TTC threshold optimization control system and method based on vehicle driving working conditions

Abstract

The invention discloses a TTC threshold optimization control system and method based on a vehicle driving working condition, and the method comprises the steps: carrying out the modeling of a vehicle braking process, and dividing an AEB-P braking process into six stages; based on the early warning safety distance dwa and the braking safety distance dbr, in combination with the vehicle speed vc, the pedestrian speed vp and the safety distance d0, a dynamic TTC threshold value is deduced; a steering obstacle avoidance critical safety distance is introduced, and a TTCbr threshold value is dynamically adjusted, so that collision between braking intervention and intention of a driver is avoided; a layered TTC threshold value control strategy is adopted, and the control strategy is divided into two modes, namely a time comfort priority mode and a time safety priority mode. According to the method, the TTC threshold values of the early warning stage and the braking stage are dynamically adjusted, so that balance between safety and comfort is achieved, and the acceptance of a driver to an AEB-P system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive active safety, and particularly to a TTC threshold optimization control system and method based on vehicle driving conditions. Background Art

[0002] With the development of automotive technology, many automobile manufacturers are improving safety through automatic assisted driving and active safety systems, gradually shifting from passive safety to active protection. Among them, the AEB-P system, as an important technology, actively intervenes when detecting potential risks by real-time monitoring of the vehicle's surrounding environment, thereby preventing collisions or reducing the degree of accident damage.

[0003] When the existing AEB-P system triggers emergency braking, it usually uses a fixed TTC threshold as the intervention standard, but there are the following problems:

[0004] Firstly, there is a contradiction between comfort and safety. Excessive braking deceleration or sudden change rate of deceleration (jerk) will cause discomfort to the occupants, while excessive pursuit of comfort may not meet the emergency collision avoidance requirements. Research shows that when the braking deceleration exceeds 0.3g or jerk exceeds 10 m / s 3 , the occupants will experience significant discomfort. Secondly, it has poor adaptability to dynamic conditions. The fixed TTC threshold cannot adapt to changes in different vehicle speeds, road surface adhesion coefficients, and pedestrian movement states, which may lead to premature or late braking. Moreover, there is a conflict between steering and braking strategies. In medium and high-speed scenarios, braking intervention may interfere with the driver's steering collision avoidance intention and reduce the system acceptance.

[0005] Therefore, in order to ensure driving safety and comfortable driving experience, when the AEB-P intervenes in active braking, it is necessary to limit the maximum change rate of deceleration to avoid the situation of stepwise mutation of braking deceleration, and at the same time, the maximum expected braking deceleration needs to be constrained according to functional requirements. Summary of the Invention

[0006] In order to solve the deficiencies in the prior art, the present invention proposes a TTC threshold optimization control system and method based on vehicle driving conditions, which realizes the balance between safety and comfort and improves the driver's acceptance of the AEB-P system by dynamically adjusting the TTC thresholds in the warning and braking stages.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A TTC threshold optimization control method based on vehicle driving conditions, comprising the following steps:

[0009] Step 1: Model the vehicle braking process and divide the AEB-P braking process into 6 stages;

[0010] Step 2: Based on the warning safety distance d wa and the braking safety distance d br , combined with the speed v of the host vehicle c , the speed v of the pedestrian p and the safety distance d0, derive the dynamic TTC threshold;

[0011] Step 3: Introduce the critical safety distance for steering obstacle avoidance, and avoid the conflict between braking intervention and the driver's intention by dynamically adjusting the TTC br threshold;

[0012] Step 4: Adopt a hierarchical TTC threshold control strategy, and divide the control strategy into two modes, one is the comfort - priority mode and the other is the safety - priority mode.

[0013] Furthermore, divide the AEB - P braking process into the following 6 stages:

[0014] (1) Stage 0 - t1: The duration Δt1 from when the driver recognizes a potential danger ahead during driving to when the driver is about to make the action of stepping on the brake pedal;

[0015] (2) Stage t1 - t2: The duration Δt2 required for the driver to move the right foot to touch the brake pedal for control;

[0016] (3) Stage t2 - t3: The system delay duration Δt3 from when the brake pedal is stepped on until the braking execution coordination functions;

[0017] (4) Stage t3 - t4: The duration Δt4 consumed for the braking deceleration to increase to the peak level required during the braking process;

[0018] (5) Stage t4 - t5: The duration Δt5 of continuously applying the maximum required braking deceleration;

[0019] (6) Stage t5 - t6: The duration Δt6 of slowly releasing the brake pedal to gradually reduce the braking force to completely eliminate it.

