Automobile Chassis Domain Unified Yaw Motion Control Method and Device Based on a Three-Step Approach

Abstract

The present invention belongs to the technical field of vehicle chassis coordinated control, and specifically relates to a unified yaw motion control method and device for an automotive chassis domain based on a three-step method. It includes: calculating the required yaw target; obtaining sensor, vehicle state, and road surface information to achieve internal information resource sharing; realizing the identification of faults and failures of software and hardware to ensure the safety of corresponding driving; for a four-wheel steering distributed drive electric vehicle, designing a yaw stability integrated control system for the chassis domain based on the three-step method; distributing the additional yaw moment and distributing it to the four wheels for execution; executing the distributed yaw moment control command and the front and rear wheel steering angle commands to achieve the expected vehicle yaw dynamic control. The present invention is based on the intelligent driving requirements of L2+ and above levels, improves the vehicle dynamic performance and handling stability, and solves the problem of insufficient yaw control in traditional drive-by-wire chassis systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of vehicle chassis coordinated control, and specifically relates to an automotive chassis domain unified yaw motion control method and device based on a three-step method. Background Art

[0002] With the highly developed autonomous driving and the gradual maturity of the intelligent auxiliary driving systems independently developed by automobile manufacturers, the chassis domain architecture has emerged and gradually developed on the basis of chassis electronic control. The new chassis domain architecture and the chassis control technology under the chassis domain architecture have become one of the relevant hotspots. As a very important yaw control in vehicle dynamics control, the control based on a single electronic system has been quite mature, and the control interference and coupling problems of multiple electronic control systems under the chassis domain architecture will become more prominent with the development of the chassis domain.

[0003] Regarding yaw control, while the active front-wheel steering system and the active rear-wheel steering system achieve the desired steering, due to the steering of the tires, the magnitude of the tire force will change, which will naturally help the vehicle establish an additional yaw moment under certain working conditions. With the development of distributed drive vehicles, vehicles with four wheels independently driven by in-wheel motors bring more possibilities. The independent control of the torques of the four tires brings the freedom of individual torque change for each wheel. Subsequently, the research on the torque vector control system has emerged. It applies an additional yaw moment to the vehicle through the differential drive method to assist steering. However, in terms of the yaw problem, the control objectives of the two systems are basically the same, but the actuators are completely different, and the working areas of the two systems are restricted. Therefore, it is necessary to develop an integrated control for yaw motion. Summary of the Invention

[0004] The present invention provides an automotive chassis domain unified yaw motion control method and device based on a three-step method, which can improve the vehicle dynamic performance and handling stability based on the intelligent driving requirements at L2+ level and above, and solve the problem of insufficient yaw control in the traditional by-wire chassis system.

[0005] The technical solution of the present invention is described in conjunction with the accompanying drawings as follows:

[0006] In a first aspect, the present invention provides an automotive chassis domain unified yaw motion control method and device based on a three-step method, including the following steps:

[0007] Calculate the yaw target;

[0008] Obtain sensor, vehicle state, and road surface information to achieve internal information resource sharing;

[0009] Implement the fault and failure identification of software and hardware to ensure the safety of corresponding driving;

[0010] For four-wheel steering distributed drive electric vehicles, a chassis domain yaw stability integrated control system based on a three-step method is designed to obtain the yaw moment and the additional values of the front and rear wheel angles, and then send the additional values of the front and rear wheel angles to the vehicle;

[0011] Distribute the yaw moment to four wheels for execution;

[0012] The allocated yaw moment control command is executed, as well as the front and rear wheel angle additional value commands, to achieve the desired vehicle yaw dynamic control.

[0013] Furthermore, the specific method for calculating the yaw target is as follows:

[0014] 11) Design ideal center of mass sideslip angle ;

[0015] 12) Design the ideal yaw rate as follows:

[0016] Calculate the front and rear tire slip angles for a distributed drive four-wheel steering vehicle as follows:

[0017] ; (1)

[0018] In the formula, is the front wheel tire slip angle; is the vehicle's center of mass sideslip angle; is the vehicle yaw angular velocity; is the distance from the front axle of the chassis to the center of mass of the vehicle; is the vehicle longitudinal speed; is the front wheel turning angle; is the rear wheel tire slip angle; is the distance from the rear axle to the center of mass of the vehicle;

[0019] Combining formula (1) we can get:

[0020] ; (2)

[0021] The above formula can be further written as:

[0022] ; (3)

[0023] In the formula, is the distance between the front and rear axles, ; is the distance from the vehicle's turning center to its center of mass, which is the vehicle's turning radius;

[0024] The formula for the lateral and yaw motion of the vehicle in steady state is established as follows:

[0025] ; (4)

[0026] In the formula, is the vehicle mass; is the vehicle lateral acceleration; is the lateral force of the front axle; is the lateral force of the rear axle; is the moment of inertia of the vehicle about the vertical axis; is the yaw angular acceleration;

[0027] Calculate the lateral forces on the front and rear axles as follows:

[0028] ; (5)

[0029] In the formula, is the lateral stiffness of the front wheels; is the lateral stiffness of the rear wheels;

[0030] Since under steady state, , , the above formula is written in the following form:

[0031] ; (6)

[0032] Substitute Equation (6) and Formula (5) into Equation (3) to get:

[0033] ; (7)

[0034] The above formula is written as:

[0035] ; (8)

[0036] In the formula, is the stability factor of the vehicle, that is:

[0037] ; (9)

