A redundant control method for vehicle steer-by-wire

Abstract

The present invention discloses a vehicle steer-by-wire redundant control method, belonging to the technical field of automobile steering. The method comprises: determining whether redundant control is currently activated for the vehicle; when redundant control is activated to achieve vehicle steering, the wheels enter differential steering mode one; and simultaneously determining whether the vehicle steering angle is consistent with the desired vehicle steering angle. If so, the wheels maintain differential steering mode one; if not, determining whether the current vehicle steering angle has changed; if not, the wheels enter differential steering mode two; if so, the wheels enter differential steering mode three; when the wheels enter differential steering mode one, two, or three, a fuzzy sliding mode controller and a lower-level controller are used to output the optimal left and right front wheel driving forces in the corresponding steering mode according to the desired vehicle steering angle. The present invention enables the vehicle to steer smoothly when the steer-by-wire system fails or when a key component within the steering system malfunctions.

Description

Technical Field

[0001] The present invention belongs to the technical field of automobile steering, and in particular relates to a vehicle wire-controlled steering redundant control method. Background Art

[0002] With the advancement of intelligent and electrified vehicles, steer-by-wire technology plays a vital role in promoting the development of autonomous driving and the electrification of vehicles. However, due to the lack of a mechanical connection, if steer-by-wire fails, the vehicle loses its steering function, which can easily lead to accidents. To ensure the reliability and safety of steer-by-wire systems, increasing steering redundancy is crucial.

[0003] Existing redundancy technologies can be roughly divided into two categories: one is hardware backup redundancy technology, and the other is algorithm fault tolerance technology. Hardware backup provides backup for important components and components prone to failure. This method increases the size and quality of the system, and also increases costs; algorithm fault tolerance mainly relies on the controller's fault-tolerant algorithm to improve the redundancy of the entire system. When a steering system failure occurs, the remaining steering system devices that are working normally are controlled. However, when a key component of the steering system, such as the steering motor, fails, normal steering of the car cannot be guaranteed. Summary of the Invention

[0004] The present invention addresses the deficiencies in the prior art and provides a vehicle steer-by-wire redundant control method, which enables the vehicle to steer smoothly when the steer-by-wire system fails or a key component in the steering system malfunctions.

[0005] The present invention provides the following technical solutions:

[0006] A redundant control method for steer-by-wire vehicle driving via wheel hub motors includes:

[0007] Based on the current vehicle state, determine whether the current vehicle meets the conditions for starting redundant control; if so, start redundant control to achieve vehicle steering; if not, the vehicle steers normally;

[0008] When redundant control is activated to achieve vehicle steering, the wheels enter differential steering mode one and simultaneously determine whether the vehicle steering angle is consistent with the desired vehicle steering angle. If so, the wheels maintain differential steering mode one. If not, it is determined whether the current vehicle steering angle has changed. If not, the wheels enter differential steering mode two. If so, the wheels enter differential steering mode three. The differential steering mode one utilizes the rolling of the left and right front wheels to achieve vehicle differential steering; the differential steering mode two utilizes the sliding of the left and right front wheels to achieve vehicle differential steering; and the differential steering mode three utilizes the sliding and rolling of the left and right front wheels to achieve vehicle differential steering.

[0009] When the wheels enter differential steering mode one, two or three, the fuzzy sliding mode controller and the lower-level controller output the optimal left and right front wheel driving forces in the corresponding steering mode according to the desired vehicle turning angle.

[0010] Optionally, when the wheels enter differential steering mode one, two, or three, the fuzzy sliding mode controller and the lower-layer controller are used to output the optimal left front wheel driving force and right front wheel driving force in the corresponding steering mode according to the desired vehicle turning angle. The process is as follows:

[0011] Construct a two-degree-of-freedom vehicle differential model and calculate the desired vehicle turning angle δ fd , get the vehicle's desired yaw rate ω d and the desired sideslip angle β d ;

[0012] The fuzzy sliding mode controller is based on the desired vehicle steering angle δ fd , desired yaw rate ω d , expected center of mass sideslip angle β d , the actual vehicle yaw rate ω and the actual center of mass sideslip angle β, output the desired vehicle turning angle δ fd Required resultant moment M d , longitudinal total expected driving force F xd and the total expected lateral driving force F yd ;

[0013] The lower controller outputs the left front wheel driving force and the right front wheel driving force that meet the optimal objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheel.

