Fault-tolerant control method for steering system of multi-shaft distributed driving vehicle

Abstract

The invention relates to the technical field of multi-axle vehicle chassis control, in particular to a fault-tolerant control method for a steering system of a multi-axle distributed driving vehicle, which comprises the following steps of: calculating a steering angle proportional relation of each axle in real time based on fault identification and a proportional controller, and acquiring a steering angle signal of a wheel in real time through a wheel steering angle sensor; and the active steering torque of the steering motor is calculated through the PID controller according to the target turning angle, so that the turning angle of each wheel reaches the target value. By means of the technical scheme, the maneuverability of the multi-axle distributed steering vehicle can be improved when several kinds of different wheel steering faults occur, and extra guarantee is provided for the vehicle to automatically move to a maintenance position under the condition that no external rescue exists.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-axle vehicle chassis control, and particularly relates to a fault-tolerant control method for a steering system of a multi-axle distributed drive vehicle. Background Art

[0002] In recent years, with the development of the automotive industry, vehicles have been widely used in various industries. Multi-axle vehicles have also been applied to more scenarios due to their good passability.

[0003] The main working environments of some multi-axle special vehicles are harsh working conditions such as unpaved roads, and various forms of steering failures often occur. Therefore, due to the harsh and complex working environment of multi-axle special vehicles, when a failure occurs, external rescue vehicles often cannot arrive at the failure site in time for rescue. This requires the vehicle itself to have the ability to move autonomously to a certain extent when a failure occurs and go to the repair location by itself. However, existing multi-axle special vehicles do not have the ability to move autonomously when a steering system failure occurs. Summary of the Invention

[0004] The purpose of the present invention is to provide a fault-tolerant control method for a steering system of a multi-axle distributed drive vehicle, so as to solve the problem that some multi-axle special vehicles do not have the ability to move autonomously when a steering system failure occurs.

[0005] To achieve the above purpose, the present invention provides a fault-tolerant control method for a steering system of a multi-axle distributed drive vehicle. The fault-tolerant control method for a steering system of a multi-axle distributed drive vehicle includes the following steps:

[0006] Based on the distributed steering system, complete fault identification, and based on the fault controller, adopt corresponding fault control schemes according to the fault location;

[0007] Obtain system calculation parameters;

[0008] Obtain the wheel angle signal through the angle sensor;

[0009] Based on different fault control schemes, adopt corresponding proportional control coefficients, and use the proportional angle controller to calculate the angle proportional relationship between non-faulty axles;

[0010] Adjust the three parameters kp, ki, and kd of the PID controller to achieve the tracking control of the target wheel angle;

[0011] Calculate the active steering torque of the steering motor and issue a control command;

[0012] The current controller controls the actuator;

[0013] The wheel angle continuously approaches the expectation.

[0014] The specific content of the step "Complete fault identification based on the distributed steering system" is: according to the following response characteristics of the steering wheel to the target angle issued by the controller, when the steering system cannot execute the angle control command, the steering system fault of the wheel can be identified. The steering system fault types include the following:

[0015] Steering failure of one of the wheels on the front axle;

[0016] Steering failure of two wheels on the front axle;

[0017] Steering failure of one wheel on the middle axle;

[0018] Steering failure of two wheels on the middle axle;

[0019] Steering failure of one wheel on the rear axle;

[0020] Steering failure of two wheels on the rear axle.

[0021] Among them, in the step of "obtaining system calculation parameters", the calculation parameters include the vehicle mass, the wheel angle of each axle, the fault angle and the longitudinal speed of the vehicle.

[0022] The specific content of the step "obtaining the wheel angle signal through the wheel angle sensor" is: using the wheel angle sensor to collect the wheel angle signal of each wheel in real time act , and sent to the steering motor torque calculation module of the PID controller in real time.

[0023] Among them, in the step of "adjusting the three parameters kp, ki, kd of the PID controller", kp is the proportional parameter, ki is the integral parameter, and kd is the differential parameter.

