ESC vehicle driving dynamics control method based on rear-wheel steering system

Abstract

The present invention discloses an ESC vehicle driving dynamics control method based on a rear-wheel steering system, belonging to the field of vehicle dynamics control. The method comprises the following steps: S1, determining the vehicle's steering gear ratio; S2, determining the vehicle's generalized characteristic speed under various operating conditions; S3, introducing the rear-wheel steering angle to determine a reference vehicle yaw velocity; S4, determining whether the ESC system is activated based on the difference between the reference vehicle yaw velocity and the actual vehicle yaw velocity, and executing step S5 when the ESC system is activated; S5, calculating a control variable using the difference as a return value for closed-loop control. The method employs the rear-wheel steering system-based ESC vehicle driving dynamics control method, introducing the rear-wheel steering angle into a two-degree-of-freedom model, improving the calculation accuracy of the ESC reference yaw velocity and avoiding the problem of ESC malfunction or inaction caused by the two-degree-of-freedom model not considering the influence of the rear-wheel yaw angle on the vehicle's dynamic characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle dynamic control, and in particular to an ESC vehicle driving dynamic control method based on a rear-wheel steering system. Background Art

[0002] The traditional ESC (electronic stability control system) calculates the reference vehicle yaw rate ω based on the two-degree-of-freedom vehicle model and the steering wheel angle input by the driver. ref (Reference yaw rate). At the same time, the system measures the actual vehicle yaw rate ω through the inertial sensor IMU act (actual yaw rate) to determine the current stability of the vehicle and control it accordingly.

[0003] However, because traditional two-degree-of-freedom vehicle models only consider the front wheel yaw angle as input, this model can relatively accurately calculate the reference vehicle yaw rate for conventional vehicles using only front-wheel steering. However, for vehicles equipped with rear-wheel steering, when the driver steers the vehicle using the steering wheel, the front wheels are mechanically connected to the steering wheel. The front wheel yaw angle is determined by the driver's steering input, while the rear-wheel steering system, based on its own control logic (the rear wheel yaw angle is determined by the rear-wheel steering software and control strategy), drives the rear steering rod via the drive motor to change the rear wheel yaw angle.

[0004] As can be seen, because the traditional two-degree-of-freedom vehicle model only incorporates the front wheel yaw angle in its calculations, it cannot identify the impact of the rear wheel yaw angle on the vehicle's yaw rate. Therefore, when both front and rear wheels yaw simultaneously, the reference vehicle yaw rate calculated by the ESC system based on the traditional two-degree-of-freedom model will be distorted and fail to accurately reflect the vehicle's true stability. This distortion can cause the ESC system to over-control or under-control under certain operating conditions, thereby reducing the vehicle's handling stability.

[0005] At the same time, in the traditional vehicle dynamics definition, the vehicle speed at which the yaw rate gain reaches its maximum value in the vehicle steady-state response is called the characteristic vehicle speed V char , to express the understeering characteristics of the vehicle, which is determined by the vehicle's steering geometry and chassis design. It can be seen that for non-rear-wheel steering vehicles, the characteristic speed is a unique value, and the unique characteristic speed V char The yaw rate gain characteristics of rear-wheel steering vehicles cannot be fully described. Summary of the Invention

[0006] The purpose of the present invention is to provide an ESC vehicle driving dynamics control method based on a rear-wheel steering system to solve the above technical problems.

[0007] To achieve the above object, the present invention provides an ESC vehicle driving dynamics control method based on a rear-wheel steering system, comprising the following steps:

[0008] S1. Determine the vehicle's steering gear ratio and store it in the ESC system for easy reference when the vehicle is running.

[0009] S2. Determine the generalized characteristic speed of the vehicle under various operating conditions, and input the generalized characteristic speed into a three-dimensional map for table lookup during vehicle operation;

[0010] S3, based on the output results of step S1 and step S2, importing the rear wheel steering angle to determine the reference vehicle yaw rate;

[0011] S4. Determine whether the ESC system is activated based on the difference between the reference vehicle yaw rate obtained in step S3 and the actual vehicle yaw rate, and if the ESC system is activated, execute step S5;

[0012] S5. Using the difference between the reference vehicle yaw rate and the actual vehicle yaw rate as a return value of closed-loop control, calculate a control value, and perform control based on the control value.

[0013] Preferably, in step S1, the front wheels of the vehicle are parked on a horizontally rotating angle measuring instrument, the driver turns the steering wheel from the maximum left steering angle to the maximum right angle, and reads the steering wheel angle signal SAR through the CAN bus, and at the same time reads the front wheel swing angle δ through the angle measuring instrument front , and calculate the vehicle's steering gear ratio SGR using the following formula:

[0014] SGR=SAR×δ front .