[0014] Optionally, the lower controller outputs the left front wheel driving force and the right front wheel driving force that meet the optimal objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheel.

[0015] The objective function is:

[0016]

[0017] Where J is the tire load rate, μ is the road adhesion coefficient, F xij is the longitudinal driving force of tire ij, F yij is the lateral driving force of tire ij, F zij is the vertical load force of tire ij, i=f,r; j=l,r, where ij=fl represents the left front wheel, ij=fr represents the right front wheel, ij=rl represents the left rear wheel, and ij=rr represents the right rear wheel.

[0018] Optionally, the lower controller outputs the left front wheel driving force and the right front wheel driving force that meet the optimal objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheel.

[0019] The constraints of differential steering mode 1 are:

[0020]

[0021] Among them, F xfl and F yfl are the longitudinal and lateral driving forces of the left front wheel, respectively, and F xfr and F yfr are the longitudinal and lateral driving forces of the right front wheel, respectively, and F xrl and F yrl are the longitudinal and lateral driving forces of the left rear wheel, respectively, and F xrr and F yrr are the longitudinal and lateral driving forces of the right rear wheel, ΔM is the driving torque difference between the left and right front wheels, r is the distance from the wheel to the kingpin, l is the distance from the wheel to the center axis of the vehicle, h1 and h2 are the lengths of the lever arms for the longitudinal and lateral driving forces of the left front wheel rotating around the center point, h3 and h4 are the lengths of the lever arms for the longitudinal and lateral driving forces of the right front wheel rotating around the center point, a and b are the lengths from the center of mass of the vehicle to the front and rear axles, α and α′ are the wheel turning angles of the left and right front wheels, respectively. fl and T fr are the driving torques of the left and right front wheels respectively, T max is the set maximum driving torque;

[0022] The driving torque difference ΔM between the left front wheel and the right front wheel is obtained through the front wheel differential steering model, which is:

[0023]

[0024] Among them, J e is the equivalent moment of inertia of the vehicle steering system, B e Steering damping of the vehicle steering system, and They are the vehicle's expected turning angle δ fd First and second derivatives over time, τ a is the total aligning torque of the left and right front wheels, τ f is the friction torque of the vehicle steering system;

[0025] The constraints of differential steering mode 2 are:

[0026]

[0027] Where, ω is the actual yaw rate, ω max is the maximum yaw rate that the current road surface can provide, is the first-order derivative of ω, I z ′ is the yaw moment of inertia of the vehicle corresponding to differential steering mode 2;

[0028] The constraints of differential steering mode 3 are:

[0029]

[0030] Among them, I z ″ is the yaw moment of inertia of the vehicle corresponding to differential steering mode 3.

[0031] Optionally, the two-degree-of-freedom vehicle differential model is constructed, and the desired vehicle turning angle δ fd , get the vehicle's desired yaw rate ω d and the desired sideslip angle β d middle,

[0032] The desired vehicle turning angle δ fd for:

[0033] δ fd =δ w ×K0

[0034] Among them, δ w is the steering wheel angle, K0 is the steering ratio;

[0035] The two-degree-of-freedom vehicle differential model is:

[0036]

[0037] Among them, C f and C r are the stiffness of the front and rear axles of the vehicle, m is the vehicle weight, v x is the lateral velocity of the vehicle, a and b are the lengths from the center of mass of the vehicle to the front and rear axles, I z is the vehicle's yaw moment of inertia, ΔM z is the additional yaw moment applied to the vehicle.

[0038] Optionally, the condition for determining whether the current vehicle meets the conditions for starting redundant control is: whether the vehicle turning angle of the current vehicle is consistent with the expected vehicle turning angle; and the vehicle turning angle is acquired based on detection by a sensor installed on the vehicle.