[0038] 13) Introduce the understeer degree factor , as follows:

[0039] ; (10)

[0040] Therefore, convert Equation (8) to:

[0041] ; (11)

[0042] 14) Set the front wheel steering angle to the Ackermann steering angle and the dynamic steering angle, as follows:

[0043] ; (12)

[0044] ; (13)

[0045] ; (14)

[0046] Wherein, is the Ackermann steering angle; is the dynamic steering angle; is the actual front wheel steering angle;

[0047] (15) Convert Equation (11) to:

[0048] ; (15)

[0049] (16) Set the reference yaw rate to:

[0050] ; (16)

[0051] Wherein, is the reference yaw rate;

[0052] (17) Set the constraint of the ideal yaw rate to:

[0053] ; (17)

[0054] Wherein, is the road surface adhesion coefficient; is the gravitational acceleration; 0.85 is the set safety factor;

[0055] (18) Calculate the actual reference yaw rate as follows:

[0056] ; (18)

[0057] Wherein, is the Laplace operator; is the appropriate first-order inertia link time constant

[0058] (19) Introduce a fitting function and add a non-linear steering characteristic fitting curve to calculate the lateral acceleration as follows:

[0059] ;

[0060] Wherein, is the lateral acceleration limit value in the linear region; is the maximum achievable lateral acceleration;

[0061] Calculate the dynamic front wheel steering angle as follows:

[0062] ;

[0063] The ideal yaw rate of the design is obtained as follows:

[0064] .

[0065] Furthermore, obtaining sensor, vehicle state, and road surface information includes obtaining longitudinal and lateral vehicle speeds, longitudinal and lateral accelerations, road surface adhesion coefficient, and tire longitudinal and lateral forces.

[0066] Furthermore, for the vehicle of a four-wheel steering distributed drive electric vehicle, the specific method for designing a yaw stability integrated control system for the chassis domain based on the three-step method is as follows:

[0067] 41) Establish the vehicle dynamics equations for the lateral and yaw motions of the vehicle as follows:

[0068] ; (19)

[0069] ; (20)

[0070] In the formula, is the center-of-mass sideslip angular velocity; is the yaw angular acceleration; is the additional yaw moment brought by differential drive; and are the lateral reaction forces of the ground on the front and rear axles where the vehicle's front and rear wheels are located; is the vehicle mass; is the yaw moment of inertia of the vehicle;

[0071] 42) Define the relationship between the front and rear wheel steering angles; define the ratio of the rear wheel steering angle to the front wheel steering angle as:

[0072] ; (21)

[0073] In the formula, is the front wheel steering angle; is the rear wheel steering angle;

[0074] 43) Establish the ratio relationship between the lateral forces of the front and rear axles and the rear wheel steering angle and the front wheel steering angle, specifically as follows:

[0075] ; (22)

[0076] In the formula, is the lateral force ratio coefficient of the front and rear axles;

[0077] 44) Set the control variables of the three-step method as , and ;

[0078] 45) Calculate the steady-state value based on the current measured values of the vehicle as follows:

[0079] Let and in equations (19) and (20) to obtain the steady-state control input quantity, denoted by , and as follows:

[0080] ;

[0081] ;

[0082] ;

[0083] Solve for the desired steady-state control input as follows:

[0084] ;

[0085] ;

[0086] ;

[0087] where is the steady-state control input quantity of ; is the steady-state control input quantity of ; is the steady-state control input quantity of

[0088] 46) Introduce the feedforward control of the reference dynamics, consider the transient responses of the sideslip angle and yaw rate of the center of mass, and set the control input conditions as follows:

[0089] ;

[0090] ;

[0091] ;

[0092] where , , are the feedforward control quantities;

[0093] Substitute into equations (19), (20), and (22), where , and are the feedforward control quantities;

[0094] ;

[0095] ;

[0096] ;

[0097] Let , The feedforward control input is solved as follows:

[0098] ;

[0099] ;

[0100] ;

[0101] 47) Introduce tracking error feedback control and set the control input as follows:

[0102] ;

[0103] ;

[0104] ;

[0105] Substitute into formulas (19), (20) and (22), where , and are the feedback control quantities:

[0106] ;

[0107] ;

[0108] ;

[0109] Express the steady-state control and the feedforward control input using , , and , and to get:

[0110] ; (23)

[0111] ; (24)

[0112] ; (25)

[0113] Define the tracking error as follows:

[0114] ; ; (26)

[0115] In the formula, is the vehicle centroid sideslip angle error; is the vehicle yaw rate error; is the reference centroid sideslip angle; is the reference yaw rate;

[0116] Then, equations (23) and (24) become:

[0117] ; (27)

[0118] ; (28)

[0119] Select a certain control error term, that is, the centroid sideslip angle and yaw rate errors in equation (26), so that equations (27) and (28) become an exponentially asymptotically stable situation;

[0120] Simultaneously combine equations (27) and (28) with equation (25) and write them in the following form:

[0121] ; (29)

[0122] ; (30)

[0123] In the formula, is the proportional gain; is the integral gain;

[0124] That is, the values of , and are obtained:

[0125] ;

[0126] ;

[0127] ;

[0128] 48) Set the control law of the three-step controller as follows:

[0129] ; (31)

[0130] In the formula, is the control input; is the steady-state control term; is the feedforward control term; is the error feedback control term; and there is:

[0131] ;

[0132] ;

[0133] ;

[0134] 49) Based on the three-step control law, by calculating the lateral forces of the front and rear wheels, the yaw moment is converted into tire angles and additional moments output as follows:

[0135] Before calculation, analyze the resultant lateral force of the front and rear axles;

[0136] Establish the vehicle's motion equations in three degrees of freedom as follows:

[0137] ; (32)

[0138] In the formula, is the total longitudinal force of the vehicle; is the total lateral force of the vehicle; and , i = 1, 2, 3, 4, are the longitudinal and lateral forces of the two front wheels and two rear wheels of the vehicle respectively; is the wheelbase of the front and rear wheels; is the rear wheel angle;

[0139] Establish the relationship between the four-wheel sideslip angles and the four-wheel angles as follows:

[0140] ;

[0141] ;

[0142] ;

[0143] ;

[0144] In the formula, , , , are the tire sideslip angles of the four wheels respectively;

[0145] Therefore, the lateral forces of the four tires are expressed as follows:

[0146] ;

[0147] ;

[0148] ;

[0149] ;

[0150] The resultant lateral force of the front and rear axles is expressed as follows:

[0151] ;

[0152] ;

[0153] Therefore, by inverse-solving the above formula, the front and rear wheel steering angle decision values are obtained:

[0154] ;

[0155] ;

[0156] In the formula, is the calculated front wheel steering angle value; is the calculated rear wheel steering angle value, and the nominal front wheel steering angle is obtained through the driver's steering wheel angle and the steering system transmission ratio . The nominal rear wheel steering angle is constantly 0. Therefore, the final front and rear wheel steering angle additional values are obtained to complete the final control output, as shown below:

[0157] ;

[0158] .

[0159] In a second aspect, the present invention further provides an automotive chassis domain unified yaw motion control device based on a three-step method for implementing an automotive chassis domain unified yaw motion control method based on a three-step method, including:

[0160] A unified yaw motion controller 110 for calculating a yaw target;

[0161] An environment analysis module 120 for uniformly acquiring sensor, vehicle state, and road surface information to achieve internal information resource sharing;

[0162] A failure redundancy control module 130 for identifying software and hardware failure failures to ensure the safety of corresponding driving;

[0163] A sub-function control module 140 for designing a yaw stability integrated control system for the chassis domain based on a three-step method for a four-wheel steering distributed drive electric vehicle, obtaining a yaw moment and front and rear wheel steering angle additional values, and sending the front and rear wheel steering angle additional values to the vehicle;

[0164] An output arbitration module 150 for distributing the additional yaw moment and distributing it to four-wheel execution;

[0165] An actuator 160 is used to execute the yaw moment control instruction after distribution and execute the additional front and rear wheel steering angle commands to achieve the expected vehicle yaw dynamic control.

[0166] The beneficial effects of the present invention are as follows:

[0167] 1) The present invention is beneficial for each independent system to learn from each other's strengths and make up for weaknesses. The combined functions of the subsystems make joint decisions to avoid coordination problems. At the same time, the independent control algorithms are retained, which not only avoids failure problems but also retains the ability of the subsystems to work independently, improves the stability margin and handling stability of the vehicle, simplifies the automotive electronic and electrical architecture, and provides a feasible solution to the redundant in-vehicle wiring harness and the complexity and independence of each controller.

[0168] 2) The present invention aims at the unified ideal yaw target for yaw movement, replaces the original simple linear steering characteristics, reintroduces a fitting function, adds a non-linear steering characteristics fitting curve, and the change trend of the ideal target is closer to the basic steering characteristics curve of the vehicle. Therefore, the chassis domain yaw control algorithm can better approach the ideal target and thus better improve the dynamic performance and handling stability of the vehicle. Description of the Drawings

[0169] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0170] Figure 1 It is a schematic diagram of a unified yaw movement control device for an automotive chassis domain based on the three-step method according to the present invention;

[0171] Figure 2 It is a schematic diagram of a unified yaw movement control method for an automotive chassis domain based on the three-step method according to the present invention;

[0172] Figure 3 It is a schematic diagram of the comparison of the sideslip angles of the center of mass under three controls;

[0173] Figure 4 It is a schematic diagram of the comparison of the actual yaw angular velocities under three controls;

[0174] Figure 5 It is a schematic diagram of the front wheel steering angle and the additional front and rear wheel steering angles;

[0175] Figure 6 It is a schematic diagram of the comparison of the steering wheel angles under three controls. Detailed Embodiments

[0176] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0177] Embodiment 1:

[0178] See also Figure 1 This embodiment provides a unified yaw motion control method for the chassis domain of an automobile based on a three-step method. The specific method is as follows:

[0179] A. Calculate the yaw target as follows:

[0180] 11) Since the driver expects the vehicle to be stable and the center of mass slip angle to be as small as possible, the ideal center of mass slip angle is designed. ;

[0181] 12) Design the ideal yaw rate;

[0182] Calculate the front and rear tire slip angles for a distributed drive four-wheel steering vehicle as follows:

[0183] ; (1)

[0184] In the formula, is the front wheel tire slip angle; is the vehicle's center of mass sideslip angle; is the vehicle yaw angular velocity; is the distance from the front axle of the chassis to the center of mass of the vehicle; is the vehicle longitudinal speed; is the front wheel turning angle; is the rear wheel tire slip angle; is the distance from the rear axle to the center of mass of the vehicle;

[0185] Combining formula (1) we can get:

[0186] ; (2)

[0187] The above formula can be further written as:

[0188] ; (3)

[0189] In the formula, is the distance between the front and rear axles, ; is the distance from the vehicle's turning center to its center of mass, which is the vehicle's turning radius;

