A multi-axis controlled chassis capable of improving driving safety and a coordinated control method thereof

Abstract

The present invention proposes a multi-axis control chassis and a coordinated control method thereof that can improve driving safety, comprising: a vehicle frame; a suspension system; a wire-controlled brake, an independent steering and a drive device; a signal acquisition and wireless remote control device; matching the above structure, in the low-speed stage, the wire-controlled chassis controls the wire-controlled independent wheel steering device according to the curvature of the target driving trajectory and the obstacle distance, adopts a combination of multiple steering mode switching and independently and accurately controls the steering angle through an electric servo cylinder to achieve safe and efficient steering driving, and the hub motor adopts average torque control to avoid energy consumption caused by frequent torque adjustment; in the high-speed stage, the wire-controlled hub motor control device applies a highly robust fuzzy sliding mode controller to perform differentiated torque control, adjust the steering posture of the wire-controlled chassis and improve trajectory tracking accuracy; the wireless remote control and the wire-controlled steering drive device are combined for coordinated control to improve the steering safety of the wire-controlled chassis under all road conditions and the safe passing ability of narrow road conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-axle vehicle chassis design, and in particular to a multi-axle axle-controlled chassis capable of improving driving safety and a coordinated control method thereof. Background Art

[0002] Multi-axle vehicles, as core engineering equipment, play a vital role in transportation, military transport, and construction, and are developing towards electrification and intelligentization. High-performance multi-axle chassis and coordinated steering control technology can significantly enhance low-speed maneuverability and high-speed handling stability. This has become a key technology in measuring the development level of multi-axle vehicle chassis.

[0003] Multi-axle vehicles often operate in harsh construction sites such as mines, ports, and construction projects. As vehicle length increases and the weight they carry increases, they suffer from disadvantages such as poor low-speed maneuverability and a large turning radius. Consequently, multi-axle vehicles are required to have high maneuverability, a small turning radius, and high steering sensitivity. However, the steering trapezoidal mechanism commonly used in conventional multi-axle vehicle steering systems determines its parameters by fitting the left and right wheel angle relationship for a pure rolling steering mode. This method generally meets the requirements for tire angle relationships near zero. Larger tire angles cannot meet the requirements for pure rolling precision steering, which can easily cause tire drag and wear, and degrade vehicle trajectory tracking capabilities. Furthermore, the commonly used steering trapezoidal mechanism is a single-degree-of-freedom system that can only fit a single steering mode and cannot meet the diverse steering modes required by multi-axle vehicles.

[0004] In terms of the powertrain, traditional multi-axle vehicles transmit engine power to the tires via the transmission system and the differential. During steering, the differential does not differentiate between speed and torque. When excessive understeer or severe oversteer occur during steering, the steering posture of the multi-axle vehicle cannot be adjusted by changing the drive torque.

[0005] To further investigate these core issues, the use of streamlined and reliable experimental chassis to simulate full-vehicle experiments has attracted significant attention from research institutions and businesses due to its ability to shorten R&D cycles and align with actual results. For example, patent (202011277273.2) discloses an electric vehicle chassis that coordinates front wheel tie rod steering and mid-rear axis-controlled steering to improve steering maneuverability to a certain extent. Steering posture control primarily involves applying an additional yaw torque to multi-axle vehicles through differential braking, improving steering safety (see patent 201910884468.4).

[0006] Existing technologies help to improve the steering maneuverability and steering safety of multi-axle vehicles to a certain extent, but there are still some shortcomings, which are mainly manifested as follows:

[0007] 1) Conventional multi-axle vehicle chassis steering drive structures are complex, resulting in relatively low transmission efficiency and cumbersome operation, increasing driver workload. Tire angle errors are large, and because the front axle still utilizes traditional tie rod steering, it still cannot meet the requirements of multiple steering modes. Furthermore, it cannot meet the requirements for pure rolling precision steering even at large steering angles. Tires are prone to rolling and slipping, and multi-axle vehicle trajectory tracking accuracy is relatively low, making it inadequate for steering multi-axle vehicles in narrow road conditions.

[0008] 2) When multi-axle vehicles travel on roads with low adhesion coefficients or experience excessive lateral acceleration while turning, they are prone to instability and safety issues. Traditional multi-axle chassis use braking to control steering stability, which can easily cause speed loss and relatively poor ride comfort, reducing the multi-axle vehicle's dynamic performance and causing significant loss of kinetic energy. There is even the risk of drifting or loss of steering ability, and the vehicle's dynamic performance cannot be fully utilized in complex and harsh road conditions.

[0009] 3) Traditional multi-axle vehicles mainly use PID for longitudinal control. When the vehicle is subject to lateral and longitudinal interference, the overshoot increases, which can easily cause system oscillation and increase the adjustment time. Especially when the vehicle enters a nonlinear state, the poor robustness of the control system can easily lead to vehicle stall, poor stability and other driving safety issues. Summary of the Invention

[0010] The present invention proposes a multi-axis controlled chassis and a coordinated control method thereof that can improve driving safety. The multi-axis controlled chassis can realize all-wheel independent steering of the 6×2 controlled-by-wire chassis, and the steering mode can be switched according to different driving conditions, thereby improving the vehicle's steering maneuverability and passability.

[0011] The present invention adopts the following technical solutions.

[0012] A multi-axis controlled chassis capable of improving driving safety is a 6×2 all-wheel steering controlled-by-wire chassis driven by wheel hub motors, characterized by comprising a frame (E), a suspension system (D), a controlled-by-wire hydraulic brake device (F), a controlled-by-wire independent wheel steering device (A), a controlled-by-wire wheel hub motor drive device (C), and a signal acquisition and wireless remote control device (B).

[0013] The frame is a rectangular parallelepiped assembly consisting of longitudinal beams (4), transverse beams (5) and vertical beams connected together, and is used to provide a location for equipment installation;

[0014] The suspension system consists of a wishbone (1), a shock absorber and a column, which is symmetrically installed on both sides of the frame (E) of the first, second and third axes of the multi-axis controlled chassis and between the tires, and is used to transmit force and torque between the tires and the frame, and to buffer the impact force caused by uneven road surface;

[0015] The wire-controlled hydraulic brake device is composed of a caliper (11), a brake disc (12), a brake master cylinder (15), a remote control electric cylinder (14) and a remote control device, which are symmetrically installed on the driving wheel side system and the non-driving wheel side system respectively, and provide braking force to the tire through the remote control system operation;

[0016] The wire-controlled independent wheel steering device is symmetrically mounted between the first, second and third axle frames and columns (3) and the steering rocker arm (7) for accurately and independently controlling the steering angle of each tire;

[0017] The wire-controlled wheel hub motor drive devices are symmetrically mounted inside the tires of the third axle and are used to drive the vehicle;

[0018] In the signal acquisition and wireless remote control device, the signal acquisition device collects the steering posture and driving trajectory data of the vehicle when the vehicle is driving for feedback control; the wireless remote control device is used to send steering drive driving instructions for the three-axle vehicle.

[0019] When the drive-by-wire chassis is traveling, control commands are sent through a wireless remote control device to adapt to different working conditions. Under low-speed conditions, the drive-by-wire independent wheel steering device adopts a multi-steering mode switching combination to maintain safe and efficient steering according to the target trajectory curvature and obstacle distance of the drive-by-wire chassis. Under high-speed conditions, the drive-by-wire chassis working condition data collected by the signal acquisition device is input into the vehicle status judgment module. When the drive-by-wire chassis has excessive understeer and severe oversteer, the drive-by-wire hub motor control device adjusts the steering posture of the drive-by-wire chassis by increasing additional yaw torque to improve driving safety.

[0020] The wire-controlled independent wheel steering device controls all-wheel steering through an electric servo cylinder. In the all-wheel steering, each steering wheel is controlled by a separate electric servo cylinder. The control of the electric servo cylinder is achieved by the electronic control unit according to the steering mode of the vehicle controller and the wireless remote control device. Different steering modes are formed by different steering angle combinations. It consists of a steering rocker arm (7), an electric servo cylinder and a servo controller. The upper controller sends a message to the servo controller via CAN communication to accurately control the tire angle. The single-side structure of the wire-controlled independent wheel steering device includes:

[0021] Steering rocker arm, one end of which is fixed to the column and the other end is connected to the electric servo cylinder;

[0022] The electric servo cylinder (6) is an integrated structure of a servo motor and a ball screw, which converts the rotational motion of the servo motor into linear motion. It is connected to the steering rocker arm and the other end is fixedly connected to the vehicle frame. The servo driver receives the angle signal from the vehicle controller through CAN communication and is used to control the electric servo cylinder to accurately and independently control the tire angle.

[0023] When the by-wire chassis is steering, six servo controllers receive commands from the vehicle controller to control the electric servo cylinders, independently and precisely controlling the steering angle of each tire. In different steering modes, the six servo controllers work in tandem, switching rapidly. Simultaneously, closed-loop control of the steering angle based on feedback from the steering angle sensors ensures accurate steering and minimizes tire wear.

