Control method for an electric vehicle, vehicle controller and electric vehicle

Abstract

The application discloses a control method, a vehicle controller and an electric vehicle for the electric vehicle, relates to the field of new energy vehicles, and can be applied to pure electric vehicles and hybrid vehicles. The control method comprises the following steps: in the process of steering driving on a first road surface, the steering angle of a steering wheel is a first steering angle, a road feeling motor of a steer-by-wire system outputs a first feedback torque; after driving from the first road surface to a second road surface, in the process that the steering angle of the steering wheel still remains the first steering angle, the road feeling motor is actively controlled to output a second feedback torque which is greater than the first feedback torque; after the steering wheel is returned to the original position, in the process of straight driving on the second road surface, the road feeling motor is controlled to reduce to a third feedback torque; and in the process of straight driving after driving out of the second road surface and driving into the first road surface again, the road feeling motor is actively controlled to output a feedback torque which is reduced to be less than the third feedback torque. According to the scheme, the driving safety is improved, the requirement for the driving ability of a driver is reduced, and the vehicle instability caused by misoperation is avoided.

Description

Technical Field

[0001] This application relates to the field of electric vehicles, and more specifically, to a control method for electric vehicles, a vehicle controller, and an electric vehicle. Background Technology

[0002] As the automotive industry undergoes a profound upgrade towards intelligence and electrification, vehicle speeds continue to increase, and users' demands for driving safety are becoming increasingly stringent. Current mainstream intelligent driving systems primarily rely on non-contact sensors such as lidar and cameras, which can identify abnormal road conditions with significant differences. While they can achieve a certain degree of advanced perception, their recognition accuracy is limited and easily affected by lighting and weather conditions. They struggle to effectively identify dangerous low-adhesion road surfaces with weak visual features, such as black ice and thin ice. When encountering sudden changes in the coefficient of friction at high speeds, this can easily lead to a loss of control. Faced with sudden changes in road surface adhesion, drivers with insufficient experience or limited emergency response capabilities may find it difficult to react quickly and correctly, further amplifying safety hazards.

[0003] Therefore, improving the stability of vehicles driving on low-friction surfaces is a problem that needs to be solved. Summary of the Invention

[0004] This application provides a control method, vehicle controller, and electric vehicle for electric vehicles. Utilizing the mechanical decoupling characteristic of the steering wheel and wheels in a steer-by-wire system, the steer-by-wire system actively takes over the feedback torque of the road feel motor. At the upper level, it provides tactile warnings and resists misoperation by increasing the steering wheel hand force, preventing the electric vehicle from becoming unstable due to lateral force saturation. It reminds and assists the driver, avoids misoperation from exacerbating the instability of the electric vehicle, improves driving safety, and reduces the requirements for the driver's driving skills.

[0005] Firstly, this application provides a control method for an electric vehicle. The method adjusts the feedback torque of the road feeler motor in a steer-by-wire system to adapt to changes in road surface adhesion during the electric vehicle's turning and driving over abrupt road surfaces. The abrupt road surface includes a first road surface and a second road surface, where the coefficient of adhesion of the first road surface is greater than that of the second road surface. The control method includes controlling the road feeler motor of the steer-by-wire system to output a first feedback torque during the electric vehicle's turning motion on the first road surface, while the steering wheel angle remains at the first angle. After the electric vehicle turns from the first road surface to the second road surface, while the steering wheel angle remains at the first angle, actively controlling the road feeler motor to output a second feedback torque greater than the first feedback torque. After the steering wheel returns to center, during the electric vehicle's straight-line driving on the second road surface, controlling the feedback torque output by the road feeler motor to decrease to a third feedback torque. During the electric vehicle's straight-line driving after exiting the second road surface and re-entering the first road surface, actively controlling the feedback torque output by the road feeler motor to decrease to less than the third feedback torque.

[0006] Steer-by-wire (SBW) is a steering system that completely replaces traditional mechanical connections with electronic signals. It eliminates the rigid mechanical transmission connection between the steering wheel and the steering wheels, removing the physical connection (such as the steering column) and achieving complete decoupling. Its core workflow involves sensors acquiring the driver's steering intentions and converting them into electrical signals. These signals are then processed by the electronic control unit to drive the steering motor and control wheel rotation. A steer-by-wire system includes an upper steering wheel assembly (hand wheel actuator, HWA) and a lower steering actuator assembly (road wheel actuator, RWA). The upward steering wheel assembly is primarily responsible for simulating driver feel and steering intentions. It includes an upward steering controller and a road feel motor. The upward steering controller collects the driver's input steering angle and torque, converts them into standardized electrical signals, and sends the front wheel angle command representing the driver's intention to the chassis controller area network (CAN). The road feel motor provides hand torque damping based on the driver's steering wheel angle and speed. Based on road feedback electrical signals, the road feel motor outputs damping, return torque, and other simulated steering feedback forces to reproduce the steering feel. The downward steering actuator assembly is primarily responsible for completing the front wheel steering action according to the driver's intentions. It includes a downward steering controller and a steering motor. The downward steering controller receives the front wheel angle command and simultaneously controls the steering motor to drive the front wheels to achieve the steering action.

[0007] Electric vehicles are prone to loss of control when encountering sudden changes in road surface adhesion coefficients, such as transitioning from dry asphalt to icy, wet, or slippery surfaces. In this situation, the road surface the electric vehicle is traveling on includes a first and a second intersecting surface, with the first surface having a higher adhesion coefficient than the second. Sudden changes in road surface adhesion coefficient refer to a rapid shift in the coefficient of friction. Sudden changes include both high-adhesion and low-adhesion surfaces. The first surface is a high-adhesion surface, with an adhesion coefficient greater than a preset value. The second surface is a low-adhesion surface, meaning it has a low coefficient of friction with the wheels. The adhesion coefficient is the ratio of adhesion force to the normal pressure exerted by the wheel, determined by the road surface and tires; a higher coefficient means greater usable adhesion. The second surface has an adhesion coefficient less than a preset value. When an electric vehicle enters a low-adhesion surface, the adhesion coefficient between the wheels and the road surface decreases. When an electric vehicle travels on a low-adhesion surface, the wheels have less grip, making it prone to slippage or wheel lock-up, resulting in lower stability.

[0008] During the turning maneuver of the electric vehicle on the first surface (high-friction surface), the driver turns the steering wheel to the first turning angle. At this time, the road-sensor motor controlling the steer-by-wire system outputs the first feedback torque. This first feedback torque is mainly based on the current vehicle speed and the first turning angle, simulating the centering characteristics and lateral torque generated by the tires under normal high-friction surface conditions. It provides the driver with a basic feedback torque that conforms to normal driving habits, allowing the driver to clearly perceive the normal steering resistance of the vehicle on a safe surface, ensuring smooth and easy handling during daily driving.

[0009] When an electric vehicle transitions from the first road surface to the second road surface (a low-friction surface), and the steering wheel angle remains at the first angle, the stability margin of the electric vehicle decreases significantly due to the sudden drop in the road surface adhesion coefficient. At this point, the electric vehicle actively intervenes, controlling the road feel motor to output a second feedback torque greater than the first feedback torque. This avoids the phenomenon of the steering wheel becoming lighter on low-friction surfaces due to the decrease in tire return torque, a common problem with traditional mechanical steering. By actively increasing the output of the road feel motor, a noticeable resistance is created. This instantaneous increase in steering wheel resistance provides a direct physical warning to the driver, indicating that the road surface adhesion conditions have severely deteriorated. On low-friction surfaces, because the lateral force of the tires easily saturates, if the driver continues to apply excessive steering wheel angle input, it will easily lead to vehicle skidding and loss of control. The increase in second feedback torque suppresses driver error, increasing the difficulty for the driver to continue steering, effectively resisting and filtering oversteering errors caused by panic or lack of experience, and maintaining the electric vehicle's driving state within its safe limits.

[0010] After the steering wheel is straightened, the electric vehicle enters a straight-line driving state on the second road surface. At this time, the feedback torque output by the road feel motor decreases to the third feedback torque. The third feedback torque is a torque set for straight-line driving on low-friction surfaces. By applying a certain system friction torque or damping torque through the road feel motor, the backlash in the mechanism is eliminated and the road feel is reconstructed. This provides a clear straight-line driving feel and enhances stability. When driving straight on a low-friction surface, the road surface's anti-interference ability is weak. The presence of the third feedback torque makes the steering wheel maintain a certain sense of stability and weight, which can effectively prevent the driver's slight hand tremors or unintentional misoperations from being converted into unexpected lateral movements of the vehicle, thereby significantly improving the path-keeping ability when driving straight at high speed on low-friction surfaces.

[0011] When the electric vehicle leaves the second road surface and re-enters the first road surface to continue driving straight, the road conditions return to safety. At this point, the feedback torque output by the active control road-sensing motor decreases to less than the third feedback torque, thus restoring the basic feedback state for normal straight-line driving on a high-friction surface. The electric vehicle leaves the low-friction danger zone, releasing the additional restraining torque applied for anti-skid purposes, and restoring a normal, light, and responsive straight-line driving feel. This avoids increasing driver muscle fatigue caused by a continuously heavy steering wheel, achieving a smooth switch and dynamic balance between safety intervention and everyday comfortable driving, significantly improving the driving experience.

[0012] According to the solution of this application, by utilizing the mechanical decoupling characteristics of the steering wheel and wheels of the steer-by-wire system, the steer-by-wire system actively takes over the feedback torque of the road feel motor. At the upper level, it provides tactile warnings and resists misoperation by increasing the steering wheel force, thereby preventing the electric vehicle from becoming unstable due to lateral force saturation. At different stages such as steering, straightening, and driving straight, it provides the driver with tactile warnings and force limits that match the road adhesion state and the stability boundary of the electric vehicle, thereby ensuring driving safety in all aspects.

[0013] In conjunction with the first aspect, in some implementations of the first aspect, the control method includes controlling the road feel motor of the steer-by-wire system to maintain a constant third feedback torque when the coefficient of adhesion of the second road surface is less than a preset value during the straight-line travel of the electric vehicle on the second road surface. Conversely, during the straight-line travel of the electric vehicle after it leaves the second road surface and re-enters the first road surface, when the coefficient of adhesion of the first road surface is greater than a preset value, the road feel motor of the steer-by-wire system is controlled to reduce the feedback torque.

[0014] By introducing a preset value as a benchmark for measuring whether the road surface provides sufficient grip for safe driving, and leveraging the fully decoupled and independently reconfigurable road feel of the steer-by-wire system, the driver can increase steering effort to ensure stability when the electric vehicle is in a low-traction, hazardous state, and quickly release steering effort once the vehicle is fully on a safe surface. This optimizes the driver's experience and comfort while ensuring driving safety. This preset value is pre-calibrated based on real-vehicle experiments and / or model calculations, or it can be pre-set considering overall vehicle requirements and performance.

[0015] While the electric vehicle is traveling straight on the second road surface, it is determined that the coefficient of friction of the second road surface is less than a preset value. At this time, the road feel motor of the active control steer-by-wire system maintains a constant third feedback torque. On roads with a low coefficient of friction, the road surface's lateral disturbance resistance is extremely poor, and even minor lateral disturbances can lead to loss of control. In this situation, the road feel motor continuously and stably outputs the third feedback torque to maintain a high drag torque, providing and maintaining a clear, solid feel and stability in the steering wheel. This continuous drag effectively filters and absorbs slight hand tremors caused by road bumps or driver tension, or unconscious minor steering inputs caused by arm weight, keeping the electric vehicle on a straight driving path and enhancing the psychological sense of safety during low-friction, high-speed straight driving.

[0016] During the straight-line movement of the electric vehicle after exiting the second road surface and re-entering the first road surface, the road-sensing motor of the active control steer-by-wire system reduces the feedback torque. When the road surface adhesion boundary fully meets the requirements of normal safe driving, it is no longer necessary to apply additional anti-slip safety restraint torque. At this time, the output command of the road-sensing motor is reduced in real time, releasing the high-hand force under low-adhesion conditions.

