Speed control method for autonomous vehicle on ice and snow curved road

Abstract

The application discloses a kind of automatic driving vehicle speed control methods suitable for ice and snow curved road surface, comprising: according to the coupling relationship of tire and ice and snow road surface, the external resistance of tire on ice and snow road surface is calculated, and the main influencing factor of vehicle travel is determined;External resistance is mainly provided by rolling resistance;Based on car-tire-ice coupling mechanism, brake master cylinder pressure is calculated according to brake master cylinder effective diameter, brake master cylinder stress and ice and snow road surface safety steering speed, to adjust vehicle speed by controlling master cylinder pressure;According to the coupling relationship of vehicle and ice and snow road surface, the two-degree-of-freedom dynamics model of automatic driving vehicle containing ice and snow curved road surface low adhesion coefficient is established, and the yaw angular velocity of vehicle is constrained.The whole process modeling and simulation are carried out from the perspective of car-tire-ice coupling, the problem of steering speed control of automatic driving vehicle on ice and snow road surface is solved, and the problem of steering speed fluctuation and driving sideslip risk in ice and snow curved road scene is overcome.

Description

Technical Field

[0001] This invention relates to the field of autonomous driving technology, and specifically to a speed control method for autonomous vehicles applicable to icy and snowy curved roads. Background Technology

[0002] The widespread adoption and popularization of autonomous vehicles requires overcoming common icy and snowy road conditions. In icy and snowy environments, the reduced coefficient of friction and decreased anti-skid performance make vehicle speed control during steering particularly difficult. To adapt to driving on icy and snowy winding roads, autonomous driving systems need to possess high adaptability, responsiveness, and precise dynamic control.

[0003] Existing methods for vehicle driving in icy and snowy scenarios primarily focus on decision-making regarding safe driving speed and trajectory, but they neglect the dynamic characteristics of individual vehicles, thus failing to determine the vehicle's adaptability to decision-making strategies in real-world environments. Current vehicle control methods typically only consider normal road environments and scenarios, neglecting special scenarios such as curves in icy and snowy conditions. Furthermore, while some studies have modeled vehicles in icy and snowy curve scenarios, these models only independently model elements such as vehicle dynamics and tires, ignoring the integration of these elements with the road environment and the coupling relationships between them. In terms of control method design, the impact of the road environment on control performance has not been fully considered, resulting in insufficient accuracy in the designed control methods.

[0004] To address the aforementioned issues, this invention employs a full-process modeling and simulation approach from the perspective of vehicle-tire-ice coupling to solve the problem of steering speed control for autonomous vehicles on icy and snowy roads. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a speed control method for autonomous vehicles applicable to icy and snowy curved roads that overcomes the problems of steering speed fluctuation and driving sideslip risk in the above-mentioned icy and snowy curve scenarios.

[0006] This invention provides a speed control method for autonomous vehicles applicable to icy and snowy curved roads, comprising:

[0007] Based on the coupling relationship between the tire and the icy and snowy road surface, the external resistance of the tire on the icy and snowy road surface is calculated to determine the main influencing factors on vehicle driving.

[0008] Based on the vehicle-tire-ice coupling mechanism, the brake master cylinder pressure is calculated according to the effective diameter of the brake master cylinder, the force on the brake master cylinder and the safe steering speed on icy and snowy roads, so as to adjust the vehicle speed by controlling the master cylinder pressure.

[0009] Based on the coupling relationship between the vehicle and the icy and snowy road surface, a two-degree-of-freedom dynamic model of an autonomous vehicle with low adhesion coefficient on icy and snowy curved road surfaces is established, and the yaw rate of the vehicle is constrained.

[0010] In one alternative approach, the formula for calculating the brake master cylinder pressure is:

[0011]

[0012] in, For braking master cylinder pressure, D The effective diameter of the brake master cylinder, The brake master cylinder is under force. For safe turning speed on icy and snowy roads, for Vehicle speed at all times.

