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

Abstract

A control method for an electric vehicle, a vehicle controller and an electric vehicle relate to the field of new energy vehicles, and can be applied to pure electric vehicles and hybrid vehicles. The control method is used to suppress shimmy of two front wheels of the electric vehicle through a steer-by-wire system during driving of the electric vehicle. The control method comprises: in a normal straight driving process in which a steering wheel of the electric vehicle is not turned, controlling a steering motor of the steer-by-wire system to keep output torque unchanged. In a steering driving process after the steering wheel is turned, the steering motor of the steer-by-wire system is controlled to output steering torque to drive the two front wheels to steer. In a straight driving process in which shimmy occurs in the two front wheels of the electric vehicle, before the steering wheel is turned, the steering motor of the steer-by-wire system is controlled to output periodic compensation torque. According to the scheme, the shimmy amplitude of the front wheels is reduced, tire wear is reduced, dynamic load of the steering mechanism is reduced, and fuel economy, driving stability and power are improved.

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] Steer-by-wire (SBW) is a car steering system that completely replaces the traditional mechanical connection with electronic signals. It eliminates 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 (ECU) to drive the steering motor and control wheel rotation. During vehicle operation, the front wheels may experience periodic lateral oscillations around the kingpin due to factors such as road surface unevenness, tire dynamic imbalance, or mechanical resonance—a phenomenon known as front wheel shimmy. Because the physical connection between the steering wheel and the front wheel steering actuators is completely severed in the SBW system, the steering actuators become a relatively isolated vibration system within the chassis architecture. Prolonged front wheel shimmy causes the steering actuators (such as the steering motor, rack, and tie rod ends) to continuously bear high-frequency dynamic alternating loads, severely shortening the fatigue life of related components. It also accelerates abnormal tire wear, increases vehicle drag, and ultimately reduces driving stability, power, and fuel economy.

[0003] Therefore, how to effectively suppress front wheel shimmy in a steer-by-wire system 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. When front wheel shimmy occurs in an electric vehicle, the steering motor is controlled to output periodic compensation torque to counteract the periodic shimmy, rapidly reducing the reciprocating vibration of the wheels and preventing the electric vehicle from deviating from its lane due to shimmy loss of control. This greatly improves driving safety under extreme conditions, actively suppresses wheel shimmy, thereby significantly reducing the dynamic alternating load on various mechanical components of the system, effectively reducing abnormal tire wear, and significantly extending the overall service life of the chassis and steering actuator.

[0005] Firstly, this application provides a control method for an electric vehicle. The method suppresses shimmy of the two front wheels of the electric vehicle during operation via a steer-by-wire system. The method includes maintaining a constant output torque of the steering motor of the steer-by-wire system during normal straight-line driving when the steering wheel is not turned. During steering maneuvers after the steering wheel is turned, the steering motor of the steer-by-wire system outputs steering torque to drive the two front wheels to steer. During straight-line driving when the two front wheels shimmy, the steering motor of the steer-by-wire system outputs periodic compensation torque before the steering wheel is turned.

[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. 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 mass production stage. 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] Front wheel shimmy is a nonlinear dynamic phenomenon characterized by reciprocating oscillations around the kingpin. In vehicle dynamics, front wheel shimmy is classified into two mechanisms: forced vibration and self-excited vibration. Forced vibration is typically caused by external excitations such as wheel mass imbalance, radial and lateral force fluctuations in the tires, or periodic fluctuations in braking torque; its excitation frequency is often proportional to the wheel speed. Self-excited vibration, on the other hand, originates from the energy feedback mechanism within the system, such as the relaxation length during the establishment of lateral force in the tires, and nonlinear factors such as structural clearances in the moving pairs of the steering transmission mechanism. These factors can cause the system to evolve from a steady state to limit cycle oscillations or even chaotic motion. When front wheel shimmy occurs, the vehicle's steering axle experiences continuous reciprocating oscillations. This high-frequency alternating load not only directly causes severe periodic vibrations in the steering wheel, deteriorating the driving experience, but also accelerates fatigue damage to the steering actuator, suspension bushings, and tires, and significantly reduces the vehicle's lateral handling stability under certain operating conditions, seriously threatening active driving safety. For steer-by-wire systems, although the direct mechanical connection between the steering wheel and the wheels is eliminated, the violent swaying of the front wheels is transmitted directly to the steering actuator through the tie rod. Physically, this manifests as alternating impact of force on the lower rack, that is, in the rack force that should normally tend to be stable, periodic abnormal fluctuation signals with specific oscillation frequency and amplitude are generated.

[0008] During normal straight-line driving of an electric vehicle with the steering wheel not turned, it is determined that the driver's intention is to maintain straight-line driving, and the electric vehicle is not subjected to any abnormal disturbances that would cause shimmy. At this time, the output torque of the steering motor controlling the steer-by-wire system remains constant. By maintaining a constant (or zero) output torque, the current straight-line posture of the front wheels is locked, preventing the motor from generating unnecessary movements that could interfere with the vehicle's straight-line stability, while also reducing unnecessary energy consumption of the system. It should be understood that during normal straight-line driving of an electric vehicle with the steering wheel not turned, the steering motor often still needs to output a small amount of torque to counteract minor road surface deviations or suspension clearances in order to keep the front wheels centered. This small torque fluctuation can also be considered as the range within which the steering motor's output torque remains constant.

[0009] During the steering process after the steering wheel is turned, the system recognizes the driver's clear steering intention. At this time, the steering motor controlling the steer-by-wire system outputs the corresponding steering torque, thereby overcoming the frictional resistance between the front wheels and the road surface and the return torque, directly driving the two front wheels to deflect to the target angle, thus precisely executing the driver's steering operation.

[0010] During straight-line travel in an electric vehicle, front wheel shimmy occurs. Front wheel shimmy is essentially a reciprocating, periodic oscillation of the wheel around its kingpin with a certain frequency and amplitude. During this straight-line travel, when both front wheels are shimming—meaning the steering wheel is not turned and the driver has not input a steering command—keeping the torque constant alone is insufficient to counteract the periodic vibration energy transmitted from the wheels. In this condition, the steering motor actively outputs a periodic compensation torque. Front wheel shimmy manifests as periodic mechanical vibration. By controlling the steering motor to output a compensation torque that varies periodically over time, this periodic torque directly acts on the steering transmission mechanism of the front wheels, forming an alternating torque that counteracts the shimmy excitation force. Through this dynamic compensation of periodic torque, the periodic energy causing wheel shimmy can be offset or weakened at its physical source, thus autonomously suppressing front wheel shimmy without driver intervention by turning the steering wheel.

[0011] According to the solution in this application, the steering motor outputs periodic compensation torque. Leveraging the motor's fast response and high control precision, the periodic compensation torque directly counteracts periodic shimmy. This allows the electric vehicle to actively and in real-time cancel energy out when sudden shimmy occurs while driving straight, rapidly reducing wheel vibration and preventing the electric vehicle from deviating from its lane due to shimmy loss of control, thus greatly improving driving safety under extreme conditions. Within the architecture of the wire-controlled steering system, shimmy is suppressed through torque compensation of the underlying steering motor. Because the steering wheel and front wheels are mechanically decoupled, abnormal front wheel vibration and the motor's periodic compensation action are isolated at the chassis actuator. The driver does not need to turn the steering wheel or experience any severe steering wheel kicking or vibration; the electric vehicle actively eliminates safety hazards, providing an extremely smooth driving experience. Front wheel shimmy generates high-frequency alternating stress, accelerating the wear and fatigue of mechanical connecting components of the steering system, such as tie rods, ball joints, and suspension components. By controlling the motor to output periodic compensation torque, the mechanical oscillation of the wheels is actively suppressed, thereby significantly reducing the dynamic alternating load on various mechanical components of the system, effectively reducing abnormal tire wear, and significantly extending the overall service life of the chassis and steering actuator.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes controlling the frequency of the periodic compensation torque output by the steering motor of the steer-by-wire system to vary with the sway frequency of the two front wheels, and controlling the amplitude of the periodic compensation torque to vary with the sway amplitude of the two front wheels.