[0024] The single-side structure of the wire-controlled hub motor drive device includes:

[0025] A hub motor (10), one end of which is connected to the tire via a hub bolt, and the other end of which is connected to the column via a wedge key;

[0026] The wheel hub motor controller (16) is mounted on the vehicle frame through fasteners, converts the two-phase electricity of the vehicle's high-voltage battery into the three-phase electricity required by the wheel hub motor, and establishes information exchange with the wheel hub motor and the vehicle controller through CAN communication according to the message protocol;

[0027] The two wheel hub motor controllers receive control instructions from the vehicle controller via CAN communication. Based on the vehicle status judgment module, they adjust different control modes to achieve precise control of the wheel hub motor speed or torque within the full speed range, and feed back the wheel hub motor status information to the vehicle controller.

[0028] The control modes include average torque mode control and differential torque mode control. In average torque mode, the wheel hub motor speed is precisely controlled by the electronic differential control algorithm to achieve differential speed without torque difference; in differential torque mode, the wheel hub motor torque is precisely controlled to reach the desired value.

[0029] The suspension system is composed of a fork arm (1), a shock absorber (2), a lifting lug and a column (3); the fork arm includes an upper fork arm and a lower fork arm;

[0030] The signal acquisition and wireless remote control device includes:

[0031] Six tire speed sensors (9) are mounted on the column. The wheel speed sensors are kept at a certain distance from the gear ring mounted on the rotating shaft. The Hall effect is used to generate electromotive force for measuring the tire speed and the pulse signal is sent to the vehicle controller.

[0032] Six tire angle sensors are respectively installed on the upper fork arms and connected to the column (3) through elastic couplings. The center line of the sensor main shaft coincides with the main pin of the fork arm. The tire angle signal is measured in real time and converted into a voltage analog value and sent to the vehicle controller.

[0033] The gyroscope is installed near the center of mass of the vehicle and is used to measure the yaw rate and acceleration in the lateral, longitudinal and vertical directions of the three-axis vehicle. It sends the vehicle status information to the vehicle controller via CAN communication.

[0034] Combined inertial navigation, including the XW-G15651MEMS equipped with a MEMS gyroscope and accelerometer and a surveying-grade multi-mode, multi-frequency GNSS receiver, uses dual antennas to assist in rapid, high-precision orientation, collecting real-time motion trajectory information from the steer-by-wire chassis and feeding it back to the vehicle controller to correct deviations.

[0035] The wireless remote control device includes a remote control handle, a wireless transmitter, and a wireless receiver. The remote control handle control signal is sent from the wireless transmitter to the wireless receiver. The wireless receiver sends the control signal to the vehicle controller via CAN communication. The vehicle controller adjusts the control mode of the wire-controlled chassis according to the received signal.

[0036] The wireless remote control device sends instructions to the vehicle controller, which receives information from the wireless remote control device and the signal acquisition device for status feedback requirements of the vehicle status judgment module and the controller, and finally adjusts the control mode of the independent wheel steering device and the hub motor drive device according to the control requirements.

[0037] A coordinated control method for a multi-axis steerable chassis capable of improving driving safety, using the aforementioned 6×2 all-wheel steer-by-wire chassis, comprises the following steps:

[0038] Step S1: Sending vehicle speed and turning angle signals to the vehicle controller via a wireless remote control device;

[0039] Step S2: The vehicle controller controls the steering drive of the by-wire chassis based on the instructions of the wireless remote control device and the information collected by the signal acquisition device. At low speeds, the wheel hub motor drive device of the by-wire chassis adopts average torque control, and the independent wheel steering device changes the relationship between the wheel angles according to the steering mode switching module to achieve efficient and high-precision steering.

[0040] Step S3: At high speeds, the actual longitudinal speed of the controlled-by-wire chassis is estimated based on the tire speed information collected by the sensor. The actual longitudinal speed and the absolute value of the deviation between the actual yaw rate and the ideal yaw rate are input into the vehicle status monitoring module to switch the steering and drive control modes.

[0041] Under low-speed conditions, the steering mode switching module switches the steering mode according to the curvature of the target driving trajectory curve and the obstacle distance of the wire-controlled chassis;

[0042] The wheel hub motor uses the average torque control mode to drive the four steering modes of the independent wheel steering device: the front two-axle steering mode F4WS, three-axle steering (6WS), crab steering and on-the-spot steering mode switching combination, and controls the wire-controlled chassis for steering.

[0043] Under high-speed conditions, the vehicle state monitoring module determines the steering-by-wire chassis driving mode based on the input actual vehicle speed, yaw rate deviation absolute value, and lateral and longitudinal acceleration;

[0044] When the longitudinal speed of the controlled-by-wire chassis is greater than the speed threshold and the absolute value of the yaw rate deviation is less than the yaw rate deviation threshold, the wheel hub motor adopts the differential torque control mode, and the independent wheel steering system can adopt the F4WS or 6WS steering mode;

[0045] When the absolute value of the yaw rate deviation is greater than the yaw rate deviation threshold, the wheel hub motor adopts the differential torque control mode and the independent wheel steering system adopts the F4WS steering mode;

[0046] At the same time, the vehicle status monitoring module also monitors whether the tire lateral force enters the nonlinear region. When the tire is in the nonlinear region, the hub motor control mode switches to the differential torque mode.

[0047] The torque in the wheel hub motor average torque control mode is obtained by a PID controller, and the torque in the differential torque control mode is obtained by a fuzzy sliding mode controller:

[0048] The input of the PID controller includes the speed deviation, and the output is the total torque of the three-axle vehicle tires;

[0049] The fuzzy sliding mode controller takes yaw rate and sideslip angle deviation as inputs and outputs an additional yaw torque. A fuzzy controller is introduced to blur the discontinuous output signal of the sliding mode controller into a continuous torque signal, thereby mitigating the chattering problem in the steering drive coordinated control system caused by the variable load of a multi-axle vehicle and the uncertainty of system parameters.

[0050] The sliding mode surface designed by the fuzzy sliding mode controller based on the yaw rate and the sideslip angle deviation of the center of mass is:

[0051] s=(ω r -ω des )+η(β r -β des )Formula 1;

[0052] Where, ω r is the actual yaw rate of the wire-controlled chassis, ω des is the ideal yaw rate, β r is the actual center of mass side slip angle of the wire-controlled chassis, β des is the ideal center of mass sideslip angle, η is the joint control parameter;

[0053] Combining the two-degree-of-freedom differential equation of motion of a three-axle vehicle and adopting the more robust saturation function constant velocity reaching law, the coordinated control system of the wire-controlled chassis steering drive is ensured to quickly reach the designed sliding surface. Finally, the additional yaw moment control rate of the three-axle vehicle is obtained as follows:

[0054]

[0055] Where, I Z is the vehicle moment of inertia, k is the sliding mode gain, and sat(s / ε) is the saturation function;

[0056] The control method adopts fuzzy control method to reduce the chattering caused by sliding mode control, and blurs the discontinuous signal of sliding mode control into a continuous signal to soften the chattering problem. The method is:

[0057] Fuzzy controller selection s, As input, u is used as output to construct a fuzzy controller; r The equation s composed of the sideslip angle β and the center of mass is fuzzified, and five fuzzy subsets {NB, NS, ZO, PS, PB} covering the fuzzy domain [-2, 2] are selected. The membership function is the Gaussian function, and the fuzzy control rule table is constructed as shown in Table 2.

[0058] Table 2. Fuzzy control rules table

[0059]

[0060] The final control rate additional yaw moment output of the three-axis vehicle fuzzy sliding mode controller is expressed as:

[0061]

[0062] The specific method of step S1 is as follows: wherein the driver operates the wireless remote control device, the steering device adopts the 6WS steering mode when just starting, and the hub motor adopts the average torque control mode;

[0063] The specific method of step S2 is as follows: the steering angle signal is the steering angle of the left front wheel of the first axis. The vehicle controller calculates the expected yaw rate and expected center of mass sideslip angle of the vehicle when turning according to the received steering angle signal and vehicle speed signal, combined with the two-degree-of-freedom dynamic equation of the three-axis vehicle; in order to improve the vehicle trajectory tracking capability, the ideal center of mass sideslip angle is set to zero.

[0064] The ideal two-degree-of-freedom dynamic equation for a three-axle vehicle is as follows:

[0065]

[0066] Where C1, C2, and C3 are the tire cornering stiffnesses of the first, second, and third axles of a three-axle vehicle, respectively; a, b, and c are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively; and β, ω are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively. r are the sideslip angle and yaw rate of the center of mass respectively, m is the mass of the three-axle vehicle, u, δ1 are the vehicle speed and the wheel angle of the first axis, I Z is the vehicle's moment of inertia;

[0067] Ideal yaw rate of a three-axle vehicle:

[0068]

[0069] Where L is the distance from the first axis to the third axis;

[0070] The vehicle controller designs a PID speed controller based on the received vehicle speed signal to calculate the total torque of the three-axis vehicle hub motor drive;

[0071]

[0072] Where, T PID is the total output torque of the three-axle vehicle speed control module, e v is the deviation between the actual speed and the ideal speed, K P ,K I ,K D are the proportional, integral and differential coefficients respectively;

[0073] The specific method of step S3 is as follows: the actual longitudinal speed is estimated based on the tire speed information collected by the sensor, and the absolute value of the difference between the actual longitudinal speed, the actual yaw rate and the ideal yaw rate is input into the steering angle control module and the wheel hub motor control module. At the same time, the three-axis vehicle lateral acceleration information collected by the gyroscope is used to determine whether the tire has entered the nonlinear region. When the lateral acceleration is greater than 0.4g, the risk of vehicle instability increases, and the wheel hub motor needs to switch to the differential torque control mode to provide additional yaw torque for the vehicle to improve the vehicle's steering stability. The specific mode switching rules are shown in Table 1 below.