[0020] Furthermore, the steps for deriving the dynamic TTC threshold include:

[0021] Step 2.1: Obtain the speed v of the host vehicle c , the speed v of the pedestrian p , and the road surface adhesion coefficient μ through in - vehicle sensors;

[0022] Step 2.2: Calculate the braking deceleration change rate jerk according to the relationship between longitudinal acceleration and time;

[0023] Step 2.3: Derive the braking safety distance d br through the analysis of the warning braking mode;

[0024] Step 2.4: Combine the road surface adhesion coefficient μ to derive the warning safety distance d wa and the braking safety distance d br ;

[0025] Step 2.5: According to the analysis of d wa and d br derive the dynamic TTC threshold, including the warning TTC threshold TTC wa and the braking TTC threshold TTC br .

[0026] Furthermore, the braking deceleration change rate jerk is expressed as:

[0027]

[0028] where Δa is the change in the braking deceleration a within Δt.

[0029] Furthermore, the braking safety distance d br derived in Step 2.3 is denoted as:

[0030]

[0031] where D4 is the longitudinal braking distance of the vehicle, D6 is the longitudinal driving distance of the pedestrian after the start of braking control, d is the longitudinal distance maintained between the vehicle and the pedestrian when the vehicle stops, v c , v p are the vehicle speed and the pedestrian speed respectively, v rel is the longitudinal relative speed between the vehicle and the target object, d0 is the minimum safety distance that the vehicle should maintain from the target pedestrian in front, and a dmax is the maximum braking deceleration of the vehicle under the maximum adhesion coefficient of the current road surface.

[0032] Furthermore, Step 2.4 derives the warning safety distance d wa and the braking safety distance d br , denoted as:

[0033]

[0034] where t w is the warning reserve time.

[0035] Furthermore, the dynamic TTC threshold derived in Step 2.5, including the warning TTC threshold TTC wa and the braking TTC threshold TTC br , are respectively denoted as:

[0036]

[0037] In the formula, vc represents the vehicle speed before the vehicle's own warning or braking, v p represents the longitudinal speed of the pedestrian before the vehicle warns or brakes, and d0 represents the minimum safe distance that should be maintained between the vehicle and the target pedestrian ahead.

[0038] Furthermore, the TTC threshold control strategy is divided into two control strategy modes. When the braking deceleration and jerk are strictly limited within the comfort range, a dmax ≤ 0.3g, applicable to low-speed scenarios where the vehicle speed ≤ 58 km / h; when the braking safety distance d br exceeds 20 m, the comfort constraint is relaxed, a dmax ≤ 0.85g, ensuring that the TTC threshold ≤ 2 s.

[0039] Furthermore, the critical safety distance for steering to avoid obstacles is introduced. When the vehicle speed is higher than 43 km / h, braking control is preferred; when the speed is lower than this value, the driver is allowed to steer to avoid obstacles.

[0040] A TTC threshold optimization control system based on vehicle driving conditions is used to implement the above-mentioned TTC threshold optimization control method based on vehicle driving conditions.

[0041] Advantages of the present invention:

[0042] The present invention proposes a TTC threshold optimization control system and method based on vehicle driving conditions, which adjusts the TTC threshold in real time according to the vehicle speed, road surface conditions, and pedestrian movement state, improves braking accuracy, realizes dynamic adaptability, and at the same time balances the braking intensity and occupant comfort through a hierarchical control strategy, avoids sudden changes in stepwise deceleration, realizes the optimization of comfort, and then combines the critical distance for steering to avoid obstacles, reduces the interference of the system to the driver's operation, improves acceptance, and promotes human-machine cooperation. Description of the Drawings

[0043] Figure 1 is a logical framework diagram for optimizing the TTC threshold algorithm based on vehicle driving conditions provided by an embodiment of the present invention.

[0044] Figure 2 is the relationship between longitudinal acceleration and time.

[0045] Figure 3 is a schematic diagram of the warning braking mode.

[0046] Figure 4 is a diagram of the TTCbr relationship of the AEB-P system when the road surface adhesion coefficient is 0.6.

[0047] Figure 5 is a diagram of the TTCbr relationship of the AEB-P system when the vehicle speed is 40 km / h.

[0048] Figure 6 It is a critical safety distance relationship diagram for braking and steering.

[0049] Figure 7 It is the intervention moment of AEB-P under different braking intensities. Specific implementation manners

[0050] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] A TTC threshold optimization control method based on vehicle driving conditions includes the following steps:

[0052] Step 1: Model the vehicle braking process and divide the AEB-P braking process into 6 stages.