[0190] When the vehicle is in steady state, the lateral and yaw motions of the vehicle are determined by the following formulas:

[0191] ; (4)

[0192] Wherein, is the vehicle mass; is the vehicle lateral acceleration; is the lateral force on the front axle; is the lateral force on the rear axle; is the moment of inertia of the vehicle about the vertical axis; is the yaw angular acceleration;

[0193] Calculate the lateral forces on the front and rear axles as follows:

[0194] ; (5)

[0195] Wherein, is the front wheel lateral stiffness; is the rear wheel lateral stiffness;

[0196] Since in the steady state, , Therefore, the above formula is written in the following form:

[0197] ; (6)

[0198] Substitute Equation (6) and Equation (5) into Equation (3) to get:

[0199] ; (7)

[0200] The above formula is written as:

[0201] ; (8)

[0202] Wherein, is the stability factor of the vehicle, that is:

[0203] ; (9)

[0204] 13) In order to distinguish from the stability factor , introduce the understeer degree factor and set it as , which is only multiplied by a more than the stability factor , as follows:

[0205] ; (10)

[0206] Wherein, is the understeer degree factor;

[0207] Therefore, convert Equation (8) to:

[0208] ; (11)

[0209] 14) It can be clearly seen from Equation (11) that the front wheel steering angle consists of two parts. The first part is the Ackermann steering angle, and the second part can be understood as the dynamic steering angle, that is:

[0210] ; (12)

[0211] ; (13)

[0212] ; (14)

[0213] In the formula, is the Ackermann steering angle; is the dynamic steering angle; is the actual front wheel steering angle;

[0214] 15) Convert Equation (11) to:

[0215] ; (15)

[0216] 16) Set the reference yaw rate to:

[0217] ; (16)

[0218] In the formula, is the reference yaw rate;

[0219] 17) In the above formula, the tire limit force condition is not considered. Due to the influence of the road surface adhesion coefficient, the ideal yaw rate is restricted as follows:

[0220] ; (17)

[0221] In the formula, is the road surface adhesion coefficient; is the gravitational acceleration; 0.85 is the set safety factor;

[0222] 18) In practical applications, a first-order inertial link is applied to provide a smoothing effect. The actual reference yaw rate is:

[0223] ; (18)

[0224] In the formula, is the Laplace operator; is a suitable first-order inertial link time constant.

[0225] Among them, Equation (16) describes the linear relationship between the dynamic steering angle and the lateral acceleration. It fits accurately when the lateral acceleration is small and can represent the approximate value of a real vehicle. However, it deviates significantly from the actual vehicle characteristics when the lateral acceleration is large. Therefore, through the curve fitting design of the lateral acceleration, the steering characteristics of the vehicle tend to be able to exert the maximum performance of the vehicle and change continuously at any change in the lateral acceleration.

[0226] 19) Therefore, the steering characteristics are designed, a fitting function is reintroduced, and a non-linear steering characteristic fitting curve is added. The lateral acceleration is:

[0227] ;

[0228] In the formula, is the limit value of the lateral acceleration in the linear region, is the maximum achievable lateral acceleration;

[0229] The dynamic front wheel angle is calculated as:

[0230] ;

[0231] Furthermore, the designed ideal yaw rate can be obtained as follows:

[0232] ;

[0233] B. Obtain sensor, vehicle state, and road surface information to achieve internal information resource sharing;

[0234] Among them, the information includes the longitudinal and lateral vehicle speeds, longitudinal and lateral accelerations, road surface adhesion coefficient, and longitudinal and lateral tire forces.

[0235] C. The vehicle control in the case of software and hardware failures, i.e., the failure state control, includes torque vector control (TVC) / integrated braking control (IBC) to achieve steering, and the IBC fault redundant braking unit (RBU) starts the failure redundant control algorithm to ensure the safety of corresponding driving;

[0236] D. For a four-wheel steering distributed drive electric vehicle, design a yaw stability integrated control system for the chassis domain based on the three-step method, specifically as follows:

[0237] 41) Establish the vehicle dynamics equations for the lateral motion and yaw motion of the vehicle, specifically as follows:

[0238] ; (19)

[0239] ; (20)

[0240] In the formula, is the yaw rate of the center of mass; is the yaw angular acceleration; is the additional yaw moment brought by differential drive; and are the lateral reaction forces of the ground on the front and rear axles where the vehicle's front and rear wheels are located; is the vehicle mass; is the yaw moment of inertia of the vehicle;

[0241] 42) The definition of the front and rear wheel steering angle relationship determines the steering characteristics of the vehicle. This proportionality coefficient is used to describe the dependence relationship between the rear wheel steering angle and the front wheel steering angle; therefore, the front and rear wheel steering angle relationship is defined; define the ratio of the rear wheel steering angle to the front wheel steering angle as:

[0242] ; (21)

[0243] In the formula, is the front wheel steering angle; is the rear wheel steering angle;

[0244] 43) The lateral force is the force generated by the interaction between the tire and the ground. Its magnitude and direction determine the driving stability of the vehicle. Define the formula for the ratio of the lateral forces on the front and rear axles. This ratio reflects the distribution of the lateral forces on the front and rear axles and is crucial for stability control; therefore, establish the ratio relationship between the lateral forces on the front axle and the rear axle and the rear wheel steering angle and the front wheel steering angle as follows:

[0245] ; (22)

[0246] In the formula, is the proportionality coefficient of the lateral forces on the front and rear axles;

[0247] 44) Set the control variables of the three-step method as , and ;

[0248] The three-step method control is used in the vehicle stability control system and is decomposed into three control variables: the lateral force on the rear axle (adjust the lateral force of the rear wheels to affect the sideslip angle of the vehicle's center of mass), the additional yaw moment (generate an additional yaw moment through differential drive or other means to directly adjust the yaw angular velocity), and the lateral force on the front axle : adjust the lateral force of the front wheels to assist in stabilizing the yaw motion of the vehicle. The control variables cooperate with each other to ensure the stability and maneuverability of the vehicle under different driving conditions.

