacement y t The maximum permissible lateral acceleration for stable steering; after obtaining the shortest longitudinal displacement using an optimization algorithm, combined with the lateral displacement y t That is, the extreme avoidance trajectory R under the current state can be determined. obs,a Furthermore, considering that the computational complexity of the optimal algorithm may be difficult to solve quickly in an embedded controller, the minimum longitudinal displacement corresponding to each lateral displacement can be calculated offline using a computer, and the corresponding table can be built and stored in the controller. During assisted steering, the controller only needs to obtain the shortest longitudinal displacement under the target lateral displacement by looking up the table, and then obtain the corresponding extreme avoidance trajectory R. obs,a .

[0055] In a preferred embodiment of the present invention, the shortest distance between the vehicle and different obstacles ahead in step S2 is calculated using the following formula:

[0056]

[0057] In the formula, x ego,i y ego,i x tar,i y tar,i , where are the coordinates of reference points on the vehicle and the obstacle, respectively; n and m are the number of reference points on the vehicle and the obstacle ahead, respectively. The vehicle is considered safe when the shortest distance is greater than the sum of the safety radii of the two reference points; otherwise, a collision occurs. To account for control and calculation errors, a safety margin is added, and the safety boundary L′ between the vehicle and the obstacle is defined. min Specifically, it is expressed as follows:

[0058]

[0059] In the formula, R ego With R obs These are the radii of the decomposed circles representing the reference points on the vehicle and the obstacle, respectively, and Ψ is the set safety margin;

[0060] The security cost function is specifically defined as follows:

[0061]

[0062] Based on the vehicle's speed and the obstacle ahead, and the maximum time τ when they collide. max and minimum time τ min Determine the sampling range F for the bisection search as follows. s :

[0063] F s ∈[F s,min ,F s,max ]

[0064]

[0065] In the formula, v tar The longitudinal velocity of the obstacle ahead;

[0066] The specific termination condition for the binary search is:

[0067] L safe,max ≥J safe ≥L safe,min

[0068] In the formula, L safe,max L safe,min These represent the maximum and minimum allowable errors for the search, respectively.

[0069] Once the termination condition is met, the midpoint of the search interval is taken as the minimum turning point coordinate D. st And use this coordinate point as the extreme avoidance trajectory R obs,a The starting point is thus used to obtain the latest extreme avoidance trajectory.

[0070] In a preferred embodiment of the present invention, the lane safety boundary D in step S3 b Specifically, it is determined by the following formula:

[0071]

[0072] In the formula, D ego,w D is the longest distance from each reference point on the vehicle to the vehicle's outline. safe This refers to the safe distance margin between vehicles and road boundaries.

[0073] In a preferred embodiment of the present invention, in step S4, the stability envelope of the vehicle attitude parameters is mainly limited by the vehicle's stable yaw rate and the rear tire slip angle under maximum lateral tire force. Therefore, given a tire model or characteristic curve and the assumption of quasi-steady-state cornering, the vehicle yaw rate ω r And the centroid side slip angle β constraint, such as Figure 2 As shown, the specific settings are as follows:

[0074]

[0075]

[0076] In the formula, μ is the adhesion coefficient of the road surface, and α max,i α min,i Let g be the tire slip angle of the i-th axle of the vehicle, g be the acceleration due to gravity, and l be the speed of motion. i Let be the distance from the i-th axis of the vehicle to the vehicle's center of mass.

[0077] In step S5, the latest limit avoidance trajectory, lane safety boundary, and stability safety constraint obtained in the previous steps are sequentially superimposed and applied to the driving assistance strategy. Specifically, before the vehicle travels along the lane to the latest turning point obtained in step S2, the vehicle reference trajectory is updated to the forward obstacle safety boundary. On this reference trajectory, the road safety boundary can be defined as the boundary values ​​of the lateral error and heading error relative to the reference trajectory, and the stability constraint acts on the vehicle's yaw rate ω. r And the centroid sideslip angle β, thus forming a safe envelope region. Adaptive updates are performed within each cycle, the update steps are as follows: Figure 3 As shown, safety constraints are updated when an obstacle is detected ahead; otherwise, the vehicle continues along the initial trajectory. This allows the controller to intervene in the turning input when the vehicle touches the safety envelope boundary, ensuring that the vehicle travels within a safe area with a certain safety margin.