[0074] Table 1. Steering mode and wheel hub motor control mode switching rules

[0075]

[0076] When the vehicle is in a neutral steering condition, the wheel hub motor torque is evenly distributed, and the value is:

[0077] T 3l =T 3r =T PID / 2 Formula 7;

[0078] Where, T 3lis the torque of the left wheel hub motor of the third axis, T 3r is the torque of the right wheel hub motor of the third axis;

[0079] When the vehicle is in excessive understeer, the vehicle's trajectory deviates outward from the ideal trajectory. At this time, it is necessary to apply an additional counterclockwise yaw moment to the three-axle vehicle by controlling the torque of the wheel hub motor to keep the vehicle's yaw rate and center of mass sideslip angle within a reasonable range.

[0080] When the vehicle is in a severe oversteering state, the vehicle's driving trajectory deviates inward from the ideal trajectory. At this time, it is necessary to control the torque of the wheel hub motor to apply an additional clockwise yaw moment to the three-axle vehicle so that the vehicle's yaw rate and center of mass sideslip angle are within a reasonable range; the steering trajectory keeps up with the ideal trajectory;

[0081] The calculation of the additional yaw moment is mainly based on the error between the actual and ideal yaw rate and sideslip angle of the multi-axle vehicle through a fuzzy sliding mode controller. The design process is as follows:

[0082] The designed sliding surface is:

[0083] s=(ω r -ω des )+η(β r -β des )Formula 8;

[0084] Where, ω r is the actual yaw rate of the wire-controlled chassis, ω des is the ideal yaw rate, β r is the actual center of mass side slip angle of the wire-controlled chassis, β des is the ideal center of mass sideslip angle, η is the joint control parameter;

[0085] Reachable conditions:

[0086]

[0087] Where k is the sliding mode gain;

[0088] Combined with the two-degree-of-freedom differential equation of motion of the three-axis vehicle in step S2, we can obtain:

[0089]

[0090] In order to make the three-axis vehicle control system quickly reach the designed sliding surface, the constant velocity reaching law is selected and the saturation function with better robustness is adopted:

[0091] u=-k*sat(s) Formula 11;

[0092] in, Therefore, the final additional yaw moment control rate of the three-axle vehicle is:

[0093]

[0094] Where, I Z is the vehicle moment of inertia, k is the sliding mode gain, and sat(s / ε) is the saturation function;

[0095] When the wheel hub motors are in differential torque control mode, the additional torques of the wheel hub motors on both sides of the third axis are one positive and one negative, and are equal in magnitude. The positive and negative values ​​and magnitudes are determined by the vehicle's steering direction and steering state. The steering direction is left or right, and the steering state is oversteering or understeering, ensuring that the speed of the control-by-wire chassis is not significantly affected. That is, the additional yaw torque does not change the total longitudinal torque. The final wheel hub motor drive torque is obtained by adding the PID control torque and the fuzzy sliding mode control torque, as shown in Table 3 below.

[0096] Table 3. Additional yaw moment distribution table

[0097]

[0098] The present invention designs and develops a multi-axle electric drive-by-wire chassis driven by wheel hub motors, which includes a wheel hub motor drive unit and an independent wheel steering unit. The wheel hub motor drive unit drives the tires by the wheel hub motor of the third axle, and can adjust the wheel hub motor control mode according to the vehicle's steering posture, thereby improving the steering safety of the multi-axle vehicle. The independent wheel steering unit drives the wheels of the three-axle chassis to steer using six electric cylinders, achieving all-wheel independent steering of the 62-axle drive-by-wire chassis. The steering mode can be switched according to different driving conditions, improving the vehicle's steering maneuverability and passability. In addition, in conjunction with the above structure, a coordinated control method for a multi-axle drive-by-wire chassis that can improve driving safety has been designed and developed. At low speeds, the independent wheel steering unit can switch between multiple steering modes according to the target trajectory curvature and obstacle distance of the drive-by-wire chassis for safe and efficient steering. The wheel hub motor control unit adopts average torque control to avoid frequent switching and increased energy consumption. At high speeds, the data collected by the signal acquisition device is input into the vehicle status judgment module. When the wire-controlled chassis exhibits excessive understeer and severe oversteer, the wire-controlled wheel hub motor control device adjusts the steering posture of the wire-controlled chassis and improves driving safety by increasing additional yaw torque.

[0099] Compared with the prior art, the present invention has the following beneficial effects:

[0100] 1) The 6×2 all-wheel independent steering-by-wire chassis provided by the present invention, driven by in-wheel motors, combines intelligent wireless remote control with a streamlined, in-wheel electric steering drive. It relies on automated programs for mode switching and steering posture adjustment, thereby enhancing the intelligence and electrification of multi-axle in-wheel steering chassis. The independent wheel steering device provides multiple steering modes, enabling the vehicle to have a smaller turning radius. This allows multi-axle vehicles to safely and efficiently navigate narrow spaces by switching between different steering modes, thereby improving their steering maneuverability and high passability. Furthermore, high-precision electric servo cylinders precisely and independently control the steering angle of each tire, reducing tire wear caused by steering errors. Compared to traditional multi-axle vehicle power systems, in-wheel motor drive systems offer advantages such as simple structure, fast response speed, high control accuracy, flexible speed and torque distribution, and high energy efficiency, which are conducive to unleashing the driving potential of multi-axle vehicles.

[0101] 2) The present invention provides a multi-axle controlled chassis and coordinated control method for enhancing steering safety. This system utilizes a designed independent wheel steering system and in-wheel motor system to enhance the maneuverability of the multi-axle vehicle by switching between different steering modes. Under normal operating conditions, the in-wheel motors utilize average torque control to avoid the energy consumption associated with frequent torque adjustments. However, under hazardous conditions, the vehicle status monitoring module identifies and adjusts the in-wheel motors to differential torque control mode to adjust the multi-axle vehicle's steering posture. These two systems coordinate control, adjusting the steering drive mode based on the vehicle's status, ensuring high trajectory tracking capability and excellent steering safety even in complex and harsh road conditions.

[0102] 3) This invention addresses the issue of steering instability in multi-axis controlled chassis on low-adhesion roads, at high speeds, and when tires are in the nonlinear region. By employing a highly robust fuzzy sliding mode controller for lateral and longitudinal control, it counteracts external interference and mitigates the chattering associated with sliding mode control. While maintaining longitudinal velocity stability, an additional yaw torque is added to adjust steering posture, improving steering safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0104] Attachment Figure 1 This is a schematic diagram of the structure of a 6×2 wire-controlled chassis vehicle capable of achieving all-wheel independent steering according to an embodiment of the present invention;

[0105] Attachment Figure 2 Schematic diagram of a distributed drive system and independent wheel steering system according to an embodiment of the present invention;

[0106] Attachment Figure 3 This is a block diagram of the steering drive coordination control of a 6×2 all-wheel steer-by-wire chassis according to an implementation example of the present invention.

[0107] Attachment Figure 4 This is a schematic diagram of adjusting the steering posture by adding additional yaw torque by wheel hub motors when there is excessive understeering in a multi-axle vehicle according to an embodiment of the present invention;

[0108] Attachment Figure 5 This is a schematic diagram of adjusting the steering posture by adding additional yaw torque by wheel hub motors when a multi-axle vehicle has severe oversteering according to an embodiment of the present invention;

[0109] Attachment Figure 6 This is a diagram of the input-output membership function of the fuzzy sliding mode controller according to an embodiment of the present invention;

[0110] Attachment Figure 7 This is a diagram showing the coordinated control effect of an implementation case of the present invention;

[0111] In the figure: 1-fork arm; 2-shock absorber; 3-column; 4-longitudinal beam; 5-cross beam; 6-electric servo cylinder; 7-steering rocker arm; 8-wheel core; 9-tire speed sensor; 10-wheel hub motor; 11-caliper; 12-brake disc; 13-rotation angle sensor; 14-remote control electric cylinder; 15-brake master cylinder; 16-wheel hub motor controller; A-wire-controlled independent wheel steering device; B-signal acquisition and wireless remote control device; C-wire-controlled wheel hub motor drive device; D-suspension system; E-frame; F-wire-controlled hydraulic brake device. DETAILED DESCRIPTION

[0112] As shown in the figure, a multi-axis controlled chassis that can improve driving safety is a 6×2 all-wheel steering-by-wire chassis driven by wheel hub motors. It is characterized by: including a frame E, a suspension system D, a wire-controlled hydraulic brake device F, a wire-controlled independent wheel steering device A, a wire-controlled wheel hub motor drive device C, and a signal acquisition and wireless remote control device B;

[0113] The frame is a rectangular assembly consisting of longitudinal beams 4, cross beams 5 and vertical beams connected together, which is used to provide a location for equipment installation;

[0114] The suspension system consists of a wishbone 1, shock absorbers, and uprights, and is symmetrically mounted on both sides of the frame E and between the tires of the first, second, and third axes of the multi-axis controlled chassis. It is used to transmit forces and moments between the tires and the frame, and to cushion the impact caused by uneven road surfaces.