[0013] During actual operation of electric vehicles, due to changes in vehicle speed, differences in road surface excitation, and the transfer of transient loads on the vehicle chassis, front wheel shimmy is not a static vibration but a nonlinear dynamic phenomenon whose frequency and amplitude change dynamically in real time with the driving state. To achieve precise suppression, a dynamic adaptive following mechanism is further introduced when controlling the output of periodic compensation torque from the steering motor. The actual shimmy frequency and amplitude of the two front wheels are detected and acquired in real time. When controlling the output of periodic compensation torque from the steering motor of the steer-by-wire system, this compensation torque is not a fixed preset parameter but is configured to dynamically update in real time with the actual shimmy state of the front wheels. The frequency of the control periodic compensation torque changes synchronously with the change in the front wheel shimmy frequency. When the shimmy frequency of the front wheels increases or decreases due to external excitation or system resonance, the alternating frequency of the motor output torque also changes synchronously. The amplitude of the control periodic compensation torque changes synchronously with the change in the front wheel shimmy amplitude. When the front wheel oscillates violently, i.e., the amplitude enters the peak region, the steering motor outputs a compensation torque with a larger peak value to provide sufficient counteracting energy. When the front wheel oscillation weakens or even decays, i.e. the amplitude becomes smaller, the steering motor proportionally reduces the output force of the compensation torque. Thus, the steering motor can always output a dynamic compensation torque that precisely matches the instantaneous oscillation state of the front wheel, thereby achieving vibration energy offsetting.

[0014] According to the solution in this application, when an electric vehicle accelerates, decelerates, or crosses road surfaces with different friction coefficients, the excitation characteristics of shimmy will undergo drastic changes. By dynamically following the compensation torque frequency and amplitude, it is ensured that the output compensation energy of the steering motor is always precisely offset against the actual excitation energy, preventing suppression failure due to insufficient compensation (undercompensation) during severe shimmy, and avoiding the artificial introduction of new vibration sources into the steering system due to excessive compensation (overcompensation) during weak shimmy. This ensures the suppression accuracy across the entire frequency band and amplitude range, enabling the steer-by-wire system to adapt to tires with different wear levels, suspension components with different aging, and unpredictable complex road impacts, greatly improving the control robustness of the steer-by-wire system throughout the entire life cycle of the electric vehicle and under extreme operating conditions. By using amplitude follow-up control, a large torque is output only to intervene when the shimmy is severe, and the output is automatically reduced when the shimmy is weak or about to disappear. This avoids the steering motor being in a redundant output state of high load or high frequency broadband for a long time, effectively reducing the overall power consumption of the steer-by-wire system, reducing the risk of overheating of the motor and related drive modules, and improving the operational safety and lifespan of the underlying execution hardware.

[0015] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes controlling the frequency of the periodic compensation torque output by the steering motor of the steer-by-wire system to be equal to the shimmy frequency of the two front wheels, and the phase of the compensation torque being opposite to the phase of the shimmy of the two front wheels.

[0016] In the field of vibration control, if the frequency of the compensation torque deviates slightly from the actual shimmy frequency, their superposition will not only fail to eliminate the original vibration but will also induce complex and highly destructive "beating" or broadband chaotic motion. To ensure that the periodic compensation torque output by the steering motor can achieve effective and rapid shimmy suppression without triggering new control conflicts, the frequency and phase domain characteristics of this compensation torque are defined. Specifically, the frequency of the periodic compensation torque output by the steering motor controlling the steer-by-wire system is equal to the shimmy frequency of the two front wheels, and the phase of the compensation torque is opposite to the phase of the shimmy of the two front wheels. The wave-vibration interference principle in physics states that when two periodic oscillation signals have the same frequency and a phase difference of 180 degrees (i.e., opposite phases), they will undergo destructive interference, and the vibration energy within the system will cancel each other out to zero. Front wheel shimmy, as a periodic nonlinear dynamic oscillation, has its specific transient excitation frequency and phase characteristics. By controlling the frequency of the compensating torque output by the steering motor to be equal to the actual shimmy frequency of the two front wheels, the suppression energy output by the steering motor is ensured to be synchronized with the abnormal mechanical oscillation of the front wheels in the time domain, ensuring that a corresponding compensating torque exists in each oscillation cycle. Simultaneously, by controlling the phase of this compensating torque to be opposite to the phase of the front wheel shimmy, in any oscillation cycle, when the front wheels experience the greatest abnormal shimmy tendency to one side (e.g., to the left) due to external excitation (i.e., the oscillation peak), the steering motor outputs the maximum compensating torque to the right (i.e., the oscillation trough) at the exact same moment. This synchronous and anti-phase control allows the dynamic compensating torque generated by the steering motor to directly, in real-time, and precisely counteract the periodic excitation force transmitted from the front wheels at the steering actuator, achieving active elimination of vibration energy using the principle of destructive interference.

[0017] According to the solution in this application, by controlling the compensation torque to be in the same frequency and out of phase with the front wheel shimmy signal, and using the interference cancellation mechanism, it is ensured that the compensation torque of the motor is used to cancel the abnormal vibration, so that the shimmy amplitude of the front wheel converges to zero in the shortest time after it occurs. This provides the most efficient anti-shimmy active safety protection for electric vehicles. By limiting the motor output frequency to be equal to the shimmy frequency, the possibility of frequency coupling misalignment is eliminated. This ensures that when the steer-by-wire system applies active intervention torque, it will not introduce secondary high-frequency vibration, additional mechanical impact or new noise sources to the chassis. It achieves precise offsetting of the steering motor output, avoids useless output and energy superposition of incorrect phase, and while efficiently canceling the front wheel shimmy, it significantly reduces the risk of redundant heating of the steering motor, maintaining the excellent energy economy and thermal stability of the underlying hardware of the steer-by-wire system.

[0018] In conjunction with the first aspect, in some implementations of the first aspect, the steering motor adjusts the magnitude of the rack force on the racks of the two front wheels by adjusting the magnitude of its output torque. Specifically, the control method includes controlling the output torque of the steering motor to remain constant during normal straight-line driving when the steering wheel is not turned, so that the rack force on the rack remains zero. During steering driving after the steering wheel is turned, the rack force on the rack is controlled to change with the steering wheel rotation to drive the two front wheels to turn to one side. During straight-line driving of the electric vehicle, when the rack force on the rack periodically exceeds a preset value, before the steering wheel is turned, the steering motor of the steer-by-wire system is controlled to output a periodic compensation torque to reduce the amplitude of the rack force.

[0019] The steering of the two front wheels is driven by the lateral movement of the racks connected to them. Therefore, controlling the steer-by-wire system involves adjusting the output torque of the steering motor, which directly adjusts the rack force on the two front wheels in physical transmission. During normal straight-line driving when the steering wheel is not turned, the front wheels do not need to overcome additional steering resistance because the electric vehicle travels smoothly. At this time, the output torque of the steering motor remains constant, thus keeping the rack force on the racks zero. This dynamic balance of zero rack force prevents unnecessary lateral displacement of the racks, thereby locking the straight-line posture of the two front wheels.