[0015] Preferably, in step S2, the vehicle is started, the ESC system software control function is turned off, and the rear wheel steering system is turned on. The driver drives the vehicle in a steady state around a circular road with a fixed radius at various speeds, and measures and records the generalized characteristic vehicle speed Vchar under various working conditions. gen , get the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc The relationship between the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc Input the 3D spectrum map for reference when the vehicle is running.

[0016] Preferably, in step S3, the vehicle is started, the ESC system software control function and the rear-wheel steering system are turned on, and the driver drives the vehicle normally. The ESC system calculates the reference vehicle yaw rate ω using the following expression: ref :

[0017]

[0018] Where, δ rear Indicates the rear wheel swing angle;

[0019] Among them, the steering gear ratio SGR and the generalized characteristic speed Vchar gen All are obtained by looking up the table.

[0020] Preferably, in step S4, when the reference vehicle yaw angular velocity ω ref The actual vehicle yaw rate ω measured by the inertial sensor IMU act When the difference Δω between them exceeds a preset threshold, the ESC system is activated and step S5 is executed; otherwise, the vehicle keeps running normally.

[0021] Preferably, in step S5, the control amount u is calculated as follows:

[0022] u=u P +u I +u D

[0023] Where u P represents the proportional term, and u P =K P ×Δω,K P represents the proportional gain, Δω represents the error; u I represents the integral term, and u I =K I ×∫Δω,dt,K I Indicates the integral gain; u D represents the differential term, and K D represents the differential gain;

[0024] When Δω is greater than the positive threshold, the ESC system determines that the vehicle is oversteering. Based on the current steering wheel angle of the vehicle and the actual vehicle yaw rate ω read by the IMU, the vehicle act and lateral acceleration Lat Acc p determines the current vehicle steering direction and converts u into the brake pressure request BrakePressureRequest_OuterFront of the outer front wheel according to the conversion coefficient KTorqueToPressure:

[0025] BrakePressureRequest_OuterFront=KTorqueToPressure×u

[0026] The ESC system's own pressure control module brakes the outer front wheel to reduce the actual vehicle yaw rate ω act , which in turn reduces oversteering and restores vehicle stability;

[0027] When Δω is less than the negative threshold, the ESC system determines that the vehicle is understeering and brakes the inner wheels of the vehicle through the actuator to increase the actual vehicle yaw angular velocity ω act , which in turn reduces understeer and restores vehicle stability.

[0028] Therefore, the present invention adopts the above-mentioned ESC vehicle driving dynamic control method based on the rear-wheel steering system, which has the following beneficial effects:

[0029] 1. Improve vehicle stability: By accurately calculating and controlling the vehicle's yaw rate, the system ensures vehicle stability under complex driving conditions such as high-speed cornering and emergency obstacle avoidance.

[0030] The addition of rear-wheel steering (ACK) further enhances the vehicle's handling, especially at low and high speeds.

[0031] 2. Optimized steering response: Through precise calculation of the steering gear ratio (SGR) and generalized characteristic vehicle speed (Vchar_gen), the vehicle's response is more sensitive and accurate at different speeds and steering angles.

[0032] 3. Improved driving safety: When the ESC system detects that the vehicle's yaw rate deviates from the target value by more than a threshold, it can intervene and adjust the vehicle's state in a timely manner to prevent loss of control or skidding.

[0033] Real-time monitoring and closed-loop control mechanisms improve vehicle safety performance;

[0034] 4. The addition of rear-wheel steering (ACK) not only improves vehicle handling performance but also provides additional stability support in emergency situations. For example, at low speeds, the rear wheels turn in opposite directions to reduce the turning radius and improve maneuverability; at high speeds, the rear wheels turn in the same direction to improve straight-line stability.

[0035] 5. Improved driving experience: Through precise control and optimized steering response, drivers can experience a smoother and safer driving experience, reducing driving fatigue and risks caused by vehicle instability.

[0036] In summary, by comprehensively considering the vehicle's front-wheel steering, rear-wheel steering, and real-time yaw rate control, the vehicle's stability and safety are significantly improved under various driving conditions. This is of great significance for improving the driving experience and reducing traffic accidents.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of the ESC vehicle driving dynamics control method based on the rear-wheel steering system of the present invention;

[0039] Figure 2 A two-dimensional representation of the ESC vehicle driving dynamics control method based on the rear-wheel steering system of the present invention;

[0040] Figure 3 A schematic diagram of a three-dimensional map of the ESC vehicle driving dynamics control method based on a rear-wheel steering system according to the present invention;

[0041] Figure 4 This is a comparison chart of the yaw rate of a reference vehicle calculated using the traditional method and the actual vehicle yaw rate for a real vehicle verification example;

[0042] Figure 5 This is a comparison chart of the yaw rate of a reference vehicle calculated using the method of the present invention and the actual vehicle yaw rate in a real vehicle verification example. DETAILED DESCRIPTION

[0043] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is usually placed when in use. These are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention. In the description of the present invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0045] like Figure 1As shown, a driving dynamics control method of an ESC vehicle based on a rear-wheel steering system includes the following steps:

[0046] S1. Determine the vehicle's steering gear ratio and store it in the ESC system for easy reference when the vehicle is running.

