Vehicle steer-by-wire redundancy control method

Abstract

The invention discloses a vehicle steer-by-wire redundancy control method, which belongs to the technical field of automobile steering and comprises the following steps: judging whether a current vehicle starts redundancy control or not, when the redundancy control is started to realize steering of the vehicle, enabling wheels to enter a differential steering mode I, judging whether a vehicle steering angle is consistent with a vehicle expected steering angle or not, and if yes, starting a differential steering mode II; if yes, the wheels are kept in the first differential steering mode, if not, whether the current turning angle of the vehicle changes or not is judged, if not, the wheels enter the second differential steering mode, and if yes, the wheels enter the third differential steering mode; and when the wheels enter the differential steering mode I, the differential steering mode II or the differential steering mode III, outputting the optimal left front wheel driving force and the optimal right front wheel driving force in the corresponding steering mode by utilizing the fuzzy sliding mode controller and the lower-layer controller according to the expected steering angle of the vehicle. When the steer-by-wire system loses efficacy or key components in the steering system break down, the automobile can steer stably.

Description

Technical Field

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

[0002] With the development of intelligent and electrified vehicles, wire-controlled technology plays an important role in promoting the development of autonomous driving and the electrification of vehicles. However, due to the lack of mechanical connection, when the wire-controlled steering fails, the vehicle will lose its steering function, which can easily cause safety accidents. In order to ensure the reliability and safety of the wire-controlled steering system, it is extremely important to increase steering redundancy.

[0003] Existing redundancy technologies can be roughly divided into two categories: one is hardware backup redundancy technology, and the other is algorithm fault-tolerant technology. Hardware backup provides backup for important components and components prone to failure. This method will increase the size and quality of the system, as well as the cost. Algorithm fault tolerance mainly relies on the fault-tolerant algorithm of the controller 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 key components of the steering system, such as the steering motor, fail, normal steering of the vehicle cannot be guaranteed. Summary of the invention

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

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

[0006] A redundant control method for vehicle steer-by-wire, wherein the vehicle is driven by a wheel hub motor, comprising:

[0007] 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;

[0008] When redundant control is started to realize the steering of the vehicle, the wheels enter differential steering mode 1, and at the same time determine whether the vehicle steering angle is consistent with the expected steering angle of the vehicle. If consistent, the wheels maintain differential steering mode 1; if inconsistent, determine whether the current vehicle steering angle changes; if not, the wheels enter differential steering mode 2; if changed, the wheels enter differential steering mode 3; the differential steering mode 1 realizes vehicle differential steering by rolling of the left front wheel and the right front wheel; the differential steering mode 2 realizes vehicle differential steering by sliding of the left front wheel and the right front wheel; the differential steering mode 3 realizes vehicle differential steering by sliding and rolling of the left front wheel and the right front wheel;

[0009] When the wheels enter differential steering mode one, two or three, the fuzzy sliding mode controller and the lower-level 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 turning angle of the vehicle.

[0010] Optionally, when the wheels enter differential steering mode one, two or three, according to the desired turning angle of the vehicle, the fuzzy sliding mode controller and the lower controller are used to output the optimal left front wheel driving force and right front wheel driving force in the corresponding steering mode, and 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 expected yaw angular velocity 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 sideslip angle β d , the actual yaw rate ω and the actual sideslip angle β of the vehicle, and the output of the desired turning angle δ fd The required torque M d 、Total expected longitudinal 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 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.

[0014] Optionally, 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.

[0015] The objective function is:

[0016]

[0017] Where J is the tire load factor, μ is the road adhesion coefficient, and 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 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.

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

[0020]

[0021] Among them, F xfl and F yfl are the longitudinal driving force and lateral driving force 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 driving force and lateral driving force of the right rear wheel, ΔM is the driving torque difference between the left front wheel and the right front wheel, 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 of the longitudinal driving force and lateral driving force of the left front wheel rotating around the center point, h3 and h4 are the lengths of the lever arms of the longitudinal driving force and lateral driving force 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 axle and the rear axle, α and α′ are the wheel turning angles of the left front wheel and the right front wheel, respectively, T 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, and the front wheel differential steering model is:

[0023]

[0024] Among them, J e is the equivalent moment of inertia of the vehicle steering system, B e Steering damping of vehicle steering system, and The expected turning angle δ of the vehicle is fd First and second derivatives with time, τ a is the total self-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 three.