[0017] According to the solution in this application, during straight-line driving on a low-friction second surface, the feedback torque of the road feel motor is maintained at a constant third feedback torque, ensuring the continuity and consistency of the straight-line driving feel. This effectively prevents the driver from panicking or making unnecessary steering corrections due to abnormal feel, significantly reducing the risk of loss of control under low-friction straight-line driving conditions and improving driving safety. At the moment the vehicle re-enters a high-friction surface from a low-friction surface, the feedback torque of the road feel motor is actively reduced, avoiding an unnatural experience of a still heavy or overly stiff steering wheel feel. This allows the feel feedback to accurately and in real-time reflect the improvement in the physical adhesion characteristics of the road surface, greatly enhancing the human-machine interaction comfort of the steer-by-wire system and reducing driver fatigue.

[0018] In conjunction with the first aspect, in some implementations of the first aspect, the electric vehicle includes in-tire sensors disposed within the tires of the wheels for detecting electric vehicle information. Specifically, the control method includes, during the straight-moving process of the electric vehicle, when the road surface adhesion coefficient indicated by the electric vehicle information from the in-tire sensors is greater than a preset value, controlling the feedback torque of the road feel motor of the steer-by-wire system to remain constant. When the road surface adhesion coefficient indicated by the electric vehicle information from the in-tire sensors is less than the preset value, controlling the feedback torque of the road feel motor of the steer-by-wire system to increase.

[0019] In-tire sensors refer to various physical quantity sensing components directly installed or adhered inside the tire, such as in the inner liner of the tire crown, under the tread blocks, or in the valve assembly. In-tire sensors include accelerometers (inertial measurement units, IMUs), strain sensors, and optical sensors. As the tire rotates and contacts the road surface, the tire body deforms and vibrates; in-tire sensors directly collect data from this process. When the road surface adhesion coefficient changes, the contact force between the tire and the road changes, causing corresponding changes in the amplitude, frequency, and fluctuation characteristics of the signal. Traditional chassis sensing solutions require waiting for the electric vehicle to produce significant slippage or yaw before sensing, resulting in a time lag. In contrast, in-tire sensors are located directly on the contact surface between the tire and the road surface. When the wheel travels over different road surfaces, the different road media directly cause significant changes in tire deformation and high-frequency vibration signals. By processing this acceleration information, the true adhesion coefficient of the current road surface can be calculated within a very short period of wheel rotation.

[0020] When the in-tire sensor indicates that the road surface adhesion coefficient is greater than a preset value, it means the current road surface provides sufficient adhesion, and the electric vehicle is in a safe driving state. At this time, there is no need to change the steering wheel turning force; the steer-by-wire system maintains a constant output torque from the road sensor motor, preserving the predetermined steering wheel operating resistance. When the in-tire sensor's acceleration information indicates that the road surface adhesion coefficient is less than a preset value, it means the electric vehicle has entered a low-traction road surface. At this time, the lateral force limit that the tires can provide decreases. The steer-by-wire system increases the feedback torque through the road sensor motor, increasing the steering wheel turning force. This physically prevents the driver from applying excessive or rapid steering wheel angle input during straight-line driving, reducing the saturation of wheel lateral forces caused by excessive steering angles.

[0021] According to the solution in this application, by installing in-tire sensors within the tires of electric vehicles to detect vehicle information, dynamic physical quantities of the tire-road contact area are directly acquired, and tire acceleration information is collected in real time to calculate the road surface adhesion coefficient. This method achieves active, direct, and rapid measurement of the road surface adhesion coefficient without relying on external cameras or other devices susceptible to light interference, nor on delayed vehicle dynamics feedback. It can acquire road surface conditions before the vehicle becomes unstable, shortening the road surface condition recognition delay. Combined with the torque adjustment capability of steer-by-wire, it improves the vehicle's handling safety when traveling straight on low-traction roads.

[0022] In conjunction with the first aspect, in some implementations of the first aspect, the in-tire sensor is used to detect acceleration information. Specifically, the control method includes, during the straight-line movement of the electric vehicle, when the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is greater than a preset characteristic frequency, controlling the feedback torque of the road feel motor of the steer-by-wire system to remain constant. When the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is less than the preset characteristic frequency, controlling the road feel motor of the steer-by-wire system to increase the feedback torque.

[0023] Different road surfaces with varying materials and adhesion conditions, such as dry asphalt, ice, or snow, possess different physical stiffness and damping characteristics, resulting in different frequency vibration responses when a tire rolls on them. As the tire rolls over the surface, the road texture interacts with the tire rubber, exciting specific vibration frequencies within the tire structure. On high-adhesion surfaces like dry asphalt, the micro-texture of the road surface effectively excites resonance in the tire structure, and the acceleration signal collected by the in-tire sensor exhibits a high natural frequency characteristic in the frequency domain. When the road surface transitions to low-adhesion surfaces such as ice, snow, or wet surfaces, the micro-texture weakens, reducing the frictional tearing effect between the tire and the road surface, leading to attenuation of high-frequency vibrations. Consequently, the natural frequency characteristic of the acceleration signal collected by the in-tire sensor decreases in the frequency domain.

[0024] During the straight-line movement of the electric vehicle, in-tire sensors collect real-time acceleration information when the tire contacts the road surface. This acceleration information is then analyzed using frequency domain transformation. When the calculated natural frequency corresponding to this acceleration is greater than a preset characteristic frequency, the system determines that the current road surface is a high-adhesion surface and maintains the feedback torque of the road feel motor in the steer-by-wire system unchanged. At this point, the higher natural frequency indicates that the road surface can provide sufficient lateral force support, therefore the control system maintains the current feedback torque output command.

[0025] During the straight-line movement of an electric vehicle, when the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is lower than a preset characteristic frequency, the road-sensing motor of the steer-by-wire system increases the feedback torque. By using the natural frequency attenuation characteristics of the acceleration signal in the frequency domain as a discrimination criterion, compared to directly comparing acceleration amplitudes, it is better able to eliminate random high-frequency noise interference caused by vehicle speed fluctuations and uneven road surfaces, thus improving the accuracy of identifying dangerous road surfaces such as ice and snow.

[0026] According to the solution in this application, road surface judgment is based on the inherent frequency characteristics of the acceleration signal from the in-tire sensor in the frequency domain, which can directly reflect the changes in the microscopic contact state between the tire and the road surface. It eliminates the need to rely on dynamic responses such as vehicle slippage or yaw; judgment is made based on changes in vibration frequency as the wheel rolls over a low-traction surface, improving the accuracy of low-traction surface identification. When passing through a low-traction surface, the feedback torque of the road sensor motor is increased, directly increasing the steering wheel's rotational resistance. This resistance provides counterforce in the initial stage when the driver attempts to turn the steering wheel, preventing the driver from making steering angle inputs exceeding the tire's current adhesion limit, avoiding wheel lateral force saturation due to excessive steering angle, and reducing the risk of vehicle instability on low-traction surfaces. When the inherent frequency is greater than the preset characteristic frequency, the feedback torque of the road sensor motor remains constant, avoiding unnecessary torque fluctuations on normal road surfaces.

[0027] In conjunction with the first aspect, in some implementations of the first aspect, the electric vehicle includes a chassis observer for identifying road surface adhesion based on wheel force. Specifically, during the straight-line movement of the electric vehicle, when the road surface adhesion indicated by wheel adhesion information from the chassis observer is greater than a preset adhesion, the feedback torque of the road-sensing motor of the steer-by-wire system is kept constant. When the road surface adhesion indicated by wheel adhesion information from the chassis observer is less than the preset adhesion, the feedback torque of the road-sensing motor of the steer-by-wire system is increased.

[0028] The chassis observer acquires the actual force state of the wheels, including longitudinal force, lateral force, and vertical load, and calculates the actual utilization degree of the wheels' road surface adhesion, i.e., road surface utilization adhesion. Since the limit of road surface utilization adhesion varies significantly when electric vehicles travel on different road surfaces, the road surface utilization adhesion calculated in real time by the chassis observer is numerically compared with a pre-set adhesion value representing a safety boundary. During the dynamic response of the wheels, the road surface utilization adhesion calculated through wheel force can objectively and accurately reflect the true adhesion state between the tires and the current road surface.

[0029] When the road surface adhesion indicated by the chassis observer is greater than the preset adhesion, it indicates that the current road surface can provide sufficient adhesion, and the electric vehicle is within a safe driving range. The steer-by-wire system maintains a constant feedback torque from the road feeler motor, keeping the steering wheel at a predetermined normal turning effort. When the road surface adhesion indicated by the chassis observer is less than the preset adhesion, it indicates that the electric vehicle has entered a low-traction surface, and the lateral limits provided by the tires are reduced. The road feeler motor of the steer-by-wire system increases the feedback torque, thereby directly increasing the steering wheel turning effort. The increased resistance provides counterforce when the driver applies steering input, limiting the driver from accidentally inputting steering angles exceeding the tire's lateral limits under low-traction straight-line conditions.

[0030] According to the scheme of this application, the chassis observer calculates the road surface adhesion based on the actual force and dynamic response of the wheels, which has high recognition accuracy. The recognition results of the chassis observer are used to control the feedback torque of the road sensor motor, ensuring that the torque adjustment action is based on accurate physical force data, thus improving the reliability of the control. When the vehicle travels straight through a low-adhesion road surface and the road surface adhesion is less than the preset adhesion, the feedback torque of the road sensor motor is increased by controlling it, increasing the steering wheel turning force. This resistance physically hinders the driver's steering operation, preventing the driver from blindly turning the steering wheel too much on a low-adhesion road surface, which could lead to wheel lateral force saturation, thereby ensuring the driving stability of the electric vehicle when traveling straight on a low-adhesion road surface. When driving on a high-adhesion road surface where the road surface adhesion is greater than the preset adhesion, the system controls the feedback torque of the road sensor motor to remain constant, avoiding unnecessary torque fluctuations on normal, good road surfaces and ensuring the continuity of steering wheel operation resistance.

[0031] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, during the process of the electric vehicle turning on the first road surface, during the turning process after the steering wheel begins to turn, the feedback torque of the road feel motor controlling the steer-by-wire system increases with the increase of the steering wheel rotation angle and with the increase of the electric vehicle speed.

[0032] On surfaces with good traction, as the steering wheel angle increases, the wheel deflection angle increases, leading to an increase in the lateral force and self-centering torque generated by the tires. The road feel motor is controlled to synchronously increase the feedback torque, causing the steering wheel effort to increase positively with the steering angle. This change in resistance provides the driver with physical resistance matching the current steering range, maintaining a positive correlation between steering resistance and steering range. At the same steering wheel angle, the higher the vehicle speed of an electric vehicle, the greater the lateral acceleration and centrifugal response, and the more sensitive the lateral dynamics. Controlling the road feel motor to output greater feedback torque at higher speeds increases the steering wheel effort during high-speed steering. This increased resistance increases the steering effort required to turn the steering wheel, reducing the sensitivity of steering operations at high speeds.

[0033] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, during the process of the electric vehicle turning on the second road surface, when the stability margin of the electric vehicle is less than a first threshold but greater than a second threshold, increasing the feedback torque of the road feel motor of the steer-by-wire system by a first ratio as the steering wheel rotation angle or the vehicle speed increases. When the stability margin of the electric vehicle is less than the second threshold, increasing the feedback torque of the road feel motor of the steer-by-wire system by a second ratio greater than the first ratio as the steering wheel rotation angle or the vehicle speed increases, wherein the stability margin varies with changes in vehicle speed and road surface adhesion coefficient.

[0034] During cornering on low-friction surfaces, feedback torque is increased by dividing the vehicle into intervals based on stability margin and using different ratios. Stability margin is used to quantitatively assess the physical boundary between the electric vehicle's current dynamic state and the tire's lateral adhesion limit. The lower the road adhesion coefficient, the smaller the maximum lateral force the tire can generate; the higher the vehicle speed, the greater the lateral force required for steering. Therefore, stability margin decreases accordingly with increasing vehicle speed or decreasing road adhesion coefficient. When the stability margin is below a first threshold but above a second threshold, it indicates a potential risk of insufficient lateral force when the electric vehicle is cornering on low-friction surfaces, but it has not yet reached the limit of tire lateral force saturation. At this point, the feedback torque is increased with a lower first ratio, causing the steering wheel effort to increase at a gradual slope with the steering angle or vehicle speed, providing the driver with steering physical resistance commensurate with the level of risk. When the stability margin is below the second threshold, it indicates that the vehicle's lateral acceleration or steering angle is approaching the current road adhesion limit; further increasing the steering angle will trigger tire lateral force saturation and vehicle sideslip instability. At this point, switching to a larger second ratio increases the feedback torque, causing the steering wheel turning force to increase rapidly with the increase in steering angle or vehicle speed. This rapidly increasing steering force creates a significant physical resistance, hindering the driver from further turning the steering wheel in the original steering direction and limiting excessive steering angle input.