[0039] Optionally, a PID controller is introduced to correct the left front wheel driving force and the right front wheel driving force output by the lower controller to achieve steering. The specific process is:

[0040] Determine the actual yaw rate ω and the expected yaw rate ω d Whether the following requirements are met:

[0041] ω≤1.1ω d

[0042] If satisfied, the PID controller is used to correct the left front wheel driving force and the right front wheel driving force output by the lower controller to achieve steering;

[0043] If not, the PID controller will not be started, and the left front wheel driving force and the right front wheel driving force output by the lower controller will be used to achieve steering.

[0044] Optionally, the PID controller is configured to generate a desired yaw rate ω. d The difference between the actual yaw rate ω and the actual yaw rate ω is used as input, and the specific control equation of the PID controller is:

[0045]

[0046] Among them, e(t) is the real-time error, F x ' f ' l and F x ' f ' r are the corrected longitudinal driving forces required for the left and right front wheels to maintain the current vehicle speed, K p is the scale parameter, K i is the integration parameter, K d is the differential parameter;

[0047] The left front wheel driving force F corrected by the PID controller x ' fl and right front wheel drive force F x ' fr for:

[0048]

[0049] Among them, F xfl and F xfr They are the left front wheel driving force and the right front wheel driving force output by the lower controller respectively.

[0050] Optionally, the PID controller is based on the desired vehicle turning angle δ fd and the actual heading angle δ f The specific control equation of the PID controller is:

[0051]

[0052] Among them, e(t) is the real-time error, F x 'f ' l and F x ' f ' r are the corrected longitudinal driving forces required for the left and right front wheels to maintain the current vehicle speed, K p is the scale parameter, K i is the integration parameter, K d is the differential parameter;

[0053] The left front wheel driving force F corrected by the PID controller x ' fl and right front wheel drive force F x ' fr for:

[0054]

[0055] Among them, F xfl and F xfr They are the left front wheel driving force and the right front wheel driving force output by the lower controller respectively.

[0056] Optionally, the method further includes: in the process of starting redundant control to realize vehicle steering, if the actual yaw angular velocity ω exceeds the maximum yaw angular velocity that can be provided by the current road surface, using differential braking to realize vehicle direction control.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The redundant control method of the steer-by-wire system of the present invention realizes redundant control of the steer-by-wire system of the vehicle, that is, it does not increase the cost of use. At the same time, when the steer-by-wire system fails or a key component in the steering system fails, the vehicle can enter different differential steering modes according to the steering situation of the front wheels of the steering system, thereby achieving smooth steering of the vehicle.

[0059] (2) The present invention improves the vehicle's yaw rate response speed by introducing a PID controller, thereby improving the vehicle's operational performance while ensuring smooth steering control of the vehicle.

[0060] (3) The present invention ensures that the vehicle steering system can maintain normal steering capabilities in the face of various failure modes, and utilizes differential braking to achieve stable parking when the vehicle fails uncontrollably, thereby significantly improving the vehicle's safety performance and handling stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a flow chart of a vehicle steer-by-wire redundant control method of the present invention;

[0062] Figure 2 It is a schematic diagram of the principle of achieving steering in three differential steering modes of the present invention;

[0063] Figure 3 Schematic diagram of the forces acting on each wheel in differential steering mode 1 of the present invention;

[0064] Figure 4 Schematic diagram of the forces acting on each wheel in differential steering mode 2 of the present invention;

[0065] Figure 5 It is the flow chart of the fuzzy sliding mode controller. DETAILED DESCRIPTION

[0066] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0067] It should be noted that the term "comprise" and any variations thereof in the description and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or are inherent to these processes, methods, products or apparatus.

[0068] like Figure 1 and 2 As shown, a redundant control method for vehicle steer-by-wire is provided. The vehicle is driven by in-wheel motors, which are directly mounted in or near the drive wheels. This method features a simple structure, a short transmission path, and high transmission efficiency. Because the drive motors can be controlled independently, the different drive torques output by the left and right motors generate an additional yaw torque to achieve vehicle steering.

[0069] The redundancy control method specifically includes:

[0070] Based on the current state of the vehicle, determine whether the current vehicle meets the conditions for starting redundant control; if so, start redundant control to achieve vehicle steering; if not, the vehicle steers normally.