[0249] 45) The first step of the three-step method: The calculation of the steady-state value is based on the dynamic equation of the vehicle during steady driving. Assume that the vehicle reaches the steady state ( , ), the desired steady-state control inputs can be solved, and these steady-state control inputs are used to calculate the target lateral force and yaw moment of the vehicle. Therefore, according to the current measured values of the vehicle, the steady-state values are calculated to ensure that the vehicle operates within the linear range of yaw rate and sideslip angle to avoid excessive tire slip:

[0250] Let , , the steady-state control input quantities are obtained, and are represented by , and as follows:

[0251] ;

[0252] ;

[0253] ;

[0254] Let , The feedforward control input is solved as:

[0255] ;

[0256] ;

[0257] ;

[0258] In the formula, is the steady-state control input quantity; is the steady-state control input quantity; steady-state control input quantity;

[0259] 46) The second step of the three-step method: To improve the transient response of the vehicle, a feedforward control of the reference dynamics needs to be introduced. When the dynamic model changes dynamically, the system can react to it in a timely manner, improving the rapidity and transient characteristics of the system response; considering the transient response of the center-of-mass sideslip angle and yaw rate, let the control input satisfy:

[0260] ;

[0261] ;

[0262] ;

[0263] In the formula, 、 、 is the feedforward control quantity;

[0264] Substitute into formulas (19), (20) and (22), where , and is the feedforward control quantity;

[0265] ;

[0266] ;

[0267] ;

[0268] Let , The feedforward control input is solved as:

[0269] ;

[0270] ;

[0271] ;

[0272] 44) The third step of the three-step method: To further improve the control accuracy, it is necessary to add tracking error feedback control; define the error as formula (26), and design a proportional-integral (PI) feedback control law to make the error decay exponentially. This error feedback control can effectively compensate for the possible deviations in steady-state control and feedforward control, so that the system reaches the desired trajectory, specifically as follows:

[0273] Let the control input satisfy:

[0274] ;

[0275] ;

[0276] ;

[0277] In the formula, is the additional yaw moment;

[0278] Substitute into formulas (19), (20) and (22), where , and are the feedback control quantities:

[0279] ;

[0280] ;

[0281] ;

[0282] The steady-state control and feedforward control inputs are used with , , and , and expressed as:

[0283] ; (23)

[0284] ; (24)

[0285] ; (25)

[0286] Define the tracking error,

[0287] ; ; (26)

[0288] wherein, is the vehicle's center-of-mass sideslip angle error; is the vehicle's yaw rate error; is the reference center-of-mass sideslip angle; is the reference yaw rate;

[0289] Then, equations (23) and (24) become:

[0290] ; (27)

[0291] ; (28)

[0292] To ensure that the error exponent is asymptotically stable, an appropriate error feedback control law is usually selected, such as proportional control (P control) or PI control (proportional-integral control), so that equations (27) and (28) become the case of e-exponential asymptotic stability.

[0293] Equations (27) and (28) are simultaneously combined with equation (25) and written in the following form:

[0294] ; (29)

[0295] ; (30)

[0296] wherein, is the proportional gain; is the integral gain;

[0297] That is, the values of , and are obtained:

[0298] ;

[0299] ;

[0300] ;

[0301] 48) Set the control law of the three-step controller. The total control law of the three-step controller consists of three parts: : The steady-state control term, which calculates the control input based on the steady-state conditions; : The feed-forward control term, which is used to improve the transient response. : The error feedback control term, which is used to compensate for system errors;

[0302] The control law of the controller is as follows:

[0303] ; (31)

[0304] In the formula, is the control input; is the steady-state control term; is the feed-forward control term; is the error feedback control term; and there is:

[0305] ;

[0306] ;

[0307] ;

[0308] 49) Based on the three-step control law, by calculating the lateral forces of the front and rear wheels, the yaw moment is converted into tire angles and additional torques output, specifically as follows:

[0309] Before calculation, analyze the resultant lateral force of the front and rear axles;

[0310] The force condition of the vehicle is given by the motion equation. The motion equation of the vehicle in three degrees of freedom is as follows:

[0311] ; (32)

[0312] In the formula, is the total longitudinal force of the vehicle; is the total lateral force of the vehicle; and , i = 1, 2, 3, 4, are the longitudinal and lateral forces of the two front wheels and two rear wheels of the vehicle respectively; is the wheelbase of the front and rear wheels; is the rear wheel angle;

[0313] The subsequent calculation of the tire lateral force depends on the slip angle. Therefore, the slip angle calculation formula is given as follows:

[0314] ;

[0315] ;

[0316] ;

[0317] ;

[0318] In the formula, , , , are the slip angles of the tires of the four wheels respectively;

[0319] The reasonable derivation and calculation of the lateral forces of the front and rear axles depend on the lateral forces of the four-wheel tires. The lateral forces of the four-wheel tires are expressed as follows:

[0320] ;

[0321] ;

[0322] ;

[0323] ;

[0324] One of the control variables in the control law is the resultant lateral force of the front and rear axles. The resultant lateral force of the front and rear axles is:

[0325] ;

[0326] ;

[0327] Therefore, by solving the above formula inversely, the decision values of the front and rear wheel steering angles for the control requirements of the four-wheel steering system are obtained as follows:

[0328] ;

[0329] ;

[0330] In the formula, is the calculated value of the front wheel steering angle; is the calculated value of the rear wheel steering angle. The nominal value of the front wheel steering angle is obtained through the driver's steering wheel angle and the transmission ratio of the steering system. The nominal value of the rear wheel steering angle is constantly 0. Therefore, the final additional values of the front and rear wheel steering angles are obtained to complete the final control output;

[0331] ;

[0332] 。

[0333] So far, the control law and control output of the three-step method are completed, and the additional front and rear wheel steering angles obtained are sent to the vehicle.

[0334] Among them, the additional yaw moment and the additional front and rear wheel steering angles are two core control outputs of the three-step controller. They interact with each other and jointly affect the stability of the vehicle.

[0335] The additional yaw moment directly adjusts the driving torques of the four wheels to achieve yaw stability control. It mainly optimizes the driving force distribution of the tires through the torque vector control (TVC) mechanism, so that the vehicle can maintain stability under high-speed and complex working conditions.

[0336] The additional front and rear wheel steering angles directly affect the steering actuator and determine the changes in the front and rear wheel steering angles of the vehicle. They mainly optimize the steering characteristics of the vehicle through the four-wheel steering (4WS) mechanism and reduce the risk of sideslip.

[0337] E. Distribute the additional yaw moment and execute it on the four wheels.

[0338] The present invention does not limit the specific structure of the yaw moment distribution controller, as long as it can complete the function. In a preferred mode of real-time deployment on a real vehicle, the average distribution method is used for yaw moment distribution.

[0339] F. Execute the distributed yaw moment control command and the front and rear wheel steering angle command to achieve the expected vehicle yaw dynamic control.

[0340] Embodiment 2:

[0341] This embodiment provides a double lane change condition at 80 km / h on a low adhesion road surface: the set vehicle speed is 80 km / h, the road surface adhesion coefficient is set to 0.3, and simulation verification is carried out under the double lane change condition. The control effects of the three-step controller are compared with those without control and only turning on the torque vector control (TVC) function through PID control.

[0342] As Figure 3 and Figure 4 shown, the vehicle without control can complete the double lane change test, but the sideslip angle of the center of mass and the yaw angular velocity are both large; only turning on the TVC algorithm will suppress the yaw angular velocity and the sideslip angle of the center of mass, getting closer to the ideal target; after the unified yaw motion control algorithm is turned on, the suppression effect on the sideslip angle of the center of mass and the yaw angular velocity is more obvious, and the stability of the vehicle under low adhesion and high speed conditions is better, and there is almost no control lag, which is beneficial to maintaining control real-time performance.

[0343] AsFigure 5 As shown in the figure, it can be seen from the additional values of the front-wheel steering angle and the rear-wheel steering angle that the three-step controller makes decisions on the front-wheel steering angle and the rear-wheel steering angle simultaneously. The directions of the additional values of the front and rear wheel steering angles are opposite, but the directions of the front and rear wheel steering angles remain the same, which meets the definition of four-wheel steering and is beneficial to helping the vehicle maintain high-speed driving stability.

[0344] As Figure 6 shown in the figure, for the comparison of the steering wheel angle sizes under three types of control, for the same working condition, the smaller the steering wheel angle, the lower the operation load of the driver. Under the action of the three-step controller, after completing the double lane change working condition, the steering wheel angle applied by the driver is the smallest, with the lowest operation load.

[0345] Example 3:

[0346] Referring to Figure 2 , this embodiment provides a unified yaw motion control device for an automotive chassis domain based on the three-step method, which is used to implement a unified yaw motion control method for an automotive chassis domain based on the three-step method described in Example 1, including:

[0347] A unified yaw motion controller 110 for calculating a yaw target;

[0348] An environment analysis module 120 for obtaining sensor, vehicle state, and road surface information to achieve internal information resource sharing;

[0349] A failure redundancy control module 130 for coping with the failure identification of software and hardware to ensure the safety of corresponding driving;

[0350] A sub-function control module 140 for designing a yaw stability integrated control system for the chassis domain based on the three-step method for a four-wheel steering distributed drive electric vehicle, obtaining a yaw moment and additional values of the front and rear wheel steering angles, and sending the additional values of the front and rear wheel steering angles to the vehicle;

[0351] An output arbitration module 150 for distributing the additional yaw moment and distributing it to four-wheel execution;

[0352] An actuator 160 for executing the distributed yaw moment control instruction and executing the additional value command of the front and rear wheel steering angles to achieve the expected vehicle yaw dynamic control.

[0353] Example 4:

[0354] This embodiment provides a terminal, including:

[0355] One or more processors;

[0356] A memory for storing instructions executable by the one or more processors;

[0357] Wherein, the one or more processors are configured to:

[0358] Execute a unified yaw motion control method for an automotive chassis domain based on the three-step method described in Embodiment 1.

[0359] Embodiment 5:

[0360] This embodiment provides a non-transitory computer-readable storage medium. When the instructions in the storage medium are executed by a processor of a terminal, the terminal is enabled to execute a unified yaw motion control method for an automotive chassis domain based on the three-step method described in Embodiment 1.

