Variable instantaneous center control method for multi-wheel independent steering vehicle

Abstract

The invention discloses a variable instantaneous center control method for a multi-wheel independent steering vehicle. The variable instantaneous center control method comprises the steps that a vehicle Cartesian coordinate system, a vehicle polar coordinate system, a geodetic coordinate system, a tire slip angle coordinate system and a tire corner coordinate system are established; establishing a variable instantaneous center dynamical model of the multi-wheel independent steering vehicle, converting a model state into a sidesway and yawing motion state, and converting model input into sidesway and yawing motion input under instantaneous center control; and controlling all steering modes of the multi-wheel independent steering vehicle through the instantaneous center position change. According to the method, complex multi-wheel rotation angle control is simplified into two-dimensional input of instantaneous center coordinates, the system complexity is reduced, meanwhile, the geometric consistency of rotation angles of all tires is ensured, and motion interference is avoided; the control frame based on the instantaneous center supports smooth switching of various movement modes such as oblique movement, pivot steering and crabbing.

Description

Technical Field

[0001] The present invention belongs to the technical field of vehicle motion control, and particularly relates to a variable instantaneous center control method for a multi-wheel independent steering vehicle. Background Art

[0002] The mechanical constraints between wheels of a multi-wheel independent steering vehicle are cancelled, and multiple subsystems are highly integrated into an independent steering module, providing a new steering platform for intelligent driving. By coordinating the control of each independent steering module, various steering modes such as in the same direction and diagonal movement, reverse turning, etc. are realized, expanding the motion space of the multi-wheel independent steering vehicle.

[0003] In the existing motion control of multi-wheel independent steering, the Chinese patent application number is CN202411199796.8, and the name is "Steering System for Vehicles", which discloses a corner compensation scheme for a multi-wheel independent steering vehicle. Taking four-wheel independent steering as an example, assuming that an inappropriate steering occurs in a certain steering wheel, it is compensated by other steering wheels to achieve precise steering control. However, the control input of this technology is still the tire corner, that is, the lateral movement of the vehicle is achieved through corner control. However, for a multi-wheel independent steering vehicle, the corners of each wheel need to strictly satisfy the Ackermann steering geometry constraint, that is, the perpendicular lines of the corners of each wheel need to intersect at the same point at all times during steering and driving. The increase in the number of steering wheels will greatly increase the complexity of corner control, and it is difficult to achieve a reasonable distribution of the corners of each tire during lateral movement.

[0004] The Chinese patent application number is CN202410002004.7, and the name is "A Path Tracking Control Method and Device for a Four-Wheel Independent Steering Vehicle", which discloses a path tracking control method for a four-wheel independent steering vehicle. The upper controller calculates the steering radius based on the kinematic model, and the lower controller combines the dynamic model with uncertainties, converts the steering angle control target into a coupling constraint and outputs the torque. This method solves the problems of path tracking performance degradation and tire wear caused by steering dynamics uncertainty and inconsistency, and at the same time ensures that the control process meets the constraint conditions. However, its control method does not fully utilize the advantage of multiple steering modes, resulting in limited flexibility and adaptability of the vehicle in complex scenarios, and the potential of the multi-wheel independent steering system is not fully exerted. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a variable instantaneous center control method for a multi-wheel independent steering vehicle to solve the problems that it is difficult to distribute the corners of a multi-wheel independent steering vehicle due to geometric constraints and the advantages of multiple steering modes cannot be utilized in the existing technology.

[0006] To achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0007] A variable instantaneous center control method for a multi-wheel independent steering vehicle according to the present invention comprises the following steps:

[0008] 1) Establish a vehicle Cartesian coordinate system, a vehicle polar coordinate system, a geodetic coordinate system, a tire slip angle coordinate system, and a tire steering angle coordinate system;

[0009] 2) Establish a variable instantaneous center dynamics model for a multi-wheel independent steering vehicle, and convert the model state into a side shift and yaw motion state, and convert the model input into a side shift and yaw motion input under instantaneous center control;

[0010] 3) Control all steering modes of the multi-wheel independent steering vehicle by changing the instantaneous center position.