[0024] Among them, in the step of "calculating the active steering torque of the steering motor", the calculation formula of the steering torque of a single wheel in each calculation cycle is:

[0025]

[0026] Among them, δ ref is the steering angle of each wheel calculated by the proportional controller, δ act It is the actual steering angle of the wheel detected by the steering angle sensor.

[0027] Among them, the specific content of the step "current controller controls the actuator" is: the current controller controls the current required by the actuator in real time according to the control instructions of the distributed drive vehicle steering controller.

[0028] Among them, the specific content of the step "the wheel angle continues to approach the expected value" is: the actuator applies the required active torque to the wheel in real time under the action of current control, so that the wheel angle continues to approach the target value.

[0029] A fault-tolerant control method for a multi-axis distributed drive vehicle steering system according to the present invention calculates the angular ratio relationship of each axis in real time based on fault identification and a proportional controller, and collects the angular signals of the wheels in real time through wheel angular sensors, and calculates the active steering torque of the steering motor through a PID controller according to the target angle, so that the angle of each wheel reaches the target value. It ensures that the multi-axis distributed steering vehicle still has the ability to move autonomously when a steering fault occurs. Adopting this technical solution can improve the maneuverability of the multi-axis steering vehicle when several different wheel steering faults occur, and provides additional guarantee for the vehicle to still have the ability to move autonomously to the repair place without external rescue. Brief Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 is the application block diagram of the fault-tolerant control method for the multi-axis distributed drive vehicle steering system provided by the present invention.

[0032] Figure 2 is the step flow chart of the fault-tolerant control method for the multi-axis distributed drive vehicle steering system provided by the present invention.

[0033] Figure 3 is the schematic diagram of a steering fault of a certain wheel on the front axle provided by the present invention.

[0034] Figure 4 is the schematic diagram of a steering fault of two wheels on the front axle provided by the present invention.

[0035] Figure 5 is the schematic diagram of a steering fault of a certain wheel on the middle axle provided by the present invention.

[0036] Figure 6 is the schematic diagram of a steering fault of two wheels on the middle axle provided by the present invention.

[0037] Figure 7 is the schematic diagram of a steering fault of a certain wheel on the rear axle provided by the present invention.

[0038] Figure 8 is the schematic diagram of a steering fault of two wheels on the rear axle provided by the present invention.

[0039] Figure 9 is the simplified diagram of the vehicle two-degree-of-freedom dynamics model provided by the present invention. Detailed Embodiments

[0040] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where like or similar reference numerals denote like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0041] Please refer to Figure 1 , the present invention provides a fault-tolerant control method for a multi-axis distributed drive vehicle steering system. The fault-tolerant control method for the multi-axis distributed drive vehicle steering system includes the following steps:

[0042] Based on the distributed steering system, fault identification is completed, and based on the fault controller, corresponding fault control schemes are adopted according to the fault location;

[0043] Obtain system calculation parameters;

[0044] Obtain the wheel steering angle signal through the steering angle sensor;

[0045] Based on different fault control schemes, corresponding proportional control coefficients are adopted, and the proportional relationship of the steering angles between non-faulty axes is calculated using the proportional steering angle controller;

[0046] Adjust the three parameters kp, ki, and kd of the PID controller to achieve the tracking control of the target wheel steering angle;

[0047] Calculate the active steering torque of the steering motor and issue a control command;

[0048] The current controller controls the actuator;

[0049] The wheel steering angle continuously approaches the expectation.

[0050] In this embodiment, the technical solution calculates the proportional relationship of the steering angles of each axis in real time based on fault identification and the proportional controller, and collects the steering angle signals of the wheels in real time through the wheel steering angle sensor, and calculates the active steering torque of the steering motor through the PID controller according to the target steering angle, so that the steering angle of each wheel reaches the target value. It is ensured that the multi-axis distributed steering vehicle still has the ability to move autonomously when a steering fault occurs. Adopting this technical solution can improve the maneuverability of the multi-axis steering vehicle when several different types of wheel steering faults occur, and provides an additional guarantee for the vehicle to still have the ability to move autonomously to the repair location without external rescue.