[0115] The wire-controlled hydraulic brake device consists of a caliper 11, a brake disc 12, a brake master cylinder 15, a remote-controlled electric cylinder 14, and a remote control device, which are symmetrically installed on the driving wheel side system and the non-driving wheel side system respectively, and provide braking force to the tire through the remote control system operation;

[0116] The wire-controlled independent wheel steering device is symmetrically installed between the first, second and third axle frames and the column 3 and the steering rocker arm 7, and is used to accurately and independently control the steering angle of each tire;

[0117] The wire-controlled wheel hub motor drive devices are symmetrically mounted inside the tires of the third axle and are used to drive the vehicle;

[0118] In the signal acquisition and wireless remote control device, the signal acquisition device collects the steering posture and driving trajectory data of the vehicle when the vehicle is driving for feedback control; the wireless remote control device is used to send steering drive driving instructions for the three-axle vehicle.

[0119] When the drive-by-wire chassis is traveling, control commands are sent through a wireless remote control device to adapt to different working conditions. Under low-speed conditions, the drive-by-wire independent wheel steering device adopts a multi-steering mode switching combination to maintain safe and efficient steering according to the target trajectory curvature and obstacle distance of the drive-by-wire chassis. Under high-speed conditions, the drive-by-wire chassis working condition data collected by the signal acquisition device is input into the vehicle status judgment module. When the drive-by-wire chassis has excessive understeer and severe oversteer, the drive-by-wire hub motor control device adjusts the steering posture of the drive-by-wire chassis by increasing additional yaw torque to improve driving safety.

[0120] The steer-by-wire independent wheel steering system uses electric servo cylinders to control all-wheel steering. Each steering wheel is controlled by a separate electric servo cylinder. This electric servo cylinder is controlled by an electronic control unit based on the vehicle controller's steering mode and a wireless remote control device. Different steering angle combinations create different steering modes. It consists of a steering rocker arm 7, an electric servo cylinder, and a servo controller. The upper-level controller sends messages to the servo controller via CAN communication to precisely control the tire angle. The single-side structure of the steer-by-wire independent wheel steering system includes:

[0121] Steering rocker arm, one end of which is fixed to the column and the other end is connected to the electric servo cylinder;

[0122] The electric servo cylinder 6 is an integrated structure of a servo motor and a ball screw, which converts the rotational motion of the servo motor into linear motion. It is connected to the steering rocker arm and the other end is fixedly connected to the frame;

[0123] The servo driver receives the rotation angle signal from the vehicle controller via CAN communication, and is used to control the electric servo cylinder to accurately and independently control the tire rotation angle;

[0124] When the by-wire chassis is steering, six servo controllers receive commands from the vehicle controller to control the electric servo cylinders, independently and precisely controlling the steering angle of each tire. In different steering modes, the six servo controllers work in tandem, switching rapidly. Simultaneously, closed-loop control of the steering angle based on feedback from the steering angle sensors ensures accurate steering and minimizes tire wear.

[0125] The single-side structure of the wire-controlled hub motor drive device includes:

[0126] The in-wheel motor 10 has one end connected to the tire via a hub bolt and the other end connected to the column via a wedge key. The in-wheel motor controller 16 is mounted on the vehicle frame via fasteners and converts the two-phase power from the vehicle's high-voltage battery into the three-phase power required by the in-wheel motor. It then communicates with the in-wheel motor and the vehicle controller via CAN communication according to the message protocol.

[0127] The two wheel hub motor controllers receive control instructions from the vehicle controller via CAN communication. Based on the vehicle status judgment module, they adjust different control modes to achieve precise control of the wheel hub motor speed or torque within the full speed range, and feed back the wheel hub motor status information to the vehicle controller.

[0128] The control modes include average torque mode control and differential torque mode control. In average torque mode, the wheel hub motor speed is precisely controlled by the electronic differential control algorithm to achieve differential speed without torque difference; in differential torque mode, the wheel hub motor torque is precisely controlled to reach the desired value.

[0129] The suspension system is composed of a fork arm 1, a shock absorber 2, a lifting lug and a column 3; the fork arm includes an upper fork arm and a lower fork arm;

[0130] The signal acquisition and wireless remote control device includes:

[0131] Six tire speed sensors 9 are mounted on the column. The wheel speed sensors are kept at a certain distance from the ring gear mounted on the rotating shaft. They generate electromotive force through the Hall effect to measure the tire speed and send pulse signals to the vehicle controller.

[0132] Six tire angle sensors are installed on the upper fork arms and connected to the column 3 via elastic couplings. The centerline of the sensor spindle coincides with the kingpin of the fork arm. The real-time tire angle signal is converted into a voltage analog value and sent to the vehicle controller.

[0133] The gyroscope is installed near the center of mass of the vehicle and is used to measure the yaw rate and acceleration in the lateral, longitudinal and vertical directions of the three-axis vehicle. It sends the vehicle status information to the vehicle controller via CAN communication.

[0134] Combined inertial navigation, including the XW-G15651MEMS equipped with a MEMS gyroscope and accelerometer and a surveying-grade multi-mode, multi-frequency GNSS receiver, uses dual antennas to assist in rapid, high-precision orientation, collecting real-time motion trajectory information from the steer-by-wire chassis and feeding it back to the vehicle controller to correct deviations.

[0135] The wireless remote control device includes a remote control handle, a wireless transmitter, and a wireless receiver. The remote control handle control signal is sent from the wireless transmitter to the wireless receiver. The wireless receiver sends the control signal to the vehicle controller via CAN communication. The vehicle controller adjusts the control mode of the wire-controlled chassis according to the received signal.

[0136] The wireless remote control device sends instructions to the vehicle controller, which receives information from the wireless remote control device and the signal acquisition device for status feedback requirements of the vehicle status judgment module and the controller, and finally adjusts the control mode of the independent wheel steering device and the hub motor drive device according to the control requirements.

[0137] A coordinated control method for a multi-axis steerable chassis capable of improving driving safety, using the aforementioned 6×2 all-wheel steer-by-wire chassis, comprises the following steps:

[0138] Step S1: Sending vehicle speed and turning angle signals to the vehicle controller via a wireless remote control device;

[0139] Step S2: The vehicle controller controls the steering drive of the by-wire chassis based on the instructions of the wireless remote control device and the information collected by the signal acquisition device. At low speeds, the wheel hub motor drive device of the by-wire chassis adopts average torque control, and the independent wheel steering device changes the relationship between the wheel angles according to the steering mode switching module to achieve efficient and high-precision steering.

[0140] Step S3: At high speeds, the actual longitudinal speed of the controlled-by-wire chassis is estimated based on the tire speed information collected by the sensor. The actual longitudinal speed and the absolute value of the deviation between the actual yaw rate and the ideal yaw rate are input into the vehicle status monitoring module to switch the steering and drive control modes.

[0141] Under low-speed conditions, the steering mode switching module switches the steering mode according to the curvature of the target driving trajectory curve and the obstacle distance of the wire-controlled chassis;

[0142] The wheel hub motor uses the average torque control mode to drive the four steering modes of the independent wheel steering device: the front two-axle steering mode F4WS, three-axle steering (6WS), crab steering and on-the-spot steering mode switching combination, and controls the wire-controlled chassis for steering.

[0143] Under high-speed conditions, the vehicle state monitoring module determines the steering-by-wire chassis driving mode based on the input actual vehicle speed, yaw rate deviation absolute value, and lateral and longitudinal acceleration;

[0144] When the longitudinal speed of the controlled-by-wire chassis is greater than the speed threshold and the absolute value of the yaw rate deviation is less than the yaw rate deviation threshold, the wheel hub motor adopts the differential torque control mode, and the independent wheel steering system can adopt the F4WS or 6WS steering mode;

[0145] When the absolute value of the yaw rate deviation is greater than the yaw rate deviation threshold, the wheel hub motor adopts the differential torque control mode and the independent wheel steering system adopts the F4WS steering mode;

[0146] At the same time, the vehicle status monitoring module also monitors whether the tire lateral force enters the nonlinear region. When the tire is in the nonlinear region, the hub motor control mode switches to the differential torque mode.

[0147] The torque in the wheel hub motor average torque control mode is obtained by a PID controller, and the torque in the differential torque control mode is obtained by a fuzzy sliding mode controller:

[0148] The input of the PID controller includes the speed deviation, and the output is the total torque of the three-axle vehicle tires;

[0149] The fuzzy sliding mode controller takes yaw rate and sideslip angle deviation as inputs and outputs an additional yaw torque. A fuzzy controller is introduced to blur the discontinuous output signal of the sliding mode controller into a continuous torque signal, thereby mitigating the chattering problem in the steering drive coordinated control system caused by the variable load of a multi-axle vehicle and the uncertainty of system parameters.