[0011] Further, the step 1) specifically includes:

[0012] 11) The vehicle polar coordinate system βoρ is established as follows: taking the vehicle center of mass o as the pole, on the right side of the vehicle longitudinal axis, the straight line passing through the center of mass and perpendicular to the vehicle longitudinal axis as the polar axis, the distance from the center of mass to the instantaneous center as the polar radius R, also known as the steering radius, taking its reciprocal ρ = 1 / R, called the steering curvature, and the angle between the polar axis and the polar radius as the polar angle β, also known as the center of mass side slip angle;

[0013] 12) The geodetic coordinate system XOY is used to describe the position of the center of mass of the multi-wheel independent steering vehicle in the environment;

[0014] 13) The vehicle Cartesian coordinate system xoy is established as follows: taking the vehicle center of mass o as the origin, the vehicle longitudinal axis as the x-axis, the vehicle forward direction as the positive direction of the x-axis, and rotating the x-axis counterclockwise by 90 degrees around the center of mass o to obtain the y-axis;

[0015] 14) The tire slip angle coordinate system O tire x tire is established as follows: taking the tire contact center O tire as the pole, the tire longitudinal center line x tire as the polar axis, the tire rolling direction as the positive direction of the x tire axis, and the angle between it and the actual tire rolling direction as the tire slip angle α;

[0016] 15) The tire steering angle coordinate system O tire x δ is established as follows: taking the tire contact center O tire as the pole, the x δ axis passing through the tire contact center and parallel to the x-axis as the polar axis, the forward direction of the multi-wheel independent steering vehicle as the positive direction of the x δ axis, and the angle between it and the x tire as the tire steering angle x δ .

[0017] Furthermore, the instant center is defined as follows: the common intersection point of the perpendicular lines of all wheel angles during the driving process of a multi-wheel independent steering vehicle. When turning, the instant center is located in a bounded space, and when driving straight, the instant center is located at infinity.

[0018] Furthermore, in step 1), the angles in each coordinate system are defined with the clockwise direction being positive and the counterclockwise direction being negative.

[0019] Furthermore, all steering tires of the multi-wheel independent steering vehicle are arranged under the same chassis.

[0020] Furthermore, the establishment and conversion steps of the variable instant center dynamics model of the multi-wheel independent steering vehicle in step 2) are as follows:

[0021] 21) Through Newton's second law, perform a force analysis on the multi-wheel independent steering vehicle, ignoring the change in the longitudinal velocity of the center of mass, and the longitudinal force of the tire is zero; in the vehicle Cartesian coordinate system, the following formula can be obtained:

[0022]

[0023] In the formula, m, v y , v x , r respectively represent the mass of the multi-wheel independent steering vehicle, the lateral velocity of the center of mass, the longitudinal velocity of the center of mass, and the yaw angular velocity around the center of mass; F yi represents the lateral force of the i-th tire, l i represents the abscissa of the i-th tire in the vehicle Cartesian coordinate system, I z represents the yaw moment of inertia of the multi-wheel independent steering vehicle; i = 2, 3, 4,..., n represents the number of tires of the multi-wheel independent steering vehicle;

[0024] The calculation formula of the tire lateral force adopts a simplified magic tire formula, which is expressed as follows:

[0025] F yi = μF zi sin(DarctanBα i ) (2)

[0026] In the formula, μ represents the road surface adhesion coefficient, B and D are coefficients to be fitted, F zi represents the vertical load of the i-th tire, α i represents the side slip angle of the i-th tire, which is expressed as follows:

[0027]

[0028] In the formula, δ i represents the angle of the i-th tire, d i represents the ordinate of the i-th tire in the vehicle Cartesian coordinate system;

[0029] 22) The specific process of converting the model state into the lateral displacement and yaw motion states is as follows:

[0030] Define the sideslip angle of the vehicle's center of mass as follows:

[0031]

[0032] Equation (4) is used to describe the lateral displacement motion state of a multi-wheel independent steering vehicle;

[0033] Define the steering curvature of the vehicle as follows:

[0034]

[0035] Equation (5) is used to describe the yaw motion state of a multi-wheel independent steering vehicle;

[0036] Take the first derivative of Equations (4) and (5), and then substitute them into Equation (1) to obtain:

[0037]

[0038] Substitute Equations (4) and (5) into (3) to obtain:

[0039]

[0040] 23) The specific process of converting the model input into the lateral displacement and yaw motion inputs is as follows:

[0041] Let the coordinates of the instantaneous center in the vehicle Cartesian coordinate system be (x s , y s ), then its coordinates in the vehicle polar coordinate system are (β s , ρ s ), and the following relationship exists between them:

[0042]