[0013] In an alternative approach, adjusting the vehicle speed by controlling the master cylinder pressure further includes:

[0014] By controlling the master cylinder pressure, the vehicle can decelerate smoothly and evenly to a safe steering speed during driving, and pass through icy and snowy curved roads with a smooth oscillation angular velocity and a safe steering speed.

[0015] In one alternative approach, the speed constraint equation for the vehicle during its journey is:

[0016]

[0017] in, for Vehicle speed at all times To reduce speed for vehicle comfort, Braking time, For safe turning speed on icy and snowy roads, for Vehicle speed at all times.

[0018] In one alternative approach, during vehicle braking, the master cylinder pressure is calculated based on the autonomous vehicle's motion state on the icy, curved road surface and changes in the autonomous vehicle's position.

[0019] In one alternative approach, the motion state of the autonomous vehicle is:

[0020]

[0021] in, Braking distance, , They are respectively and Vehicle location at any given time For vehicle quality;

[0022] The change in the position of the autonomous vehicle is as follows:

[0023]

[0024] in, for Constantly apply pressure to the master cylinder. for Rolling resistance coefficient at all times;

[0025] The formula for calculating the master cylinder pressure is:

[0026] .

[0027] In one alternative approach, the expression for constraining the vehicle's yaw rate is:

[0028]

[0029] in, The coefficient of adhesion for icy and snowy roads. For vehicle speed, ω represents the yaw rate.

[0030] In one alternative approach, the equilibrium equations of the two-degree-of-freedom vehicle dynamics model are:

[0031]

[0032] in, For the lateral acceleration of the vehicle, The sideslip angle is the angle of the center of mass. For the front wheel steering angle, , These are the distances from the center of mass to the front and rear axles, respectively. , The equivalent lateral stiffness of the front and rear axles, Let be the vehicle's moment of inertia about a direction perpendicular to the ground.

[0033] In an alternative approach, the method further includes:

[0034] By introducing Laplace variables, the transfer state of the two-degree-of-freedom vehicle dynamics model is obtained, and then converted into standard form to obtain the steady-state gain of yaw rate and center of mass sideslip angle, thereby obtaining the expression of the two-degree-of-freedom model of autonomous vehicles on icy and snowy roads.

[0035] In one alternative approach, the two-degree-of-freedom model expression for the autonomous vehicle is:

[0036]

[0037] in, , For vehicle stability factor, , These are the distances from the center of mass to the front and rear axles, respectively. , The equivalent lateral stiffness of the front and rear axles.

[0038] According to the solution provided by this invention, the external resistance of the tire on the icy and snowy road surface is calculated based on the coupling relationship between the tire and the icy and snowy road surface, and the main influencing factors on vehicle driving are determined; wherein, the external resistance is mainly provided by rolling resistance; based on the vehicle-tire-ice coupling mechanism, the brake master cylinder pressure is calculated according to the effective diameter of the brake master cylinder, the force on the brake master cylinder, and the safe steering speed on the icy and snowy road surface, so as to adjust the vehicle speed by controlling the master cylinder pressure; based on the coupling relationship between the vehicle and the icy and snowy road surface, a two-degree-of-freedom vehicle dynamics model of the autonomous vehicle including the low adhesion coefficient of the icy and snowy road surface is established, and the yaw rate of the vehicle is constrained. This invention performs full-process modeling and simulation from the perspective of vehicle-tire-ice coupling, solves the problem of steering speed control of autonomous vehicles on icy and snowy roads, and overcomes the problems of steering speed fluctuation and driving sideslip risk in icy and snowy curve scenarios.

[0039] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0040] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0041] Figure 1 A flowchart illustrating an embodiment of the present invention for a speed control method for autonomous vehicles on icy and snowy curved roads is shown.

[0042] Figure 2 A schematic diagram of the overall flow of an autonomous vehicle speed control method applicable to icy and snowy curved roads according to an embodiment of the present invention is shown.

[0043] Figure 3 This diagram illustrates the forces acting on the wheels of an autonomous vehicle on a level road surface, according to an embodiment of the present invention.