[0047] In step S1, the front wheels of the vehicle are placed on a horizontally rotating angle measuring instrument. The driver turns the steering wheel from the maximum left steering angle to the maximum right angle, and reads the steering wheel angle signal SAR through the CAN bus. At the same time, the front wheel swing angle δ is read through the angle measuring instrument. front , and calculate the vehicle's steering gear ratio SGR using the following formula:

[0048] SGR=SAR×δ front .

[0049] S2. Determine the generalized characteristic speed of the vehicle under various operating conditions, and input the generalized characteristic speed into a three-dimensional map for table lookup during vehicle operation;

[0050] In step S2, the vehicle is started, the ESC system software control function is turned off, and the rear wheel steering system is turned on. The driver drives the vehicle in a steady state around a circular road with a fixed radius at various speeds, and measures and records the generalized characteristic vehicle speed Vchar under various working conditions. gen , get the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc The relationship between the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc Input the 3D spectrum map for reference when the vehicle is running.

[0051] S3, based on the output results of step S1 and step S2, importing the rear wheel steering angle to determine the reference vehicle yaw rate;

[0052] In step S3, the vehicle is started, the ESC system software control function and the rear-wheel steering system are turned on, and the driver drives the vehicle normally. The ESC system calculates the reference vehicle yaw rate ω using the following expression: ref :

[0053]

[0054] Where, δ rear Represents the rear wheel swing angle; among them, the steering gear ratio SGR and the generalized characteristic vehicle speed Vchar gen All are obtained by looking up the table, such as Figure 2As shown, in this embodiment, SGR is obtained by looking up a two-dimensional table with SAS as input; Figure 3 As shown, Vchar gen By checking V ref and Lat Acc It is obtained by inputting the three-dimensional pulse spectrum table.

[0055] S4. Determine whether the ESC system is activated based on the difference between the reference vehicle yaw rate obtained in step S3 and the actual vehicle yaw rate, and if the ESC system is activated, execute step S5;

[0056] In step S4, when the reference vehicle yaw rate ω ref The actual vehicle yaw rate ω measured by the inertial sensor IMU act When the difference Δω between them exceeds a preset threshold, the ESC system is activated and step S5 is executed; otherwise, the vehicle keeps running normally.

[0057] S5. Using the difference between the reference vehicle yaw rate and the actual vehicle yaw rate as a return value of closed-loop control, calculate a control value, and perform control based on the control value.

[0058] In step S5, the control amount u is calculated as follows:

[0059] u=u P +u I +u D

[0060] Where u P represents the proportional term, and u P =K P ×Δω,K P represents the proportional gain, Δω represents the error; u I represents the integral term, and u I =K I ×∫Δω,dt,K I Indicates the integral gain; u D represents the differential term, and K D represents the differential gain;

[0061] When Δω is greater than the positive threshold, the ESC system determines that the vehicle is oversteering. Based on the current steering wheel angle of the vehicle and the actual vehicle yaw rate ω read by the IMU, the vehicle act and lateral acceleration Lat Acc p determines the current vehicle steering direction and converts u into the brake pressure request BrakePressureRequest_OuterFront of the outer front wheel according to the conversion coefficient KTorqueToPressure:

[0062] BrakePressureRequest_OuterFront=KTorqueToPressure×u

[0063] The ESC system's own pressure control module brakes the outer front wheel to reduce the actual vehicle yaw rate ω act , thereby reducing oversteering and restoring vehicle stability;

[0064] When Δω is less than the negative threshold, the ESC system determines that the vehicle is understeering and brakes the inner wheels of the vehicle through the actuator to increase the actual vehicle yaw angular velocity ω act , which in turn reduces understeer and restores vehicle stability.

[0065] Actual vehicle verification example

[0066] In a vehicle ESC system equipped with a rear-wheel steering system, first flash the traditional method to calculate the traditional reference vehicle yaw rate ωref old Then, the software of the present invention was rewritten in the ESC system of the same vehicle to calculate the reference vehicle yaw rate ωref. new The software was used to conduct sinusoidal steering input experiments.