[0150] The sliding mode surface designed by the fuzzy sliding mode controller based on the yaw rate and the sideslip angle deviation of the center of mass is:

[0151] s=(ω r -ω des )+η(β r -β des )Formula 1;

[0152] Where, ω r is the actual yaw rate of the wire-controlled chassis, ω des is the ideal yaw rate, β r is the actual center of mass side slip angle of the wire-controlled chassis, β des is the ideal center of mass sideslip angle, η is the joint control parameter;

[0153] Combining the two-degree-of-freedom differential equation of motion of a three-axle vehicle and adopting the more robust saturation function constant velocity reaching law, the coordinated control system of the wire-controlled chassis steering drive is ensured to quickly reach the designed sliding surface. Finally, the additional yaw moment control rate of the three-axle vehicle is obtained as follows:

[0154]

[0155] Where, I Z is the vehicle moment of inertia, k is the sliding mode gain, and sat(s / ε) is the saturation function;

[0156] The control method adopts fuzzy control method to reduce the chattering caused by sliding mode control, and blurs the discontinuous signal of sliding mode control into a continuous signal to soften the chattering problem. The method is:

[0157] Fuzzy controller selection s, As input, u is used as output to construct a fuzzy controller; r The equation s composed of the sideslip angle β and the center of mass is fuzzified, and five fuzzy subsets {NB, NS, ZO, PS, PB} covering the fuzzy domain [-2, 2] are selected. The membership function is the Gaussian function, and the fuzzy control rule table is constructed as shown in Table 2.

[0158] Table 2. Fuzzy control rules table

[0159]

[0160] The final control rate additional yaw moment output of the three-axis vehicle fuzzy sliding mode controller is expressed as:

[0161]

[0162] The specific method of step S1 is as follows: wherein the driver operates the wireless remote control device, the steering device adopts the 6WS steering mode when just starting, and the hub motor adopts the average torque control mode;

[0163] The specific method of step S2 is as follows: the steering angle signal is the steering angle of the left front wheel of the first axis. The vehicle controller calculates the expected yaw rate and expected center of mass sideslip angle of the vehicle when turning according to the received steering angle signal and vehicle speed signal, combined with the two-degree-of-freedom dynamic equation of the three-axis vehicle; in order to improve the vehicle trajectory tracking capability, the ideal center of mass sideslip angle is set to zero.

[0164] The ideal two-degree-of-freedom dynamic equation for a three-axle vehicle is as follows:

[0165]

[0166] Where C1, C2, and C3 are the tire cornering stiffnesses of the first, second, and third axles of a three-axle vehicle, respectively; a, b, and c are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively; and β, ω are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively. r are the sideslip angle and yaw rate of the center of mass respectively, m is the mass of the three-axle vehicle, u, δ1 are the vehicle speed and the wheel angle of the first axis, I Z is the vehicle's moment of inertia;

[0167] Ideal yaw rate of a three-axle vehicle:

[0168]

[0169] Where L is the distance from the first axis to the third axis;

[0170] The vehicle controller designs a PID speed controller based on the received vehicle speed signal to calculate the total torque of the three-axis vehicle hub motor drive;

[0171]

[0172] Where, T PID is the total output torque of the three-axle vehicle speed control module, e v is the deviation between the actual speed and the ideal speed, K P ,K I ,K D are the proportional, integral and differential coefficients respectively;

[0173] The specific method of step S3 is as follows: the actual longitudinal speed is estimated based on the tire speed information collected by the sensor, and the absolute value of the difference between the actual longitudinal speed, the actual yaw rate and the ideal yaw rate is input into the steering angle control module and the wheel hub motor control module. At the same time, the three-axis vehicle lateral acceleration information collected by the gyroscope is used to determine whether the tire has entered the nonlinear region. When the lateral acceleration is greater than 0.4g, the risk of vehicle instability increases, and the wheel hub motor needs to switch to the differential torque control mode to provide additional yaw torque for the vehicle to improve the vehicle's steering stability. The specific mode switching rules are shown in Table 1 below.

[0174] Table 1. Steering mode and wheel hub motor control mode switching rules

[0175]

[0176] When the vehicle is in a neutral steering condition, the wheel hub motor torque is evenly distributed, and the value is:

[0177] T 3l =T 3r =T PID / 2 Formula 7;

[0178] Where, T 3lis the torque of the left wheel hub motor of the third axis, T 3r is the torque of the right wheel hub motor of the third axis;

[0179] When the vehicle is in excessive understeer, the vehicle's trajectory deviates outward from the ideal trajectory. At this time, it is necessary to apply an additional counterclockwise yaw moment to the three-axle vehicle by controlling the torque of the wheel hub motor to keep the vehicle's yaw rate and center of mass sideslip angle within a reasonable range.

[0180] When the vehicle is in a severe oversteering state, the vehicle's driving trajectory deviates inward from the ideal trajectory. At this time, it is necessary to control the torque of the wheel hub motor to apply an additional clockwise yaw moment to the three-axle vehicle so that the vehicle's yaw rate and center of mass sideslip angle are within a reasonable range; the steering trajectory keeps up with the ideal trajectory;

[0181] The calculation of the additional yaw moment is mainly based on the error between the actual and ideal yaw rate and sideslip angle of the multi-axle vehicle through a fuzzy sliding mode controller. The design process is as follows:

[0182] The designed sliding surface is:

[0183] s=(ω r -ω des )+η(β r -β des ) Formula 8;

[0184] Where, ω r is the actual yaw rate of the wire-controlled chassis, ω des is the ideal yaw rate, β r is the actual center of mass side slip angle of the wire-controlled chassis, β des is the ideal center of mass sideslip angle, η is the joint control parameter;

[0185] Reachable conditions:

[0186]

[0187] Where k is the sliding mode gain;

[0188] Combined with the two-degree-of-freedom differential equation of motion of the three-axis vehicle in step S2, we can obtain:

[0189]

[0190] In order to make the three-axis vehicle control system quickly reach the designed sliding surface, the constant velocity reaching law is selected and the saturation function with better robustness is adopted:

[0191] u=-k*sat(s) Formula 11;

[0192] in,

[0193] Therefore, the final additional yaw moment control rate of the three-axle vehicle is:

[0194]

[0195] Where, I Z is the vehicle moment of inertia, k is the sliding mode gain, and sat(s / ε) is the saturation function;

[0196] When the wheel hub motors are in differential torque control mode, the additional torques of the wheel hub motors on both sides of the third axis are one positive and one negative, and are equal in magnitude. The positive and negative values ​​and magnitudes are determined by the vehicle's steering direction and steering state. The steering direction is left or right, and the steering state is oversteering or understeering, ensuring that the speed of the control-by-wire chassis is not significantly affected. That is, the additional yaw torque does not change the total longitudinal torque. The final wheel hub motor drive torque is obtained by adding the PID control torque and the fuzzy sliding mode control torque, as shown in Table 3 below.

[0197] Table 3. Additional yaw moment distribution table

[0198]

[0199] Example 1

[0200] like Figure 1 As shown, the 6×2 all-wheel steering-by-wire chassis driven by in-wheel motors described in the present invention specifically comprises: a frame E, a suspension system D, a wire-controlled hydraulic brake device F, a wire-controlled independent wheel steering device A, a wire-controlled in-wheel motor drive device C, and a signal acquisition and wireless remote control device B. The suspension system D is mounted on both sides of the frame E, transmitting force and torque between the tires and the frame, thereby buffering impact forces caused by road irregularities. The wire-controlled independent wheel steering devices A are symmetrically and independently mounted between the frames and uprights 3 and the steering rocker arms 7 of the first, second, and third axles, enabling multiple steering modes. The wire-controlled in-wheel motor drive devices C are symmetrically mounted inside the tires of the third axle to drive the vehicle. The wire-controlled hydraulic brake devices F are symmetrically mounted on the drive wheel side system and the non-drive wheel side system, providing braking force to the tires via a remote control system. The signal acquisition and wireless remote control device B is primarily used to collect vehicle steering posture and driving trajectory data for feedback control. The wireless remote control device is used to transmit steering and driving commands for the three-axle vehicle.

[0201] The vehicle frame E is composed of longitudinal beams 4 and transverse beams 5. To enhance the frame's bending strength, a transverse beam is designed near the double-wishbone suspension ears of the first, second, and third axles to withstand the impact of forces and moments from the suspension D. The 6×2 all-wheel independent steering-by-wire chassis driven by in-wheel motors described in this invention is applicable to any frame type. In this example, the frame E is a relatively common square frame.

[0202] The suspension system D consists of upper and lower wishbones 1, shock absorbers 2, suspension lugs, and uprights 3. The shock absorbers 2 are selected based on the vehicle's mass and ground clearance requirements. The design of the upper and lower wishbones 1 and uprights 3 primarily considers load capacity and ensuring the overall track meets vehicle design requirements.