[0078] It should be understood that the sequence number of each step in the embodiments of the present invention does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0079] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calculating safety constraints of multi-axle distributed vehicle assisted steering, characterized in that: Specifically, the following steps are included: S1. For a forward obstacle while driving, based on the current vehicle speed and lateral acceleration in the vehicle coordinate system, determine the limit steering trajectory that allows the vehicle to reach the lateral safe distance the fastest, and the shortest longitudinal displacement that satisfies steering stability, so as to obtain the limit avoidance trajectory of the vehicle in the current state. S2. Determine the shortest distance and safety cost function between the vehicle and different obstacles ahead. Determine the sampling range based on the speed of the vehicle and the obstacle and the maximum and minimum time of mutual collision. Perform a bisection search within the sampling range to find the minimum turning point that satisfies the allowable error of the safety cost function. Use this minimum turning point as the starting point of the extreme avoidance trajectory to obtain the latest extreme avoidance trajectory. S3. Set lane safety boundaries based on the actual vehicle profile and the safety distance margin from the road boundary; S4. Set constraints on the vehicle yaw rate and center of gravity sideslip angle under the maximum tire performance for the stability envelope of the vehicle attitude, as stability safety constraints. S5. Continuously update the latest limit avoidance trajectory, lane safety boundary and stability safety constraint, and use them for vehicle-assisted steering decision-making; In step S1, it is specifically assumed that the vehicle is traveling along the lane at both the initial and final moments of the avoidance trajectory. Therefore, under the constraints of the current vehicle speed and lateral acceleration, the following fifth-order polynomial form of the limiting steering trajectory is defined: In the formula, y The coordinates of the vehicle's lateral position. x The longitudinal position coordinates of the vehicle, y t This represents the lateral displacement of the vehicle, specifically the lateral distance from the end of the steering trajectory to the initial moment. x t This represents the longitudinal displacement of the vehicle, specifically the longitudinal distance from the end of the steering trajectory to the initial moment. The lateral displacement of the vehicle when steering to avoid the obstacle is selected as half the distance of the front obstacle from the adjacent lane, and the shortest longitudinal displacement is solved using the following equation : In the formula, v x For the longitudinal speed of the vehicle, a y,max,yt For the vehicle in lateral displacement y t The maximum permissible lateral acceleration for stable steering; after obtaining the shortest longitudinal displacement using an optimization algorithm, combined with the lateral displacement... y t That is, it can determine the extreme avoidance trajectory under the current state. R obs,a ; Step S2: The shortest distance between the vehicle and different obstacles in front is calculated using the following formula: In the formula, x ego,i , y ego,i , x tar,i , y tar,i These are the coordinates of reference points on the vehicle and the obstacle, respectively; n , m These represent the number of reference points for the vehicle and the obstacle ahead. The vehicle is considered safe when the shortest distance is greater than the sum of the shortest distances of these two reference points; otherwise, a collision occurs. A safety margin is added to account for control and calculation errors, defining the safety boundary between the vehicle and the obstacle. L’ min Specifically, it is expressed as follows: In the formula, R ego and R obs These are the radii of the decomposed circles representing the reference points on the vehicle and the obstacle, respectively, and Ψ is the set safety margin; The security cost function is specifically defined as follows: Based on vehicle and front obstacle speed and maximum time to mutual collision τ max and minimum time τ min Determine the following sampling range for binary search F s : In the formula, v tar is the longitudinal velocity of the front obstacle; The specific termination condition for the binary search is: wherein L safe,max , L safe,min are the maximum and minimum errors allowed for the search, respectively; When the termination condition is reached, the middle value of the search interval is taken as the minimum turning point coordinate D st ， and the coordinate point is taken as the starting point of the limit avoidance trajectory R obs,a to obtain the latest limit avoidance trajectory.

2. The method of claim 1, wherein: Lane safety boundary in step S3 D b Specifically, it is determined by the following formula: wherein D ego,w is the longest distance from each reference point on the vehicle to the vehicle's outline, D safe is the safety distance margin of the vehicle from the road boundary.

3. The method of claim 2, wherein: the vehicle yaw rate in step S4 ω r and the center of mass side slip angle β The constraints are specifically set to: wherein μ is the adhesion coefficient of the travel surface, α max,i , α min,i is the tire side slip angle of the first i axle of the vehicle, g is the acceleration of gravity, l i is the length of the first i axle of the vehicle from the center of mass of the vehicle.

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