[0071] Specifically, it is determined whether the current vehicle turning angle is consistent with the expected vehicle turning angle. If not, the wire-controlled steering system fails, and redundant control is activated to achieve vehicle steering; the vehicle turning angle is obtained based on detection by sensors installed on the vehicle.

[0072] Vehicle expected turning angle δ fd for:

[0073] δ fd =δ w ×K0 (1)

[0074] Among them, δ wis the steering wheel angle, K0 is the steering ratio, and the steering wheel angle can be obtained from the vehicle CAN signal.

[0075] When redundant control is started to achieve vehicle steering, the wheels enter differential steering mode one, and at the same time determine whether the vehicle steering angle is consistent with the vehicle's expected steering angle. If consistent, the wheels maintain differential steering mode one. If inconsistent, it is determined whether the current vehicle steering angle has changed. If not changed, the wheels enter differential steering mode two. If changed, the wheels enter differential steering mode three. The differential steering mode one utilizes the rolling of the left front wheel and the right front wheel to achieve vehicle differential steering; the differential steering mode two utilizes the sliding of the left front wheel and the right front wheel to achieve vehicle differential steering; the differential steering mode three utilizes the sliding and rolling of the left front wheel and the right front wheel to achieve vehicle differential steering.

[0076] Differential steering mode 1, that is, the wheels can rotate normally according to the kingpin, and the wire-controlled steering system may fail due to interference or other communication failures.

[0077] Differential steering mode 2 means that the wheels cannot be steered around the kingpin. The steer-by-wire system may cause the wheels to get stuck due to faults such as the steering motor getting stuck.

[0078] Differential steering mode three means that the wheels can only rotate at a small angle around the kingpin, and the wire-controlled steering system may fail due to faults such as the steering motor getting stuck.

[0079] When the wheels enter differential steering mode one, two or three, the fuzzy sliding mode controller and the lower-level controller output the optimal left and right front wheel driving forces in the corresponding steering mode according to the desired vehicle turning angle.

[0080] As a further step, during the process of starting redundant control to realize the vehicle steering, if the actual yaw rate ω exceeds the maximum yaw rate ω that the current road surface can provide max , differential braking is used to achieve vehicle directional control; the method of achieving vehicle directional control by differential braking can refer to the existing technology, that is, using differential braking to generate additional yaw torque to compensate for the additional additional yaw torque to keep the vehicle within the stable area.

[0081] In this embodiment, when the wheels enter differential steering mode 1, 2, or 3, the fuzzy sliding mode controller and the lower-layer controller are used to output the optimal left and right front wheel driving forces in the corresponding steering mode according to the desired vehicle turning angle. The process is as follows:

[0082] Step S1: Construct a two-degree-of-freedom vehicle differential model and calculate the desired vehicle turning angle δ fd , get the vehicle's desired yaw rate ω d and the desired sideslip angle β d .

[0083] The two-degree-of-freedom vehicle differential model is:

[0084]

[0085] Among them, C f and C r are the stiffness of the front and rear axles of the vehicle, m is the vehicle weight, v x is the lateral velocity of the vehicle, a and b are the lengths from the center of mass of the vehicle to the front and rear axles, I z is the vehicle's yaw moment of inertia, ΔM z is the additional yaw moment applied to the vehicle.

[0086] According to formula (2) and the vehicle's desired turning angle δ fd , get the desired yaw rate ω of the vehicle d and the desired sideslip angle β d .

[0087] Step S2: The fuzzy sliding mode controller is based on the desired vehicle turning angle δ fd , desired yaw rate ω d , expected center of mass sideslip angle β d , the actual vehicle yaw rate ω and the actual center of mass sideslip angle β, output the desired vehicle turning angle δ fd Required resultant moment M d , longitudinal total expected driving force F xd and the total expected lateral driving force F yd .

[0088] Specifically, the fuzzy sliding mode controller includes a fuzzy controller and a sliding mode controller; the actual yaw angular velocity ω and the actual sideslip angle β of the vehicle can be obtained according to the existing technology.

[0089] Based on the set fuzzy rule table, the fuzzy controller calculates the driver's steering wheel angle δ w and the road adhesion coefficient μ are used to obtain the control parameters k and ε of the sliding mode controller.