[0361] In summary, the present invention can improve the dynamic performance and handling stability of a vehicle, and solve the problem of insufficient yaw control in a traditional by-wire chassis system.

[0362] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A unified yaw motion control method for automotive chassis domain based on a three-step approach, characterized in that, The following steps are involved: Calculate yaw target; Obtain sensor, vehicle status, and road surface information to achieve internal information resource sharing; Identify software and hardware failures to ensure driving safety; For four-wheel steering distributed drive electric vehicles, a chassis-domain yaw stability integrated control system based on a three-step method is designed to obtain additional yaw torque and additional values of front and rear wheel steering angles, and transmit the additional values of front and rear wheel steering angles to the vehicle. The three-step method is specifically as follows: The first step of the three-step method is to calculate the steady-state value based on the vehicle's dynamic equations during stable driving. Based on the vehicle's current measured values, the steady-state value is calculated to ensure that the vehicle operates within the linear range of yaw rate and sideslip angle. The second step of the three-step method: To improve the vehicle's transient response, it is necessary to introduce feedforward control of the reference dynamics. When the dynamic model undergoes dynamic changes, the system can respond to them in a timely manner, improving the rapidity of the system response and transient characteristics. The third step of the three-step method: To further improve control accuracy, tracking error feedback control needs to be added. The error is defined, and a proportional-integral feedback control law is designed to ensure exponential and stable decay of the error. Error feedback control can effectively compensate for any deviations between steady-state control and feedforward control, allowing the system to achieve the desired trajectory. Distribute the yaw moment to four wheels for execution; The allocated yaw moment control command is executed, as well as the front and rear wheel angle additional value commands, to achieve the desired vehicle yaw dynamic control.

2. A unified yaw motion control method for an automotive chassis domain based on a three-step method according to claim 1, characterized in that The specific method for calculating the yaw target is as follows: 11) Design the ideal sideslip angle β of the centroid * = 0; 12) Design the ideal yaw rate as follows: Calculate the front and rear tire slip angles for a distributed drive four-wheel steering vehicle as follows: where α f is the side slip angle of the front wheel tire; β is the side slip angle of the vehicle center of mass; γ is the vehicle yaw rate; l f is the distance from the front axle of the chassis to the vehicle center of mass; v x is the vehicle longitudinal speed; δ f is the front wheel steering angle; α r is the side slip angle of the rear wheel tire; l r is the distance from the rear axle of the vehicle to the vehicle center of mass; Combining formula (1) we can get: The above formula can be further written as: where l is the distance between the front and rear axles, l = l f + l r ; R is the distance from the vehicle's steering center to the center of mass, which is the vehicle's turning radius; The formula for the lateral and yaw motion of the vehicle in steady state is established as follows: where m is the vehicle mass; a y is the lateral acceleration of the vehicle; F yf is the lateral force of the front axle; F yr is the lateral force of the rear axle; I z is the moment of inertia of the vehicle about the vertical axis; is the yaw angular acceleration; Calculate the lateral forces on the front and rear axles as follows: where K f is the lateral stiffness of the front wheel; K r is the lateral stiffness of the rear wheel; Since in the steady state, the above equation can be written in the following form: Substituting formula (6) and formula (5) into formula (3), we can obtain: The above formula is written as: Where K is the stability factor of the car, namely: 13) Introduce the understeer factor K us , as follows: Therefore, transform formula (8) into: 14) Set the front wheel angles to the Ackermann steering angle and dynamic steering angle as shown below: δ sw,dyn = K us a y = Kla y ; (13) δ sw = δ sw,kin + δ sw,dyn ; (14) where δ sw,kin is the Ackermann steering angle; δ sw,dyn is the dynamic steering angle; δ sw is the actual front wheel steering angle; 15) Convert equation (11) to: 16) Set the reference yaw rate to: where γ * is the reference yaw rate; 17) The ideal yaw rate is constrained to be: Where μ is the road adhesion coefficient; g is the acceleration of gravity; 0.85 is the set safety factor; 18) Calculate the actual reference yaw rate as follows: Where s is the Laplace operator; τ1 is the appropriate first-order inertia link time constant; 19) Introduce the fitting function and add the nonlinear steering characteristic fitting curve to calculate the lateral acceleration, as shown below: In the formula, is the lateral acceleration limit value in the linear region; a y,MAX is the maximum achievable lateral acceleration; Calculate the dynamic front wheel angle as follows: The ideal yaw rate of the design is obtained as follows:

3. A unified yaw motion control method for an automotive chassis domain based on a three-step method according to claim 1, characterized in that, The acquisition of sensor, vehicle status, and road surface information includes acquiring transverse and longitudinal vehicle speeds, transverse and longitudinal accelerations, road surface adhesion coefficients, and tire longitudinal lateral forces.