[0051] Please refer to Figures 2 to 9 , the present invention provides a fault-tolerant control method for a multi-axis distributed drive vehicle steering system. The fault-tolerant control method for the multi-axis distributed drive vehicle steering system includes the following specific steps:

[0052] S1. Distributed steering system fault identification

[0053] According to the following response characteristics of the steering wheel to the target turning angle issued by the controller, the steering system failure of the wheel can be identified when the steering system cannot execute the turning angle control command. By analyzing the failure forms of the multi-axis distributed steering system, the following steering wheel failure failures are considered (here failure failure refers to the failure of the wheel to respond to the steering command):

[0054] A steering failure of one of the wheels on the front axle (such as Figure 3 shown);

[0055] Steering failure of two wheels on the front axle (such as Figure 4 shown);

[0056] A wheel steering failure on the central axle (such as Figure 5 shown);

[0057] Steering failure of two wheels on the middle axle (such as Figure 6 shown);

[0058] A wheel steering failure on the rear axle (such as Figure 7 shown);

[0059] Steering failure of two wheels on the rear axle (such as Figure 8 shown).

[0060] exist Figures 3 to 9 In, δ fl is the left front wheel turning angle, δ f is the average of the left and right wheel angles of the first axle, δ fr is the right front wheel turning angle, δ ml is the left middle wheel turning angle, δ m is the average of the left and right wheel angles of the second axle, δ mr is the right middle wheel turning angle, δ rl is the left rear wheel turning angle, δ r is the average of the left and right wheel angles of the third axle, δ rr is the right rear wheel turning angle.

[0061] S2. Obtain system calculation parameters:

[0062] The equivalent model diagram of the controlled object of the distributed drive vehicle steering fault control system provided by this technical solution is as follows Figure 9 As shown, Figure 9 A simplified diagram representing the two-degree-of-freedom dynamic model of the entire vehicle.

[0063] S3, obtaining wheel angle signal:

[0064] The wheel angle sensor collects the angle signal of each wheel in real time. act, and is sent to the steering motor torque calculation module of the PID controller in real time.

[0065] S4. Calculate the target angle of each axis using the proportional angle controller:

[0066] The following two-degree-of-freedom vehicle model is used globally:

[0067]

[0068] When the vehicle is in steady-state steering, the yaw angular acceleration satisfies From the fact that a multi-axle vehicle is in a stable state during steering, the following conditions can be obtained:

[0069]

[0070] (1) Steering failure of one wheel on the front axle:

[0071] When there is a steering system failure of one wheel on the front axle, the steering system loses the angle control function of this wheel at this time. In order to offset the lateral steering force brought by the damaged wheel, the angle of the undamaged wheel in the first axle is adjusted to the position equal in magnitude and opposite in direction to the damaged wheel, so that the equivalent angle of the two wheels on the front axle is zero, and the vehicle's steering operation is achieved only by relying on the steering of the rear two axles. Figure 3 shows the motion sketch of the vehicle in this fault condition.

[0072] In the case of manual driving, the input of the vehicle system is only the steering wheel angle. When there is a front axle fault, this steering wheel angle is mapped to the angle of the rear axle wheels. And there is the following proportional relationship between the angle of the middle axle wheels and the angle of the rear axle:

[0073] δ m =k 23 δ r (3)

[0074] Substitute Equation (2) and Equation (3) into Equation (1), and we get:

[0075]

[0076] When only one wheel on the front axle fails, at this time let δ f =0 and substitute it into Equation (3) and Equation (4), and we get:

[0077]

[0078] It is stipulated that the relationship between the steering wheel angle and the wheel angle is:

[0079]

[0080] where L 3 =L 13 ,L 3is the distance from the vehicle's rotation center to the rear axle, L 13 is the distance from the front axle to the rear axle. Then, from Equation (3), the target steering angle value of the middle axle wheel is obtained.

[0081] (2) Steering failure of the two front axle wheels:

[0082] If both wheels of the front axle are damaged to varying degrees, resulting in inconsistent steering angle values for the two, then at this time, the average value of the two steering angles is used as the equivalent steering angle of the front axle as shown in Equation (7), and this value is substituted into the lateral two-degree-of-freedom model as a known parameter, and the proportionality coefficient between the middle axle and the rear axle is solved using a method similar to that in the conventional steering mode. As Figure 4 shown is the kinematic diagram of the vehicle in this failure case.