[0035] According to the solution of this application, by setting a first threshold and a second threshold, the instability risk under low-adhesion road surface steering conditions is divided into different levels. The stability margin is defined as a parameter that dynamically changes with vehicle speed and road surface adhesion coefficient. It can adapt to different low-adhesion road surface conditions and different driving speeds, improve the matching accuracy between resistance control action and actual physical limits. When the electric vehicle approaches the instability limit, the feedback torque is rapidly increased by a second ratio greater than the first ratio, which significantly increases the operating force required to further increase the steering angle. This resistance effectively limits the driver's behavior of mistakenly applying too large a steering angle due to panic, prevents wheel lateral force saturation, and ensures the driving safety of electric vehicles under low-adhesion road surface extreme steering conditions.

[0036] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes controlling the angular transmission ratio of the steer-by-wire system to a first transmission ratio during the turning motion of the electric vehicle on the first road surface. During the turning motion of the electric vehicle on the second road surface, the angular transmission ratio of the steer-by-wire system is controlled to a second transmission ratio greater than the first transmission ratio.

[0037] The angular gear ratio refers to the numerical ratio between the steering wheel angle and the equivalent deflection angle of the steering wheels in an electric vehicle. It is calculated by dividing the maximum unidirectional rotation angle of the steering wheel by the maximum unidirectional deflection angle of the steering wheels. In traditional mechanical steering systems, the angular gear ratio is typically set to a fixed value or varies within a very small range. In steer-by-wire systems, because the mechanical connection between the steering wheel and the steering wheels is eliminated, the steering wheel angle does not directly control the wheel steering. Relying on the decoupling control capability of the steer-by-wire system, the angular gear ratio is dynamically adjusted based on data such as the electric vehicle's real-time speed, vehicle operating status, and driver input parameters. This allows the real-time ratio of the steering wheel angle to the steering wheel deflection angle to change without altering the inherent dimensional parameters of the steering mechanical hardware. In traditional variable gear ratio schemes, the angular gear ratio is designed to be relatively small when the electric vehicle is traveling at low speeds, allowing the electric vehicle to generate a large steering wheel angle with a small steering wheel angle, meeting the requirement of easy steering at low speeds. Conversely, when the electric vehicle is traveling at high speeds, the angular gear ratio is designed to be relatively large, allowing a larger steering wheel angle to generate a smaller steering wheel angle, thus improving the vehicle's handling stability at high speeds.

[0038] During the first road surface turning operation of the electric vehicle, the angular transmission ratio of the steer-by-wire system is the first transmission ratio. The first road surface has a high coefficient of adhesion, providing sufficient lateral and longitudinal force grip for the tires. Under this condition, the first transmission ratio is set to a relatively small value, allowing the steering wheel angle to be directly converted into the wheel deflection angle at a high proportion. This ensures basic steering response capability: maintaining a small first transmission ratio ensures that the electric vehicle has a normal lateral dynamic response rate on normal safe road surfaces, meeting the vehicle's maneuverability and steering follow-through requirements in daily driving. During the second road surface turning operation, based on the change in road surface adhesion, the angular transmission ratio of the steer-by-wire system is controlled to a second transmission ratio, which is greater than the first transmission ratio. The second road surface has a low coefficient of adhesion, and the physical limits of tire anti-lateral deviation and lateral force provision are significantly reduced. By increasing the value of the angular transmission ratio through an algorithm, when the driver inputs the same steering wheel angle, the target angle calculated and output to the wheel steering motor by the lower-level controller of the steer-by-wire system decreases. This prevents the lateral force of the tires from reaching saturation, thus preventing irreversible understeer or sideslip and ensuring the physical stability of the vehicle under dangerous low-traction road conditions.

[0039] According to the solution in this application, in emergency situations where the road surface adhesion coefficient suddenly drops, drivers are prone to panic or misjudging the road grip and making sudden steering wheel movements. By increasing the angular transmission ratio, the excessive steering wheel angle input from the driver is physically reduced and filtered proportionally at the bottom-level actuator, preventing the large steering angle command from being directly and fully transmitted to the wheels. This avoids causing severe understeer or fishtailing and loss of control of the vehicle, ensuring that the tires can still maintain an effective lateral force grip utilization rate on low-adhesion roads. This minimizes the risk of vehicle skidding due to misoperation and significantly improves the ultimate physical stability of electric vehicles when turning on suddenly low-adhesion roads.

[0040] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes maintaining the angular transmission ratio of the steer-by-wire system unchanged while the steering wheel angle remains at the first angle after the electric vehicle turns from the first road surface to the second road surface.

[0041] After an electric vehicle transitions from a high-traction first surface to a low-traction second surface, the angular ratio of the steer-by-wire system should ideally switch to a larger second ratio. However, upon entering the second surface, the lateral forces on the tires easily approach their saturation boundary. If the angular ratio is changed further without any driver input, the actual wheel angle will spontaneously change. This change causes abrupt shifts in the tire slip angle, leading to uninstructed fluctuations in the tire's lateral force. Therefore, maintaining the current angular ratio ensures that the actual wheel deflection angle remains constant.

[0042] According to the solution of this application, after the electric vehicle turns from the first road surface to the second road surface, while the steering wheel angle remains at the first angle (i.e., the driver does not make further angle corrections), the steering input remains steady, and the angular transmission ratio of the steer-by-wire system remains unchanged. This ensures that the actual driving path of the electric vehicle conforms to the driver's steering operation command, avoids unexpected lateral deviations, and reduces the probability of the driver panicking due to path deviations and causing secondary misoperations, thereby improving driving safety.

[0043] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, during the turning process of the electric vehicle on a second road surface and when the steering wheel angle is less than a preset angle, controlling the steer-by-wire system to drive the two front wheels to rotate with the rotation of the steering wheel. During the turning process when the steering wheel angle is greater than the preset angle, controlling the steer-by-wire system to keep the rotation angle of the two front wheels constant.

[0044] The electric vehicle is traveling on a road surface with a low coefficient of friction and is in a turning state after the steering wheel has been turned. During turning when the steering wheel angle is less than a preset angle, the control system controls the steer-by-wire system to drive the two front wheels of the vehicle to turn with the steering wheel, maintaining a predetermined transmission correspondence between the wheel rotation angle and the steering wheel rotation angle. Within the range where the steering wheel angle is less than the preset angle, the lateral force required for the electric vehicle to turn has not yet reached the limit of the tire lateral force provided by the road surface. The steering actuator of the steer-by-wire system converts the steering wheel angle command into the front wheel steering angle, driving the two front wheels to turn, ensuring that the vehicle responds normally to the driver's steering intentions.

[0045] When the steering wheel angle continues to increase and exceeds the preset angle, the control system sends a control command to the steer-by-wire system, keeping the steering angles of the two front wheels constant. Even if the steering wheel angle continues to increase beyond the preset angle, the actual steering angles of the two front wheels remain at the wheel steering angle values ​​corresponding to the preset angle. On roads with low coefficient of friction, the maximum lateral force that tires can generate is limited by the road surface adhesion limit. If the front wheel deflection angle is too large, it will cause the tire slip angle to exceed the linear limit region, leading to tire lateral force saturation or even a decrease in lateral force. Electric vehicles will then experience severe understeer or lose lateral adhesion. When the steering wheel angle exceeds the preset angle, the control system utilizes the decoupling characteristic of the steer-by-wire system to cut off the steering wheel angle command at the execution end, keeping the actual steering angles of the two front wheels constant. This control limits the wheel deflection angle to within the effective lateral force utilization angle boundary under current road conditions, preventing deterioration of dynamic response due to excessive wheel angles.

[0046] According to the solution in this application, by locking the front wheel rotation angle after the steering wheel angle is greater than a preset angle, the phenomenon of excessive tire slip angle caused by excessive front wheel deflection angle is directly avoided, preventing the tire from entering a slip state with saturated lateral force. This ensures the lateral grip and lateral stability of the electric vehicle when turning on a low-adhesion road surface, and prevents the driver from accidentally applying excessive steering wheel angle due to panic. The steer-by-wire system can limit the wheel deflection angle within a safe angle, reducing the difficulty of operation for the driver and improving driving safety.

[0047] In conjunction with the first aspect, in some implementations of the first aspect, the electric vehicle further includes an image sensor for detecting road surface information, and the control method further includes, during the straight-moving process of the electric vehicle, when the image information from the image sensor indicates that the electric vehicle is about to enter a road surface with a coefficient of friction less than a preset value, controlling the electric vehicle to send a prompt message to the driver, the prompt message being used to remind the driver via screen or voice that the electric vehicle is about to enter a low-friction road surface.

[0048] Electric vehicles have image sensors, such as cameras and radar, for detecting information about the road surface ahead. These image sensors, mounted at the front of the vehicle, capture optical characteristics of the road surface area, such as reflection intensity, surface texture, grayscale, and color distribution, before the tires physically contact the road. When the road surface ahead contains low-adhesion media such as ice, snow, or slippery surfaces, its optical characteristics differ significantly from those of conventional high-adhesion roads. The image recognition and observation module extracts physical optical features from the acquired image information. For example, if the image shows patches of bright light indicating strong specular reflection from media such as ice, which differs from the diffuse reflection of ordinary high-adhesion roads, and the texture features are smooth with minimal texture, then the image is determined to match the optical properties of a typical low-adhesion road surface. The control system then identifies the image information to determine if the electric vehicle is about to enter a low-adhesion road surface.

[0049] During the operation of the electric vehicle, image sensors continuously collect road surface images ahead. When the image information from the image sensors indicates that the electric vehicle is about to enter a low-friction surface with a coefficient of friction less than a preset value, the display terminal or voice terminal controlling the electric vehicle issues a control command to send a warning message to the driver. The system actively coordinates with the cockpit domain controller to control the electric vehicle to send the warning message to the driver. Specifically, a trigger electrical signal is sent to the cockpit controller to control the display module of the central control screen in the cockpit to display a visual warning sign, or to control the cockpit audio module to play a specific voice alarm audio. The warning message serves as a physical medium, through the screen or voice, to clearly remind the driver that the electric vehicle is about to enter a low-friction surface.

[0050] According to the solution in this application, before entering a low-adhesion surface, a screen or voice prompt is sent to the driver in advance. This allows the driver to be informed of the reduced road surface adhesion coefficient through visual and auditory channels before the driver perceives the changes in vehicle dynamics. This enables the driver to understand the changes in road conditions in advance and prevents the driver from making inappropriate steering or braking operations due to a lack of anticipation of road conditions after entering a low-adhesion surface. This improves the active safety performance of electric vehicles when driving on complex and abrupt road surfaces.

[0051] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes controlling the electric vehicle to send a prompt message to the driver when acceleration information from an in-tire sensor indicates that the road surface adhesion coefficient is less than a preset value.

[0052] Non-contact image sensors have blind spots in complex lighting conditions, nighttime, or inclement weather, potentially leading to missed detections. To overcome this environmental limitation of non-contact sensing, in-tire sensors are introduced as contact-based physical sensing nodes. These sensors are directly attached to the inside of the tire, rolling with the wheel and directly contacting the road surface. When the wheel actually enters a low-traction surface, the change in the physical medium of the tire contact surface causes a sudden change in high-frequency vibration acceleration. During the operation of an electric vehicle, if the non-contact image sensor fails to detect abnormal road conditions ahead, such as thin ice or black ice sections with weak visual features, the in-tire sensor inside the tire begins to collect real-time acceleration information of the tire-road interaction the moment the electric vehicle's wheel enters that section. The control system's perception fusion module receives this acceleration information and calculates the actual adhesion coefficient of the current road surface. When this adhesion coefficient is less than a preset value, it is determined that the vehicle has physically contacted and is driving on a low-traction, dangerous surface. At this point, the control system sends a trigger signal to the cockpit domain controller, controlling the electric vehicle to output a visual warning through the central control screen or a voice alarm through the audio system, sending a prompt message to the driver.