[0044] Figure 4The diagram shows the changes in AV parameters under dual-track conditions according to an embodiment of the present invention. (a) shows the changes in trajectory offset parameters, (b) shows the changes in yaw rate parameters, and (c) shows the changes in centroid sideslip angle parameters. Detailed Implementation

[0045] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0046] For scenarios involving icy and snowy curves, considering the limitations imposed on autonomous vehicles by road surface adhesion coefficient and vehicle dynamics during operation, such as... Figure 2 As shown, this invention first analyzes the tire forces when a vehicle is driving on icy and snowy roads based on the coupling relationship between the tires and the road surface. Based on the coupling relationship between the vehicle's dynamic performance and the tires, the speed fluctuation problem of the vehicle on icy and snowy roads is solved by adjusting the brake master cylinder pressure acting on the tires, thus achieving safe and smooth deceleration of the vehicle. Secondly, by introducing the adhesion coefficient of icy and snowy roads and combining it with the vehicle's dynamic characteristics, a two-degree-of-freedom model of the vehicle incorporating the characteristics of icy and snowy roads is constructed. This solves the problem of organically combining the state of icy and snowy roads with the dynamic constraints of the vehicle driving on icy and snowy roads, enabling the vehicle to maintain a low yaw rate and a stable center-of-gravity sideslip angle while accurately driving along the center line of the lane, significantly improving the vehicle's steering stability.

[0047] Figure 1 This diagram illustrates a flow chart of an automated vehicle speed control method for icy and snowy curved roads according to an embodiment of the present invention. Specifically, as shown... Figure 1 As shown, it includes the following steps:

[0048] Step S101: Based on the coupling relationship between the tire and the icy and snowy road surface, calculate the external resistance of the tire on the icy and snowy road surface and determine the main influencing factors on vehicle driving.

[0049] In this embodiment, the tire forces of an autonomous vehicle driving on icy and snowy roads are analyzed based on the coupling relationship between the tires and the road surface. Autonomous vehicles driving on icy and snowy roads are affected by various external resistances, primarily tire rolling resistance. The external resistances during the driving process are as follows:

[0050]

[0051] in, For rolling resistance, For air resistance, For slope resistance, To increase resistance.

[0052] This embodiment primarily addresses the braking control challenge on icy and snowy horizontal curves. It considers that the external resistance experienced by the vehicle tires is provided by the rolling resistance of the wheels, and the forces exerted on the tires when driving on icy and snowy roads are as follows: Figure 3 As shown.

[0053] The forces acting on an autonomous vehicle are as follows:

[0054]

[0055] Further derivation yields:

[0056]

[0057] in, It is the rolling resistance torque. It is the normal force on the ground. It is the distance the normal force moves forward. It is the driving force. It is the wheel radius. It is the rolling resistance coefficient. It is the wheel load.

[0058] The rolling resistance coefficient is the ratio of the driving force required to roll a wheel under specific conditions to the wheel load. Therefore, rolling resistance is equal to the product of the rolling resistance coefficient and the wheel load, as shown below:

[0059]

[0060] in, For vehicle quality, This is the acceleration due to gravity.

[0061] Step S102: Based on the vehicle-tire-ice coupling mechanism, the brake master cylinder pressure is calculated according to the effective diameter of the brake master cylinder, the force on the brake master cylinder, and the safe steering speed on the icy and snowy road surface, so as to adjust the vehicle speed by controlling the master cylinder pressure.

[0062] In this embodiment, based on the vehicle-tire-ice coupling mechanism, the speed and position changes of an autonomous vehicle before turning on an icy and snowy curved road surface are analyzed, and an autonomous vehicle braking pressure control algorithm is constructed.

[0063] Autonomous vehicles are also constrained by the braking force of the vehicle's internal brakes during operation. The braking force is provided by the pressure of the master cylinder, which, under the influence of its effective radius, outputs braking pressure and distributes this pressure to the tires. The changes in braking pressure during braking are shown below:

[0064]

[0065] in, Where D is the brake master cylinder pressure, and D is the effective diameter of the brake master cylinder. The brake master cylinder is under force. For safe turning speed on icy and snowy roads, for Vehicle speed at all times.