[0090] As shown in Table 1, a specific example of a fuzzy rule table is given.

[0091] Table 1 Fuzzy rules table

[0092]

[0093] According to the fuzzy rule diagram in Table 1, the MAP diagram is generated, and the fuzzy controller driver's steering wheel angle δ w and the road adhesion coefficient μ are used to obtain the control parameters k and ε of the sliding mode controller.

[0094] like Figure 5As shown, the longitudinal velocity, lateral velocity and yaw rate tracking errors are defined as:

[0095]

[0096] The sliding surface is selected for the above parameters as follows:

[0097]

[0098] Where c1, c2, and c3 are controller parameters that satisfy the Hurwitz condition, and their values ​​are all greater than zero.

[0099] The exponential reaching law method is used to eliminate chattering, and the expression is:

[0100]

[0101] Among them, ε1, ε2 and ε3 are the first control parameters of the sliding surfaces s1, s2 and s3, respectively, and k1, k2 and k3 are the second control parameters of the sliding surfaces s1, s2 and s3, respectively. They are all greater than zero and are obtained by the fuzzy controller, as shown in Table 1.

[0102] From equations (3)-(5), the required resultant force and moment are:

[0103]

[0104] Where, F xd is the required longitudinal force, F yd is the required lateral force, M d is the total torque required by the vehicle.

[0105] Step S3: The lower controller outputs the left front wheel driving force and the right front wheel driving force that optimally meet the objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheel.

[0106] The lower controller receives the resultant torque M output by the sliding mode controller d , longitudinal total expected driving force F xd and the total expected lateral driving force F yd .

[0107] The objective function is:

[0108]

[0109] Where J is the tire load rate, μ is the road adhesion coefficient, F xij is the longitudinal driving force of tire ij, F yij is the lateral driving force of tire ij, F zijis the vertical load force of tire ij, i=f,r; j=l,r, where ij=fl represents the left front wheel, ij=fr represents the right front wheel, ij=rl represents the left rear wheel, and ij=rr represents the right rear wheel.

[0110] like Figure 3 As shown in Figure 1, the constraints of differential steering mode 1 are:

[0111]

[0112] Among them, F xfl and F yfl are the longitudinal and lateral driving forces of the left front wheel, respectively, and F xfr and F yfr are the longitudinal and lateral driving forces of the right front wheel, respectively, and F xrl and F yrl are the longitudinal and lateral driving forces of the left rear wheel, respectively, and F xrr and F yrr are the longitudinal and lateral driving forces of the right rear wheel, ΔM is the driving torque difference between the left and right front wheels, r is the distance from the wheel to the kingpin, l is the distance from the wheel to the center axis of the vehicle, h1 and h2 are the lengths of the lever arms for the longitudinal and lateral driving forces of the left front wheel rotating around the center point, h3 and h4 are the lengths of the lever arms for the longitudinal and lateral driving forces of the right front wheel rotating around the center point, a and b are the lengths from the center of mass of the vehicle to the front and rear axles, α and α′ are the wheel turning angles of the left and right front wheels, respectively. fl and T fr are the driving torques of the left and right front wheels respectively, T max is the set maximum driving torque;

[0113] The driving torque difference ΔM between the left front wheel and the right front wheel is obtained through the front wheel differential steering model, which is:

[0114]

[0115] Among them, J e is the equivalent moment of inertia of the vehicle steering system, B e Steering damping of the vehicle steering system, and They are the vehicle's expected turning angle δ fd First and second derivatives over time, τ a is the total aligning torque of the left and right front wheels, τ f is the friction torque of the vehicle steering system; J e 、B e , τ a and τ fThe specific method is determined according to the properties of the vehicle's steering system, and reference can be made to the existing technology.

[0116] like Figure 4 As shown in the figure, differential steering mode 2 is slip steering. Slip steering means that the wheel direction remains fixed. By controlling the left and right drive motors to output different driving forces, additional yaw torque is generated to cause the wheels to slip, thereby changing the vehicle's direction of travel and completing the turn. At this time, the vehicle angle is assumed to be 0.