[0083]

[0084] At this time, δ f is regarded as known. According to Equation (7), we have:

[0085]

[0086] Assuming the steering angle of the third axle is known, the steering angles of the second and third axles should satisfy the following relationship:

[0087]

[0088] From the expression of the proportionality coefficient between the steering angles of the second and third axles, it can be seen that if k 23 is calculated, first obtain the expression for the distance L 3 from the steering center O to the front axle. Let the sideslip angle β of the vehicle's center of mass be 0, and the sideslip angular velocity of the center of mass When the vehicle is in steady-state steering, the yaw angular acceleration satisfies According to Equations (8) and (9), we get:

[0089]

[0090] Substitute Equations (2), (8), (9), and (10) into the two-degree-of-freedom motion differential equation of the vehicle and solve to get:

[0091]

[0092] It is stipulated that the relationship between the steering wheel angle and the wheel steering angle is:

[0093]

[0094] D r represents the maximum value of the rear wheel steering angle at the current speed and is expressed as:

[0095]

[0096] After obtaining L 3 , substitute it into Equation (9) to solve for k 23 . Then, obtain the rear wheel steering angle value from Equation (12). Further, calculate δ m .

[0097] (3) Steering failure of a wheel on the middle axle:

[0098] When the steering of one wheel on the middle axle fails, the system loses the control over the steering angle of this wheel. To counteract the lateral steering force caused by the damaged wheel, the steering angle of the undamaged wheel on the second axle is adjusted to the position with the same magnitude but opposite direction as the damaged wheel, so that the equivalent steering angle of the two front axle wheels is zero, and the vehicle steering is achieved only by relying on the steering of the first and third axles. As Figure 5 shown is the kinematic diagram of the vehicle under this fault condition.

[0099] In the case of manual driving, the input of the vehicle system is only the steering wheel angle. When there is a middle axle fault, this steering wheel angle is mapped to the steering angle of the front axle wheels. And there is the following proportional relationship between the front axle wheel steering angle and the rear axle steering angle:

[0100] δ r = k 13 δ f (14)

[0101] Substitute Equation (2) and Equation (14) into Equation (1), we get:

[0102]

[0103] When only one wheel on the front axle fails, at this time let δ m = 0 and substitute it into Equation (15), we get:

[0104]

[0105] It is stipulated that the relationship between the steering wheel angle and the wheel steering angle is:

[0106]

[0107] where L 1 = L 12 , L 1 is the distance from the vehicle rotation center to the front axle, and L 12 is the distance from the front axle to the middle axle. Then, obtain the steering angle value of the rear axle wheel from Equation (14).

[0108] (4) Steering failures of two wheels on the middle axle:

[0109] If both wheels of the central axis are damaged to varying degrees, resulting in inconsistent cornering values for the two, then the average value of the two cornering angles is used as the equivalent cornering angle of the central axis as shown in Equation (18). This value is then substituted into the lateral two-degree-of-freedom model as a known parameter, and the proportionality coefficients of the front and rear axles are solved using a method similar to that in the conventional steering mode. As Figure 6 shown is the kinematic diagram of the vehicle under this fault condition.

[0110]

[0111] δ m is regarded as known. According to Equation (3-24), we have:

[0112]

[0113] Assuming that the cornering angle of the first axis is known, the cornering angles of the first and third axes should satisfy the following relationship:

[0114]

[0115] From the expression of the proportionality coefficient of the cornering angles of the first and third axes, it can be seen that if we calculate k 13 , we first obtain the expression for the distance L 1 from the steering center O to the front axle. Let the sideslip angle β of the vehicle's center of mass be 0, and the sideslip angular velocity of the vehicle. When the vehicle is in steady-state steering, the yaw angular acceleration satisfies According to Equations (18) and (19), we get:

[0116]

[0117] Substituting Equations (2), (19), and (21) into the two-degree-of-freedom motion differential equation (1) of the vehicle and solving, we get:

[0118]

[0119] It is stipulated that the relationship between the steering wheel angle and the wheel angle is:

[0120]

[0121] D r represents the maximum value of the rear wheel angle at the current speed and is expressed as:

[0122]

[0123] After solving for L 1 , substituting it into Equation (20) to solve for k 13 , obtaining the front wheel angle value from Equation (21). Further, δ r is obtained according to Equation (21).