[0067] The result is as follows Figure 4 and Figure 5 As shown, it can be seen that when the traditional method is used, the reference vehicle yaw angular velocity ωref is calculated old and the actual vehicle yaw rate ω act The large difference causes the ESC system to control the vehicle's yaw too early and too strongly, which in turn causes the vehicle to yaw unexpectedly, thus reducing the vehicle's handling performance. new and the actual vehicle yaw rate ω act The difference is small and is within the threshold for activating the ESC system's stability control. The ESC system will not be activated prematurely, the degree of control is appropriate, and the vehicle's handling stability is improved, thereby verifying the effectiveness of the present invention.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for controlling vehicle driving dynamics using an ESC system based on a rear-wheel steering system, characterized by: The following steps are involved: S1. Determine the vehicle's steering gear ratio and store it in the ESC system for easy reference when the vehicle is running. S2. Determine the generalized characteristic speed of the vehicle under various operating conditions, and input the generalized characteristic speed into a three-dimensional map for table lookup during vehicle operation; In step S2, the vehicle is started, the ESC system software control function is turned off, and the rear wheel steering system is turned on. The driver drives the vehicle in a steady state around a circular road with a fixed radius at various speeds, and measures and records the generalized characteristic vehicle speed Vchar under various working conditions. gen , get the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc The relationship between the generalized characteristic speed Vchar gen , vehicle speed V ref and lateral acceleration Lat Acc Input 3D spectrum map for vehicle operation lookup; S3, based on the output results of step S1 and step S2, importing the rear wheel steering angle to determine the reference vehicle yaw rate; In step S3, the vehicle is started, the ESC system software control function and the rear-wheel steering system are turned on, and the driver drives the vehicle normally. The ESC system calculates the reference vehicle yaw rate ω using the following expression: ref : Where, δ rear Represents the rear wheel swing angle; V ref Indicates vehicle speed; SAS indicates steering wheel angle signal; SGR indicates steering gear ratio; Vchar gen represents the generalized characteristic vehicle speed; Among them, the steering gear ratio SGR and the generalized characteristic speed Vchar gen All are obtained by looking up the table; S4. Determine whether the ESC system is activated based on the difference between the reference vehicle yaw rate obtained in step S3 and the actual vehicle yaw rate, and if the ESC system is activated, execute step S5; S5. Using the difference between the reference vehicle yaw rate and the actual vehicle yaw rate as a return value of closed-loop control, calculate a control value, and perform control based on the control value.

2. The ESC vehicle driving dynamics control method based on a rear-wheel steering system according to claim 1, characterized in that: In step S1, the front wheels of the vehicle are placed on a horizontally rotating angle measuring instrument. The driver turns the steering wheel from the maximum left steering angle to the maximum right angle, and reads the steering wheel angle signal SAS through the CAN bus. At the same time, the front wheel swing angle δ is read through the angle measuring instrument. front , and calculate the vehicle's steering gear ratio SGR using the following formula: SGR=SAS / δ front 。 3. The ESC vehicle driving dynamics control method based on a rear-wheel steering system according to claim 2, characterized in that: In step S4, when the reference vehicle yaw rate ω ref The actual vehicle yaw rate ω measured by the inertial sensor IMU act When the difference Δω between them exceeds a preset threshold, the ESC system is activated and step S5 is executed; otherwise, the vehicle keeps running normally.

4. The ESC vehicle driving dynamics control method based on a rear-wheel steering system according to claim 3, characterized in that: In step S5, the control amount u is calculated as follows: in=in P +in I +in D Where u P represents the proportional term, and u P =K P ×Δω,K P represents the proportional gain, Δω represents the error; u I represents the integral term, and u I =K I ×∫Δω,dt,K I Indicates the integral gain; u D represents the differential term, and K D represents the differential gain; When Δω is greater than the positive threshold, the ESC system determines that the vehicle is oversteering. Based on the current steering wheel angle of the vehicle and the actual vehicle yaw rate ω read by the IMU, the vehicle act and lateral acceleration Lat Acc Determine the current vehicle steering direction and convert u into the brake pressure request BrakePressureRequest_OuterFront for the outer front wheel based on the conversion coefficient KTorqueToPressure: BrakePressureRequest_OuterFront=KTorqueToPressure×u The ESC system's own pressure control module brakes the outer front wheel to reduce the actual vehicle yaw rate ω act , which in turn reduces oversteering and restores vehicle stability; When Δω is less than the negative threshold, the ESC system determines that the vehicle is understeering and brakes the inner wheels of the vehicle through the actuator to increase the actual vehicle yaw angular velocity ω act , which in turn reduces understeer and restores vehicle stability.

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