[0117] The constraints of differential steering mode 2 are:

[0118]

[0119] Where, ω is the actual yaw rate, ω max is the maximum yaw rate that the current road surface can provide, is the first-order derivative of ω, I z ′ is the yaw moment of inertia of the vehicle corresponding to differential steering mode 2;

[0120] In formula (10), is the torque balance equation of the vehicle around the Z axis in the differential steering mode 2. The yaw moment of inertia of the entire vehicle corresponding to the differential steering mode 2 can be obtained according to the existing technology.

[0121] In formula (10), ω<0.9ω max The yaw rate restriction condition is a condition for the vehicle to slide and turn. A higher additional yaw moment is required when the vehicle is sliding and turning. However, the additional yaw moment increases the vehicle's yaw rate. Therefore, in order to ensure stable driving of the vehicle, the yaw rate is limited.

[0122] The constraints of differential steering mode 3 are:

[0123]

[0124] Among them, I z ″ is the yaw moment of inertia of the vehicle corresponding to differential steering mode 3.

[0125] In formula (11), is the equilibrium equation of the vehicle around the Z axis in differential steering mode three. The yaw moment of inertia of the entire vehicle corresponding to differential steering mode three can be obtained based on existing technology.

[0126] It's worth noting that because differential steering modes two and three require the vehicle to slide steer, using slide steer can easily cause the tires to enter a nonlinear zone while driving. Therefore, if differential steering modes two and three are engaged, the vehicle speed should be reduced. If the vehicle is traveling at a higher speed, excessive steering speed can easily cause the wheels to enter a nonlinear zone, making the vehicle difficult to control. In this case, slide steer in differential steering mode two should be used for steering. The specific upper speed value can be set based on expert experience.

[0127] Example 2

[0128] The difference between Example 2 and Example 1 is that in order to enable the differential steering to quickly respond to the driver's steering wheel angle, so that when the vehicle's wire-controlled steering system fails, it can control the steering of the vehicle body while timely tracking the driver's steering wheel angle, thereby reducing the lag of the control system, a PID controller is introduced to correct the left front wheel driving force and the right front wheel driving force output by the lower-level controller to achieve steering.

[0129] The specific process is: judge the actual yaw angular velocity ω and the expected yaw angular velocity ω d Whether it meets the requirements of formula (12):

[0130] ω≤1.1ω d (12)

[0131] If the conditions are met, the PID controller is used to correct the left front wheel driving force and the right front wheel driving force output by the lower controller to achieve steering.

[0132] If not, the PID controller will not be started, and the left front wheel driving force and the right front wheel driving force output by the lower controller will be used to achieve steering.

[0133] Increasing the difference between the left and right driving forces can make the vehicle respond more quickly to the driver's steering wheel angle and complete the turn. However, in order to prevent the vehicle from becoming unstable, formula (12) limits the vehicle's yaw rate.

[0134] As an alternative, the PID controller is used with the desired yaw rate ω d The difference between the actual yaw rate ω and the actual yaw rate ω is used as input, and the specific control equation of the PID controller is:

[0135]

[0136] Among them, e(t) is the real-time error, F x ' f ' l and F x ' f ' r are the corrected longitudinal driving forces required for the left and right front wheels to maintain the current vehicle speed, Kp is the scale parameter, K i is the integration parameter, K d is the differential parameter;

[0137] The left front wheel driving force F corrected by the PID controller x ' fl and right front wheel drive force F x ' fr for:

[0138]

[0139] Among them, F xfl and F xfr They are the left front wheel driving force and the right front wheel driving force output by the lower controller respectively.

[0140] As another option, the vehicle is equipped with a heading angle sensor such as a gyroscope, and the PID controller is used to calculate the desired turning angle δ of the vehicle. fd and the actual heading angle δ f The specific control equation of the PID controller is:

[0141]

[0142] Among them, e(t) is the real-time error, F x ' f ' l and F x ' f ' r are the corrected longitudinal driving forces required for the left and right front wheels to maintain the current vehicle speed, K p is the scale parameter, K i is the integration parameter, K d is the differential parameter;

[0143] The left front wheel driving force F corrected by the PID controller x ' fl and right front wheel drive force F x ' fr See formula (14).