[0053] According to the solution in this application, a dual warning triggering path is formed by combining the forward-looking recognition of the image sensor and the physical contact recognition of the in-tire sensor. Even if the forward-looking image recognition misses a warning due to ambient light or unclear road surface visual features, the in-tire sensor can supplement the warning information by sending a warning message the moment the tire contacts the low-traction road surface, preventing the warning function from failing. For low-traction road surfaces with indistinct visual features, such as black ice or thin ice, the in-tire sensor directly identifies the warning based on the changes in acceleration characteristics caused by physical contact, unaffected by the optical environment and road surface appearance features, ensuring the reliability of the warning information triggering. The warning information is sent via screen or voice the moment the vehicle enters the low-traction road surface, allowing the driver to quickly know that the current road surface adhesion has decreased, avoiding the driver from making sharp turns or braking without warning, and reducing the risk of loss of control of the vehicle due to improper operation on low-traction road surfaces.

[0054] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, after the electric vehicle has been continuously sending a prompt message to the driver for a first duration, if the acceleration information from the in-tire sensor indicates that the road surface adhesion coefficient is greater than a preset value, controlling the electric vehicle to stop sending the prompt message to the driver.

[0055] Non-contact image sensors extracting road surface visual features have a probability of misjudgment, such as misidentifying a high-adhesion wet or reflective surface as a low-adhesion ice surface. In-tire sensors, which directly contact the road surface medium, possess extremely high physical measurement accuracy but suffer from spatial lag. During the process of controlling the electric vehicle to send a warning message to the driver, the warning message is maintained for a first duration. The numerical setting of this first duration is based on the electric vehicle's current longitudinal speed and the forward physical distance of the target road surface identified by the image sensor. The first duration characterizes the time span required for the electric vehicle to travel from the image recognition trigger point to the front tires actually contacting the target road surface. The field of view distance of the image sensor in front of the vehicle is mapped to the vehicle's travel time. After the warning trigger lasts for this first duration, the wheels have physically traveled to the road segment previously identified by the image sensor. At this point, the acceleration information from the in-tire sensors is used for physical verification. If the verification result indicates that the actual road surface adhesion coefficient is normal, it is determined that the visual perception has misreported or the electric vehicle has left the low-adhesion area, and the warning is actively canceled. The accuracy of the warning information is ensured through spatiotemporal alignment and cross-validation of multiple sensor sources.

[0056] According to the solution in this application, by setting a first duration condition for the continuous transmission of warning information, the stable display of the warning information is ensured, avoiding frequent flashing and jumping of the warning information caused by local unevenness of the road surface or critical signal interference, thus ensuring the reliability of the warning function. Relying on in-tire sensors to directly collect acceleration information during the tire-road contact process to determine if the road surface has returned to a high-traction state, the high accuracy and real-time nature of contact sensing ensures that the warning is accurately deactivated after the tire truly contacts the high-traction road surface, avoiding delays or misjudgments in warning cancellation. The transmission of warning information is promptly stopped after the electric vehicle re-enters the high-traction road surface, preventing invalid warning information from occupying screen display resources for extended periods or continuously emitting voice interference, reducing the cognitive load on the driver under safe road conditions, and improving the human-computer interaction experience.

[0057] Secondly, this application provides a vehicle controller for electric vehicles, which implements the control methods described in the first aspect and its various implementations.

[0058] Thirdly, this application provides an electric vehicle, which includes an accelerator pedal, a brake pedal, a steering wheel, and a vehicle controller as described in the second aspect; the accelerator pedal is used to indicate driving the electric vehicle; the brake pedal is used to indicate outputting braking force to the wheels of the electric vehicle; and the steering wheel is used to indicate the steering angle of the wheels of the electric vehicle.

[0059] Other beneficial effects can be found in the description of the first aspect, and will not be repeated here. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of a scenario involving an electric vehicle provided in an embodiment of this application; Figure 2 This is a schematic diagram of an electric vehicle provided in an embodiment of this application; Figure 3 This is a schematic diagram of the architecture of the steer-by-wire system provided in the embodiments of this application; Figure 4 This is a schematic diagram of an electric vehicle control process provided in an embodiment of this application; Figure 5 This is a schematic diagram of another electric vehicle control process provided in an embodiment of this application; Figure 6 This is a schematic diagram of the module and component architecture for electric vehicle control provided in an embodiment of this application; Figure 7 This is a schematic diagram of the adaptive control logic architecture for electric vehicles provided in the embodiments of this application. Detailed Implementation

[0061] The technical solutions in this application will now be described in conjunction with the accompanying drawings. The detailed descriptions and drawings of the following embodiments are used to exemplarily illustrate the principles of this application, but should not be used to limit the scope of this application; that is, this application is not limited to the described embodiments.

[0062] Figure 1 and Figure 2 This is a schematic diagram of the architecture of the electric vehicle 10 provided in the embodiments of this application.

[0063] like Figure 1 As shown, the electric vehicle 10 includes a vehicle controller 20, a drive system 50, a steer-by-wire system 60, a power battery (not shown), and multiple wheels. The drive system 50 includes a drive motor 30 and a motor controller 40. The motor controller 40 outputs current to the drive motor 30 to control the drive motor 30 to output torque to drive the wheels of the electric vehicle 10.

[0064] The vehicle controller provided in this application is the vehicle controller 20 of the electric vehicle 10, or a steering controller, or a motor controller 40, or a separately configured controller with control capabilities.

[0065] The electric vehicle 10 can be a rear-wheel drive vehicle, with the two rear wheels driven by a drive motor 30. Alternatively, the electric vehicle 10 can have a distributed four-motor drive architecture, with the drive motors positioned beside the driving wheels and controlled by individual motor controllers 40. The electric vehicle 10 can also have a centralized drive motor architecture, with the drive motors for driving the two front wheels or the two rear wheels grouped together. There can be one or more motor controllers 40. The motor controller 40 can correspond one-to-one with the drive motors 30, or one motor controller 40 can correspond to multiple drive motors 30. The motor controller 40 is used to control the output torque of one or more drive motors 30 to drive the electric vehicle 10.

[0066] In one embodiment, such as Figure 2 As shown in (a), the electric vehicle 10 can be a distributed four-motor drive architecture, with the drive motors positioned beside the driving wheels and controlled by individual motor controllers. The electric vehicle 10 can also be as follows: Figure 2 The centralized four-drive motor drive architecture shown in (b) has two drive motors for driving the two front wheels or the two rear wheels set together.

[0067] For example, the electric vehicle 10 includes four motor controllers: motor controller 41, motor controller 42, motor controller 43, and motor controller 44. Four drive motors include drive motor 31, drive motor 32, drive motor 33, and drive motor 34. Motor controller 41 controls drive motor 31 to drive wheel 51, motor controller 42 controls drive motor 32 to drive wheel 52, motor controller 43 controls drive motor 33 to drive wheel 53, and motor controller 44 controls drive motor 34 to drive wheel 54.

[0068] In one embodiment, the electric vehicle 10 may also be as follows: Figure 2 The centralized drive motor architecture shown in (c) uses one drive motor to drive the two front wheels of the electric vehicle 10, and two drive motors to drive the two rear wheels of the electric vehicle 10 respectively.

[0069] In one embodiment, the various architectures mentioned above can also be combined, for example, the front drive adopts a distributed drive motor architecture and the rear drive adopts a centralized drive motor architecture.

[0070] The electric vehicle 10 also includes an accelerator pedal, a brake pedal, and a steering wheel. The accelerator pedal is used to indicate the torque output to the wheels of the electric vehicle 10. The brake pedal is used to indicate the braking force output to the wheels of the electric vehicle 10, and the steering wheel angle is used to indicate the steering angle of the wheels.

[0071] In one embodiment, the vehicle controller also acquires vehicle signals from the vehicle controller 20 or other sensors of the electric vehicle 10 via a signal interface. The vehicle signals are used to indicate the vehicle speed, yaw rate, and sideslip angle of the electric vehicle 10.

[0072] In one embodiment, the motor controller 40 can be connected to the vehicle controller 20 via a controller area network (CAN) bus, a local interconnect network (LIN) bus, a high-speed fault-tolerant network protocol (FlexRay), or other types of connection methods, and exchange signals.

[0073] The steer-by-wire system 60 is a steering system that completely replaces traditional mechanical connections with electronic signals. It eliminates the rigid mechanical transmission connection between the steering wheel and the steering wheels, and removes the physical connection between the steering wheel and the steering wheels (such as the steering column), achieving complete decoupling. Its core workflow involves sensors acquiring the driver's steering intentions and converting them into electrical signals. These signals are then processed by the electronic control unit to drive the steering motor and control the wheel rotation. This technology is considered a major innovation in automotive steering systems, providing crucial technical support for advanced autonomous driving. Furthermore, due to its flexible variable steering ratio and potential for freeing up interior space, it is entering the stage of mass production.

[0074] like Figure 3 As shown, the steer-by-wire system 60 architecture includes an upper steering wheel assembly and a lower steering actuator assembly. The upper steering wheel assembly is mainly responsible for simulating driver feel and steering intention. It includes an upper steering controller and a road feel motor. The upper steering controller collects the steering angle and steering torque input by the driver and converts them into standardized electrical signals. It then sends the front wheel angle command representing the driver's intention to the chassis controller's local area network bus. The road feel motor provides hand torque damping based on the driver's steering wheel angle and speed. Based on the road feedback electrical signals, the road feel motor outputs damping, return torque, and other simulated steering feedback forces to reproduce the steering feel. The upper steering wheel assembly and the lower steering actuator assembly communicate via the chassis CAN network wiring harness. It can realize functions such as parameterized calibration of steering feel program and decoupling of steering wheel and steering wheel movement. It does not require a through-type steering column mechanical structure and can adapt to high-level autonomous driving control commands to directly intervene in the steering execution flow.

[0075] As the automotive industry undergoes a profound upgrade towards intelligence and electrification, vehicle speeds continue to increase, and users' demands for driving safety are becoming increasingly stringent. Accurate perception and early prediction of road surface adhesion status have become a core technological bottleneck in ensuring high-speed driving safety. Current vehicles perceive sudden road conditions primarily through two channels: First, the intelligent driving perception level relies on external sensors such as LiDAR and cameras to acquire road information, identifying only clearly distinguishable abnormal road surfaces such as large potholes and obstacles, achieving a certain degree of advanced perception. Second, the chassis control level employs passive recognition, only identifying changes in road surface adhesion status and then implementing control after the vehicle shows a clear tendency to become unstable. When a sudden road surface change is detected, traditional control schemes only provide a warning through screen display or actively switch driving modes to adjust the drive system's torque mode.

[0076] However, external sensors cannot effectively identify special road surfaces with weak visual features, such as black ice, creating blind spots and lacking overall perception accuracy. Chassis control only intervenes after the vehicle becomes unstable; sudden changes in road surface adhesion coefficient at high speeds can easily lead to loss of control, posing a significant safety hazard. Furthermore, they cannot provide clear and timely warnings of danger to the driver, making it difficult for inexperienced drivers or those with weak emergency response capabilities to quickly take effective emergency actions, thus amplifying safety risks.

[0077] To address the aforementioned issues, this application provides a control method, vehicle controller, and electric vehicle 10 for an electric vehicle 10. Utilizing the mechanical decoupling between the steering wheel and wheels of the steer-by-wire system 60, the steer-by-wire system 60 actively takes over the feedback torque of the road feel motor. At a higher level, it increases steering wheel force to provide tactile warnings and resist misoperation, preventing the electric vehicle 10 from becoming unstable due to lateral force saturation. This alerts and assists the driver, preventing misoperation from exacerbating instability of the electric vehicle 10, thus improving driving safety and reducing the demands on the driver's driving skills.