[0043] The coordinates of the grounding center of the i-th tire in the vehicle Cartesian coordinate system are:

[0044] (x i , y i ) = (l i , d i ) (9)

[0045] The slope of the line where the instantaneous center and the grounding center of the tire are located satisfies the following relationship:

[0046] tanδ i *k i = —1 (10)

[0047] In the formula, k iis the slope of the straight line where the instantaneous center and the grounding center of the i-th tire are located, and it satisfies the following straight line equation:

[0048] (x i -x s ) + tanδ i (y i -y s ) = 0 (11)

[0049] Substituting equations (8) and (9) into (11), the relationship between the steering angle of the i-th tire and the position of the instantaneous center is as follows:

[0050]

[0051] Substituting equation (12) into (7) can convert the steering angle input (δ fl , δ fr , δ rl , δ rr ) into the instantaneous center coordinate input (β s , ρ s );

[0052] The dynamic model of a multi-wheel independent steering vehicle with a variable instantaneous center is established, which is jointly composed of equations (2), (6), (7) and (12). Its state is the vehicle's center of mass sideslip angle β and steering curvature ρ, and the inputs are the sideslip motion β s and the yaw motion ρ s .

[0053] Furthermore, the first coordinate β s of the instantaneous center controls the sideslip motion of the vehicle, and the second coordinate ρ s of the instantaneous center controls the yaw motion of the vehicle.

[0054] Furthermore, the sideslip motion is as follows: the magnitudes and directions of the steering angles of all wheels of the multi-wheel independent steering vehicle are the same.

[0055] Furthermore, the yaw motion is as follows: taking the vehicle's transverse axis passing through the center of mass as the dividing line, the vehicle is divided into front and rear regions. The steering angles of the wheels in the front region of the vehicle are opposite to those in the rear region of the vehicle, the steering angles of the vehicles on the dividing line are zero, and the line connecting the center of mass and the instantaneous center is always perpendicular to the vehicle's longitudinal axis.

[0056] Furthermore, the specific method of controlling all motion modes of the multi-wheel independent steering vehicle by changing the position of the instantaneous center in step 3) is as follows:

[0057] 31) Keeping the second component ρ s of the instantaneous center coordinate unchanged and only changing the first component β s of the instantaneous center coordinate, at this time the yaw motion input remains unchanged, and only the sideslip motion is used to control the motion of the multi-wheel independent steering vehicle;

[0058] 32) Keep the first component β of the instantaneous center coordinate s unchanged and only change the second component ρ of the instantaneous center coordinate s . At this time, the lateral movement input remains unchanged, and the multi-wheel independent steering vehicle movement is controlled only through the yaw movement;

[0059] 33) The first component β and the second component ρ of the instantaneous center coordinate s change together. At this time, the multi-wheel independent steering vehicle movement is controlled by coordinating the lateral movement and the yaw movement. s

[0060] Furthermore, all movement modes of the multi-wheel independent steering vehicle include: single-axis fixed steering, same-direction steering, reverse steering, and in-place steering. All movement modes are composed of the lateral movement and the yaw movement controlled by the instantaneous center, and the instantaneous center position determines the movement mode.

[0061] Furthermore, the single-axis fixed steering movement mode is: the steering angle of the tires on a certain axis is always zero. At this time, the instantaneous center position is on the single-axis fixed steering line, that is, the line connecting the instantaneous center position and the grounding center position of the tires on this axis is perpendicular to the longitudinal axis of the vehicle.

[0062] Furthermore, the same-direction steering movement mode is: all tire angles turn in the same direction. At this time, the instantaneous center position is in the same-direction steering area, that is, outside the range surrounded by the first axis and the last axis.

[0063] Furthermore, the reverse steering movement mode is: there are tire angles with directions opposite to those of other tire angles. At this time, the instantaneous center position is in the reverse steering area, that is, inside the range surrounded by the first axis and the last axis.

[0064] Furthermore, the in-place steering movement mode is: the intersection point of the perpendicular lines of all tire angles coincides with the center of mass, and the instantaneous center position is at the in-place steering point, that is, the instantaneous center coincides with the center of mass.