[0144] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0145] Those skilled in the art will clearly understand that the techniques in the embodiments of the present invention can be implemented using software plus a necessary general-purpose hardware platform. Based on this understanding, the technical solutions in the embodiments of the present invention, or the portion that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments of the present invention or certain portions of the embodiments.

[0146] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A redundant control method for vehicle steer-by-wire, wherein the vehicle is driven by an in-wheel motor, characterized in that: include: Based on the current vehicle status, determine whether the current vehicle meets the conditions for starting redundant control; If satisfied, redundant control is activated to achieve vehicle steering; If not, the vehicle turns normally; When redundant control is activated to achieve vehicle steering, the wheels enter differential steering mode one and simultaneously determine whether the vehicle steering angle is consistent with the desired vehicle steering angle. If so, the wheels maintain differential steering mode one. If not, it is determined whether the current vehicle steering angle has changed. If not, the wheels enter differential steering mode two. If so, the wheels enter differential steering mode three. The differential steering mode one utilizes the rolling of the left and right front wheels to achieve vehicle differential steering; the differential steering mode two utilizes the sliding of the left and right front wheels to achieve vehicle differential steering; and the differential steering mode three utilizes the sliding and rolling of the left and right front wheels to achieve vehicle differential steering. When the wheels enter differential steering mode one, two or three, the fuzzy sliding mode controller and the lower-level controller output the optimal left and right front wheel driving forces in the corresponding steering mode according to the desired vehicle turning angle.

2. The vehicle steer-by-wire redundant control method according to claim 1, characterized in that: When the wheels enter differential steering mode 1, 2, or 3, the fuzzy sliding mode controller and the lower layer controller are used to output the optimal left front wheel driving force and right front wheel driving force in the corresponding steering mode according to the desired vehicle turning angle. The process is as follows: Construct a two-degree-of-freedom vehicle differential model and calculate the desired vehicle turning angle δ fd , get the vehicle's desired yaw rate ω d and the desired sideslip angle β d ; The fuzzy sliding mode controller is based on the desired vehicle steering angle δ fd , desired yaw rate ω d , expected center of mass sideslip angle β d , the actual vehicle yaw rate ω and the actual center of mass sideslip angle β, output the desired vehicle turning angle δ fd Required resultant moment M d , longitudinal total expected driving force F xd and the total expected lateral driving force F yd ; The lower controller outputs the left front wheel driving force and the right front wheel driving force that meet the optimal objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheel.

3. The vehicle steer-by-wire redundant control method according to claim 2, characterized in that: The lower controller outputs the left front wheel driving force and the right front wheel driving force that meet the optimal objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheel. The objective function is: Where J is the tire load rate, μ is the road adhesion coefficient, F xij is the longitudinal driving force of tire ij, F yij is the lateral driving force of tire ij, F zij is the vertical load force of tire ij, i=f,r; j=l,r, where ij=fl represents the left front wheel, ij=fr represents the right front wheel, ij=rl represents the left rear wheel, and ij=rr represents the right rear wheel.

4. The vehicle steer-by-wire redundant control method according to claim 2, characterized in that: The lower controller outputs the left front wheel driving force and the right front wheel driving force that meet the optimal objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheel. The constraints of differential steering mode 1 are: Among them, F xfl and F yfl are the longitudinal and lateral driving forces of the left front wheel, respectively, F xfr and F yfr are the longitudinal and lateral driving forces of the right front wheel, respectively, and F xrl and F yrl are the longitudinal and lateral driving forces of the left rear wheel, respectively, and F xrr and F yrr are the longitudinal and lateral driving forces of the right rear wheel, ΔM is the driving torque difference between the left and right front wheels, r is the distance from the wheel to the kingpin, l is the distance from the wheel to the center axis of the vehicle, h1 and h2 are the lengths of the lever arms for the longitudinal and lateral driving forces of the left front wheel rotating around the center point, h3 and h4 are the lengths of the lever arms for the longitudinal and lateral driving forces of the right front wheel rotating around the center point, a and b are the lengths from the center of mass of the vehicle to the front and rear axles, α and α′ are the wheel turning angles of the left and right front wheels, respectively. fl and T fr are the driving torques of the left and right front wheels respectively, T max is the set maximum driving torque; The driving torque difference ΔM between the left front wheel and the right front wheel is obtained through the front wheel differential steering model, which is: Among them, J e is the equivalent moment of inertia of the vehicle steering system, B e Steering damping of the vehicle steering system, and They are the vehicle's expected turning angle δ fd First and second derivatives over time, τ a is the total aligning torque of the left and right front wheels, τ f is the friction torque of the vehicle steering system; The constraints of differential steering mode 2 are: Where, ω is the actual yaw rate, ω max is the maximum yaw rate that the current road surface can provide, is the first-order derivative of ω, I z ′ is the yaw moment of inertia of the vehicle corresponding to differential steering mode 2; The constraints of differential steering mode 3 are: Among them, I z ″ is the yaw moment of inertia of the vehicle corresponding to differential steering mode 3.