[0066] By controlling the master cylinder pressure and adjusting the vehicle speed, the vehicle decelerates smoothly and evenly to a safe steering speed, and traverses icy and curved roads with a stable angular velocity and safe steering speed. The speed constraints during vehicle operation are shown in the equation:

[0067]

[0068] in, for Vehicle speed at all times To reduce speed for vehicle comfort, This refers to the braking time.

[0069] During braking, the autonomous vehicle's motion on the icy, curved road surface is as follows:

[0070]

[0071] in, Braking distance, , They are respectively and The vehicle's location at any given time.

[0072] Further derivation yields the following changes in the position of the autonomous vehicle:

[0073]

[0074] in, for Constantly apply pressure to the master cylinder. for The rolling resistance coefficient at all times. Therefore, the formula for calculating the master cylinder pressure during the driving process of an autonomous vehicle is rewritten as follows:

[0075]

[0076] Step S103: Based on the coupling relationship between the vehicle and the icy and snowy road surface, establish a two-degree-of-freedom vehicle dynamics model for the autonomous vehicle that includes the low adhesion coefficient of the icy and snowy curved road surface, and constrain the yaw rate of the vehicle.

[0077] In this embodiment, the adhesion coefficient constraint of icy and snowy road surface is introduced, and combined with the vehicle dynamics characteristics, a vehicle dynamics model suitable for icy and snowy curve scenarios is established.

[0078] On icy and snowy winding roads, yaw rate directly affects the vehicle's response speed and accuracy to steering input. A stable yaw rate can reduce the risk of oversteering or understeering, decrease the possibility of autonomous vehicles losing control, and improve driving safety and passenger comfort. Introducing the coefficient of friction for icy and snowy surfaces, the vehicle's yaw rate is constrained as follows:

[0079]

[0080] We derive that:

[0081]

[0082] in, For the lateral acceleration of the vehicle, The coefficient of adhesion for icy and snowy roads. For vehicle speed, ω represents the yaw rate.

[0083] Autonomous vehicles turning on icy and snowy roads essentially need to solve the core control problem of two degrees of freedom: lateral (lateral) and longitudinal (forward and backward). Therefore, this invention uses a two-degree-of-freedom (DOF) dynamic model to characterize the turning dynamics of autonomous vehicles. The two-DOF model is applicable to various vehicle types and scenarios, and is not limited by vehicle characteristics or driving style. Based on the coupling relationship between the vehicle and the icy and snowy road surface, and combined with the vehicle's dynamic characteristics, a two-DOF model considering the low adhesion coefficient of icy and snowy curved road surfaces is established. The equilibrium equations of the two-DOF vehicle model are as follows:

[0084]

[0085] in, The sideslip angle is the angle of the center of mass. For the front wheel steering angle, , These are the distances from the center of mass to the front and rear axles, respectively. , The equivalent lateral stiffness of the front and rear axles, Let be the vehicle's moment of inertia about a direction perpendicular to the ground.

[0086] Laplace variables are often introduced to simplify complex mathematical models or physical problems. By introducing appropriate variable transformations, the original problem can be transformed into a more tractable form, which facilitates the analysis and solution of differential equations and the analysis of dynamic behavior. Therefore, the transitive state of a two-degree-of-freedom model obtained by introducing Laplace variables is shown in the equation:

[0087]

[0088] In the formula, For Laplace variables, This is the vehicle stability factor.