[0053] (1) Stage 0 - t1: The duration from when the driver recognizes a potential danger ahead during driving to when the driver is about to step on the brake pedal is Δt1;

[0054] (2) Stage t1 - t2: The duration required for the driver to move the right foot to touch the brake pedal is Δt2;

[0055] (3) Stage t2 - t3: After stepping on the brake pedal, the system delay duration Dt3 until the braking execution coordination functions;

[0056] (4) Stage t3 - t4: The duration required for the braking deceleration to increase to the peak level required during the braking process is Δt4;

[0057] (5) Stage t4 - t5: The duration of continuously applying the maximum required braking deceleration is Δt5;

[0058] (6) Stage t5 - t6: The duration of slowly releasing the brake pedal to gradually reduce the braking force until it is completely eliminated is Δt6.

[0059] Step 2: Based on the warning safety distance (d wa ) and the braking safety distance (d br ), combined with the vehicle speed (v c ), the pedestrian speed (v p ) and the safety distance (d0), deduce the dynamic TTC threshold. The specific process is as follows:

[0060] Step 2.1: Obtain parameters such as the vehicle speed (v c ), the pedestrian speed (v p ), and the road surface adhesion coefficient (μ) through in-vehicle sensors.

[0061] Step 2.2: Calculate the deceleration change rate jerk based on the relationship between the longitudinal acceleration and time. If the change in braking deceleration a within Δt is Δa, then the braking deceleration change rate jerk is expressed as:

[0062]

[0063] Step 2.3: Derive the braking safety distance (d br ) through the analysis of the warning braking mode. During the derivation of d br , the following assumptions are specified: Before the vehicle starts braking, both the vehicle and the pedestrian move at a constant speed longitudinally. When the longitudinal speed of the host vehicle is greater than the longitudinal speed of the pedestrian in front, the deceleration change rate during the deceleration increase stage and the vehicle braking end stage remains constant. Therefore, during the vehicle braking process after the AEB-P intervention, the expression for the expected braking deceleration (a des ) changing with time is:

[0064]

[0065] where jerk1 and jerk2 are the braking deceleration change rates during the rising and releasing processes respectively (the meanings of the subscripts 1 and 2 need to be explained); a dmax is the maximum braking deceleration of the vehicle under the maximum adhesion coefficient of the current road surface.

[0066] Thus, combined with the vehicle braking process and the schematic diagram of the warning braking mode, the braking safety distance (d br ) is derived:

[0067]

[0068] where D4 is the longitudinal braking distance of the vehicle, D6 is the longitudinal driving distance of the pedestrian after the braking control starts, d is the longitudinal distance maintained between the vehicle and the pedestrian when the vehicle stops, v c , v p are the vehicle speed and the pedestrian speed respectively, v rel is the longitudinal relative speed between the vehicle and the target object, and d0 is the minimum safety distance that should be ensured between the vehicle and the target pedestrian in front.

[0069] Step 2.4: Combine the road surface adhesion coefficient (μ) to derive the warning safety distance (d wa ) and the braking safety distance (d br ). According to the experimental data obtained from in-depth research, to ensure the comfort of the driver during braking, the maximum braking deceleration is limited to -0.6g, and the absolute value of the maximum deceleration change rate cannot exceed 10 m / s 3。Meanwhile, when the road surface adhesion coefficient is less than 0.6, the maximum braking deceleration that the vehicle can currently achieve depends on the maximum adhesion coefficient provided by the road. Based on this, the requirements for ride comfort are as follows:

[0070] a dmax = min{-0.6g, -μg}

[0071] |jerk| max = 10m / s 3

[0072] From this, it can be deduced that the buffer durations Δt4 and Δt6 of the change in braking deceleration before and after are equal.

[0073]

[0074] From this, a warning safety distance d wa and a braking safety distance d br can be obtained, which are based on the vehicle driving conditions, ensure driving safety, and consider ride comfort:

[0075]

[0076] Step 2.5: According to the analysis of d wa and d br , deduce the dynamic TTC thresholds, including the warning TTC threshold (TTC wa ) and the braking TTC threshold (TTC br ).

[0077]

[0078] In the formula, v c represents the vehicle speed before warning or braking of the host vehicle, v p represents the longitudinal speed of the pedestrian before the vehicle warns or brakes, and d0 represents the minimum safety distance that should be ensured between the vehicle and the target pedestrian in front.

[0079] Step 3: Introduce the critical safety distance for steering to avoid obstacles, and avoid conflicts between braking intervention and driver intention by dynamically adjusting the TTC br threshold.