[0020] During steering, once the steering wheel is turned, the driver inputs a clear steering request. The steering motor dynamically outputs torque, causing the rack force to change linearly or non-linearly with the steering wheel's rotation. This changing, directional rack force overcomes road friction and tire self-centering torque, directly driving the two front wheels to steer in the direction the driver intends.

[0021] During straight-line travel in an electric vehicle, abnormal vibrations may occur in the front wheels due to road surface excitation or nonlinear factors within the system itself, which are then transmitted upwards along the mechanical structure to the rack. By monitoring the rack's stress state in real time, when it is detected that the rack force not only exhibits periodic fluctuations but also that the amplitude of these fluctuations periodically exceeds a preset value, it is determined that front wheel shimmy has occurred, thus avoiding the impact of road surface potholes. Before the steering wheel is turned, i.e., before the driver notices or makes any manual corrections, the steering motor of the electric vehicle's steer-by-wire system outputs a periodic compensation torque. This periodic compensation torque, after being transmitted to the rack, forms a counteracting force against the abnormal shimmy force, thereby directly reducing the amplitude of the rack force and causing the rack force to return to within the preset safe and stable threshold.

[0022] According to the solution in this application, the rack force is directly adjusted by outputting torque from the steering motor, shortening the control link between physical feedback and compensation intervention. This allows for rapid counterbalancing of shimmy energy at the underlying execution level, improving the response speed and physical effectiveness of shimmy suppression. It can distinguish between normal road bumps and continuous shimmy; compensation torque is only output when abnormal rack force forms regular periodic oscillations and exceeds the safety boundary. This avoids ineffective and frequent intervention by the steering motor under normal bumpy road conditions, ensuring the stability of the control system and the smoothness of vehicle driving. It also significantly reduces the dynamic fatigue stress on key hardware such as the rack, steering tie rod, and steering motor, improving the reliability and service life of the drive-by-wire chassis system.

[0023] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes controlling the magnitude of the periodic compensation torque output by the steering motor of the steer-by-wire system to increase with the increase of the axial speed of the rack and the increase of the acceleration of the axial movement of the rack.

[0024] The severity of front wheel shimmy varies continuously in the time domain. To ensure the steering motor's compensation action accurately mitigates shimmy, the amplitude of the periodic compensation torque output by the steering motor in the steer-by-wire system is correlated with the axial motion state (velocity and acceleration) of the rack. The rack's motion state can be detected by sensors. When front wheel shimmy occurs while the electric vehicle is traveling straight, the abnormal alternating excitation force forces the rack to undergo unexpected axial reciprocating motion. The rack's axial velocity and acceleration are acquired in real time and used as a reference for adjusting the compensation torque amplitude. The compensation torque amplitude increases with the rack's axial velocity; velocity represents transient kinetic energy, and applying velocity-related damping force effectively suppresses vibration. Therefore, when the rack's axial velocity increases, it indicates that the front wheels are experiencing rapid and severe shimmy, prompting the steering motor to synchronously increase the amplitude of the output periodic compensation torque. This is equivalent to introducing active, variable electronic damping into the rack, rapidly absorbing and dissipating the rack's kinetic energy during rapid movement by outputting a larger counteracting torque. The compensation torque amplitude increases with the acceleration of the rack's axial movement. The rack's axial acceleration reflects the abruptness of the front wheel shimmy during reversal and the magnitude of the transient impact force. When the rack's axial acceleration increases, it indicates that the front wheel is experiencing a harsh, high-frequency vibration impact, and the rack tends to accelerate suddenly or reverse abruptly. The steering motor is then controlled to instantaneously increase the compensation torque amplitude. This provides active inertial compensation for the rack, utilizing the peak torque generated instantaneously by the steering motor to counteract the destructive mechanical impact caused by high acceleration, thereby coping with high-frequency, sudden vibration spikes.

[0025] According to the scheme of this application, by increasing the amplitude of the compensation torque with the increase of rack speed, the decay rate of shimmy energy is accelerated. By increasing the amplitude with the increase of rack acceleration, the huge inertial impact force at the moment of shimmy reversal can be predicted and countered, enabling the steer-by-wire system to quickly suppress front wheel shimmy of various frequencies and intensities. The output amplitude of the steering motor strictly follows the real-time kinematic parameter changes of the rack, achieving stronger compensation for stronger vibrations and softer compensation for weaker vibrations. This avoids steering mechanism jamming and stiffness due to excessive compensation torque, and also avoids the danger of failing to suppress severe shimmy due to insufficient torque. It eliminates rigid collisions between the rack and other mechanical transmission components, significantly improving the lifespan and reliability of the underlying mechanical structure of the steer-by-wire system.

[0026] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, during the steering process in which the two front wheels of the electric vehicle oscillate, after the steering wheel is turned, controlling the steering motor of the steer-by-wire system to output a periodic compensation torque while simultaneously superimposing the output steering torque.

[0027] In actual driving of electric vehicles, front wheel shimmy can occur not only during straight-line driving but also suddenly during cornering, lane changes, or emergency obstacle avoidance. When an electric vehicle experiences sudden shimmy in a curve, the front wheels, already bearing enormous lateral forces and load transfers, will experience extremely severe chassis mechanical shocks due to the shimmy. The tires' lateral grip can easily exceed its limits, leading to loss of vehicle control. Therefore, during steering maneuvers where the two front wheels of an electric vehicle shimmy—that is, when the driver inputs a steering command by turning the steering wheel and the front wheels are simultaneously subjected to abnormal external vibrations—the steer-by-wire system must balance steering and vibration suppression. In a steer-by-wire system, because the steering wheel and front wheels are physically decoupled, the output of the steering motor is no longer limited to a single mechanical transmission command but can receive and execute multi-dimensional composite electrical signals. After the steering wheel is turned, the steer-by-wire system first calculates the basic steering torque used to drive the vehicle to the target path based on the steering wheel's rotation state, including the angle and angular velocity. Simultaneously, the steer-by-wire system monitors the shimmy state of the front wheels in real time and calculates the periodic compensation torque to counteract abnormal front wheel oscillations. Then, the steering motor controlling the steer-by-wire system outputs the periodic compensation torque while simultaneously superimposing the output steering torque. This is equivalent to superimposing the low-frequency reference signal representing the steering intention with the high-frequency compensation signal representing the vibration damping intention in the time domain. Upon receiving this superimposed signal, the steering motor continuously outputs a steering force to smoothly drive the front wheels to one side, accompanied by a high-frequency alternating torque matching the shimmy frequency and amplitude, thereby achieving destructive interference between steering and vibration energy.

[0028] According to the scheme in this application, by controlling the steering motor to output two types of torque in a superimposed manner, it is ensured that even under strong anti-shield intervention, the driver's steering intention can still be transmitted to the front wheels without loss and with precision. This prevents the vehicle from deviating from the target path due to shield suppression actions in corners, greatly improving the vehicle's active safety under extremely complex conditions. The steering torque and the periodic compensation torque are calculated independently and do not interfere with each other. Ultimately, the torque is physically superimposed only at the output end of the steering motor, reducing the coupling complexity of the control system, improving the real-time performance of the underlying electronic control response, and avoiding control delays under complex conditions.