[0065] Advantages of the present invention:

[0066] The present invention defines two most basic movement modes of the multi-wheel independent steering vehicle: lateral movement and yaw movement. Combinations of different proportions of lateral movement and yaw movement can achieve all steering modes of the multi-wheel independent steering vehicle. On this basis, the control quantities of multiple tire angles are decoupled into instantaneous center coordinate input quantities, and the lateral movement and yaw movement of the multi-wheel independent steering vehicle are controlled respectively through the two components of the instantaneous center coordinate, thereby indirectly coordinating the control of the lateral movement of the multi-wheel independent steering vehicle for all steering modes;

[0067] ​The method of the present invention simplifies the complex multi-round corner control into a two-dimensional input of the instantaneous center coordinates, reduces the complexity of the control of a multi-wheel independent steering vehicle, and at the same time ensures the geometric consistency of the corner angles of each tire to avoid motion interference; the control framework based on the instantaneous center supports smooth switching between various motion modes such as side shift, in-place steering, and crab walking. Description of the Drawings

[0068] Figure 1 is the schematic diagram of the method of the present invention;

[0069] Figure 2 is the analysis diagram of the vehicle and coordinate system of the present invention;

[0070] Figure 3 is the schematic diagram of the vehicle side shift motion in the present invention;

[0071] Figure 4 is the schematic diagram of the vehicle yaw motion in the present invention;

[0072] Figure 5a is the schematic diagram of the vehicle co-directional steering motion mode in the present invention;

[0073] Figure 5b is the schematic diagram of the vehicle reverse steering motion mode in the present invention;

[0074] Figure 5c is the schematic diagram of the vehicle single-axis fixed steering motion mode in the present invention;

[0075] Figure 5d is the schematic diagram of the vehicle in-place steering motion mode in the present invention;

[0076] Figure 6 is the schematic diagram of all steering modes of the vehicle and the instantaneous center position in the present invention. Detailed Embodiment

[0077] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with the embodiments and the drawings. The content mentioned in the embodiments does not limit the present invention.

[0078] Refer to Figure 1 、 Figure 2 As shown, a variable instantaneous center control method for a multi-wheel independent steering vehicle of the present invention comprises the following steps:

[0079] 1) Establish a vehicle Cartesian coordinate system, a vehicle polar coordinate system, a geodetic coordinate system, a tire slip angle coordinate system, and a tire corner coordinate system; the specific steps of step 1) include:

[0080] 11) The steps to establish the vehicle polar coordinate system βop are as follows: Taking the vehicle center of mass o as the pole, on the right side of the vehicle longitudinal axis, the straight line passing through the center of mass and perpendicular to the vehicle longitudinal axis is the polar axis, the distance from the center of mass to the instantaneous center is the polar radius R, also known as the turning radius. Taking its reciprocal ρ = 1 / R, which is called the turning curvature, and the angle between the polar axis and the polar radius is the polar angle β, also known as the center of mass side slip angle;

[0081] 12) The earth coordinate system XOY is used to describe the position of the center of mass of the multi-wheel independent steering vehicle in the environment;

[0082] 13) The steps to establish the vehicle Cartesian coordinate system xoy are as follows: Taking the vehicle center of mass o as the origin, the vehicle longitudinal axis as the x-axis, the vehicle forward direction as the positive direction of the x-axis, and rotating the x-axis counterclockwise by 90 degrees around the center of mass o to obtain the y-axis;

[0083] 14) Tire side slip angle coordinate system O tire x tire The steps to establish it are as follows: Taking the tire ground contact center O tire as the pole, the longitudinal center line x tire of the tire as the polar axis, the tire rolling direction as the positive direction of the x tire axis, and the angle between it and the actual rolling direction of the tire is the tire side slip angle α;

[0084] 15) Tire steering angle coordinate system O tire x δ The steps to establish it are as follows: Taking the tire ground contact center O tire as the pole, the x δ axis passing through the tire ground contact center and parallel to the x-axis as the polar axis, the forward direction of the multi-wheel independent steering vehicle as the positive direction of the x δ axis, and the angle between it and the x tire is the tire steering angle δ.

[0085] Among them, all wheels of the multi-wheel independent steering vehicle can be independently steered, and are located under the same chassis. The number of steering wheels is at least 2, and the multi-wheel independent steering vehicle needs to always satisfy the steering geometric constraint during driving, that is, the perpendicular lines of all wheel steering angles need to intersect at the same point at all times.

[0086] The instantaneous center is defined as follows: The common intersection point of the perpendicular lines of all wheel steering angles of the multi-wheel independent steering vehicle during driving. When turning, the instantaneous center is located in a bounded space, and when driving straight, the instantaneous center is located at infinity.