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

[0032] The desired turning angle δ of the vehicle 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 weight of the vehicle, 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, respectively, 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 satisfies the conditions for starting redundant control is: whether the vehicle turning angle of the current vehicle is consistent with the expected turning angle of the vehicle; 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 Do you meet the following requirements:

[0041] ω≤1.1ω d

[0042] If it is 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 difference is taken as input, and 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, it also includes: in the process of starting redundant control to realize the steering of the vehicle, if the actual yaw angular velocity ω exceeds the maximum yaw angular velocity that the current road surface can provide, differential braking is used to realize the direction control of the vehicle.

[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 realizing smooth steering of the vehicle.

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

[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 redundant control method for vehicle steer-by-wire of the present invention;

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

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

[0064] Figure 4 is a schematic diagram of the forces acting on each wheel in the second differential steering mode of the present invention;

[0065] Figure 5 It is the flow chart of 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 solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0067] It should be noted that the term "comprises" and any variations of the term in the specification 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 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, wherein the vehicle is driven by a wheel hub motor, that is, the wheel hub motor is directly installed in or near the drive wheel, and has the characteristics of simple structure, short transmission path, high transmission efficiency, etc. Since the drive motor can be controlled separately, the left and right motors output different driving torques to generate additional yaw torque, so that the vehicle can complete the steering.

[0069] The redundant 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 acquired based on detection by sensors installed on the vehicle.

[0072] Expected turning angle of vehicle 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 1, 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 1. If inconsistent, it is determined whether the current vehicle steering angle has changed. If not, the wheels enter differential steering mode 2. If changed, the wheels enter differential steering mode 3. The differential steering mode 1 utilizes the rolling of the left front wheel and the right front wheel to achieve vehicle differential steering; the differential steering mode 2 utilizes the sliding of the left front wheel and the right front wheel to achieve vehicle differential steering; the differential steering mode 3 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 control steering system may fail due to interference and other communication failures.

[0077] Differential steering mode 2, that is, the wheels cannot be steered around the kingpin, and the wire-controlled steering 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 steering motor jamming.

[0079] When the wheels enter differential steering mode one, two or three, the fuzzy sliding mode controller and the lower-level 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 turning angle of the vehicle.

[0080] As a further step, in the process of starting redundant control to realize the steering of the vehicle, 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 directional control of the vehicle; the method of achieving directional control of the vehicle 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 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 turning angle of the vehicle. 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 expected yaw angular velocity 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 weight of the vehicle, 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, respectively, 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 expected 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 sideslip angle β d , the actual yaw rate ω and the actual sideslip angle β of the vehicle, and the output of the desired turning angle δ fd The required torque M d 、Total expected longitudinal 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 center of mass sideslip angle β of the vehicle can be obtained according to the prior art.

[0089] Based on the set fuzzy rule table, the fuzzy controller calculates the driver's steering wheel angle δ w and road adhesion coefficient μ 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] The MAP diagram is generated according to the fuzzy rule diagram in Table 1. The fuzzy controller driver's steering wheel angle δ w and road adhesion coefficient μ 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 sliding surfaces s1, s2 and s3 respectively, and k1, k2 and k3 are the second control parameters of sliding surfaces s1, s2 and s3 respectively, all of which are 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 obtained as follows:

[0103]

[0104] In the formula, 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 satisfy the objective function in the corresponding steering mode according to the objective function and the constraints of the steering mode currently entered by the wheels.

[0106] The lower controller receives the resultant torque M output by the sliding mode controller d 、Total expected longitudinal 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 factor, μ is the road adhesion coefficient, and 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 driving force and lateral driving force 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 driving force and lateral driving force of the right rear wheel, ΔM is the driving torque difference between the left front wheel and the right front wheel, 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 of the longitudinal driving force and lateral driving force of the left front wheel rotating around the center point, h3 and h4 are the lengths of the lever arms of the longitudinal driving force and lateral driving force 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 axle and the rear axle, α and α′ are the wheel turning angles of the left front wheel and the right front wheel, respectively, T 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 vehicle steering system, and The expected turning angle δ of the vehicle is fd First and second derivatives with time, τ a is the total self-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 fIt is determined according to the properties of the vehicle's steering system, and the specific method can refer to the existing technology.

[0116] like Figure 4 As shown, differential steering mode 2 is sliding steering, which means that the direction of the wheel remains unchanged, and the left and right drive motors are controlled to output different driving forces to generate additional yaw torque to make the wheels slip and change the direction of the vehicle to complete the steering. At this time, it is assumed that the vehicle angle is 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 whole vehicle corresponding to the differential steering mode 2 can be obtained according to the existing technology.