5. The vehicle steer-by-wire redundant control method according to claim 2, characterized in that: The two-degree-of-freedom vehicle differential model is constructed, and the desired vehicle turning angle δ fd , get the vehicle's desired yaw rate ω d and the desired sideslip angle β d middle, The desired vehicle turning angle δ fd for: d fd =d w ×K0 Among them, δ w is the steering wheel angle, K0 is the steering ratio; The two-degree-of-freedom vehicle differential model is: Among them, C f and C r are the stiffness of the front and rear axles of the vehicle, m is the vehicle weight, v x is the lateral velocity of the vehicle, a and b are the lengths from the center of mass of the vehicle to the front and rear axles, I z is the vehicle's yaw moment of inertia, ΔM z is the additional yaw moment applied to the vehicle.

6. The vehicle steer-by-wire redundant control method according to claim 1, characterized in that: The condition for determining whether the current vehicle meets the conditions for starting redundant control is: whether the vehicle turning angle of the current vehicle is consistent with the expected vehicle turning angle; the vehicle turning angle is obtained by detection based on a sensor installed on the vehicle.

7. The vehicle steer-by-wire redundant control method according to claim 2, characterized in that: It also includes introducing a PID controller to correct the left front wheel driving force and the right front wheel driving force output by the lower controller to achieve steering; the specific process is: Determine the actual yaw rate ω and the expected yaw rate ω d Whether the following requirements are met: ω≤1.1ω d If satisfied, the PID controller is used to correct the left front wheel driving force and the right front wheel driving force output by the lower controller to achieve steering; If not, the PID controller will not be started, and the left front wheel driving force and the right front wheel driving force output by the lower controller will be used to achieve steering.

8. The vehicle steer-by-wire redundant control method according to claim 7, characterized in that: The PID controller is used to calculate the desired yaw rate ω d The difference between the actual yaw rate ω and the actual yaw rate ω is used as input, and the specific control equation of the PID controller is: Among them, e(t) is the real-time error, F x ' f ' l and F x ' f ' r are the corrected longitudinal driving forces required for the left and right front wheels to maintain the current vehicle speed, K p is the scale parameter, K i is the integration parameter, K d is the differential parameter; The left front wheel driving force F corrected by the PID controller x ' fl and right front wheel drive force F x ' fr for: Among them, F xfl and F xfr They are the left front wheel driving force and the right front wheel driving force output by the lower controller respectively.

9. The vehicle steer-by-wire redundant control method according to claim 7, characterized in that: The PID controller is based on the vehicle's desired turning angle δ fd and the actual heading angle δ f The specific control equation of the PID controller is: Among them, e(t) is the real-time error, F x ' f ' l and F x ' f ' r are the corrected longitudinal driving forces required for the left and right front wheels to maintain the current vehicle speed, K p is the scale parameter, K i is the integration parameter, K d is the differential parameter; The left front wheel driving force F corrected by the PID controller x ' fl and right front wheel drive force F x ' fr for: Among them, F xfl and F xfr They are the left front wheel driving force and the right front wheel driving force output by the lower controller respectively.

10. The vehicle steer-by-wire redundant control method according to claim 1, characterized in that: Also includes: During the process of activating redundant control to realize vehicle steering, if the actual yaw rate ω exceeds the maximum yaw rate that the current road surface can provide, differential braking is used to realize vehicle directional control.

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