[0124] (5) Steering failure of a certain wheel on the rear axle:

[0125] When the steering of one wheel on the rear axle fails, the system loses the control of the steering angle of this wheel. To counteract the lateral steering force caused by the damaged wheel, the steering angle of the undamaged wheel on the third axle is adjusted to the position with the same magnitude but opposite direction as the damaged wheel, so that the equivalent steering angle of the two wheels on the rear axle is zero, and the vehicle steering is achieved only by the steering of the first and second axles. As Figure 7 shown is the kinematic diagram of the vehicle in this fault condition.

[0126] In the case of manual driving, the input of the vehicle system is only the steering wheel angle, and when there is a middle axle fault, this steering wheel angle is mapped to the steering angle of the front axle wheels. And there is the following proportional relationship between the steering angle of the front axle wheels and the steering angle of the rear axle:

[0127] δ m =k 12 δ f (25)

[0128] Substitute Equation (2) and Equation (25) into Equation (1), we get:

[0129]

[0130] When only one wheel on the rear axle fails, at this time let δ r =0 and substitute it into Equation (26), we get:

[0131]

[0132] It is stipulated that the relationship between the steering wheel angle and the wheel steering angle is:

[0133]

[0134] where L 1 =L 13 , L 1 is the distance from the vehicle rotation center to the front axle, and L 13 is the distance from the front axle to the rear axle. Then the steering angle value of the middle axle wheel can be obtained from Equation (25).

[0135] (6) Steering failure of two wheels on the rear axle:

[0136] If both wheels on the rear axle are damaged to varying degrees, resulting in inconsistent steering angle values of the two, then at this time, the average value of the two steering angles is used as the equivalent steering angle of the rear axle as shown in Equation (29), and this value is substituted into the lateral two-degree-of-freedom model as a known parameter, and the proportional coefficients of the front axle and the middle axle are solved by a method similar to that in the conventional steering mode. As Figure 8 shown is the kinematic diagram of the vehicle in this fault condition.

[0137]

[0138] δ r Regarded as known, according to Equation (29), we have:

[0139]

[0140] Assuming that the rotation angle of the first axis is known, the rotation angles of the first and second axes should satisfy the following relationship:

[0141]

[0142] From the expression of the rotation angle ratio coefficient between the first axis and the second axis, if calculating k 12 , first obtain the expression of the distance L from the steering center O to the front axle 1 . Let the sideslip angle β of the vehicle's center of mass be 0, and the sideslip angular velocity of the center of mass The yaw angular acceleration of the vehicle during steady-state steering satisfies According to Equation (30) and Equation (31), we get:

[0143]

[0144] Substitute Equations (2), (30), and (31) into the two-degree-of-freedom motion differential equation (1) of the vehicle and solve to obtain:

[0145]

[0146] Specify the relationship between the steering wheel angle and the wheel angle as:

[0147]

[0148] where D f represents the maximum value of the front wheel angle at the current speed, expressed as:

[0149]

[0150] After solving for L 1 , substitute it into Equation (31) to solve for k 12 , obtain the front wheel angle value from Equation (33), and further, calculate δ m .

[0151] S5. Adjust the three parameters kp, ki, and kd of the PID control;

[0152] Considering the PID control, reasonably adjust the weights of the proportional term, integral term, and differential term to achieve the tracking control of the target wheel angle.

[0153] S6. Calculate the active steering torque of the steering motor

[0154] The steering torque calculation formula for a single wheel within each calculation cycle is as follows:

[0155]

[0156] Where δ ref is the steering angle of each wheel calculated by the proportional controller, and δ act is the actual steering angle of the wheel detected by the sensor.

[0157] Within each calculation cycle, the PID control calculates a torque increment. If the wheel has not reached the target steering angle value, the torque will continue to increase until the target value is reached. Then, based on the wheel steering angle signal collected by the sensor, the active torque required for steering control can be calculated using the above formula, and a control command is issued.