[0089] The above expression is converted to its standard form as shown in the following process:

[0090]

[0091]

[0092] The steady-state gain of yaw rate and sideslip angle is obtained as shown in the following equations:

[0093]

[0094] The resulting expression for the two-degree-of-freedom model of an autonomous vehicle on icy and snowy roads is shown in the following equation:

[0095]

[0096] This embodiment uses CarSim to customize vehicle parameters and road conditions, employing a CarSim / Simulink co-simulation method. A double-lane-change icy / snowy road surface is selected to test the feasibility of the proposed curve dynamic control method. Experimental results show that the established braking control algorithm and two-degree-of-freedom model can enable the vehicle to maintain a low yaw rate and a stable center-of-gravity sideslip angle while precisely traveling along the lane centerline, significantly improving vehicle steering stability. The experimental procedure is as follows:

[0097] (1) Experimental scenario construction

[0098] The experiment requires incorporating vehicle parameters, constructing a curve scenario considering the road surface adhesion coefficient, enabling data interaction during vehicle operation, and outputting three evaluation metrics. CarSim allows for customization of vehicle parameters and different road conditions, meeting the testing requirements of icy and snowy road scenarios; Simulink enables visual modeling, file sharing between multiple working environments, and data exchange. CarSim / Simulink co-simulation testing can simulate braking control and double lane change scenarios on icy and snowy roads, validating curve dynamic control methods. Vehicle parameters and front wheel parameters are set on the CarSim platform, and a double lane change scenario on icy and snowy roads is constructed and tested through the co-simulation platform. The simulation data is then processed, visualized, and compared.

[0099] (2) Analysis of experimental results

[0100] Under dual-track traffic conditions on icy and snowy roads, vehicles were driven at constant speeds of 30 km / h, 40 km / h, and 50 km / h without a control algorithm. After the control method was introduced, the trajectory deviation, yaw rate, and sideslip angle were extracted and analyzed. Figure 4 a to Figure 4 c shows the dynamic changes of the AV's trajectory offset, yaw rate, and sideslip angle in this scenario. It can be seen that when the AV turns at a constant speed, its sideslip angle decreases with increasing turning speed, indicating that the AV needs a larger sideslip angle to complete the turn at low speeds. Furthermore, when the sideslip angle fluctuates more frequently, the AV's trajectory offset is larger. The AV trajectory offset increases with increasing turning speed, and when the AV trajectory offset is small, the fluctuation trends of the yaw rate and sideslip angle are consistent. From... Figure 4 As can be seen from b, after introducing the braking control algorithm, the vehicle can maintain a low yaw rate and a stable center of gravity sideslip angle while driving precisely along the center line of the lane, indicating that the control method can significantly improve the steering performance of the vehicle on icy and snowy roads.

[0101] According to the solution provided by this invention, the tire forces of a vehicle driving on icy and snowy roads are analyzed from a microscopic perspective. Taking into full account the speed fluctuations of the vehicle on icy and snowy roads, and based on the real-time perceived adhesion coefficient, vehicle device parameters, and the coupling relationship between vehicle dynamics and tires, braking control of the vehicle on icy and snowy roads is achieved by precisely adjusting the brake master cylinder pressure acting on the tires. The proposed control algorithm design ensures that the vehicle's braking control is closely linked to its dynamics and the road environment, guaranteeing the vehicle's adaptability, control accuracy, and stability in icy and snowy road conditions. Based on the vehicle's dynamic characteristics, the features of icy and snowy curved roads are fully incorporated, and a two-degree-of-freedom model suitable for icy and snowy curve scenarios is proposed. This effectively reduces the risk of sideslip and rollover for autonomous vehicles on icy and snowy curves, ensuring safe, reliable, and stable turning. Full-process modeling and simulation are performed from the vehicle-tire-ice coupling perspective, solving the problem of steering speed control for autonomous vehicles on icy and snowy roads and overcoming the problems of steering speed fluctuations and sideslip risks in icy and snowy curve scenarios.

[0102] Those skilled in the art will understand that modules in the device of the embodiments can be adaptively changed and placed in one or more devices different from that embodiment. Modules, units, or components in the embodiments can be combined into a single module, unit, or component, and further, they can be divided into multiple sub-modules, sub-units, or sub-components. Except where at least some of such features and / or processes or units are mutually exclusive, any combination of all features disclosed in this specification (including the accompanying claims, abstract, and drawings) and all processes or units of any method or device so disclosed can be employed. Unless expressly stated otherwise, each feature disclosed in this specification (including the accompanying claims, abstract, and drawings) may be replaced by an alternative feature that serves the same, equivalent, or similar purpose. Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination. The invention can be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In the unit claims listing several devices, several of these devices may be embodied by the same hardware item. Unless otherwise specified, the steps in the above embodiments should not be construed as limiting the order of execution.