[0087] Among them, in step 1), the angles in each coordinate system are defined as positive in the clockwise direction and negative in the counterclockwise direction.

[0088] Among them, all steering tires of the multi-wheel independent steering vehicle are arranged under the same chassis.

[0089] 2) Establish a variable instantaneous center dynamics model for a multi-wheel independent steering vehicle, and convert the model state into side-slip and yaw motion states, and convert the model input into side-slip and yaw motion inputs under instantaneous center control;

[0090] Specifically, the steps for establishing and converting the variable instantaneous center dynamics model of the multi-wheel independent steering vehicle in step 2) are as follows:

[0091] 21) Through Newton's second law, perform a force analysis on the multi-wheel independent steering vehicle, ignoring the change in the longitudinal velocity of the center of mass and setting the longitudinal tire force to zero; in the vehicle Cartesian coordinate system, the following formula can be obtained:

[0092]

[0093] In the formula, m, v y , v x , r respectively represent the mass, lateral velocity of the center of mass, longitudinal velocity of the center of mass, and yaw angular velocity about the center of mass of the multi-wheel independent steering vehicle; F yi represents the lateral force of the i-th tire, l i represents the abscissa of the i-th tire in the vehicle Cartesian coordinate system, I z represents the yaw moment of inertia of the multi-wheel independent steering vehicle; i = 1, 2, 3,..., n represents the number of tires of the multi-wheel independent steering vehicle;

[0094] The calculation formula for the tire lateral force adopts a simplified magic tire formula, expressed as follows:

[0095] F yi = μF zi sin(DarctanBα i ) (2)

[0096] In the formula, μ represents the road surface adhesion coefficient, B and D are coefficients to be fitted, F zi represents the vertical load of the i-th tire, α i represents the side slip angle of the i-th tire, expressed as follows:

[0097]

[0098] In the formula, δ i represents the rotation angle of the i-th tire, d i represents the ordinate of the i-th tire in the vehicle Cartesian coordinate system;

[0099] 22) The specific process of converting the model state into side-slip and yaw motion states is as follows:

[0100] Define the vehicle center of mass side slip angle as follows:

[0101]

[0102] Equation (4) is used to describe the side-slip motion state of a multi-wheel independent steering vehicle;

[0103] Define the vehicle steering curvature as follows:

[0104]

[0105] Equation (5) is used to describe the yaw motion state of a multi-wheel independent steering vehicle;

[0106] Take the first derivative of Equations (4) and (5), and then substitute them into Equation (1) to obtain:

[0107]

[0108] Substitute Equations (4) and (5) into (3) to obtain:

[0109]

[0110] 23) The specific process of converting the model input into side-slip and yaw motion inputs is as follows:

[0111] Let the coordinates of the instantaneous center in the vehicle Cartesian coordinate system be (x s , y s ), then its coordinates in the vehicle polar coordinate system are (β s , ρ s ), and the following relationship exists between the two:

[0112]

[0113] The coordinates of the grounding center of the i-th tire in the vehicle Cartesian coordinate system are:

[0114] (x i , y i ) = (l i , d i ) (9)

[0115] The slope of the straight line where the instantaneous center and the grounding center of the tire are located satisfies the following relationship:

[0116] tanδ i *k i = -1 (10)

[0117] In the formula, k i is the slope of the straight line where the instantaneous center and the grounding center of the i-th tire are located, and it satisfies the following straight line equation:

[0118] (x i - x s ) + tanδ i (y i - y s) = 0 (11)

[0119] Substituting equations (8) and (9) into (11), the relationship between the steering angle of the \(i\)-th tire and the instantaneous center position is as follows:

[0120]

[0121] Substituting equation (12) into (7) can convert the steering angle input (\(\delta\) fl , \(\delta\) fr , \(\delta\) rl , \(\delta\) rr ) into the instantaneous center coordinate input (\(\beta\) s , \(\rho\) s );

[0122] The dynamic model of a multi-wheel independent steering vehicle with a variable instantaneous center is established, which consists of equations (2), (6), (7), and (12). Its states are the vehicle's sideslip angle \(\beta\) and steering curvature \(\rho\), and the inputs are the sideslip motion \(\beta\) s and yaw motion \(\rho\) s .

[0123] Among them, the first coordinate \(\beta\) of the instantaneous center s controls the sideslip motion of the vehicle, and the second coordinate \(\rho\) of the instantaneous center s controls the yaw motion of the vehicle.