[0078] The following is combined Figures 4-7 The control method provided in the embodiments of this application is described below. The control method is used to adjust the feedback torque of the road feel motor in the steer-by-wire system 60 to cope with changes in road surface adhesion during the process of the electric vehicle 10 turning and driving over a sudden road surface. Figure 4 This is a schematic diagram showing the temporal changes of the steering wheel rotation angle, the feedback torque of the road sensor motor, and the road surface adhesion coefficient when the electric vehicle 10 is turning and driving through a sudden change in road surface, as provided in the embodiments of this application. Figure 5 This is a schematic diagram of the time sequence changes when an electric vehicle 10 travels straight through a road surface with a sudden change, as provided in an embodiment of this application. Figure 6 This is a schematic diagram of the module and component architecture for controlling the electric vehicle 10 provided in the embodiments of this application. Figure 7 This is a schematic diagram of the adaptive control logic architecture for the steer-by-wire system 60 of an electric vehicle 10, provided in an embodiment of this application.

[0079] The control method includes controlling the road sensor motor of the steer-by-wire system 60 to output a first feedback torque during the turning motion of the electric vehicle 10 on the first road surface, when the steering wheel angle of the electric vehicle 10 is a first angle. After the electric vehicle 10 turns from the first road surface to the second road surface, while the steering wheel angle remains at the first angle, actively controlling the road sensor motor to output a second feedback torque greater than the first feedback torque. After the steering wheel returns to center, during the straight-line movement of the electric vehicle 10 on the second road surface, controlling the feedback torque output by the road sensor motor to decrease to a third feedback torque. During the straight-line movement of the electric vehicle 10 after exiting the second road surface and re-entering the first road surface, actively controlling the feedback torque output by the road sensor motor to decrease to less than the third feedback torque.

[0080] Electric vehicle 10 is prone to loss of control when encountering dangerous situations such as sudden changes in road surface adhesion coefficient during operation, such as transitioning from dry asphalt to icy, wet, or slippery surfaces. In this situation, the road surface on which electric vehicle 10 travels includes a first road surface and a second road surface that intersect, with the adhesion coefficient of the first road surface being greater than that of the second road surface. A sudden change in road surface adhesion coefficient refers to a sudden shift in the road surface's adhesion coefficient. Sudden change in road surface adhesion includes intersecting high-adhesion and low-adhesion road surfaces. The first road surface is a high-adhesion road surface, with an adhesion coefficient greater than a preset value. The second road surface is a low-adhesion road surface, meaning it has a low adhesion coefficient with the wheels. The adhesion coefficient is the ratio of adhesion force to the wheel's normal pressure, determined by the road surface and tires; a higher adhesion coefficient means greater usable adhesion force. The adhesion coefficient of the second road surface is less than a preset value. When electric vehicle 10 enters a low-adhesion road surface during operation, the adhesion coefficient between the wheels and the road surface decreases. When electric vehicle 10 travels on a low-adhesion road surface, the wheel grip is lower, making it prone to slippage or lock-up, resulting in lower stability.

[0081] During the turning and driving of the electric vehicle 10 on the first road surface (high-friction surface), the driver turns the steering wheel to the first turning angle. At this time, the road-sensing motor controlling the steer-by-wire system 60 outputs the first feedback torque. This first feedback torque is mainly based on the current vehicle speed and the first turning angle, simulating the centering characteristics and lateral torque generated by the tires under normal high-friction road conditions. It provides the driver with a basic feedback torque that conforms to normal driving habits, allowing the driver to clearly perceive the normal steering resistance of the vehicle on a safe road surface, ensuring smooth and easy handling during daily driving.

[0082] When electric vehicle 10 moves from the first road surface to the second road surface (low-friction road surface), and the steering wheel angle remains at the first angle, the stability margin of electric vehicle 10 will significantly decrease due to the sudden drop in the road surface adhesion coefficient. At this time, electric vehicle 10 actively intervenes, controlling the output of the road feel motor to be greater than the first feedback torque, resulting in a second feedback torque. This avoids the phenomenon of the steering wheel becoming lighter on low-friction roads due to the decrease in tire return torque, which is a common problem in traditional mechanical steering. By actively increasing the output of the road feel motor, a noticeable resistance feel is created. The instantaneous increase in steering wheel resistance can provide the driver with a direct physical warning, indicating that the road surface adhesion conditions have severely deteriorated. On low-friction roads, because the lateral force of the tires is easily saturated, if the driver continues to apply excessive steering wheel angle input, it will easily lead to the vehicle skidding and losing control. The increase in the second feedback torque suppresses driver error, increases the difficulty for the driver to continue steering, effectively resists and filters oversteering errors caused by panic or lack of experience, and keeps the driving state of electric vehicle 10 within the safety capability boundary.

[0083] After the steering wheel is straightened, the electric vehicle 10 enters a straight-line driving state on the second road surface. At this time, the feedback torque output by the road feel motor is reduced to the third feedback torque. The third feedback torque is a torque set for straight-line driving on low-friction surfaces. By applying a certain system friction torque or damping torque through the road feel motor, the backlash in the mechanism is eliminated and the road feel is reconstructed. This provides a clear straight-line driving feel and enhances stability. When driving straight on a low-friction surface, the road surface's anti-interference ability is weak. The presence of the third feedback torque makes the steering wheel maintain a certain sense of stability and weight, which can effectively prevent the driver's slight hand tremors or unintentional misoperations from being converted into unexpected lateral movements of the vehicle, thereby significantly improving the path-keeping ability when driving straight at high speed on low-friction surfaces.

[0084] When electric vehicle 10 leaves the second road surface and re-enters the first road surface to continue driving straight, the road conditions return to safety. At this point, the feedback torque output by the active control road-sensing motor decreases to less than the third feedback torque, thus restoring the basic feedback state for normal straight-line driving on a high-friction surface. Electric vehicle 10 leaves the low-friction danger zone, releasing the additional restraining torque applied for anti-skid purposes, and restoring a normal, light, and responsive straight-line driving feel. This avoids increasing driver muscle fatigue caused by a continuously heavy steering wheel, achieving a smooth switch and dynamic balance between safety intervention and everyday comfortable driving, significantly improving the driving experience.

[0085] Specifically, such as Figure 4As shown, before time t1, the electric vehicle 10 is in a steering state, with the steering wheel rotation angle remaining constant at a preset first angle. At this time, the electric vehicle 10 is traveling on a first road surface with a high coefficient of friction. During this stage, the road-sensing motor of the steer-by-wire system 60 outputs a stable first feedback torque, matching the steering wheel rotation force with the first road surface coefficient of friction and the first angle. At time t1, the electric vehicle 10 crosses from the first road surface into a second road surface with a lower coefficient of friction, causing a sudden drop in the coefficient of friction to a lower value. From time t1 to time t2, the driver maintains the current steering operation, and the steering wheel rotation angle remains constant at the first angle. In response to the sudden drop in road surface coefficient of friction to the second road surface at time t1, the control system actively controls the road-sensing motor of the steer-by-wire system 60 to increase the output torque, raising the feedback torque from the first feedback torque to a larger second feedback torque, and maintaining the second feedback torque constant from time t1 to time t2, thereby increasing the steering wheel rotation force. At time t2, the steering wheel begins its return-to-center operation. The steering wheel rotation angle gradually decreases linearly from the first angle, reaching zero degrees at some point between t2 and t3. The electric vehicle 10 then completes the steering wheel return-to-center and enters a straight-line driving state. As the steering wheel rotation angle decreases, the feedback torque output by the road sensor motor decreases synchronously. After the steering wheel angle returns to zero degrees and the vehicle is still driving straight on the second road surface, the control system stabilizes the feedback torque output by the road sensor motor at a third feedback torque that is less than the second feedback torque and keeps it constant. At time t3, the electric vehicle 10 exits the second road surface and re-enters the first road surface with a higher coefficient of adhesion. The road surface adhesion coefficient abruptly recovers from a lower value to a higher value. At this time, the electric vehicle 10 continues to maintain a straight-line driving state with a steering wheel angle of zero degrees. In response to the recovery and increase of the road surface adhesion coefficient at time t3, the control system actively controls the road sensor motor to further reduce the output feedback torque, reducing the feedback torque from the third feedback torque to a value less than the third feedback torque. This restores the steering wheel turning force in the straight-line driving state to a reference level that matches the high adhesion conditions of the first road surface.

[0086] According to the solution of this application, by utilizing the mechanical decoupling characteristics of the steering wheel and wheels of the steer-by-wire system 60, the steer-by-wire system 60 actively takes over the feedback torque of the road feel motor. At the upper level, it provides tactile warnings and resists misoperation by increasing the steering wheel force, thereby preventing the electric vehicle 10 from becoming unstable due to lateral force saturation. At different stages such as steering, straightening, and driving straight, it provides the driver with tactile warnings and force limits that match the road adhesion state and the stability boundary of the electric vehicle 10, thereby ensuring driving safety in all aspects.

[0087] In one embodiment, the control method includes controlling the road feel motor of the steer-by-wire system 60 to maintain a constant third feedback torque during the process of the electric vehicle 10 traveling straight on the second road surface, when the coefficient of adhesion of the second road surface is less than a preset value. During the process of the electric vehicle 10 traveling straight after leaving the second road surface and re-entering the first road surface, when the coefficient of adhesion of the first road surface is greater than a preset value, controlling the road feel motor of the steer-by-wire system 60 to reduce the feedback torque.

[0088] By introducing a preset value as a benchmark for measuring whether the road surface possesses the grip required for normal safe driving, and leveraging the fully decoupled and independently reconfigurable road feel of the steer-by-wire system 60, the driver can increase hand force to ensure stability when the electric vehicle 10 is in a low-traction, hazardous state, and quickly release hand force once the vehicle is fully on a safe road surface. This optimizes the driver's experience and comfort while ensuring driving safety. This preset value is pre-calibrated based on real-vehicle experiments and / or model calculations, or it can be pre-set considering overall vehicle requirements and performance.

[0089] While the electric vehicle 10 is traveling straight on the second road surface, it is determined that the coefficient of friction of the second road surface is less than a preset value. At this time, the road feel motor of the active control steer-by-wire system 60 maintains a constant third feedback torque. On roads with a low coefficient of friction, the road surface's lateral disturbance resistance is extremely poor, and even minor lateral disturbances may cause loss of control. At this time, the road feel motor continuously and stably outputs the third feedback torque to maintain a high drag torque, allowing the steering wheel to provide and maintain a clear, solid feel and stability. This continuous drag can effectively filter and absorb slight hand tremors caused by driver bumps or tension, or unconscious small steering wheel inputs caused by arm gravity, keeping the electric vehicle 10 on a straight driving path and improving the psychological sense of security when traveling straight at high speed with low friction.

[0090] During the straight-line movement of electric vehicle 10 after exiting the second road surface and re-entering the first road surface, the road-sensing motor of the active control steer-by-wire system 60 reduces the feedback torque. When the road surface adhesion boundary fully meets the requirements of normal safe driving, it is no longer necessary to apply additional anti-slip safety restraint torque. At this time, the output command of the road-sensing motor is reduced in real time, releasing the high-hand force under low-adhesion conditions.

[0091] In one embodiment, the electric vehicle 10 includes in-tire sensors disposed within the tires of the wheels for detecting information about the electric vehicle 10. Specifically, during the straight-line movement of the electric vehicle 10, when the road surface adhesion coefficient indicated by the information from the in-tire sensors is greater than a preset value, the feedback torque of the road feel motor of the steer-by-wire system 60 is kept constant. When the road surface adhesion coefficient indicated by the information from the in-tire sensors is less than a preset value, the feedback torque of the road feel motor of the steer-by-wire system 60 is increased.

[0092] Current mainstream intelligent driving systems mainly rely on non-contact sensors such as LiDAR and cameras, which can only identify abnormal road conditions with relatively significant differences. Although they can achieve a certain degree of advanced perception, the recognition accuracy is limited, and they are easily affected by lighting and weather. They also have difficulty effectively identifying dangerous low-adhesion road surfaces with weak visual features, such as black ice and thin ice. To overcome the technical shortcomings of road perception—namely, "unclear visibility, inaccurate identification, and late intervention"—in-tire sensing technology with autonomous contact perception capabilities has become a hot research topic in the industry.