[0080] Combined with the dynamic TTC threshold mentioned above, keep one of the road surface adhesion coefficient and the host vehicle speed as a constant in the control algorithm, and analyze the change of TTC br with the other variable. The braking threshold TTC br is proportional to the vehicle speed and inversely proportional when the road surface adhesion coefficient is less than or equal to 0.6. When the vehicle speed is relatively fast or the road surface adhesion coefficient is relatively small, TTC brIt will be relatively large. However, if the braking TTC threshold is too large, it will affect the driver's acceptance of AEB-P and may interfere with the normal driving of the driver. At this time, from the driver's perspective, active steering control may be executed to avoid pedestrians ahead. Therefore, critical steering obstacle avoidance control is introduced to deal with some overly large TTC values obtained in real time based on vehicle driving conditions. br Constraints are imposed. According to the existing research on steering strategies, the relationship between the critical longitudinal safety distance of steering and vehicle speed can be obtained, and a relationship diagram of the longitudinal relative distance between the vehicle and the pedestrian when the AEB-P system based on TTC control intervenes in braking, which takes into account driving conditions, driving safety, and braking process comfort, is established. br

[0081] Step 4: Adopt a hierarchical TTC threshold control strategy, and divide the control strategy into two modes. One is the comfort-priority mode, and the other is the safety-priority mode.

[0082] Step 4.1: At medium and low speeds, the critical longitudinal safety distance at which the driver can execute steering control is relatively large compared to d. If the driver fails to make a steering operation in time before the latest longitudinal safety distance for steering, the TTC threshold control established in the present invention, which takes into account vehicle driving conditions and ride comfort, will be activated to help the driver avoid collisions. br

[0083] Step 4.2: When the vehicle speed exceeds 43 km / h, the preset dynamic TTC braking threshold of the system will be triggered prior to the driver's steering reaction critical point. This may interfere with the driving intention. Therefore, it is necessary to analyze the dual impacts of braking intensity on safety and comfort under medium and high-speed conditions and balance system intervention and driving behavior. Four hypothetical comparative analyses are carried out in the present invention:

[0084] (1) During the AEB-P braking process, both the maximum braking deceleration and the maximum braking deceleration change rate are within the defined range that satisfies driving comfort.

[0085] (2) During the AEB-P braking process, the maximum braking deceleration change rate does not exceed the defined range that satisfies ride comfort. When the vehicle brakes, the maximum braking deceleration that the vehicle can achieve is determined by the maximum adhesion coefficient provided by the current road conditions.

[0086] (3) During the AEB-P braking process, the maximum braking deceleration does not exceed the defined range that satisfies ride comfort and is a constant braking deceleration, that is, the times of Δt4 and Δt6 are ignored.

[0087] (4) During the AEB-P braking process, neither the braking deceleration nor the braking deceleration rate considers comfort, and the times of Δt4 and Δt6 are ignored.

[0088] Based on the above four situations, considering that pedestrians usually only appear in non-highway scenarios where the vehicle speed is generally 20 km / h - 80 km / h, the AEB-P intervention time at different braking intensities is plotted under this condition.

[0089] Step 4.3: To ensure that the driver can accept the AEB-P system, not only does the system need to implement the braking and deceleration function, but also the TTC threshold should not exceed 2 seconds. Analyzing the four assumed situations, it is concluded that when assumption (2) is met, the braking deceleration change rate is within the defined range of ride comfort and the braking deceleration is at a braking intensity of 0.85g or 1g, it is possible to ensure driving safety, take into account partial ride comfort and driver acceptance when the longitudinal relative speed between the vehicle and the pedestrian is 20 km / h - 80 km / h.

[0090] Step 4.4: By analyzing the critical safety distance curves for braking and steering and the AEB-P intervention time curves at different braking intensities, the improved TTC corresponding to the braking distance considering ride comfort is obtained. br Range.

[0091]

[0092] Based on the above TTC threshold optimization control method based on vehicle driving conditions, the present invention also proposes a TTC threshold optimization control system based on vehicle driving conditions, which can realize the TTC threshold optimization control based on vehicle driving conditions.

[0093] The above embodiments are only used to illustrate the design concept and characteristics of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made according to the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A TTC threshold optimization control method based on vehicle driving conditions, characterized in that, It includes the following steps: Step 1: Model the vehicle braking process and divide the AEB-P braking process into 6 stages; Step 2: Based on the warning safety distance d wa and the braking safety distance d br , combined with the speed v of the host vehicle c , the speed v of the pedestrian p and the safety distance d0, derive the dynamic TTC threshold; Step 3: Introduce the critical safety distance for steering and obstacle avoidance, and avoid conflicts between braking intervention and driver intention by dynamically adjusting the br TTC threshold; Step 4: Adopt a hierarchical TTC threshold control strategy, and divide the control strategy into two modes. One is the comfort priority mode, and the other is the safety priority mode.