[0029] In conjunction with the first aspect, in some implementations of the first aspect, the control method specifically includes, during the process of controlling the steering motor of the steer-by-wire system to output periodic compensation torque, when the opening of the brake pedal increases, controlling the frequency of the output periodic compensation torque to decrease, and the amplitude of the periodic compensation torque to increase.

[0030] In actual driving of electric vehicles, front wheel shimmy is affected not only by constant vehicle speed but also by longitudinal acceleration and deceleration, especially braking conditions. When the driver depresses the brake pedal during front wheel shimmy in an electric vehicle, the vehicle's dynamic state undergoes a drastic transient change. To maintain shimmy suppression during braking, the output of the steering motor in the steer-by-wire system is adjusted according to the brake pedal opening during the periodic compensation torque output.

[0031] When the brake pedal opening increases, the driver is applying or increasing braking force, and the electric vehicle is decelerating. At this time, the periodic compensation torque output by the steer-by-wire system is adjusted synchronously. The frequency of the periodic compensation torque output decreases. The excitation frequency of front wheel shimmy, especially the forced vibration frequency, is usually positively correlated with the electric vehicle's speed and wheel rotation speed. When the brake pedal opening increases, causing the vehicle speed and wheel rotation speed to decrease, the actual mechanical shimmy frequency of the front wheels will also decrease synchronously. Therefore, the frequency of the periodic compensation torque output by the steer-by-wire system actively controls the steering motor to decrease accordingly, ensuring that the steering motor's compensation frequency can match the actual shimmy frequency that decreases due to deceleration in real time, maintaining synchronization. The amplitude of the periodic compensation torque output increases. The deceleration caused by the increased brake pedal opening will trigger a sharp forward shift of the vehicle's center of gravity, i.e., a longitudinal load transfer. This transient load transfer will cause a rapid and significant increase in the vertical load on the front axle and both front wheels. The surge in vertical pressure not only significantly alters the tire's lateral stiffness but also instantaneously compresses all movement clearances of the steering transmission mechanism to their limits, easily inducing strong self-excited shimmy or causing a destructive surge in the original shimmy amplitude—a dramatic amplification of vibration energy. To counteract this sudden increase in mechanical excitation energy due to the transfer of braking load, the steer-by-wire system controls the steering motor to instantaneously increase the amplitude of its output periodic compensation torque, using a stronger, opposite-phase physical torque to offset the enormous shimmy impact force generated during braking.

[0032] According to the solution in this application, by linking the frequency and amplitude of the periodic compensation torque with the brake pedal opening, the sudden increase in amplitude caused by the transfer of braking load is precisely overcome, preventing vehicle loss of control. A large torque is used to cancel out the shimmy energy in the initial stage before it is about to amplify uncontrollably, ensuring the stability of the front wheels under extreme braking conditions and improving the active safety baseline of electric vehicles. By synchronously reducing the frequency of the compensation torque during braking, ensuring complete frequency matching, the vibration energy is canceled out throughout the entire deceleration cycle. This ensures that the tires maintain rolling friction contact with the road surface in the most stable posture, thereby maximizing the braking efficiency of the front wheels and ensuring that the electric vehicle maintains a straight braking path even under severe conditions of combined severe shimmy and emergency braking.

[0033] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, during the process of controlling the output of the periodic compensation torque of the steering motor of the steer-by-wire system, increasing the frequency of the output periodic compensation torque as the opening of the accelerator pedal increases.

[0034] In actual operation of electric vehicles, front wheel shimmy, as a complex mechanical vibration, does not have a constant excitation frequency; rather, it is related to the vehicle's speed and the rotational state of the wheels. In order to accurately and without delay cancel shimmy even when the electric vehicle is accelerating, the steering motor of the steer-by-wire system outputs periodic compensation torque, which is adjusted based on the accelerator pedal opening.

[0035] When the accelerator pedal opening increases, it indicates that the driver has input a clear acceleration intention. This increases the longitudinal driving force of the electric vehicle, and the vehicle speed and the rotational speed of the two front wheels will increase accordingly. The forced shimmy of the front wheels caused by factors such as wheel imbalance and tire radial force fluctuations has an excitation frequency that is directly proportional to the wheel's rotational angular velocity. Therefore, as the wheel speed increases due to the increased accelerator pedal opening, the actual physical shimmy frequency of the front wheels will also increase. To cope with this change, the frequency of the periodic compensation torque output by the steer-by-wire system actively increases accordingly. The steer-by-wire system uses the increase in accelerator pedal opening as a feedforward prediction signal, and simultaneously and proactively controls the steering motor to increase the frequency of the output compensation torque as the vehicle speed and physical shimmy frequency actually increase.

[0036] According to the solution in this application, by linking the frequency of the periodic compensation torque with the accelerator pedal opening, the shimmy frequency will rise sharply when accelerating to overtake or rapidly changing lanes, causing the frequency of the compensation torque to increase synchronously with acceleration. This achieves precise synchronization of the anti-vibration energy across the entire acceleration frequency band, ensuring the effectiveness of physical destructive interference at any vehicle speed. This allows the front wheels of the electric vehicle to maintain extreme stability even under high-load conditions such as rapid acceleration, which can easily induce front axle instability, thus maximizing tire adhesion and the accuracy of the path during electric vehicle acceleration.

[0037] In conjunction with the first aspect, in certain implementations of the first aspect, the control method specifically includes controlling the steering motor of the steer-by-wire system to output a periodic first compensation torque during straight-line travel when the electric vehicle's speed is a first speed and the two front wheels are shimming, before the steering wheel is turned. During straight-line travel when the electric vehicle's speed is a second speed greater than the first speed and the two front wheels are shimming, controlling the steering motor of the steer-by-wire system to output a periodic second compensation torque before the steering wheel is turned, wherein the frequency of the second compensation torque is greater than the frequency of the first compensation torque.

[0038] During actual operation of electric vehicles, the excitation characteristics of front wheel shimmy are not statically constant but are related to the vehicle's speed. Especially for shimmy caused by rotational excitation sources such as wheel mass imbalance and tire radial force fluctuations, the excitation frequency is limited by the wheel's rotational angular velocity. To achieve precise cancellation interference of front wheel shimmy across the entire speed range, the output of the steering motor in the steer-by-wire system is adjusted based on vehicle speed when controlling the periodic compensation torque. The physical frequencies of shimmy in electric vehicles differ significantly at low and high speeds. If the steer-by-wire system uses only a fixed-frequency compensation strategy, frequency misalignment is easily generated when the vehicle speed changes, meaning the compensation torque frequency cannot keep up with the shimmy frequency at high speeds.

[0039] When an electric vehicle experiences front wheel shimmy while traveling straight, and the driver does not intervene before turning the steering wheel, the steer-by-wire system continuously monitors the vehicle's speed and outputs compensation torque with differentiated frequency characteristics based on the speed. When the vehicle is at a low speed (e.g., cruising) and both front wheels shimmy, the mechanical vibration frequency is relatively low due to the slow wheel rotation. In this case, the steering motor of the steer-by-wire system outputs a periodic first compensation torque, the alternating frequency of which is set to match the current low shimmy frequency to offset vibrations at low speeds. When the electric vehicle accelerates or travels at a speed greater than the first speed (e.g., high speed) and both front wheels shimmy, the wheel rotational angular velocity increases with the speed, causing the physical shimmy frequency to rise to a higher frequency. The steer-by-wire system then controls the steering motor to output a periodic second compensation torque, the frequency of which is higher than the frequency of the first compensation torque. Vehicle speed is used as a feedforward reference for the shimmy frequency. The higher the vehicle speed, the higher the frequency of the alternating counter-torque output by the steering motor.