[0203] The wire-controlled independent wheel steering device A is as follows: Figure 1 and 2 As shown, the all-wheel steering system features an electric servo cylinder 6 controlling all-wheel steering and a relatively simplified steering transmission mechanism. Each steering wheel is controlled by a separate electric servo cylinder 6. Control of the electric servo cylinder 6 is accomplished by the electronic control unit (ECU) based on the vehicle controller's steering mode and a wireless remote control. Different steering modes can be achieved by combining different steering angles. The system consists of a steering rocker arm 7, an electric servo cylinder 6, and a servo controller. The upper-level controller sends messages to the servo controller via CAN communication to precisely control the tire angles.

[0204] The in-wheel motor drive device C, described as controlled by wire, consists of an in-wheel motor 10 and an in-wheel motor controller 16. The vehicle controller sends messages to the in-wheel motor controller 16 via CAN communication. The device features both average torque mode and differential torque mode. In average torque mode, the electronic differential control algorithm precisely controls the in-wheel motor speed, achieving differential speed without torque difference. In differential torque mode, the in-wheel motor torque is precisely controlled to achieve the desired value.

[0205] The wire-controlled hydraulic brake device F, used to apply braking torque to the corresponding tire, consists of a brake disc 12, a caliper 11, a master cylinder 15, a remote electric cylinder 14, and a remote control device. The remote control device sends a signal to the remote electric cylinder 14, causing the master cylinder 15 to compress, pushing the caliper 11 and applying the brake disc 12.

[0206] The signal acquisition and wireless remote control device B is primarily used to capture the vehicle's steering posture and trajectory during driving. It consists of a steering angle sensor 5, a wheel speed sensor 9, a gyroscope, and a combined inertial navigation system. The steering sensor 5 is mounted on the fork arm, with the main shaft and kingpin coaxial. It is connected to the column via an elastic coupling. It measures the tire's steering angle in real time, converts it into an analog voltage, and transmits it to the vehicle controller. The Hall effect wheel speed sensor 9 is mounted on the column 3, with the ring gear mounted on the rotating shaft. The wheel speed sensor 9 maintains a distance of 1-2 mm from the ring gear. It generates an electromotive force (EMF) through the Hall effect to measure tire rotational speed. The gyroscope, mounted at the estimated vehicle center of mass, primarily measures the vehicle's longitudinal, lateral, and vertical accelerations, as well as its yaw rate during driving. It transmits vehicle status information to the vehicle controller via CAN communication. The combined inertial navigation system, the XW-G15651MEMS, is equipped with a MEMS gyroscope, an accelerometer, and a surveying-grade multi-mode, multi-frequency GNSS receiver. It enables single-antenna dynamic alignment or dual-antenna assisted rapid, high-precision orientation, enabling real-time acquisition of vehicle trajectory information. The wireless remote control system is used to control the vehicle's driving mode. It primarily consists of a remote controller, a wireless transmitter, and a wireless receiver. The transmitter sends control signals from the remote controller to the receiver, which then transmits them to the vehicle controller via CAN communication. The controller then adjusts the ride-by-wire chassis control mode based on the received signals.

[0207] The present invention provides a 6×2 all-wheel independent steering electric wire-controlled chassis driven by hub motors. For the wire-controlled independent wheel steering device A, the steering angle can be accurately and independently controlled by the servo electric cylinders 6 symmetrically installed on both sides of the three axes; for the wire-controlled hub motor drive device C, the hub motors 10 symmetrically installed on both sides of the third axis have fast response speed and high control accuracy, and the speed and torque can be flexibly distributed, and multi-mode independent control can be performed; the wireless remote control and wire-controlled steering drive are combined, and the mode switching and steering posture adjustment are performed by relying on an automated program, and the vehicle status information can be fed back in real time, which can improve work efficiency.

[0208] Example 2

[0209] A multi-axis controlled chassis and a coordinated control method thereof for improving driving safety, using the aforementioned 6×2 electric controlled-by-wire chassis, includes the following steps:

[0210] Step S1: Sending vehicle speed and turning angle signals to the vehicle controller via a wireless remote control device;

[0211] The driver operates the wireless remote control device. When the steering device is just started, it adopts the 6WS steering mode and the wheel hub motor adopts the average torque control mode.

[0212] Step S2: The vehicle controller (VCU) controls the steering drive of the steer-by-wire chassis based on the wireless remote control device's instructions and information collected by the signal acquisition device. At low speeds, the in-wheel motor drive system uses average torque control, and the independent wheel steering system adjusts the wheel angle relationship based on the steering mode switching module, achieving efficient and high-precision steering. The steering angle signal is the left front wheel angle of the first axle. The VCU calculates the desired yaw rate and desired center-of-mass slip angle during steering based on the received steering angle signal and vehicle speed signal, combined with the two-degree-of-freedom dynamic equations for a three-axle vehicle. To improve vehicle trajectory tracking capabilities, the desired center-of-mass slip angle is set to zero.

[0213] Ideal two-degree-of-freedom dynamic equations for a three-axis vehicle:

[0214]

[0215]

[0216] Where C1, C2, and C3 are the tire cornering stiffnesses of the first, second, and third axles of a three-axle vehicle, respectively; a, b, and c are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively; and β, ω are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively. r are the sideslip angle and yaw rate of the center of mass respectively, m is the mass of the three-axle vehicle, u, δ1 are the vehicle speed and the wheel angle of the first axis, I Z is the vehicle's moment of inertia.

[0217] Ideal yaw rate of a three-axle vehicle:

[0218]

[0219] Where L is the distance from the first axis to the third axis;

[0220] The vehicle controller designs a PID speed controller based on the received vehicle speed signal to calculate the total torque driven by the three-axis vehicle hub motor.

[0221]

[0222] Where, T PID is the total output torque of the three-axle vehicle speed control module, e v is the deviation between the actual speed and the ideal speed, K P ,K I ,K D are the proportional, integral and differential coefficients respectively.

[0223] Step S3: The actual longitudinal velocity is estimated based on tire speed information collected by the sensors. The actual longitudinal velocity and the absolute value of the difference between the actual yaw rate and the ideal yaw rate are then input into the steering control module and the in-wheel motor control module. Simultaneously, the three-axis lateral acceleration information collected by the gyroscope is used to determine whether the tires have entered the nonlinear region. When the lateral acceleration exceeds 0.4g, the risk of vehicle instability increases, and the in-wheel motors must switch to differential torque control mode to provide additional yaw torque and improve steering stability. The specific mode switching rules are shown in Table 1.

[0224] Table 1. Steering mode and wheel hub motor control mode switching rules

[0225]

[0226]

[0227] When the vehicle is in neutral steering, the wheel hub motor torque is evenly distributed, and the value is:

[0228] T 3l =T 3r =T PID / 2

[0229] Where, T 3l is the torque of the left wheel hub motor of the third axis, T 3r is the torque of the right wheel hub motor of the third axis.

[0230] like Figure 4 As shown in the figure, when the vehicle is in excessive understeer, the vehicle's driving trajectory deviates outward from the ideal trajectory. At this time, it is necessary to apply an additional counterclockwise yaw moment to the three-axle vehicle by controlling the torque of the wheel hub motor so that the vehicle's yaw angular velocity and center of mass sideslip angle are within a reasonable range.

[0231] like Figure 5 As shown in the figure, when the vehicle is in a severe oversteer state, the vehicle's trajectory deviates inward from the ideal trajectory. At this time, it is necessary to control the torque of the wheel hub motors to apply an additional clockwise yaw moment to the three-axle vehicle to keep the vehicle's yaw rate and sideslip angle within a reasonable range. The steering trajectory keeps up with the ideal trajectory.

[0232] The calculation of the additional yaw moment is mainly based on the error between the actual and ideal yaw rate and sideslip angle of the multi-axle vehicle through a fuzzy sliding mode controller. The main design process is as follows:

[0233] The designed sliding surface is:

[0234] s=(ω r -ω des )+η(β r -βdes );

[0235] Where, ω r is the actual yaw rate of the wire-controlled chassis, ω des is the ideal yaw rate, β r is the actual center of mass side slip angle of the wire-controlled chassis, β des is the ideal center of mass sideslip angle, η is the joint control parameter;

[0236] Reachable conditions:

[0237]

[0238] Where k is the sliding mode gain;

[0239] Combined with the two-degree-of-freedom differential equation of motion of the three-axis vehicle in step S2, we can obtain:

[0240]

[0241] In order to make the three-axis vehicle control system quickly reach the designed sliding surface, the constant velocity reaching law is selected and the saturation function with better robustness is adopted:

[0242] u=-k*sat(s);

[0243] in,

[0244] Therefore, the final additional yaw moment control rate of the three-axle vehicle is:

[0245]

[0246] Where, I Z is the vehicle moment of inertia, k is the sliding mode gain, and sat(s / ε) is the saturation function.

[0247] The complex road conditions and variable loads of multi-axle vehicles during steering pose certain interference to the steering drive control system. Furthermore, the uncertainty of system parameters can cause chattering in the steering drive coordinated sliding mode control, impacting the vehicle's normal operation. Fuzzy control theory is therefore introduced to improve the sliding mode control's resistance to external interference. Fuzzy control methods are used to mitigate chattering caused by sliding mode control, blurring the sliding mode control's discontinuous signal into a continuous signal to mitigate the chattering.

[0248] like Figure 6 As shown, select s, As input, u is used as output to construct a fuzzy controller.