[0093] In-tire sensors refer to various physical quantity sensing components directly installed or adhered inside the tire, such as in the inner liner of the tire crown, under the tread blocks, or in the valve assembly. In-tire sensors include accelerometers (inertial measurement units, IMUs), strain sensors, and optical sensors. As the tire rotates and contacts the road surface, the tire body deforms and vibrates; in-tire sensors directly collect data from this process. When the road surface adhesion coefficient changes, the contact force between the tire and the road changes, causing corresponding changes in the amplitude, frequency, and fluctuation characteristics of the signal. Traditional chassis sensing solutions require waiting for the electric vehicle 10 to produce significant slippage or yaw before sensing, resulting in a time lag. In contrast, in-tire sensors are located directly on the contact surface between the tire and the road surface. When the wheel travels over different road surfaces, the different road media directly cause significant changes in tire deformation and high-frequency vibration signals. By processing this acceleration information, the true adhesion coefficient of the current road surface can be calculated within a very short cycle of wheel rotation.

[0094] When the tire-mounted sensor indicates that the road surface adhesion coefficient is greater than a preset value, it means that the current road surface provides sufficient adhesion, and the electric vehicle 10 is in a safe driving state. At this time, there is no need to change the steering wheel turning force; the steer-by-wire system 60 maintains a constant output torque of the road sensor motor, thus maintaining the predetermined steering wheel operating resistance. When the tire-mounted sensor indicates that the road surface adhesion coefficient is less than a preset value, it means that the electric vehicle 10 has entered a low-adhesion road surface. At this time, the lateral force limit that the tire can provide decreases. The steer-by-wire system 60 increases the feedback torque through the road sensor motor, increasing the steering wheel turning force. This physically prevents the driver from applying excessive or excessively rapid steering wheel angle input during straight-line driving, reducing the wheel lateral force saturation phenomenon caused by excessive steering angle.

[0095] In one embodiment, the in-tire sensor is used to detect acceleration information. Specifically, the control method includes, during the straight-line movement of the electric vehicle 10, when the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is greater than a preset characteristic frequency, controlling the feedback torque of the road feel motor of the steer-by-wire system 60 to remain constant. When the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is less than the preset characteristic frequency, controlling the road feel motor of the steer-by-wire system 60 to increase the feedback torque.

[0096] Different road surfaces with varying materials and adhesion conditions, such as dry asphalt, ice, or snow, possess different physical stiffness and damping characteristics, resulting in different frequency vibration responses when a tire rolls on them. As the tire rolls over the surface, the road texture interacts with the tire rubber, exciting specific vibration frequencies within the tire structure. On high-adhesion surfaces like dry asphalt, the micro-texture of the road surface effectively excites resonance in the tire structure, and the acceleration signal collected by the in-tire sensor exhibits a high natural frequency characteristic in the frequency domain. When the road surface transitions to low-adhesion surfaces such as ice, snow, or wet surfaces, the micro-texture weakens, reducing the frictional tearing effect between the tire and the road surface, leading to attenuation of high-frequency vibrations. Consequently, the natural frequency characteristic of the acceleration signal collected by the in-tire sensor decreases in the frequency domain.

[0097] During the straight-line movement of the electric vehicle 10, in-tire sensors collect real-time acceleration information when the tire contacts the road surface. This acceleration information is then analyzed using frequency domain transformation. When the calculated natural frequency corresponding to this acceleration is greater than a preset characteristic frequency, the system determines that the current road surface is a high-adhesion surface and controls the feedback torque of the road feel motor in the steer-by-wire system 60 to remain constant. At this time, the higher natural frequency indicates that the road surface can provide sufficient lateral force support, therefore the control system maintains the current feedback torque output command.

[0098] During the straight-line movement of the electric vehicle 10, when the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is less than the preset characteristic frequency, the system controls the road-sensing motor of the steer-by-wire system 60 to increase the feedback torque. By using the natural frequency attenuation characteristics of the acceleration signal in the frequency domain as a discrimination criterion, compared with directly comparing the acceleration amplitude, it is better able to eliminate random high-frequency noise interference caused by vehicle speed fluctuations and uneven road surfaces, thus improving the accuracy of identifying dangerous road surfaces such as ice and snow.

[0099] In one embodiment, the electric vehicle 10 includes a chassis observer for identifying road surface adhesion based on wheel force. Specifically, during straight-line travel of the electric vehicle 10, when the road surface adhesion indicated by wheel adhesion information from the chassis observer is greater than a preset adhesion, the feedback torque of the road feel motor of the steer-by-wire system 60 is kept constant. When the road surface adhesion indicated by wheel adhesion information from the chassis observer is less than the preset adhesion, the feedback torque of the road feel motor of the steer-by-wire system 60 is increased.

[0100] The chassis observer acquires the actual force state of the wheels, including longitudinal force, lateral force, and vertical load, and calculates the actual utilization degree of the wheels' road surface adhesion, i.e., road surface utilization adhesion. Since the ultimate utilization adhesion provided by the road surface varies significantly when the electric vehicle 10 travels on different road surfaces, the road surface utilization adhesion calculated in real time by the chassis observer is numerically compared with a pre-set adhesion value representing a safety boundary. During the dynamic response of the wheels, the road surface utilization adhesion calculated through wheel force can objectively and accurately reflect the true adhesion state between the tires and the current road surface.

[0101] For example, the road surface adhesion state of the chassis observer is estimated based on the following formula, and the result is the road surface utilization adhesion. Only under large wheel dynamics does the utilization adhesion approach the true road surface adhesion: , .

[0102] When the road surface adhesion indicated by the chassis observer is greater than the preset adhesion, it indicates that the current road surface can provide sufficient adhesion, and the electric vehicle 10 is in a safe driving range. The steer-by-wire system 60 maintains a constant feedback torque from the road feeler motor, keeping the steering wheel at a predetermined normal turning force. When the road surface adhesion indicated by the chassis observer is less than the preset adhesion, it indicates that the electric vehicle 10 has entered a low-traction road surface, and the lateral limits provided by the tires are reduced. The road feeler motor of the steer-by-wire system 60 increases the feedback torque, thereby directly increasing the steering wheel turning force. The increased resistance provides counterforce when the driver applies steering input, limiting the driver from accidentally inputting a steering angle exceeding the tire's lateral limits under low-traction straight-line conditions.

[0103] In one embodiment, the control method further includes, during the turning process of the electric vehicle 10 on the first road surface, during the turning process after the steering wheel starts to turn, controlling the feedback torque of the road feel motor of the steer-by-wire system 60 to increase with the increase of the steering wheel rotation angle and with the increase of the vehicle speed of the electric vehicle 10.

[0104] In one embodiment, the control method further includes, during the process of the electric vehicle 10 turning on the second road surface, when the stability margin of the electric vehicle 10 is less than a first threshold and greater than a second threshold, controlling the feedback torque of the road feel motor of the steer-by-wire system 60 to increase by a first ratio as the steering wheel rotation angle or the vehicle speed of the electric vehicle 10 increases. When the stability margin of the electric vehicle 10 is less than the second threshold, controlling the feedback torque of the road feel motor of the steer-by-wire system 60 to increase by a second ratio greater than the first ratio as the steering wheel rotation angle or the vehicle speed of the electric vehicle 10 increases, wherein the stability margin varies with changes in vehicle speed and road surface adhesion coefficient.

[0105] During steering on low-friction surfaces, the feedback torque is increased by dividing the range based on the stability margin and using different ratios. The stability margin is used to quantitatively assess the physical boundary between the current dynamic state of the electric vehicle 10 and the tire's lateral adhesion limit. The lower the road adhesion coefficient, the smaller the maximum lateral force that the tire can generate; the higher the vehicle speed, the greater the lateral force required for steering by the electric vehicle 10. Therefore, the stability margin decreases accordingly as the vehicle speed increases or the road adhesion coefficient decreases. When the stability margin is below a first threshold but above a second threshold, it indicates that the electric vehicle 10 has a potential risk of insufficient lateral force when steering on low-friction surfaces, but has not yet reached the limit state of tire lateral force saturation. At this time, the feedback torque is increased by a lower first ratio, so that the steering wheel turning force increases with the steering angle or vehicle speed at a gradual slope, providing the driver with steering physical resistance that matches the level of risk. When the stability margin is below the second threshold, it indicates that the vehicle's lateral acceleration or steering angle is close to the current road adhesion limit; further increasing the steering angle will trigger tire lateral force saturation and vehicle sideslip instability. At this point, switching to a larger second ratio increases the feedback torque, causing the steering wheel turning force to increase rapidly with the increase in steering angle or vehicle speed. This rapidly increasing steering force creates a significant physical resistance, hindering the driver from further turning the steering wheel in the original steering direction and limiting excessive steering angle input.

[0106] In one embodiment, the control method further includes controlling the angular transmission ratio of the steer-by-wire system 60 to a first transmission ratio during the turning motion of the electric vehicle 10 on the first road surface. During the turning motion of the electric vehicle 10 on the second road surface, the angular transmission ratio of the steer-by-wire system 60 is controlled to a second transmission ratio greater than the first transmission ratio.

[0107] The angular transmission ratio refers to the numerical ratio between the steering wheel angle and the equivalent deflection angle of the steering wheel in an electric vehicle 10. It is calculated by dividing the maximum unidirectional rotation angle of the steering wheel by the maximum unilateral deflection angle of the steering wheel. In traditional mechanical steering systems, the angular transmission ratio is typically set to a fixed value or varies within a very small range. In the steer-by-wire system 60, since the mechanical connection between the steering wheel and the steering wheel is eliminated, the steering wheel angle does not directly control the wheel steering. Relying on the decoupling control capability of the steer-by-wire system 60, the angular transmission ratio is dynamically adjusted based on data such as the real-time vehicle speed, vehicle operating status, and driver input parameters. This allows the real-time ratio of the steering wheel angle to the steering wheel deflection angle to change without altering the inherent dimensional parameters of the steering mechanical hardware. In traditional variable transmission ratio schemes, the angular transmission ratio is designed to be relatively small when the electric vehicle 10 is traveling at low speeds, allowing the electric vehicle 10 to generate a large steering wheel angle with a small steering wheel angle, thus meeting the requirement of easy steering at low speeds. When electric vehicles are traveling at high speeds, the angular transmission ratio is designed to be relatively large, so that a larger steering wheel angle can produce a smaller steering wheel angle, thereby improving the handling stability of the vehicle at high speeds.

[0108] During the turning maneuver of the electric vehicle 10 on the first road surface, the angular transmission ratio of the steer-by-wire system 60 is set to the first transmission ratio. The first road surface has a high coefficient of friction, providing sufficient lateral and longitudinal force grip for the tires. Under this condition, the first transmission ratio is set to a relatively small value, allowing the steering wheel angle to be directly converted into the wheel deflection angle at a high ratio. This ensures basic steering response capability: maintaining a small first transmission ratio ensures that the electric vehicle 10 has a normal lateral dynamic response rate on conventional safe road surfaces, meeting the vehicle's maneuverability and steering follow-through requirements in daily driving. During the turning maneuver of the electric vehicle 10 on the second road surface, based on the change in road surface adhesion, the angular transmission ratio of the steer-by-wire system 60 is set to a second transmission ratio greater than the first transmission ratio. The second road surface has a low coefficient of friction, significantly reducing the physical limits of tire anti-lateral slip and lateral force provision. By increasing the angular transmission ratio through an algorithm, when the driver inputs the same steering wheel angle, the target angle calculated and output to the wheel steering motor by the lower-level controller of the steer-by-wire system 60 decreases. This prevents the lateral force of the tires from reaching saturation, thus preventing irreversible understeer or sideslip and ensuring the physical stability of the vehicle under dangerous low-traction road conditions.

[0109] In one embodiment, the control method further includes controlling the angular transmission ratio of the steer-by-wire system 60 to remain unchanged after the electric vehicle 10 turns from the first road surface to the second road surface, while the steering wheel angle remains at the first angle.

[0110] After the electric vehicle 10 travels from a high-traction first surface to a low-traction second surface, the angular ratio of the steer-by-wire system 60 should ideally switch to a larger second ratio. However, upon entering the second surface, the lateral forces on the tires easily approach the saturation boundary. If the angular ratio is changed further without any change in driver input, the actual wheel steering angle will spontaneously change. This change causes abrupt changes in the tire slip angle, leading to uninstructed fluctuations in the tire's lateral force. Therefore, maintaining the current angular ratio ensures that the actual wheel deflection angle remains constant.