[0121] In formula (10), ω<0.9ω max It is a restriction condition for the yaw rate. Since a higher additional yaw moment is required when the vehicle performs sliding steering, and the additional yaw moment will increase the yaw rate of the vehicle, the yaw rate is limited to ensure stable driving of the vehicle.

[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 three.

[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 whole vehicle corresponding to differential steering mode three can be obtained according to the existing technology.

[0126] It is worth noting that since differential steering modes 2 and 3 require the vehicle to slide and steer, the tires are likely to enter a nonlinear zone when using sliding steering while the vehicle is driving. At this time, if differential modes 2 and 3 are entered, the vehicle speed should be reduced first. If the vehicle is driving at a higher speed, the wheels are likely to enter a nonlinear zone when the steering speed is too fast, making the vehicle difficult to control. The sliding steering method of differential steering mode 2 should be used for steering. The specific value of the higher speed 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 respond quickly 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 tracking the driver's steering wheel angle in time and reduce 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: determine 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 it is 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.

[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 yaw rate of the vehicle.

[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 based on the vehicle's desired turning angle δ fd and the actual heading angle δ f The difference is taken as input, and 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 can clearly understand that the technology in the embodiments of the present invention can be implemented by means of software plus a necessary general hardware platform. Based on this understanding, the technical solution in the embodiments of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a disk, an optical disk, etc., and includes a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present invention or some parts of the embodiments.

[0146] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A redundant control method for vehicle steer-by-wire, wherein the vehicle is driven by a wheel hub motor, characterized in that: include: Based on the current state of the vehicle, determining whether the current vehicle meets the conditions for starting redundant control; If it is satisfied, the redundant control is activated to realize the steering of the vehicle; If not, the vehicle turns normally; When redundant control is started to realize the steering of the vehicle, the wheels enter differential steering mode 1, and at the same time determine whether the vehicle steering angle is consistent with the expected steering angle of the vehicle. If consistent, the wheels maintain differential steering mode 1; if inconsistent, determine whether the current vehicle steering angle changes; if not, the wheels enter differential steering mode 2; if changed, the wheels enter differential steering mode 3; the differential steering mode 1 realizes vehicle differential steering by rolling of the left front wheel and the right front wheel; the differential steering mode 2 realizes vehicle differential steering by sliding of the left front wheel and the right front wheel; the differential steering mode 3 realizes vehicle differential steering by sliding and rolling of the left front wheel and the right front wheel; When the wheels enter differential steering mode one, two or three, the fuzzy sliding mode controller and the lower-level 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 turning angle of the vehicle.

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, according to the desired turning angle of the vehicle, the fuzzy sliding mode controller and the lower controller are used to output the optimal left front wheel driving force and right front wheel driving force in the corresponding steering mode. 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 expected yaw angular velocity 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 sideslip angle β d , the actual yaw rate ω and the actual sideslip angle β of the vehicle, and the output of the desired turning angle δ fd The required torque M d 、Total expected longitudinal 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 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.

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 factor, μ is the road adhesion coefficient, and 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 driving force and lateral driving force 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 driving force and lateral driving force of the left rear wheel, respectively, and F xrr and F yrr are the longitudinal driving force and lateral driving force of the right rear wheel, ΔM is the driving torque difference between the left front wheel and the right front wheel, 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 of the longitudinal driving force and lateral driving force of the left front wheel rotating around the center point, h3 and h4 are the lengths of the lever arms of the longitudinal driving force and lateral driving force 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 axle and the rear axle, α and α′ are the wheel turning angles of the left front wheel and the right front wheel, respectively, T 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, and the front wheel differential steering model is: Among them, J e is the equivalent moment of inertia of the vehicle steering system, B e Steering damping of vehicle steering system, and The expected turning angle δ of the vehicle is fd First and second derivatives with time, τ a is the total self-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 three.

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 turning angle δ of the vehicle is fd , get the vehicle's expected yaw angular velocity ω d and the desired sideslip angle β d middle, The desired turning angle δ of the vehicle 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 weight of the vehicle, 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, respectively, 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 judging whether the current vehicle satisfies the condition for starting redundant control is: whether the vehicle turning angle of the current vehicle is consistent with the expected turning angle of the vehicle; and the vehicle turning angle is acquired through detection by 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 Do you meet the following requirements: ω≤1.1ω d If it is 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 difference is taken 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.

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

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