[0124] Among them, the sideslip motion is that the magnitudes and directions of the steering angles of all wheels of the multi-wheel independent steering vehicle are the same.

[0125] Among them, the yaw motion is that the vehicle is divided into front and rear regions with the vehicle's transverse axis passing through the center of mass as the dividing line. The steering angles of the wheels in the front region of the vehicle are opposite to those in the rear region, the steering angle of the vehicle on the dividing line is zero, and the line connecting the center of mass and the instantaneous center is always perpendicular to the vehicle's longitudinal axis.

[0126] 3) Control all steering modes of the multi-wheel independent steering vehicle by changing the instantaneous center position;

[0127] Specifically, controlling all motion modes of the multi-wheel independent steering vehicle by changing the instantaneous center position in step 3) is as follows:

[0128] 31) Keep the second component \(\rho\) of the instantaneous center coordinate s unchanged and only change the first component \(\beta\) of the instantaneous center coordinate s . At this time, the yaw motion input remains unchanged, and the motion of the multi-wheel independent steering vehicle is controlled only through the sideslip motion;

[0129] 32) Keep the first component \(\beta\) of the instantaneous center coordinate s unchanged and only change the second component \(\rho\) of the instantaneous center coordinate s, at this time, the lateral movement input remains unchanged, and only the yaw movement is used to control the movement of the multi-wheel independent steering vehicle;

[0130] 33) The first component β of the instantaneous center coordinate s and the second component ρ s change together. At this time, the movement of the multi-wheel independent steering vehicle is controlled by coordinating the lateral movement and the yaw movement.

[0131] Such as Figure 5a - Figure 5d , Figure 6 As shown, all the motion modes of the multi-wheel independent steering vehicle include: single-axis fixed steering, same-direction steering, reverse steering, and in-place steering. All the motion modes are composed of the lateral movement and the yaw movement controlled by the instantaneous center. The instantaneous center position determines the motion mode. Refer to Figure 6 as shown;

[0132] The single-axis fixed steering motion mode is: the steering angle of the tires of a certain axis is always zero. At this time, the instantaneous center position is on the single-axis fixed steering line, that is, the line connecting the instantaneous center position and the grounding center position of the tires of this axis is perpendicular to the longitudinal axis of the vehicle.

[0133] The same-direction steering motion mode is: all the tire angles turn in the same direction. At this time, the instantaneous center position is in the same-direction steering area, that is, outside the range enclosed by the first axis and the last axis.

[0134] The reverse steering motion mode is: there are tire angles with directions opposite to those of other tire angles. At this time, the instantaneous center position is in the reverse steering area, that is, inside the range enclosed by the first axis and the last axis.

[0135] The in-place steering motion mode is: the intersection of the perpendicular lines of all the tire angles coincides with the center of mass. The instantaneous center position is at the in-place steering point, that is, the instantaneous center coincides with the center of mass.

[0136] Such as Figure 3 as shown, the lateral movement is defined as follows: the magnitudes and directions of all the wheel angles of the multi-wheel independent steering vehicle are the same.

[0137] Such as Figure 4 as shown, the yaw movement is defined as follows: taking the transverse axis of the vehicle passing through the center of mass as the dividing line, the vehicle is divided into the front and rear areas. The wheel angles in the front area of the vehicle are in the opposite direction to the vehicle angles in the rear area of the vehicle. The vehicle angles on the dividing line are zero, and the line connecting the center of mass and the instantaneous center is always perpendicular to the longitudinal axis of the vehicle.

[0138] The specific application ways of the present invention are numerous. The above-mentioned are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements can still be made, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A multi-wheel independent steering vehicle variable instantaneous center control method, characterized in that, The steps are as follows: 1) Establish a vehicle Cartesian coordinate system, a vehicle polar coordinate system, a geodetic coordinate system, a tire slip angle coordinate system, and a tire steering angle coordinate system; 2) Establish a variable instantaneous center dynamics model for a multi-wheel independent steering vehicle, and convert the model state into a side slip and yaw motion state, and convert the model input into a side slip and yaw motion input under instantaneous center control; 3) Control all steering modes of a multi-wheel independent steering vehicle by changing the position of the instantaneous center.