2. The optimized control method for TTC threshold based on vehicle driving conditions according to claim 1, characterized in that, The AEB-P braking process is divided into the following 6 stages: (1) Stage 0 - t1: The duration Δt1 from when the driver recognizes a potential danger ahead of the vehicle to when the driver is about to step on the brake pedal; (2) Stage t1 - t2: The duration Δt2 required for the driver to move the right foot to touch the brake pedal; (3) Stage t2 - t3: The system delay duration Δt3 from when the brake pedal is stepped on until the brake execution coordination functions; (4) Stage t3 - t4: The duration Δt4 required for the braking deceleration to increase to the peak level required during the braking process; (5) Stage t4 - t5: The duration Δt5 of continuously applying the maximum required braking deceleration; (6) Stage t5 - t6: The duration Δt6 of slowly releasing the brake pedal to gradually reduce the braking force until it is completely eliminated.

3. The TTC threshold optimization control method based on vehicle driving conditions according to claim 1, characterized in that, The steps for deriving the dynamic TTC threshold include: Step 2.1: Obtain the vehicle speed v of the host vehicle through in-vehicle sensors c , the pedestrian speed v p , and the road surface adhesion coefficient μ; Step 2.2: Calculate the braking deceleration change rate jerk based on the relationship between the longitudinal acceleration and time; Step 2.3: Derive the braking safety distance d by analyzing the warning braking mode br therefrom; Step 2.4: Combine the road surface adhesion coefficient μ and derive the warning safety distance d wa and the braking safety distance d br for derivation; Step 2.5: Derive the dynamic TTC thresholds based on the analysis of d wa and d br , including the warning TTC threshold TTC wa and the braking TTC threshold TTC br .

4. The TTC threshold optimization control method based on vehicle driving conditions according to claim 3, wherein The braking deceleration change rate jerk is expressed as: where Δa is the change in the braking deceleration a within Δt.

5. The optimized control method for TTC threshold based on vehicle driving conditions according to claim 3, characterized in that Derive the braking safety distance d in Step 2.3 br , denoted as: Among them, D4 is the longitudinal braking distance of the vehicle, D6 is the longitudinal traveling distance of the pedestrian after the start of braking control, d is the longitudinal distance maintained between the vehicle and the pedestrian when the vehicle stops, v c , v p are the vehicle speed and the pedestrian speed respectively, v rel is the longitudinal relative speed between the vehicle and the target object, d0 is the minimum safety distance that should be ensured between the vehicle and the target pedestrian in front, a dmax is the maximum braking deceleration of the vehicle under the maximum adhesion coefficient of the current road surface.

6. The optimized control method for TTC threshold based on vehicle driving conditions according to claim 3, characterized in that, Step 2.4 Derive the warning safety distance d wa and the braking safety distance d br and denote it as: where t w is the reserved time for early warning.

7. A TTC threshold optimization control method based on vehicle driving conditions according to claim 3, characterized in that, Derive the dynamic TTC threshold in Step 2.5, including the warning TTC threshold TTC wa and the braking TTC threshold TTC br , which are respectively denoted as: where, v c represents the vehicle speed before the vehicle's warning or braking, v p represents the longitudinal speed of the pedestrian before the vehicle's warning or braking, and d0 represents the minimum safe distance that should be maintained between the vehicle and the target pedestrian ahead.

8. A TTC threshold optimization control method based on vehicle driving conditions according to claim 1, characterized in that The TTC threshold control strategy is divided into two control strategy modes. When the braking deceleration and jerk are strictly limited within the comfort range, a dmax ≤ 0.3g, which is applicable to low-speed scenarios with a vehicle speed ≤ 58 km / h; when the braking safety distance d br exceeds 20 m, the comfort constraint is relaxed, and a dmax ≤ 0.85g to ensure that the TTC threshold ≤ 2 s.

9. A TTC threshold optimization control method based on vehicle driving conditions according to claim 1, characterized in that Introduce the critical safety distance for steering to avoid obstacles. When the vehicle speed is higher than 43 km / h, braking control is preferred; when the speed is lower than this value, the driver is allowed to steer to avoid obstacles.

10. A TTC threshold optimization control system based on vehicle driving conditions, characterized in that, It is used to implement a TTC threshold optimization control method based on vehicle driving conditions as described in claim 1.

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