[0040] According to the solution in this application, by establishing coordinated control between the frequency of the periodic compensation torque and the vehicle speed, the compensation torque can always accurately keep up with the transient frequency of the oscillation, and will not cause dangerous high-frequency beat vibration or system resonance due to frequency loss.

[0041] In conjunction with the first aspect, in some implementations of the first aspect, when the second vehicle speed is less than the preset vehicle speed, the amplitude of the second compensation torque is greater than the amplitude of the first compensation torque. When the first vehicle speed is greater than the preset vehicle speed, the amplitude of the second compensation torque is less than the amplitude of the first compensation torque.

[0042] Although the frequency of shimmy increases linearly with vehicle speed, the amplitude of shimmy exhibits a non-monotonic resonant relationship with vehicle speed. Specifically, the steering and suspension systems have their inherent natural resonant frequencies. When the excitation frequency of wheel rotation approaches this natural frequency, the shimmy amplitude increases sharply; however, as the vehicle speed continues to increase and the excitation frequency deviates from the natural frequency, the shimmy amplitude decreases. To ensure that the compensation torque output by the steering motor conforms to this pattern, when controlling the periodic compensation torque output of the steering motor in the steer-by-wire system, a segmented amplitude adjustment is implemented, using a preset vehicle speed reflecting the resonance critical point of the electric vehicle as the dividing line.

[0043] When the second vehicle speed is less than the preset speed, it indicates that the electric vehicle is accelerating towards the resonance point of the steering system, meaning the wheel excitation frequency is approaching the system's natural frequency. At this time, the actual mechanical shimmy amplitude of the front wheels increases with increasing vehicle speed. Therefore, the amplitude of the second compensation torque output by the control is greater than the amplitude of the first compensation torque. Before crossing the preset resonance speed, the amplitude of the compensation torque output by the steering motor increases synchronously with increasing vehicle speed. When the first vehicle speed is greater than the preset speed, it indicates that the vehicle has accelerated past the resonance-sensitive zone and entered a higher speed range. At this time, because the excitation frequency has deviated from the natural frequency, the physical resonance effect disappears, and the actual mechanical shimmy amplitude of the front wheels decreases and decays with further increases in vehicle speed. Therefore, the amplitude of the second compensation torque output by the control is less than the amplitude of the first compensation torque. After crossing the preset speed, the amplitude of the compensation torque output by the steering motor decreases accordingly with continued increases in vehicle speed, following the trend of vibration decay.

[0044] According to the scheme of this application, by using a preset vehicle speed as the critical point, the amplitude of the periodic compensation torque is nonlinearly scheduled in segments. In the resonance zone approaching the preset vehicle speed, strong compensation is actively provided to prevent the steering wheel from violently hitting the hand. After exceeding the preset vehicle speed, the compensation force is actively weakened, ensuring that the compensation torque output by the steering motor at any vehicle speed is exactly equal to the abnormal excitation torque actually generated by the front wheel, avoiding energy mismatch and effectively suppressing wheel shimmy.

[0045] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes increasing the damping torque of the road feel motor of the steer-by-wire system during straight-line travel when the two front wheels of the electric vehicle are shimming.

[0046] In a steer-by-wire system, the mechanical connection between the steering wheel and the front wheels is eliminated, and the resistance felt by the driver when turning the steering wheel is simulated by a road-sensor motor. During straight-line driving when the two front wheels of an electric vehicle oscillate, the front wheels and chassis are in a state of severe dynamic fluctuation. At this time, any additional or improper steering input may exacerbate the vehicle's lateral instability. To maximize the stability of the driving path, the damping torque of the road-sensor motor controlling the steer-by-wire system is increased.

[0047] Damping torque is the torque that resists the rotational movement of the steering wheel. When the vehicle detects front wheel shimmy while driving straight, the steer-by-wire system actively increases the damping torque of the road feel motor, significantly increasing the rotational resistance of the steering wheel, meaning the driver perceives the steering wheel as heavier. This increase in damping is equivalent to applying a constraint force to the steering wheel's rotation axis, making the steering wheel less light and easy to turn than usual. Through this change in physical resistance, the steer-by-wire system, without issuing warnings, provides intuitive tactile feedback to encourage the driver to keep their hands firmly on the wheel. Thus, during periods of chassis instability, the heavier steering wheel physically limits and guides the driver's potential steering maneuvers.

[0048] According to the solution in this application, by increasing the damping torque of the road feel motor during straight-line driving when shimmy occurs, the steering wheel feels heavier, guiding the driver to operate more steadily. Physical feedback is directly transmitted to the driver through touch, allowing them to naturally maintain a more stable and controlled operating posture when holding the steering wheel, preventing random swaying due to an overly light steering wheel in the event of sudden situations. This effectively limits and filters out rapid, large-amplitude, or unconscious sharp steering actions that the driver might make under tension or instinctive reactions, reducing the introduction of new lateral disturbances into the system due to human error or overcorrection. This ensures that when the electric vehicle encounters extreme conditions of front wheel shimmy, not only can the chassis quickly recover calm, but the driver's path commands also remain straight and stable, greatly improving the overall driving stability and active safety performance of the electric vehicle in complex and dangerous conditions.

[0049] In conjunction with the first aspect, in some implementations of the first aspect, the control method further includes, during the straight-line process in which the two front wheels of the electric vehicle oscillate, the damping torque of the road feel motor controlling the steer-by-wire system increases with the increase of the amplitude of the periodic compensation torque.

[0050] In a steer-by-wire system, the amplitude of the periodic compensation torque output by the bottom-level steering motor is a direct and accurate quantitative indicator of the severity of transient shimmy in the front wheels. The more severe the shimmy, the greater the required compensation torque amplitude. Therefore, the steer-by-wire system uses the compensation torque amplitude as a feedforward variable for the damping control of the upper-level road feel motor. During control execution, when severe shimmy occurs, the amplitude of the periodic compensation torque output by the bottom-level steering motor increases, and the damping torque output by the upper-level road feel motor simultaneously increases, making the steering wheel feel exceptionally heavy and applying the strongest physical restraint to the driver's hands to prevent loss of control due to panicked sudden steering. When the shimmy energy begins to decay or is in a state of slight shimmy, the compensation torque amplitude of the steering motor decreases, and the damping torque of the road feel motor simultaneously decreases.

[0051] According to the solution in this application, by increasing the damping torque of the road feel motor as the compensation torque amplitude increases, the level of instability risk can be intelligently identified. The more severe the shimmy and the closer the vehicle is to the edge of loss of control, the heavier the steering wheel becomes, and the stronger the restraint on the driver's unintentional steering actions; while in the case of slight shimmy, the steering wheel only becomes moderately heavy. This on-demand distribution of physical restraint ensures safety under extreme danger while avoiding unnecessary physical burden on the driver under minor conditions.

[0052] In conjunction with the first aspect, in some implementations of the first aspect, the waveform of the compensating torque is a sine wave.

[0053] Many external excitations that cause front wheel shimmy, such as forced vibrations caused by tire mass imbalance or radial force fluctuations, typically manifest as first-order or higher harmonics related to the wheel's rotation period, naturally exhibiting periodic oscillations of sinusoidal or quasi-sine curves in the time domain. Simultaneously, when both front wheels experience regular self-excited shimmy, the reciprocating oscillations of their mechanical system often exhibit near-sine waveform characteristics with stable amplitudes. Therefore, the shimmy frequency and amplitude can be directly substituted into the sine function mathematical model. In an equivalent sinusoidal form, a sinusoidal control signal is generated. The steering motor is controlled to output compensation torque according to this sinusoidal waveform. When the anti-phase sinusoidal compensation torque output by the steering motor meets the sinusoidal excitation torque transmitted from the front wheel at the mechanical actuator, the two can achieve smooth, continuous and perfect waveform mirror cancellation at any transient point in time, thereby fundamentally neutralizing the abnormal sway energy of the front wheel.