Claims

1. A speed control method for autonomous vehicles applicable to icy and snowy curved roads, characterized in that, include: Based on the coupling relationship between the tire and the icy and snowy road surface, the external resistance of the tire on the icy and snowy road surface is calculated to determine the main influencing factors on vehicle driving. Based on the vehicle-tire-ice coupling mechanism, the brake master cylinder pressure is calculated according to the effective diameter of the brake master cylinder, the force on the brake master cylinder and the safe steering speed on icy and snowy roads, so as to adjust the vehicle speed by controlling the master cylinder pressure. Based on the coupling relationship between the vehicle and the icy and snowy road surface, a two-degree-of-freedom vehicle dynamics model for autonomous vehicles with low adhesion coefficients on icy and snowy curved road surfaces is established, and the yaw rate of the vehicle is constrained. The formula for calculating the brake master cylinder pressure is: in, For braking master cylinder pressure, D The effective diameter of the brake master cylinder, The brake master cylinder is under force. For safe turning speed on icy and snowy roads, for Vehicle speed at all times; During vehicle braking, the master cylinder pressure is calculated based on the autonomous vehicle's motion state on the icy, curved road surface and the changes in the autonomous vehicle's position; the autonomous vehicle's motion state is as follows: in, Braking distance, , They are respectively and Vehicle location at any given time; The change in the position of the autonomous vehicle is as follows: in, for Constantly apply pressure to the master cylinder. for Rolling resistance coefficient at all times For vehicle quality, It is the acceleration due to gravity; The formula for calculating the master cylinder pressure is: 。 2. The speed control method for autonomous vehicles on icy and snowy curved roads according to claim 1, characterized in that, The method of adjusting vehicle speed by controlling master cylinder pressure further includes: By controlling the master cylinder pressure, the vehicle can decelerate smoothly and evenly to a safe steering speed during driving, and pass through icy and snowy curved roads with a smooth oscillation angular velocity and a safe steering speed.

3. The speed control method for automated vehicles on icy and snowy curved roads according to claim 1, characterized in that, The speed constraint equation for a vehicle during its movement is: in, for Vehicle speed at all times To reduce speed for vehicle comfort, Braking time, For safe turning speed on icy and snowy roads, for Vehicle speed at all times.

4. The speed control method for automated vehicles on icy and snowy curved roads according to claim 1, characterized in that, The expression for constraining the vehicle's yaw rate is: in, The coefficient of adhesion for icy and snowy roads. For vehicle speed, ω represents the yaw rate.

5. The speed control method for automated vehicles on icy and snowy curved roads according to claim 1, characterized in that, The equilibrium equations of the two-degree-of-freedom vehicle dynamics model are: in, For the lateral acceleration of the vehicle, The sideslip angle is the angle of the centroid. For the front wheel steering angle, , These are the distances from the center of mass to the front and rear axles, respectively. , The equivalent lateral stiffness of the front and rear axles, For vehicles to bypass Moment of inertia of the shaft.

6. The speed control method for automated vehicles on icy and snowy curved roads according to claim 5, characterized in that, The method further includes: By introducing Laplace variables, the transfer state of the two-degree-of-freedom vehicle dynamics model is obtained, and then converted into standard form to obtain the steady-state gain of yaw rate and center of mass sideslip angle, thereby obtaining the expression of the two-degree-of-freedom model of autonomous vehicles on icy and snowy roads.

7. The speed control method for automated vehicles on icy and snowy curved roads according to claim 6, characterized in that, The expression for the two-degree-of-freedom model of the autonomous vehicle is: in, , For vehicle stability factor, , These are the distances from the center of mass to the front and rear axles, respectively. , The equivalent lateral stiffness of the front and rear axles.

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