2. The multi-wheel independent steering vehicle variable instantaneous center control method according to claim 1, characterized in that The specific content of step 1) includes: 11) The establishment steps of the vehicle polar coordinate system βoρ are as follows: Taking the vehicle center of mass o as the pole, on the right side of the vehicle longitudinal axis, the straight line passing through the center of mass and perpendicular to the vehicle longitudinal axis is the polar axis, and the distance from the center of mass to the instantaneous center is the polar radius R, also known as the turning radius. Taking its reciprocal ρ = 1 / R, which is called the turning curvature, and the angle between the polar axis and the polar radius is the polar angle β, also known as the center of mass side slip angle; 12) The geodetic coordinate system XOY is used to describe the position of the center of mass of a multi-wheel independent steering vehicle in the environment; 13) The establishment steps of the vehicle Cartesian coordinate system xoy are as follows: Taking the vehicle center of mass o as the origin, the vehicle longitudinal axis as the x-axis, and the vehicle forward direction as the positive direction of the x-axis, and rotating the x-axis counterclockwise by 90 degrees around the center of mass o to obtain the y-axis; 14) Tire slip angle coordinate system O tire x tir The establishment steps are as follows: Taking the tire contact center O tir e as the pole, the longitudinal center line x of the tire tire as the polar axis, the tire rolling direction is the positive direction of the x tire axis, and the angle between it and the actual rolling direction of the tire is the tire slip angle α; 15) Tire rotation angle coordinate system O tire x δ The establishment steps are as follows: Taking the tire ground contact center O tire as the pole, the x δ axis passing through the tire ground contact center and parallel to the x-axis as the polar axis, and the forward direction of the multi-wheel independent steering vehicle as the positive direction of the x δ axis, and the included angle between it and the x tire axis is the tire rotation angle δ.

3. The multi-wheel independent steering vehicle transient center control method according to claim 1, characterized in that The instantaneous center is defined as follows: The common intersection point of the perpendicular lines of all wheel steering angles during the driving process of a multi-wheel independent steering vehicle. When turning, the instantaneous center is located in a bounded space, and when driving straight, the instantaneous center is located at infinity.

4. The multi-wheel independent steering vehicle variable instantaneous center control method according to claim 1, characterized in that In step 1), the angles in each coordinate system are defined as positive in the clockwise direction and negative in the counterclockwise direction; All steering tires of the multi-wheel independent steering vehicle are arranged under the same chassis.

5. The multi-wheel independent steering vehicle variable instantaneous center control method according to claim 1, characterized in that The establishment and conversion steps of the variable instantaneous center dynamics model of the multi-wheel independent steering vehicle in step 2) are as follows: 21) Through Newton's second law, perform a force analysis on the multi-wheel independent steering vehicle, ignoring the change in the longitudinal speed of the center of mass and assuming the longitudinal force of the tire is zero; in the vehicle Cartesian coordinate system, the following formula is obtained: where m, v y , v x , r respectively represent the mass, the lateral velocity of the center of mass, the longitudinal velocity of the center of mass and the yaw angular velocity about the center of mass of the multi-wheel independent steering vehicle; F yi represents the lateral force of the i-th tire, l i represents the abscissa of the i-th tire in the vehicle Cartesian coordinate system, I z represents the yaw moment of inertia of the multi-wheel independent steering vehicle; i = 1, 2, 3, …, n represents the number of tires of the multi-wheel independent steering vehicle; The calculation formula for the tire side force adopts a simplified magic tire formula, which is expressed as follows: F yi = μF zi sin(Darctan Bα i ) (2) where μ represents the road surface adhesion coefficient, B and D are coefficients to be fitted, and F zi represents the vertical load of the i-th tire, and α i represents the sideslip angle of the i-th tire, which is expressed as follows: where δ i represents the steering angle of the i-th tire, and d i represents the ordinate of the i-th tire in the vehicle Cartesian coordinate system; 22) The specific process of converting the model state into a side slip and yaw motion state is as follows: Define the center of mass side slip angle of the vehicle as follows: Equation (4) is used to describe the side slip motion state of a multi-wheel independent steering vehicle; Define the vehicle turning curvature as follows: Equation (5) is used to describe the yaw motion state of a multi-wheel independent steering vehicle; Taking the first derivative of equations (4) and (5) and then substituting them into equation (1) gives: Substituting equations (4) and (5) into (3) gives: 23) The specific process of converting the model input into a side slip and yaw motion input is as follows: Let the coordinates of the instantaneous center in the vehicle Cartesian coordinate system be (x s , y s ). Then its coordinates in the vehicle polar coordinate system are (β s , ρ s ), and the relationship between them is as follows: The coordinates of the grounding center of the i-th tire in the vehicle Cartesian coordinate system are: (x i , y i ) = (l i , d i ) (9) The slope of the straight line connecting the instantaneous center and the grounding center of the tire satisfies the following relationship: tanδ i *k i = -1 (10) where k i is the slope of the line passing through the instantaneous center and the grounding center of the i-th tire, and it satisfies the following linear equation: (x i -x s ) + tanδ i (y i -y s ) = 0 (11) Substituting equations (8) and (9) into (11) gives the relationship between the steering angle of the i-th tire and the position of the instantaneous center as follows: Substituting Equation (12) into (7) can convert the corner input (δ fl , δ fr , δ rl , δ rr ) into the instantaneous center coordinate input (β s , ρ s ); The establishment of the variable instantaneous center dynamics model of a multi-wheel independent steering vehicle is completed, which is jointly composed of equations (2), (6), (7) and (12). Its states are the sideslip angle β and the steering curvature ρ of the vehicle's center of mass, and the inputs are the side movement β s and the yaw movement ρ s .