[0054] Secondly, this application provides a vehicle controller for electric vehicles, which implements the control methods described in the first aspect and its various implementations.

[0055] 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.

[0056] Other beneficial effects can be found in the description of the first aspect, and will not be repeated here. Attached Figure Description

[0057] 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 the down-steering actuator assembly provided in an embodiment of this application; Figure 5 This is a schematic diagram of a oscillation suppression control process provided in an embodiment of this application; Figure 6 This is a schematic diagram of rack stress analysis provided in an embodiment of this application; Figure 7 This is a schematic diagram of rack force frequency provided in an embodiment of this application; Figure 8 This is a schematic diagram of the compensated torque waveform provided in an embodiment of this application; Figure 9 This is a schematic diagram of the control flow provided in the embodiments of this application. Detailed Implementation

[0058] 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.

[0059] 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.

[0060] like Figure 1 As shown, the electric vehicle 10 includes a vehicle controller 20, a drive system 50, a braking system 60, a steer-by-wire system 70, 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.

[0061] 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.

[0062] 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.

[0063] 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) is a system in which two drive motors for driving two front wheels or two rear wheels are set together.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The steer-by-wire system 70 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 them (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 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.

[0071] like Figure 3 As shown, the steer-by-wire system 70 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 is driven to output 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.

[0072] like Figure 4As shown, the down-turn steering actuator assembly is mainly responsible for completing the front wheel steering action according to the driver's intention. The down-turn steering actuator assembly of the steer-by-wire system 70 mainly includes: a down-turn controller, a steering motor, a timing belt, a ball screw, a nut, and a rack. The down-turn controller is responsible for receiving the front wheel angle command and controlling the steering motor to drive the front wheels to achieve the deflection action. In terms of connection, the down-turn controller is electrically or signal connected to the steering motor to receive the front wheel angle command from the vehicle bus, such as the chassis CAN bus, and to control the torque, speed, and current output of the steering motor. The power output shaft of the steering motor is connected to the nut via a timing belt, which forms a reduction mechanism. The nut is sleeved on the outer circumference of the ball screw, and the inner wall of the nut and the outer wall of the ball screw form a rolling friction pair through circulating balls. The ball screw and the rack are arranged coaxially in the transverse direction (parallel to the axle direction). The left and right ends of the rack are mechanically connected to the front wheel mechanisms on both sides of the electric vehicle 10 through steering tie rod mechanisms, thereby converting the axial linear displacement of the rack into the angular deflection motion of the front wheels around the kingpin.

[0073] During the operation of the electric vehicle 10, the front wheels often experience periodic swaying around the kingpin due to factors such as road surface unevenness, tire dynamic imbalance, or mechanical resonance. This is known as front wheel shimmy. In traditional steering systems with a mechanical connection to the steering column, the energy released by front wheel shimmy can be transmitted upwards along the steering column and partially absorbed and actively suppressed by the physical damping within the mechanical mechanism and the driver's grip. However, in the steering-by-wire system 70, because the physical connection between the steering wheel and the front wheel steering actuator is completely severed, the lower steering actuator becomes a relatively isolated vibration system within the chassis architecture. When the electric vehicle 10 is traveling straight on a flat road, the front wheel angle command usually remains unchanged, and the system lacks a mechanism to recognize and counteract the active shimmy caused by external disturbances in the front wheels. This makes the front wheels highly susceptible to continuous periodic shimmy during straight-line driving, and due to mechanical decoupling, the driver cannot perceive this at the steering wheel end. Long-term front wheel shimmy causes steering actuators such as steering motors, racks, and tie rods to be subjected to high-frequency dynamic alternating loads, which severely shortens the fatigue life of related components. It also exacerbates abnormal tire wear, increases the driving resistance of the electric vehicle 10, and ultimately reduces the driving stability, power, and fuel economy of the electric vehicle 10.

[0074] To address the aforementioned issues, this application provides a control method, a controller, and an electric vehicle 10 for an electric vehicle 10. When front wheel shimmy occurs in the electric vehicle 10, the steering motor is controlled to output periodic compensation torque to counteract the periodic shimmy, rapidly reducing the reciprocating vibration of the wheels and preventing the electric vehicle 10 from deviating from its lane due to shimmy loss of control. This significantly improves driving safety under extreme conditions, actively suppresses wheel shimmy, thereby substantially reducing the dynamic alternating load on various mechanical components of the system, effectively reducing abnormal tire wear, and significantly extending the overall service life of the chassis and steering actuator.

[0075] The following is combined with Figures 5-9 The control method provided in the embodiments of this application is described below. The control method is used to suppress the shimmy of the two front wheels of the electric vehicle 10 through the steer-by-wire system 70 during the driving of the electric vehicle 10. Figure 5 This is a schematic diagram of the control process provided in the embodiments of this application. Figure 6 This is a schematic diagram of rack stress analysis provided in an embodiment of this application. Figure 7 This is a schematic diagram of rack force frequency provided in an embodiment of this application. Figure 8 This is a schematic diagram of the compensation torque waveform provided in the embodiments of this application. Figure 9 This is a schematic diagram of the control flow provided in the embodiments of this application.

[0076] like Figure 5 As shown, the control method includes maintaining a constant output torque of the steering motor of the steer-by-wire system 70 during normal straight-line driving when the steering wheel of the electric vehicle 10 is not turned. During steering driving after the steering wheel is turned, the steering motor of the steer-by-wire system 70 outputs steering torque to drive the two front wheels to steer. During straight-line driving when the two front wheels of the electric vehicle 10 oscillate, the steering motor of the steer-by-wire system 70 outputs periodic compensation torque before the steering wheel is turned.

[0077] Front wheel shimmy is a nonlinear dynamic phenomenon characterized by reciprocating oscillations around the kingpin. In the dynamics of electric vehicles 10, front wheel shimmy is classified into two mechanisms: forced vibration and self-excited vibration. Forced vibration is typically caused by external excitations such as wheel mass imbalance, radial and lateral force fluctuations in the tires, or periodic fluctuations in braking torque, and its excitation frequency is often proportional to the wheel speed. Self-excited vibration, on the other hand, originates from the energy feedback mechanism within the system, such as the relaxation length during the establishment of lateral force in the tires, and nonlinear factors such as structural clearances in the moving pairs of the steering transmission mechanism. These factors can cause the system to evolve from a stable state to limit cycle oscillations or even chaotic motion. When front wheel shimmy occurs, the steering axle of electric vehicle 10 experiences continuous reciprocating oscillations. This high-frequency alternating load not only directly causes severe periodic vibrations in the steering wheel, deteriorating the driving experience, but also accelerates fatigue damage to the steering actuator, suspension bushings, and tires, and significantly reduces the lateral handling stability of electric vehicle 10 under certain operating conditions, seriously threatening active driving safety. For the steer-by-wire system 70, although the direct mechanical connection between the steering wheel and the wheels is eliminated, the violent swaying of the front wheels will be directly transmitted to the steering actuator through the tie rod. Physically, this manifests as alternating impact of the lower rack force, that is, in the rack force that should normally tend to be stable, a periodic abnormal fluctuation signal with a specific oscillation frequency and amplitude is generated.