[0158] S7. The current controller controls the actuator;

[0159] The current controller controls the current required by the actuator in real time according to the control command of the distributed drive vehicle steering controller. Under the action of the current control, the actuator applies the required active torque on the wheel in real time, making the wheel steering angle continuously approach the target value.

[0160] S8. The wheel steering angle continuously approaches the expected value.

[0161] In summary, according to this technical solution, the target steering angles of each axis are calculated by the proportional controller, and the target steering angles are transmitted to the PID controller to calculate the steering torque required by the steering motor in real time and apply it to the wheel until the wheel steering angle reaches the corresponding target value, and the vehicle steering system reaches dynamic balance, thereby realizing the steering control of a multi-axis distributed drive vehicle.

[0162] The above-disclosed is only a preferred embodiment of the present invention. Of course, it cannot be used to limit the scope of the rights of the present invention. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A fault-tolerant control method for a multi-axis distributed drive vehicle steering system, characterized in that: The steps include: Complete fault identification based on the distributed steering system, and take corresponding fault control solutions based on the fault location of the fault controller; Get system calculation parameters; Obtain wheel angle signals through a wheel angle sensor; Based on different fault control schemes, corresponding proportional control coefficients are adopted, and the proportional angle controller is used to calculate the angle proportional relationship between the non-fault axes; Adjust the three parameters kp, ki, and kd of the PID controller to achieve tracking control of the target wheel angle; Calculate the active steering torque of the steering motor and issue control instructions; The current controller controls the actuator; The wheel turns closer and closer to expectations.

2. The fault-tolerant control method for a steering system of a multi-axis distributed drive vehicle according to claim 1, characterized in that: The specific content of the step "Complete fault identification based on the distributed steering system" is: according to the following response characteristics of the steering wheel to the target angle sent by the controller, when the steering system cannot execute the angle control command, the steering system fault of the wheel can be identified. The specific types of steering system faults include the following: Steering failure of one of the wheels on the front axle; Steering failure of two wheels on the front axle; Steering failure of one wheel on the middle axle; Steering failure of two wheels on the middle axle; Steering failure of one wheel on the rear axle; Steering failure of two wheels on the rear axle.

3. The fault-tolerant control method for a steering system of a multi-axis distributed drive vehicle according to claim 2, characterized in that: In the step of "obtaining system calculation parameters", the calculation parameters include the vehicle mass, the wheel angle of each axle, the fault angle and the longitudinal speed of the vehicle.

4. The fault-tolerant control method for a steering system of a multi-axis distributed drive vehicle according to claim 3, characterized in that: The specific content of the step "obtaining wheel angle signals through the angle sensor" is: using the wheel angle sensor to collect the angle signal of each wheel in real time act , and sent to the steering motor torque calculation module of the PID controller in real time.

5. The fault-tolerant control method for a steering system of a multi-axis distributed drive vehicle according to claim 4, characterized in that: In the step "adjusting the three parameters kp, ki, kd of the PID controller", kp is the proportional parameter, ki is the integral parameter, and kd is the differential parameter.

6. The fault-tolerant control method for a steering system of a multi-axis distributed drive vehicle according to claim 5, characterized in that: In the step "calculating the active steering torque of the steering motor", the steering torque calculation formula of a single wheel in each calculation cycle is: Among them, δ ref is the steering angle of each wheel calculated by the proportional controller, δ act It is the actual steering angle of the wheel detected by the steering angle sensor.

7. The fault-tolerant control method for a steering system of a multi-axis distributed drive vehicle according to claim 6, characterized in that: The specific content of the step "current controller controls the actuator" is: the current controller controls the current required by the actuator in real time according to the control instructions of the distributed drive vehicle steering controller.

8. The fault-tolerant control method for a steering system of a multi-axis distributed drive vehicle according to claim 7, characterized in that: The specific content of the step "the wheel steering angle continuously approaches the desired value" is: the actuator applies the required active torque to the wheel in real time under the action of current control, so that the wheel steering angle continuously approaches the target value.

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