[0249] The yaw angular velocity ω rThe equation s composed of the sideslip angle β and the center of mass is fuzzified, and five fuzzy subsets {NB, NS, ZO, PS, PB} covering the fuzzy domain [-2, 2] are selected. The membership function is the Gaussian function, and the fuzzy control rules are constructed as shown in Table 2.

[0250] Table 2. Fuzzy control rules table

[0251]

[0252] The final control rate output of the three-axis vehicle fuzzy sliding mode controller:

[0253]

[0254] When the in-wheel motors operate in differential torque control mode, the additional torques of the in-wheel motors on the third axle are equal, one positive and one negative. The positive and negative values ​​are determined by the vehicle's steering direction (left or right) and steering state (oversteer or understeer), ensuring that the additional yaw torque does not significantly affect the vehicle's speed. This means that the additional yaw torque does not alter the total longitudinal torque. The final in-wheel motor drive torque is the sum of the PID control torque and the fuzzy sliding mode control torque, as shown in Table 3.

[0255] Table 3. Additional yaw moment distribution table

[0256]

[0257] Figure 7 The coordinated control effect diagram of this implementation case. According to this steering drive coordinated control method, the multi-axle vehicle can better track the ideal driving trajectory under different vehicle speeds and road adhesion coefficients, and the vehicle steering safety is improved;

[0258] The present invention provides a multi-axle controlled chassis and its coordinated control method for improving driving safety. The vehicle controller communicates with the wire-controlled independent wheel steering device and the wire-controlled wheel hub motor drive device via the CAN bus, and feeds signals from the wireless remote control device and the information acquisition system back to the vehicle controller. By coordinating the steering and drive devices and switching steering modes according to different driving conditions, the multi-axle vehicle's steering maneuverability and efficiency in narrow road conditions can be improved. When the vehicle's state monitoring module determines that the multi-axle vehicle exhibits excessive understeer or severe oversteer, differential torque control applies an additional yaw torque to adjust the steering posture, improving the vehicle's trajectory tracking capability and steering safety.

[0259] Matters not covered by the present invention are known technologies.

[0260] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A multi-axis controlled chassis that can improve driving safety, which is a 6×2 all-wheel steer-by-wire chassis driven by in-wheel motors, characterized by: It includes a frame (E), a suspension system (D), a wire-controlled hydraulic brake device (F), a wire-controlled independent wheel steering device (A), a wire-controlled wheel hub motor drive device (C), and a signal acquisition and wireless remote control device (B); The frame is a rectangular parallelepiped assembly consisting of longitudinal beams (4), transverse beams (5) and vertical beams connected together, and is used to provide a location for equipment installation; The suspension system consists of a wishbone (1), a shock absorber and a column, which is symmetrically installed on both sides of the frame (E) of the first, second and third axes of the multi-axis controlled chassis and between the tires, and is used to transmit force and torque between the tires and the frame, and to buffer the impact force caused by uneven road surface; The wire-controlled hydraulic brake device is composed of a caliper (11), a brake disc (12), a brake master cylinder (15), a remote control electric cylinder (14) and a remote control device, which are symmetrically installed on the driving wheel side system and the non-driving wheel side system respectively, and provide braking force to the tire through the remote control system operation; The wire-controlled independent wheel steering device is symmetrically mounted between the first, second and third axle frames and columns (3) and the steering rocker arm (7) for accurately and independently controlling the steering angle of each tire; The wire-controlled wheel hub motor drive devices are symmetrically mounted inside the tires of the third axle and are used to drive the vehicle; In the signal acquisition and wireless remote control device, the signal acquisition device collects the steering posture and driving trajectory data of the vehicle when the vehicle is driving for feedback control; the wireless remote control device is used to send steering drive instructions for the three-axle vehicle; When the by-wire chassis is in motion, control commands are sent via a wireless remote control device to adapt to different operating conditions. At low speeds, the by-wire independent wheel steering system uses a combination of multiple steering modes to maintain safe and efficient steering, based on the curvature of the target trajectory and obstacle distance. At high speeds, the by-wire chassis operating condition data collected by the signal acquisition device is input into the vehicle status assessment module. If the by-wire chassis exhibits excessive understeer or severe oversteer, the by-wire wheel hub motor control device adjusts the steering posture of the by-wire chassis by adding additional yaw torque to improve driving safety. The wire-controlled independent wheel steering device controls all-wheel steering through an electric servo cylinder. In the all-wheel steering, each steering wheel is controlled by a separate electric servo cylinder. The control of the electric servo cylinder is achieved by an electronic control unit according to the steering mode of the vehicle controller and a wireless remote control device. Different steering modes are formed by different steering angle combinations. The device is composed of a steering rocker arm (7), an electric servo cylinder and a servo controller. The upper controller sends a message to the servo controller through CAN communication to accurately control the tire angle. The single-side structure of the wire-controlled independent wheel steering device includes: Steering rocker arm, one end of which is fixed to the column and the other end is connected to the electric servo cylinder; The electric servo cylinder (6) is an integrated structure of a servo motor and a ball screw, which converts the rotational motion of the servo motor into linear motion. It is connected to the steering rocker arm and the other end is fixedly connected to the vehicle frame. The servo driver receives the angle signal from the vehicle controller through CAN communication and is used to control the electric servo cylinder to accurately and independently control the tire angle. When the drive-by-wire chassis is steering, six servo controllers receive instructions from the vehicle controller to control the electric servo cylinders, independently and accurately controlling the steering angle of each tire; in different steering modes, the six servo controllers are controlled in a coordinated manner and switched quickly, while also performing closed-loop control of the steering angle based on feedback data from the steering angle sensor to ensure steering accuracy and reduce tire wear.

2. The multi-axis controlled chassis capable of improving driving safety according to claim 1, characterized in that: The single-side structure of the wire-controlled hub motor drive device includes: A hub motor (10), one end of which is connected to the tire via a hub bolt, and the other end of which is connected to the column via a wedge key; The wheel hub motor controller (16) is mounted on the vehicle frame through fasteners, converts the two-phase electricity of the vehicle's high-voltage battery into the three-phase electricity required by the wheel hub motor, and establishes information exchange with the wheel hub motor and the vehicle controller through CAN communication according to the message protocol; The two wheel hub motor controllers receive control instructions from the vehicle controller via CAN communication. Based on the vehicle status judgment module, they adjust different control modes to achieve precise control of the wheel hub motor speed or torque within the full speed range, and feed back the wheel hub motor status information to the vehicle controller. The control modes include average torque mode control and differential torque mode control. In average torque mode, the wheel hub motor speed is precisely controlled by the electronic differential control algorithm to achieve differential speed without torque difference; in differential torque mode, the wheel hub motor torque is precisely controlled to reach the desired value.

3. The multi-axis controlled chassis capable of improving driving safety according to claim 1, characterized in that: The suspension system is composed of a fork arm (1), a shock absorber (2), a lifting lug and a column (3); the fork arm includes an upper fork arm and a lower fork arm; The signal acquisition and wireless remote control device includes: Six tire speed sensors (9) are mounted on the column. The wheel speed sensors are kept at a certain distance from the gear ring mounted on the rotating shaft. The Hall effect is used to generate electromotive force for measuring the tire speed and the pulse signal is sent to the vehicle controller. Six tire angle sensors are respectively installed on the upper fork arms and connected to the column (3) through elastic couplings. The center line of the sensor main shaft coincides with the main pin of the fork arm. The tire angle signal is measured in real time and converted into a voltage analog value and sent to the vehicle controller. The gyroscope is installed near the center of mass of the vehicle and is used to measure the yaw rate and acceleration in the lateral, longitudinal and vertical directions of the three-axis vehicle. It sends the vehicle status information to the vehicle controller via CAN communication. Combined inertial navigation, including the XW-G15651MEMS equipped with a MEMS gyroscope and accelerometer and a surveying-grade multi-mode, multi-frequency GNSS receiver, uses dual antennas to assist in rapid, high-precision orientation, collecting real-time motion trajectory information from the steer-by-wire chassis and feeding it back to the vehicle controller to correct deviations. The wireless remote control device includes a remote control handle, a wireless transmitter, and a wireless receiver. The remote control handle control signal is sent from the wireless transmitter to the wireless receiver. The wireless receiver sends the control signal to the vehicle controller via CAN communication. The vehicle controller adjusts the control mode of the wire-controlled chassis according to the received signal. The wireless remote control device sends instructions to the vehicle controller, which receives information from the wireless remote control device and the signal acquisition device for status feedback requirements of the vehicle status judgment module and the controller, and finally adjusts the control mode of the independent wheel steering device and the hub motor drive device according to the control requirements.

4. A coordinated control method for a multi-axis controlled chassis capable of improving driving safety, comprising: The following steps are included: Step S1: Sending vehicle speed and turning angle signals to the vehicle controller via a wireless remote control device; Step S2: The vehicle controller controls the steering drive of the by-wire chassis based on the instructions of the wireless remote control device and the information collected by the signal acquisition device. At low speeds, the wheel hub motor drive device of the by-wire chassis adopts average torque control, and the independent wheel steering device changes the relationship between the wheel angles according to the steering mode switching module to achieve efficient and high-precision steering. Step S3: At high speeds, the actual longitudinal speed of the controlled-by-wire chassis is estimated based on the tire speed information collected by the sensor. The actual longitudinal speed and the absolute value of the deviation between the actual yaw rate and the ideal yaw rate are input into the vehicle status monitoring module to switch the steering and drive control modes.