[0078] During normal straight-line driving when the steering wheel of the electric vehicle 10 is not turned, it is determined that the current driver's intention is to maintain straight-line driving, and the electric vehicle 10 is not subjected to any abnormal disturbances that would cause shimmy. At this time, the output torque of the steering motor controlling the steer-by-wire system 70 remains unchanged. By maintaining a constant (or zero) output torque, the current straight-line posture of the front wheels is locked, preventing the motor from generating unnecessary movements that would interfere with the straight-line stability of the electric vehicle 10, while also reducing unnecessary energy consumption of the system. It should be understood that during normal straight-line driving when the steering wheel of the electric vehicle 10 is not turned, the steering motor often still needs to output a small amount of torque to counteract minor road surface deviations or suspension clearances in order to keep the front wheels centered. This small torque fluctuation can also be considered as the range within which the output torque of the steering motor remains constant.

[0079] During the steering process after the steering wheel is turned, the driver's clear steering intention is recognized. At this time, the steering motor of the steer-by-wire system 70 outputs the corresponding steering torque, thereby overcoming the frictional resistance between the front wheels and the road surface and the return torque, directly driving the two front wheels to deflect to the target angle, thus accurately executing the driver's steering operation.

[0080] During the straight-line movement of electric vehicle 10, front wheel shimmy occurs. Front wheel shimmy is essentially a reciprocating, periodic oscillation of the wheel around its kingpin with a certain frequency and amplitude. During this straight-line movement, when both front wheels of electric vehicle 10 are shimming, i.e., before the steering wheel is turned and the driver inputs a steering command, simply maintaining a constant torque is insufficient to counteract the periodic vibration energy transmitted from the wheel ends. In this condition, the steering motor actively outputs a periodic compensation torque. Front wheel shimmy manifests as periodic mechanical vibration. By controlling the steering motor to output a compensation torque that varies periodically over time, this periodic torque directly acts on the steering transmission mechanism of the front wheels, forming an alternating torque that counteracts the shimmy excitation force. Through this dynamic compensation of periodic torque, the periodic energy causing wheel shimmy can be offset or weakened at its physical source, thus autonomously suppressing front wheel shimmy without driver intervention by turning the steering wheel.

[0081] According to the scheme of this application, the steering motor outputs periodic compensation torque. Utilizing the motor's fast response and high control precision, the periodic compensation torque directly counteracts periodic shimmy. This allows the electric vehicle 10 to actively and in real-time cancel energy out when sudden shimmy occurs while driving straight, rapidly reducing wheel reciprocating vibrations and preventing the electric vehicle 10 from deviating from its lane due to shimmy loss of control, greatly improving driving safety under extreme conditions. Within the architecture of the wire-controlled steering system 70, shimmy is suppressed through torque compensation of the underlying steering motor. Since the steering wheel and front wheels are mechanically decoupled, abnormal front wheel vibrations and the motor's periodic compensation actions are isolated at the chassis actuator. The driver does not need to turn the steering wheel or experience any severe steering wheel kicking or vibration; the electric vehicle 10 actively eliminates safety hazards, providing an extremely smooth driving experience. Front wheel shimmy generates high-frequency alternating stress, accelerating the wear and fatigue of mechanical connecting components of the steering system, such as tie rods, ball joints, and suspension components. By controlling the motor to output periodic compensation torque, the mechanical oscillation of the wheels is actively suppressed, thereby significantly reducing the dynamic alternating load on various mechanical components of the system, effectively reducing abnormal tire wear, and significantly extending the overall service life of the chassis and steering actuator.

[0082] In other embodiments, the waveform for compensating torque is a square wave, a triangular wave, or other waveforms.

[0083] In one embodiment, the steering motor adjusts the output torque to regulate the rack force on the two front wheels. Specifically, during normal straight-line driving when the steering wheel of the electric vehicle 10 is not turned, the output torque of the steering motor is kept constant to maintain the rack force on the rack at zero. During steering after the steering wheel is turned, the rack force on the rack is varied with the steering wheel rotation to drive the two front wheels to turn to one side. During straight-line driving of the electric vehicle 10, when the rack force on the rack periodically exceeds a preset value, before the steering wheel is turned, the steering motor of the steer-by-wire system 70 is controlled to output a periodic compensation torque to reduce the amplitude of the rack force.

[0084] The deflection of the two front wheels is driven by the lateral movement of the racks connected to them. Therefore, the steer-by-wire system 70 is controlled by adjusting the output torque of the steering motor, which in turn directly adjusts the rack force on the two front wheels in terms of physical transmission. During normal straight-line driving when the steering wheel of the electric vehicle 10 is not turned, the front wheels do not need to overcome additional steering resistance because the electric vehicle 10 is driving smoothly. At this time, the output torque of the steering motor remains constant, thus keeping the rack force on the racks zero. By maintaining a dynamic balance with the rack force at zero, unnecessary lateral displacement of the racks is avoided, thereby locking the straight-line posture of the two front wheels.

[0085] During steering, once the steering wheel is turned, the driver inputs a clear steering request. The steering motor dynamically outputs torque, causing the rack force to change linearly or non-linearly with the steering wheel's rotation. This changing, directional rack force overcomes road friction and tire self-centering torque, directly driving the two front wheels to steer in the direction the driver intends.

[0086] During the straight-line movement of the electric vehicle 10, abnormal vibrations may occur in the front wheels due to road surface excitation or nonlinear factors of the system itself, which are transmitted upwards along the mechanical structure to the rack. By real-time detection of the rack's force state, when it is identified that the rack force not only exhibits periodic fluctuations but also that the amplitude of these fluctuations periodically exceeds a preset value, it is determined that the electric vehicle 10 is experiencing front wheel shimmy, thus avoiding the impact of road surface potholes. Before the steering wheel is turned, i.e., before the driver notices or makes any manual corrections, the electric vehicle 10 controls the steering motor of the steer-by-wire system 70 to output periodic compensation torque. This periodic compensation torque, after being transmitted to the rack, forms a counteracting force against the abnormal shimmy force, thereby directly reducing the amplitude of the rack force and causing the rack force to return to within the preset safe and stable threshold.

[0087] In one embodiment, a force sensor located on the lower steering mechanism detects the rack force in real time.

[0088] In one embodiment, the front wheel rack force is estimated based on the Kalman filter algorithm.

[0089] In the online steering system 70, in order to obtain the actual force state of the front wheels without increasing the cost of additional force sensors, the rack, the core translational component of the steering mechanism, is used as the object of force analysis. For example... Figure 6 As shown, in actual mechanical transmission, the torque output by the steering motor needs to be converted into a linear driving force for the lateral movement of the rack through a comprehensive reduction mechanism including a synchronous belt and ball screw nut. Based on Newton's second law and the principle of force balance, considering the rack's inertial force, damping force, the motor's equivalent driving force, and the external load, the following dynamic differential equation is established to solve for the rack force Fr: m× +Br× =Ft-Fr; Ft = k × Tm.

[0090] Where m represents the equivalent mass of the rack after conversion. Br represents the equivalent damping coefficient of the rack during axial movement. x represents the actual axial displacement of the rack (its first derivative). Let be the speed of the rack motion, and be its second derivative. (This refers to the acceleration of the rack movement). Tm represents the actual output electromagnetic torque of the steer-by-wire motor. k represents the torque-force conversion coefficient after considering the transmission ratio of the comprehensive reduction mechanism and the mechanical transmission efficiency. Ft represents the equivalent driving force of the steering motor torque acting on the rack after transmission. Fr is the external rack force exerted by the front wheel on the rack in the reverse direction through the tie rod.