6. The multi-wheel independent steering vehicle variable instantaneous center control method according to claim 1, characterized in that, The first coordinate β of the instantaneous center s controls the lateral movement of the vehicle, and the second coordinate ρ of the instantaneous center s controls the yaw movement of the vehicle.

7. The multi-wheel independent steering vehicle variable instantaneous center control method according to claim 6, characterized in that, The side slip motion is that the magnitudes and directions of the steering angles of all wheels of a multi-wheel independent steering vehicle are the same.

8. The multi-wheel independent steering vehicle variable instantaneous center control method according to claim 6, characterized in that The yaw motion is that with the vehicle transverse axis passing through the center of mass as the dividing line, the vehicle is divided into front and rear regions. The steering angles of the wheels in the front region of the vehicle are opposite to the steering angles of the wheels in the rear region of the vehicle. The steering angle of the vehicle on the dividing line is zero, and the line connecting the center of mass and the instantaneous center is always perpendicular to the vehicle longitudinal axis.

9. The method for controlling the variable instantaneous center of a multi-wheel independently steerable vehicle according to claim 1, characterized in that, The control of all motion modes of the multi-wheel independent steering vehicle by the change of the instantaneous center position in step 3) is specifically as follows: 31) Keep the second component ρ of the instantaneous center coordinate s unchanged and only change the first component β of the instantaneous center coordinate s At this time, the yaw motion input remains unchanged, and the motion of the multi-wheel independent steering vehicle is controlled only through the lateral shift motion; 32) Keep the first component β of the instantaneous center coordinate unchanged s and only change the second component ρ of the instantaneous center coordinate s At this time, the side shift motion input remains unchanged, and the multi-wheel independent steering vehicle motion is controlled only through the yaw motion; 33) The first component β of the instant center coordinate s and the second component ρ s vary together. At this time, the movement of the multi-wheel independent steering vehicle is controlled through the coordinated side shift movement and yaw movement.

10. The multi-wheel independent steering vehicle variable instantaneous center control method according to claim 9, characterized in that, All motion modes of the multi-wheel independent steering vehicle include: single-axis fixed steering, same-direction steering, reverse steering, and in-place steering. All motion modes are composed of the lateral shift and yaw motion controlled by the instantaneous center. The instantaneous center position determines the motion mode; The single-axis fixed steering motion mode is: the steering angle of the tires on a certain axis is always zero. At this time, the instantaneous center position is on the single-axis fixed steering line, that is, the line connecting the instantaneous center position and the ground contact center position of the tires on this axis is perpendicular to the longitudinal axis of the vehicle; The same-direction steering motion mode is: the steering angles of all tires turn in the same direction. At this time, the instantaneous center position is in the same-direction steering area, that is, outside the range enclosed by the first axis and the last axis; The reverse steering motion mode is: there is a tire whose steering angle is opposite to that of other tires. At this time, the instantaneous center position is in the reverse steering area, that is, inside the range enclosed by the first axis and the last axis; The in-place steering motion mode is: the intersection point of the perpendiculars of the steering angles of all tires coincides with the center of mass. The instantaneous center position is at the in-place steering point, that is, the instantaneous center coincides with the center of mass.

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