5. The coordinated control method for a multi-axis controlled chassis capable of improving driving safety according to claim 4, characterized in that: Under low-speed conditions, the steering mode switching module switches the steering mode according to the curvature of the target driving trajectory curve and the obstacle distance of the wire-controlled chassis; The wheel hub motor uses the average torque control mode to drive the four steering modes of the independent wheel steering device: the front two-axle steering mode F4WS, three-axle steering (6WS), crab steering and on-the-spot steering mode switching combination, and controls the wire-controlled chassis for steering.

6. The coordinated control method for a multi-axis controlled chassis capable of improving driving safety according to claim 4, characterized in that: Under high-speed conditions, the vehicle state monitoring module determines the steering-by-wire chassis driving mode based on the input actual vehicle speed, yaw rate deviation absolute value, and lateral and longitudinal acceleration; When the longitudinal speed of the controlled-by-wire chassis is greater than the speed threshold and the absolute value of the yaw rate deviation is less than the yaw rate deviation threshold, the wheel hub motor adopts the differential torque control mode, and the independent wheel steering system can adopt the F4WS or 6WS steering mode; When the absolute value of the yaw rate deviation is greater than the yaw rate deviation threshold, the wheel hub motor adopts the differential torque control mode and the independent wheel steering system adopts the F4WS steering mode; At the same time, the vehicle status monitoring module also monitors whether the tire lateral force enters the nonlinear region. When the tire is in the nonlinear region, the hub motor control mode switches to the differential torque mode.

7. The coordinated control method for a multi-axis controlled chassis capable of improving driving safety according to any one of claims 5 and 6, characterized in that: The torque in the wheel hub motor average torque control mode is obtained by a PID controller, and the torque in the differential torque control mode is obtained by a fuzzy sliding mode controller: The input of the PID controller includes the speed deviation, and the output is the total torque of the three-axle vehicle tires; The fuzzy sliding mode controller takes yaw rate and sideslip angle deviation as inputs and outputs an additional yaw torque. A fuzzy controller is introduced to blur the discontinuous output signal of the sliding mode controller into a continuous torque signal, thereby mitigating the chattering problem in the steering drive coordinated control system caused by the variable load of a multi-axle vehicle and the uncertainty of system parameters.

8. The coordinated control method for a multi-axis controlled chassis capable of improving driving safety according to claim 7, characterized in that: The sliding mode surface designed by the fuzzy sliding mode controller based on the yaw rate and the sideslip angle deviation of the center of mass is: s = (ω r - ω des ) + η(β r - β des ) Equation 1; Where, ω r is the actual yaw rate of the controlled-by-wire chassis, ω des is the ideal yaw rate, β r is the actual center of mass side slip angle of the wire-controlled chassis, β des is the ideal center of mass sideslip angle, η is the joint control parameter; Combining the two-degree-of-freedom differential equation of motion of a three-axle vehicle and adopting the more robust saturation function constant velocity reaching law, the coordinated control system of the wire-controlled chassis steering drive is ensured to quickly reach the designed sliding surface. Finally, the additional yaw moment control rate of the three-axle vehicle is obtained as follows: Where, I Z is the vehicle moment of inertia, k is the sliding mode gain, and sat(s / ε) is the saturation function; The control method adopts fuzzy control method to reduce the chattering caused by sliding mode control, and blurs the discontinuous signal of sliding mode control into a continuous signal to soften the chattering problem. The method is: Fuzzy controller selection s, As input, u is used as output to construct a fuzzy controller; r The equation s composed of the sideslip angle β and the center of mass is fuzzified, and five fuzzy subsets {NB, NS, ZO, PS, PB} covering the fuzzy domain [-2, 2] are selected. The membership function is the Gaussian function, and the fuzzy control rule table is constructed as shown in Table 2. Table 2. Fuzzy control rules table The final control rate additional yaw moment output of the three-axis vehicle fuzzy sliding mode controller is expressed as:

9. The coordinated control method for a multi-axis controlled chassis capable of improving driving safety according to claim 7, characterized in that: The specific method of step S1 is as follows: the driver operates the wireless remote control device, and the steering device adopts the 6WS steering mode and the wheel hub motor adopts the average torque control mode when the vehicle is just started. The specific method of step S2 is as follows: the angle signal is the left front wheel angle of the first axle, and the vehicle controller calculates the expected yaw rate and expected center of mass sideslip angle of the vehicle during steering according to the received angle signal and vehicle speed signal, combined with the two-degree-of-freedom dynamic equation of the three-axis vehicle; to improve the vehicle trajectory tracking capability, the ideal center of mass sideslip angle is set to zero; The ideal two-degree-of-freedom dynamic equation for a three-axle vehicle is as follows: Where C1, C2, and C3 are the tire cornering stiffnesses of the first, second, and third axles of a three-axle vehicle, respectively; a, b, and c are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively; and β, ω are the distances from the center of mass of the three-axle vehicle to the first, second, and third axles, respectively. r are the sideslip angle and yaw rate of the center of mass respectively, m is the mass of the three-axle vehicle, u, δ1 are the vehicle speed and the wheel angle of the first axis, I Z is the vehicle's moment of inertia; Ideal yaw rate of a three-axle vehicle: Where L is the distance from the first axis to the third axis; The vehicle controller designs a PID speed controller based on the received vehicle speed signal to calculate the total torque of the three-axis vehicle hub motor drive; Where, T PID is the total output torque of the three-axle vehicle speed control module, e v is the deviation between the actual speed and the ideal speed, K P ,K I ,K D are the proportional, integral and differential coefficients respectively; The specific method of step S3 is as follows: the actual longitudinal speed is estimated based on the tire speed information collected by the sensor, and the absolute value of the difference between the actual longitudinal speed, the actual yaw angular velocity and the ideal yaw angular velocity is input into the angle control module and the hub motor control module; at the same time, the three-axis vehicle lateral acceleration information collected by the gyroscope is used to determine whether the tire has entered the nonlinear region. When the lateral acceleration is greater than 0.4g, the risk of vehicle instability increases, and the hub motor needs to switch to the differential torque control mode to provide additional yaw torque for the vehicle to improve the vehicle's steering stability. The specific mode switching rules are shown in Table 1 below. Table 1. Steering mode and wheel hub motor control mode switching rules When the vehicle is in a neutral steering condition, the wheel hub motor torque is evenly distributed, and the value is: T 3l =T 3r =T PID / 2Formula 7; Where, T 3l is the torque of the hub motor on the left side of the third axis, T 3r is the torque of the right wheel hub motor of the third axis; When the vehicle is in excessive understeer, the vehicle's trajectory deviates outward from the ideal trajectory. At this time, it is necessary to apply an additional counterclockwise yaw moment to the three-axle vehicle by controlling the torque of the wheel hub motor to keep the vehicle's yaw rate and center of mass sideslip angle within a reasonable range. When the vehicle is in a severe oversteering state, the vehicle's driving trajectory deviates inward from the ideal trajectory. At this time, it is necessary to control the torque of the wheel hub motor to apply an additional clockwise yaw moment to the three-axle vehicle so that the vehicle's yaw rate and center of mass sideslip angle are within a reasonable range; the steering trajectory keeps up with the ideal trajectory; The calculation of the additional yaw moment is mainly based on the error between the actual and ideal yaw rate and sideslip angle of the multi-axle vehicle through a fuzzy sliding mode controller. The design process is as follows: The designed sliding surface is: s = (ω r - ω des ) + η(β r - β des ) Formula VIII; Where, ω r is the actual yaw rate of the controlled-by-wire chassis, ω des is the ideal yaw rate, β r is the actual center of mass side slip angle of the wire-controlled chassis, β des is the ideal center of mass sideslip angle, η is the joint control parameter; Reachable conditions: Where k is the sliding mode gain; Combined with the two-degree-of-freedom differential equation of motion of the three-axis vehicle in step S2, we can obtain: In order to make the three-axis vehicle control system quickly reach the designed sliding surface, the constant velocity reaching law is selected and the saturation function with better robustness is adopted: u=-k*sat(s) Formula 11; in, Therefore, the final additional yaw moment control rate of the three-axle vehicle is: Where, I Z is the vehicle moment of inertia, k is the sliding mode gain, and sat(s / ε) is the saturation function; When the hub motors are in differential torque control mode, the additional torques of the hub motors on both sides of the third axis are one positive and one negative, and are equal in magnitude. The positive and negative values ​​and magnitudes are determined by the vehicle's steering direction and steering state. The steering direction is left turn or right turn, and the steering state is oversteering or understeering, ensuring that the speed of the control-by-wire chassis is not greatly affected. That is, the additional yaw moment does not change the total longitudinal torque. The final hub motor driving torque is obtained by adding the PID control torque and the fuzzy sliding mode control torque, as shown in Table 3 below. Table 3. Additional yaw moment distribution table

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