4. A unified yaw motion control method for an automotive chassis domain based on a three-step method according to claim 2, characterized in that For the four-wheel steering distributed drive electric vehicle, a chassis domain yaw stability integrated control system based on a three-step method is designed, as follows: 41) The vehicle dynamics equations for the lateral and yaw motions of the vehicle are established as follows: In the formula, is the centroidal side slip angular velocity; is the yaw angular acceleration; ΔM z Additional yaw moment brought by differential drive; F yf And F yr are the lateral reaction forces of the ground on the front and rear axles where the front and rear wheels of the vehicle are located; m is the vehicle mass; I z is the yaw moment of inertia of the vehicle; 42) Define the relationship between the front and rear wheel steering angles; define the ratio ε of the rear wheel steering angle to the front wheel steering angle as: where δ f is the front wheel steering angle; δ r is the rear wheel steering angle; 43) Establish the ratio relationship between the lateral force of the front axle and the lateral force of the rear axle and the rear wheel steering angle and the front wheel steering angle, specifically as follows: where k F is the lateral force ratio coefficient between the front and rear axles; 44) Set the control quantity of the three-step method to F yr , ΔM z and F yf ; 45) Calculate the steady-state value according to the current measurement values of the vehicle, specifically as follows: Let the steady-state control input quantities be obtained from Eqs. (19) and (20), and denoted by u 1s , u 2s and u 3s as follows: Solve for the desired steady-state control input as follows: where, u 1s is the steady-state control input of F yr ; u 2s is the steady-state control input of ΔM z ; u 3s is the steady-state control input of F yf ; 46) Introduce the feedforward control of the reference dynamics, consider the transient response of the sideslip angle of the center of mass and the yaw rate, and set the control input conditions as follows: F yr = u 1s + u 1f ; ΔM z = u 2s + u 2f ; F yf = u 3s + u 3f ; where u 1f , u 2f , u 3f are feedforward control quantities; Substitute into formulas (19), (20) and (22), where u 1f , u 2f and u 3f are feedforward control quantities; Let The feedforward control input is solved as follows: 47) Introduce the tracking error feedback control and set the control input as follows: F yr = u 1s + u 1f + u 1e ; △M z = u 2s + u 2f + u 2e ; F yf = u 3s + u 3f + u 3e ; Substitute into formulas (19), (20) and (22), where u 1e 、u 2e and u 3e are feedback control quantities: Let the steady-state control and feedforward control inputs be u 1s , u 2s , u 3s and u 1f , u 2f and u 3f be expressed as follows: u 3e = k F u 1e ; (25) Define the tracking error as follows: e β = β * -β, e γ = γ * -γ; (26) where e β is the vehicle center-of-mass sideslip angle error; e γ is the vehicle yaw rate error; β * is the reference center-of-mass sideslip angle; γ * is the reference yaw rate; Then equations (23) and (24) become: Select a certain control error term, that is, the sideslip angle of the center of mass and the yaw rate error in equation (26), so that equations (27) and (28) become an e-exponential asymptotically stable situation; Simultaneously combine equation (27) and equation (28) with equation (25) and write it in the following form: Where K p1 is the proportional gain; K i1 is the integral gain; That is, the values of u 1e , u 2e and u 3e are obtained: 48) Set the control law of the three-step controller as follows: where, u is the control input; f s (β, γ) is the steady-state control term; is the feedforward control term; f e (e β , e γ ) is the error feedback control term; and there is: 49) On the basis of the three-step control law, by solving the lateral forces of the front and rear wheels, convert the yaw moment into the tire steering angle and additional moment output, specifically as follows: Before solving, analyze the resultant lateral force of the front and rear axles; The motion equations of the vehicle in three degrees of freedom are as follows: F x = (F x1 + F x2 ) cos δ f - (F y1 + F y2 ) sin δ f + (F x3 + F x4 ) cos δ r - (F y3 + F y4 ) sin δ r F y =(F x1 +F x2 )sinδ f +(F y1 +F y2 )cosδ f -(F x3 +F x4 )sinδ r +(F y3 +F y4 )cosδ r where F x is the total longitudinal force of the vehicle; F y is the total lateral force of the vehicle; F xi and F yi , i = 1, 2, 3, 4, are the longitudinal and lateral forces of the two front wheels and two rear wheels of the vehicle respectively; d is the wheelbase between the front and rear wheels; δ r is the rear wheel steering angle; Give the relationship between the four-wheel sideslip angles and the four-wheel steering angles as follows: In the formula, α1, α2, α3, and α4 are the tire sideslip angles of the four wheels respectively; Therefore, the lateral forces of the four-wheel tires are expressed as follows: The resultant lateral force of the front and rear axles is expressed as follows: Therefore, by inversely solving the above formula, the decision values of the front and rear wheel steering angles are obtained: where δ f_tmp is the calculated front wheel steering angle value; δ r_tmp is the calculated rear wheel steering angle value, and the nominal value of the front wheel steering angle δ sw_drv is obtained through the driver's steering wheel angle δ g and the steering system transmission ratio i f , while the nominal value of the rear wheel steering angle is constantly 0. Therefore, the final additional values of the front and rear wheel steering angles are obtained to complete the final control output as follows: Δδ r = δ r-tmp .

5. A unified yaw motion control device for an automotive chassis domain based on a three-step method, which is used to implement a unified yaw motion control method for an automotive chassis domain based on the three-step method according to any one of claims 1-4, characterized in that, Including: A unified yaw motion controller (110) for calculating the required yaw target; An environment analysis module (120) for uniformly obtaining sensor, vehicle state, and road surface information to achieve internal information resource sharing; A failure redundancy control module (130) for identifying the failures of software and hardware to ensure the safety of corresponding driving; A sub-function control module (140) for designing a yaw stability integrated control system for the chassis domain based on the three-step method for a four-wheel steering distributed drive electric vehicle; An output arbitration module (150) for distributing the additional yaw moment and distributing it to the four wheels for execution; An actuator (160) for executing the distributed yaw moment control instruction and executing the additional value command of the front and rear wheel steering angles to achieve the expected vehicle yaw dynamic control.

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