[0111] In one embodiment, the control method further includes controlling the steer-by-wire system 60 to drive the two front wheels to rotate with the steering wheel when the electric vehicle 10 is traveling on a second road surface and the steering wheel angle is less than a preset angle. When the steering wheel angle is greater than the preset angle, the steer-by-wire system 60 maintains the rotation angle of the two front wheels unchanged.

[0112] Electric vehicle 10 travels on a road surface with a low coefficient of friction and is in a turning state after the steering wheel has been turned. During turning when the steering wheel angle is less than a preset angle, the control system controls the steer-by-wire system 60 to drive the two front wheels of the vehicle to turn with the steering wheel, maintaining a predetermined transmission correspondence between the wheel rotation angle and the steering wheel rotation angle. Within the range where the steering wheel angle is less than the preset angle, the lateral force required for the electric vehicle 10 to turn has not yet reached the limit of the tire lateral force provided by the road surface. The steering actuator of the steer-by-wire system 60 converts the steering wheel angle command into the front wheel steering angle, driving the two front wheels to turn, ensuring that the vehicle responds normally to the driver's steering intentions.

[0113] When the steering wheel angle continues to increase and exceeds the preset angle, the control system sends a control command to the steer-by-wire system 60, controlling the steer-by-wire system 60 to keep the steering angle of the two front wheels constant. Even if the steering wheel angle continues to increase beyond the preset angle, the actual steering angle of the two front wheels remains at the wheel steering angle value corresponding to the preset angle. On roads with low coefficient of friction, the maximum lateral force that the tires can generate is limited by the road surface adhesion limit. If the front wheel deflection angle is too large, it will cause the tire slip angle to exceed the linear limit region, leading to tire lateral force saturation or even a decrease in lateral force. The electric vehicle 10 will then experience severe understeer or lose lateral adhesion. When the steering wheel angle exceeds the preset angle, the control system utilizes the decoupling characteristic of the steer-by-wire system 60 to cut off the steering wheel angle command that continues to increase at the execution end, keeping the actual steering angle of the two front wheels constant. This control limits the wheel deflection angle to within the effective lateral force utilization angle boundary under the current road surface conditions, preventing the deterioration of dynamic response due to excessive wheel angle.

[0114] In one embodiment, the electric vehicle 10 further includes an image sensor for detecting road surface information. The control method further includes, during the straight-moving process of the electric vehicle 10, when the image information from the image sensor indicates that the electric vehicle 10 is about to enter a road surface with a coefficient of friction less than a preset value, controlling the electric vehicle 10 to send a prompt message to the driver. The prompt message is used to remind the driver via screen or voice that the electric vehicle 10 is about to enter a low-friction road surface.

[0115] Traditional solutions cannot provide drivers with explicit and effective hazard warnings. The solution proposed in this application integrates information from vehicle sensors, cameras, and other sources to identify dangerous road conditions. The driver's end provides multi-channel alerts and assistance to avoid misoperation, while the actuator end actively corrects or restricts control commands to prevent exacerbating vehicle instability. This multi-domain collaborative solution enhances driving safety.

[0116] The electric vehicle 10 has image sensors, such as cameras and radar, for detecting information about the road surface ahead. The image sensors are mounted at the front of the electric vehicle 10 and can capture optical characteristics of the road surface area ahead, such as reflection intensity, surface texture, grayscale, and color distribution, before the tires physically contact the road surface. When there are low-adhesion media such as ice, snow, or slippery surfaces ahead, their optical characteristics differ significantly from those of conventional high-adhesion surfaces. The image recognition and observation module extracts physical optical features from the acquired image information. For example, when the image information shows patches of bright light indicating strong specular reflection from media such as ice, which differs from the diffuse reflection of ordinary high-adhesion surfaces, and the texture features are smooth with minimal texture, the image features are determined to conform to the optical properties of a typical low-adhesion surface. The control system identifies the image information and can obtain a determination result indicating that the electric vehicle 10 is about to enter a low-adhesion surface.

[0117] During the operation of the electric vehicle 10, image sensors continuously collect road surface images in front of the vehicle. When the image information from the image sensors indicates that the electric vehicle 10 is about to enter a low-friction surface with a coefficient of friction less than a preset value, the display terminal or voice terminal controlling the electric vehicle 10 issues a control command to send a warning message to the driver. The system actively coordinates with the cockpit domain controller to control the electric vehicle 10 to send the warning message to the driver. Specifically, a trigger electrical signal is sent to the cockpit controller to control the display module of the central control screen in the cockpit to display a visual warning sign, or to control the cockpit audio module to play a specific voice alarm audio. The warning message is used to clearly remind the driver, through the physical medium of screen or voice, that the electric vehicle 10 is about to enter a low-friction surface.

[0118] In one embodiment, the control method further includes controlling the electric vehicle 10 to send a prompt message to the driver when acceleration information from an in-tire sensor indicates that the road surface adhesion coefficient is less than a preset value.

[0119] Non-contact image sensors have blind spots in complex lighting, nighttime, or inclement weather conditions, potentially leading to missed detections. To overcome this environmental limitation of non-contact sensing, in-tire sensors are introduced as contact-based physical sensing nodes. These sensors are directly attached to the inside of the tire, rolling with the wheel and directly contacting the road surface. When the wheel actually enters a low-traction surface, the change in the physical medium of the tire contact surface causes a sudden change in the tire's high-frequency vibration acceleration. During the operation of the electric vehicle 10, if the non-contact image sensor fails to detect abnormal road conditions ahead, such as thin ice or black ice sections with weak visual features, the in-tire sensor inside the tire begins to collect real-time acceleration information of the tire-road interaction the instant the wheel of the electric vehicle 10 actually enters that section. The perception fusion module of the control system receives this acceleration information and calculates the actual adhesion coefficient of the current road surface. When this adhesion coefficient is less than a preset value, it is determined that the vehicle has physically contacted and is traveling on a low-traction, dangerous road surface. At this time, the control system sends a trigger electrical signal to the cockpit domain controller, controlling the electric vehicle 10 to output a visual warning through the central control screen or a voice alarm through the audio system, sending a prompt message to the driver.

[0120] In one embodiment, the control method further includes controlling the electric vehicle 10 to send a prompt message to the driver when image information from an image sensor indicates that the electric vehicle 10 is about to enter a road surface with a coefficient of adhesion less than a preset value, or when acceleration information from an in-tire sensor indicates that the coefficient of adhesion of the road surface is less than a preset value, or when wheel adhesion information from a chassis observer indicates that the road surface has a coefficient of adhesion less than a preset value.

[0121] By fusing information from three independent sensing observers—a chassis observer, a tire sensing observer, and an image sensing observer—a comprehensive identification of road surface adhesion status can be achieved. The chassis observer, based on vehicle dynamics, offers high accuracy and precision, but suffers from dynamic response lag and cannot perform identification when the vehicle is in low-dynamic conditions. The tire sensing observer senses the physical contact between the tires and the road surface, enabling identification in any dynamic vehicle scenario; however, as it relies on physical contact sensing, road surface information is only acquired after the wheels have actually rolled across the surface. The image sensing observer identifies objects based on forward-collected images, enabling non-contact, forward-looking identification of objects ahead of the vehicle that have not yet entered the road surface; however, its accuracy and precision are easily affected by ambient light and optical characteristics.

[0122] To integrate the advantages of various sensing technologies and complement their limitations, the hazard marker output by the image sensing observer is set to 1 only when the image sensing observer identifies the road surface ahead as a low-adhesion, hazardous road surface and determines that its identification confidence level is greater than a preset confidence threshold. Subsequently, the hazard marker bits output by the image sensing observer, tire sensing observer, and chassis observer are ORed. When any one of the three outputs a hazard marker bit of 1, the final overall road surface condition is determined to be a low-adhesion, hazardous road surface. This fusion strategy takes into account the forward-looking nature of image sensing, the all-scenario adaptability of tire contact sensing, and the accuracy of chassis dynamics sensing, achieving high-precision and forward-looking fusion identification of sudden changes in road surface adhesion under all operating conditions.

[0123] Upon identifying a low-adhesion, hazardous road surface, the system proactively coordinates multi-dimensional collaborative control between the cabin and chassis domains. In the cabin domain, the control system uses the cabin controller to drive the in-cabin audio equipment to play warning sounds or voice alerts, and simultaneously drives the central control screen to display visual driving risk warnings, sending road condition risk alerts to the driver from both auditory and visual perspectives. In the chassis domain, the control system acquires real-time vehicle driving status parameters (including vehicle speed, longitudinal acceleration, and lateral acceleration) and current road surface adhesion, and calculates the vehicle's current stability margin based on preset calibration data.

[0124] Based on the calculated stability margin, the control system implements the following graded auxiliary control: when it is determined that the current stability margin of the vehicle is less than the preset first threshold, the control system controls the road feel motor of the steer-by-wire system 60 to gradually increase the output feedback torque, so that the steering wheel turning force increases accordingly, and reminds the driver of the current vehicle stability state decreases through tactile perception.

[0125] When the current stability margin of the vehicle is determined to be further reduced to less than the preset second threshold, the control system controls the road feel motor to further increase the feedback torque, which greatly increases the steering wheel turning force. This physically hinders and limits the driver from applying excessive steering wheel angle input, avoiding wheel lateral force saturation and decreased lateral grip due to excessive steering input. At the same time, based on the current stability margin, the control system actively corrects and limits the actual wheel deflection angle through the steering actuator of the steer-by-wire system 60, preventing the driver's steering misoperation from causing further deterioration of the vehicle's dynamic stability.

[0126] According to the solution in this application, multi-information fusion is performed on the chassis road surface observer, inner tube sensor observer, and intelligent driving image perception observer. This complements the advantages of each independent observer and leverages the scenario advantages of each observation scheme to achieve pre-emptive, high-precision, and effective fusion perception across all scenarios. Upon identifying dangerous road conditions, the system proactively coordinates with the cockpit and chassis domains to assist and alert the driver from multiple dimensions, including auditory, visual, and tactile senses. This effectively warns of potential driving hazards and reduces the reliance on driver experience.

[0127] Specifically, the control flow provided in the embodiments of this application will be described below using another scenario as an example.

[0128] like Figure 5As shown, before time t4, the image sensor first captures the optical features of the road surface in front of the electric vehicle 10. The low-adhesion recognition signal of the image sensor jumps from low to high level first. The road condition fusion perception module, based on OR logic, controls the fusion perception low-adhesion state recognition signal to jump to high level synchronously, triggering the warning information signal to jump to high level, providing the driver with an advanced risk warning via the cockpit central control screen or voice. At time t4, the tires of the electric vehicle 10 actually roll into contact with the low-adhesion road surface. The in-tire sensor identifies the low-adhesion state through the collected acceleration features, and the in-tire sensor low-adhesion recognition signal jumps to high level. At the same time, the feedback torque output by the road-sensing motor control produces a small step increase, providing the driver with a basic resistance reference. However, due to the lag in dynamic response, the chassis observer's low-adhesion recognition signal remains at low level at this time. At time t5, the driver begins to turn the steering wheel, and the steering wheel rotation angle increases linearly. The steering controller drives the wheel rotation angle to increase linearly synchronously with the steering wheel rotation angle, resulting in a linear increase in the vehicle's lateral acceleration. During this phase, the feedback torque output by the road feel motor increases with the steering wheel rotation angle, and the output feedback torque is higher than that of the conventional scheme curve. At some point between t5 and t6, the chassis observer completes low-adhesion identification based on wheel forces and vehicle dynamics response. The chassis observer's low-adhesion identification signal jumps to a high level, reflecting the chassis observer's recognition lag compared to the image sensor and in-tire sensor. At t6, the lateral acceleration reaches the physical limit of the current low-adhesion surface and tends to level off. The vehicle stability margin decreases below the preset second threshold. At this point, the steering controller cuts off any further increases in steering wheel angle commands, keeping the wheel rotation angle fixed at the current angle to prevent tire lateral force saturation from causing a deterioration in lateral grip. From time t6 to t7, although the wheel rotation angle was locked, the driver continued to increase the steering wheel rotation angle. In response to the stability margin falling below the second threshold, the road feel motor rapidly increased the feedback torque with a higher gain gradient, causing the slope of the feedback torque solid line to become significantly steeper and higher than the dashed line in the conventional scheme. This generated physical resistance to the driver's hand force, preventing the driver from applying excessive steering input. After time t7, the steering wheel rotation angle stopped increasing and remained at its peak angle. Both the feedback torque and the wheel rotation angle remained unchanged at their corresponding peak values, and the electric vehicle 10 maintained steady-state steering.

[0129] In one embodiment, the control method further includes controlling the electric vehicle 10 to stop sending prompt information to the driver after the electric vehicle 10 has been sending prompt information to the driver for a first duration, wherein acceleration information from the in-tire sensor indicates that the road surface adhesion coefficient is greater than a preset value, and the electric vehicle 10 stops sending prompt information to the driver.

[0130] Non-contact image sensors extract road surface visual features with a probability of misjudgment, such as misidentifying a high-adhesion wet or reflective surface as a low-adhesion ice surface. In-tire sensors, which directly contact the road surface medium, possess extremely high physical measurement accuracy but suffer from spatial lag. During the process of controlling the electric vehicle 10 to send a warning message to the driver, the warning message is maintained for a first duration. The numerical setting principle of this first duration is based on the current longitudinal speed of the electric vehicle 10 and the forward physical distance of the target road surface identified by the image sensor. The first duration characterizes the time span required for the electric vehicle 10 to travel from the image recognition trigger point to the actual contact of the front tires with the target road surface. The field of view distance of the image sensor in front of the vehicle is mapped to the vehicle's travel time. After the warning trigger lasts for this first duration, the wheels have physically traveled to the road segment previously identified by the image sensor. At this time, the acceleration information from the in-tire sensors is used for physical verification. If the verification result indicates that the actual road surface adhesion coefficient is normal, it is determined that there is a false alarm in visual perception or that the electric vehicle 10 has left the low-adhesion area, and the warning is actively deactivated. The accuracy of early warning information is ensured by spatiotemporal alignment and cross-validation of multi-source sensors.

[0131] like Figure 6 As shown, in the signal perception and processing layer, the vehicle controller internally includes a chassis observer, a tire perception observer, an image recognition observer, and a road condition fusion perception module. The input of the tire perception observer is connected to the signal from the in-tire sensor located inside the tire, used to receive acceleration information collected by the in-tire sensor and extract frequency domain features. The input of the image recognition observer is connected to the signal from the image sensor located at the front of the vehicle, used to receive road surface image information from in front of the vehicle. The chassis observer calculates the road surface adhesion coefficient based on vehicle dynamics parameters and wheel forces. The outputs of the chassis observer, tire perception observer, and image recognition observer are all connected to the input signal of the road condition fusion perception module. The road condition fusion perception module performs an OR operation on the road condition recognition results output by the three observers to obtain a comprehensive road surface adhesion state determination result.

[0132] At the signal control and execution layer, the output of the road condition fusion perception module is connected to the input signals of the cockpit controller, the up-steering controller, and the down-steering controller, respectively, to transmit the comprehensive road surface adhesion state judgment results to each controller in real time. The cockpit controller, the up-steering controller, and the down-steering controller can be integrated into the vehicle controller. The output of the cockpit controller is connected to the audio and central control screen signals in the cockpit domain, respectively. When it receives a low-adhesion dangerous road surface judgment result, it drives the audio to play a voice alarm and drives the central control screen to display a visual driving risk image. The output of the up-steering controller is connected to the road sensor motor signal of the steer-by-wire system 60, to calculate the target feedback torque based on the road surface adhesion state and vehicle stability margin, and drives the road sensor motor to output the corresponding feedback torque to adjust the steering wheel turning force. The output of the down-steering controller is connected to the steering motor signal of the steer-by-wire system 60, to calculate the target wheel deflection angle based on the road surface adhesion state, steering wheel angle, and vehicle stability margin, and drives the steering motor to control wheel deflection, thereby actively limiting or correcting the actual wheel steering angle.

[0133] like Figure 7 As shown, the wheel-end sensing layer is used to acquire wheel-end sensing data in real time. This data specifically includes tire force (including longitudinal and lateral forces acting on the tire) and road surface adhesion limits. The wheel-end sensing layer transmits the acquired tire force and road surface adhesion limits to the aforementioned feel-adaptive module and tire-adaptive module. The driver intent reconstruction module remaps and dynamically limits the original steering wheel input, and sends the reconstructed intent control commands to the feel-adaptive module and tire-adaptive module respectively, to prevent the driver's commands from exceeding the current physical adhesion limits between the tire and the road surface. The feel-adaptive module receives wheel-end sensing data from the wheel-end sensing layer and control signals from the driver intent reconstruction module. Based on the tire force and road surface adhesion limits, the feel-adaptive module dynamically adjusts the output torque of the road feel motor of the steer-by-wire system 60 to achieve adaptive adjustment of the steering wheel rotation resistance. The tire-adaptive module receives wheel-end sensing data from the wheel-end sensing layer and control signals from the driver intent reconstruction module. Based on the wheel-end sensing data, the tire-adaptive module dynamically adjusts the actual deflection angle of the wheels at the steering execution end of the steer-by-wire system 60.

[0134] According to this application, by deeply applying in-tire sensing and multi-source information fusion technology, an integrated safety assistance system of "advanced perception - collaborative control - multi-level early warning" is constructed. This system provides drivers with multi-pathway safe driving assistance in all scenarios of intelligent driving and human driving, reduces the requirements for driving experience and operational ability in sudden dangerous situations, and comprehensively improves the active safety performance of vehicles on complex roads and at high speeds.

[0135] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A control method for electric vehicles, characterized in that, The control method is used to adjust the feedback torque of the road feel motor in the steer-by-wire system to cope with changes in road surface adhesion during the process of the electric vehicle turning and driving over a sudden road surface. The sudden road surface includes a first road surface and a second road surface, wherein the adhesion coefficient of the first road surface is greater than that of the second road surface. The control method includes: During the process of the electric vehicle turning on the first road surface, the steering wheel of the electric vehicle turns at the first angle, and the road feel motor of the steer-by-wire system outputs the first feedback torque. After the electric vehicle turns from the first road surface to the second road surface, while the steering wheel angle is still the first angle, the road sensor motor is actively controlled to output a second feedback torque that is greater than the first feedback torque. After the steering wheel is returned to center, the electric vehicle, while traveling straight on the second road surface, controls the feedback torque output by the road sensor motor to decrease to the third feedback torque. During the straight-line process after the electric vehicle leaves the second road surface and re-enters the first road surface, the feedback torque output by the road sensor motor is actively controlled to be reduced to less than the third feedback torque.

2. The control method according to claim 1, characterized in that, The control method includes: During the process of the electric vehicle traveling straight on the second road surface, if the adhesion coefficient of the second road surface is less than a preset value, the road feel motor of the steer-by-wire system is controlled to maintain the third feedback torque unchanged. During the straight-line process after the electric vehicle leaves the second road surface and re-enters the first road surface, if the adhesion coefficient of the first road surface is greater than the preset value, the road feel motor of the steer-by-wire system is controlled to reduce the feedback torque.

3. The control method according to claim 2, characterized in that, The electric vehicle includes in-tire sensors disposed within the tires of the wheels for detecting electric vehicle information, and the control method specifically includes: During the straight-line movement of the electric vehicle, when the road surface adhesion coefficient indicated by the electric vehicle information from the in-tire sensor is greater than the preset value, the feedback torque of the road feel motor of the steer-by-wire system remains unchanged. When the electric vehicle information from the in-tire sensor indicates that the road surface adhesion coefficient is less than the preset value, the road feel motor of the steer-by-wire system is controlled to increase the feedback torque.

4. The control method according to claim 3, characterized in that, The in-tire sensor is used to detect acceleration information, and the control method specifically includes: During the straight-line movement of the electric vehicle, when the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is greater than the preset characteristic frequency, the feedback torque of the road feel motor controlling the steer-by-wire system remains unchanged. When the natural frequency corresponding to the acceleration indicated by the acceleration information from the in-tire sensor is less than the preset characteristic frequency, the road feel motor of the steer-by-wire system is controlled to increase the feedback torque.

5. The control method according to any one of claims 1-4, characterized in that, The electric vehicle includes a chassis observer for identifying road surface adhesion based on wheel force, and the control method specifically includes: During the straight-line movement of the electric vehicle, when the road surface adhesion indicated by the wheel adhesion information from the chassis observer is greater than the preset adhesion, the feedback torque of the road feel motor of the steer-by-wire system remains unchanged. When the road surface adhesion indicated by the wheel adhesion information from the chassis observer is less than the preset adhesion, the road feel motor of the steer-by-wire system is controlled to increase the feedback torque.

6. The control method according to any one of claims 1-5, characterized in that, The control method further includes: During the process of the electric vehicle turning on the first road surface, during the turning process after the steering wheel starts to turn, the feedback torque of the road feel motor controlling the steer-by-wire system increases with the increase of the steering wheel rotation angle and with the increase of the electric vehicle speed.

7. The control method according to any one of claims 1-6, characterized in that, The control method further includes: During the process of the electric vehicle turning on the second road surface, when the stability margin of the electric vehicle is less than a first threshold and greater than a second threshold, the feedback torque of the road feel motor of the steer-by-wire system is increased by a first ratio as the rotation angle of the steering wheel or the speed of the electric vehicle increases. When the stability margin of the electric vehicle is less than the second threshold, the feedback torque of the road feel motor of the steer-by-wire system increases by a second ratio greater than the first ratio as the steering wheel rotation angle or the vehicle speed of the electric vehicle increases, wherein the stability margin changes with the vehicle speed and the road surface adhesion coefficient.

8. The control method according to any one of claims 1-7, characterized in that, The control method further includes: During the process of the electric vehicle turning and driving on the first road surface, the angular transmission ratio of the steer-by-wire system is controlled to be the first transmission ratio. During the process of the electric vehicle turning on the second road surface, the angular transmission ratio of the steer-by-wire system is controlled to be a second transmission ratio that is greater than the first transmission ratio.

9. The control method according to claim 8, characterized in that, The control method further includes: After the electric vehicle turns from the first road surface to the second road surface, while the steering wheel angle remains at the first angle, the angular transmission ratio of the steer-by-wire system remains unchanged.

10. The control method according to any one of claims 1-9, characterized in that, The control method further includes: During the turning process of the electric vehicle on the second road surface and when the steering wheel is turned at an angle less than a preset angle, the steer-by-wire system is controlled to drive the two front wheels to rotate with the rotation of the steering wheel; During steering, when the steering wheel angle is greater than the preset angle, the steer-by-wire system is controlled to keep the rotation angle of the two front wheels constant.

11. The control method according to any one of claims 1-10, characterized in that, The electric vehicle also includes an image sensor for detecting road surface information, and the control method further includes: During the straight-line movement of the electric vehicle, when the image information from the image sensor indicates that the electric vehicle is about to enter a road surface with a coefficient of friction less than a preset value, the electric vehicle is controlled to send a prompt message to the driver. The prompt message is used to remind the driver, via screen or voice, that the electric vehicle is about to enter a low-friction road surface.

12. The control method according to claim 11, characterized in that, The control method further includes: When acceleration information from the in-tire sensor indicates that the road surface adhesion coefficient is less than the preset value, the electric vehicle is controlled to send a prompt message to the driver.

13. The control method according to claim 11, characterized in that, The control method further includes: After the electric vehicle has been sending a prompt message to the driver for a first duration, acceleration information from the in-tire sensor indicates that the road surface adhesion coefficient is greater than the preset value, and the electric vehicle stops sending the prompt message to the driver.

14. A vehicle controller for electric vehicles, characterized in that, The vehicle controller is used to implement the control method as described in any one of claims 1-13.

15. An electric vehicle, characterized in that, The electric vehicle includes an accelerator pedal, a brake pedal, a steering wheel, and a vehicle controller as described in claim 14, wherein the accelerator pedal is used to indicate driving the electric vehicle, the brake pedal is used to indicate outputting braking force to the wheels of the electric vehicle, and the steering wheel is used to indicate the steering angle of the wheels of the electric vehicle.

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