[0091] Due to various frictional nonlinearities and measurement noise in the actual driving environment of electric vehicles, directly calculating Fr based on this equation is prone to errors. Therefore, a Kalman filter algorithm is introduced for optimal state estimation. Kalman filtering is a highly efficient recursive linear optimal estimation algorithm. Based on the system's previous state prediction value, it combines the actual measurement values ​​collected by sensors at the current moment (such as the current steering motor angle, speed, and current) to recursively calculate the optimal state estimate for the current moment, mathematically ensuring that the mean square error of the estimation is minimized. By incorporating the aforementioned rack force differential equation as the system state equation into the Kalman filter algorithm, the lower-wheel electronic control unit can accurately and smoothly estimate the current front wheel rack force Fr in real time within the operating cycle.

[0092] After obtaining the real-time estimated rack force Fr, the steer-by-wire system 70 performs real-time monitoring and feature extraction to determine whether shimmy occurs and to acquire excitation parameters. When the electric vehicle 10 is in a normal, stable, straight-line driving condition with the steering wheel not turned, the front wheels do not experience abnormal vibration. At this time, the estimated front wheel rack force Fr is theoretically close to zero or only has a small steady-state static load. However, when the electric vehicle 10 experiences front wheel shimmy due to road surface excitation or system instability during straight-line driving, the reciprocating vibration of the wheel around the kingpin is directly converted into alternating push-pull force on the tie rod, causing the estimated rack force Fr to no longer be zero, but instead abruptly become a periodic alternating signal with a specific fluctuation frequency and amplitude. To pinpoint the most destructive primary excitation source, the built-in software processing algorithm (such as envelope analysis or Fast Fourier Transform (FFT) frequency domain extraction algorithm) analyzes this periodic fluctuation signal, specifically extracting the feature signal with the largest oscillation amplitude. Figure 7 As shown, by extracting the signal frequency with the largest rack force shimmy amplitude, the signal frequency fd represents the core excitation frequency and specific shimmy amplitude that currently dominates the front wheel shimmy. The real-time extracted shimmy frequency fd and maximum amplitude are transmitted as key feedforward input parameters to the steering motor control logic, providing accurate data support for the subsequent generation of periodic compensation torques with the same frequency, matched amplitude, and opposite phase.

[0093] refer to Figure 5 Before time t1, both the steering wheel angle and the output torque of the steering motor remain stable at zero. The rack force also remains zero (or a very small straight-line centering torque). During normal straight-line driving without steering wheel rotation, the output torque of the steering motor is kept constant, keeping the rack force on the rack at zero. At time t1, the two front wheels of the electric vehicle 10 suddenly shiver. The electric vehicle 10 continues straight-line driving, and before the steering wheel turns, the steering motor outputs periodic compensation torque to reduce the amplitude of the rack force. Under the adjustment of active anti-phase torque compensation, the amplitude of the rack force exhibits a smooth convergence characteristic from large to small, indicating that the shiver is effectively suppressed.

[0094] In one embodiment, the control method specifically includes controlling the frequency of the periodic compensation torque output by the steering motor of the steer-by-wire system 70 to vary with the sway frequency of the two front wheels, and controlling the amplitude of the periodic compensation torque to vary with the sway amplitude of the two front wheels.

[0095] During the actual operation of the electric vehicle 10, due to changes in vehicle speed, differences in road surface excitation, and the transfer of transient loads on the chassis of the electric vehicle 10, the front wheel shimmy is not a static vibration that remains unchanged, but rather a nonlinear dynamic phenomenon whose frequency and amplitude change dynamically in real time with the driving state. To achieve precise suppression, a dynamic adaptive following mechanism is further introduced when controlling the output of the periodic compensation torque of the steering motor. The actual shimmy frequency and amplitude of the two front wheels are detected and acquired in real time. When controlling the output of the periodic compensation torque of the steering motor in the steer-by-wire system 70, this compensation torque is not a fixed preset parameter, but is configured to dynamically update in real time with the actual shimmy state of the front wheels. The frequency of the periodic compensation torque changes synchronously with the change in the front wheel shimmy frequency. When the shimmy frequency of the front wheels increases or decreases due to external excitation or system resonance, the alternating frequency of the motor output torque also changes synchronously. The amplitude of the periodic compensation torque changes synchronously with the change in the front wheel shimmy amplitude. When the front wheel oscillates violently, i.e., the amplitude enters the peak region, the steering motor outputs a compensation torque with a larger peak value to provide sufficient counteracting energy. When the front wheel oscillation weakens or even decays, i.e. the amplitude becomes smaller, the steering motor proportionally reduces the output force of the compensation torque. Thus, the steering motor can always output a dynamic compensation torque that precisely matches the instantaneous oscillation state of the front wheel, thereby achieving vibration energy offsetting.

[0096] In one embodiment, the control method specifically includes controlling the frequency of the periodic compensation torque output by the steering motor of the steer-by-wire system 70 to be equal to the shimmy frequency of the two front wheels, and the phase of the compensation torque being opposite to the phase of the shimmy of the two front wheels.

[0097] In the field of vibration control, if the frequency of the compensation torque deviates slightly from the actual shimmy frequency, their superposition will not only fail to eliminate the original vibration but will also induce complex and highly destructive "beating" or broadband chaotic motion. To ensure that the periodic compensation torque output by the steering motor achieves effective and rapid shimmy suppression without triggering new control conflicts, the frequency and phase domain characteristics of this compensation torque are defined. Specifically, the frequency of the periodic compensation torque output by the steering motor controlling the steer-by-wire system 70 is equal to the shimmy frequency of the two front wheels, and the phase of the compensation torque is opposite to the phase of the shimmy of the two front wheels. The wave-vibration interference principle in physics states that when two periodic oscillation signals have the same frequency and a phase difference of 180 degrees (i.e., opposite phases), they will undergo destructive interference, and the vibration energy within the system will cancel each other out to zero. Front wheel shimmy, as a periodic nonlinear dynamic oscillation, has its specific transient excitation frequency and phase characteristics. By controlling the frequency of the compensating torque output by the steering motor to be equal to the actual shimmy frequency of the two front wheels, the suppression energy output by the steering motor is ensured to be synchronized with the abnormal mechanical oscillation of the front wheels in the time domain, ensuring that a corresponding compensating torque exists in each oscillation cycle. Simultaneously, by controlling the phase of this compensating torque to be opposite to the phase of the front wheel shimmy, in any oscillation cycle, when the front wheels experience the greatest abnormal shimmy tendency to one side (e.g., to the left) due to external excitation (i.e., the oscillation peak), the steering motor outputs the maximum compensating torque to the right (i.e., the oscillation trough) at the exact same moment. This synchronous and anti-phase control allows the dynamic compensating torque generated by the steering motor to directly, in real-time, and precisely counteract the periodic excitation force transmitted from the front wheels at the steering actuator, achieving active elimination of vibration energy using the principle of destructive interference.

[0098] In one embodiment, the control method specifically includes controlling the magnitude of the periodic compensation torque output by the steering motor of the steer-by-wire system 70 to increase with the increase of the axial speed of the rack and the increase of the acceleration of the axial movement of the rack.

[0099] The severity of front wheel shimmy varies continuously in the time domain. To ensure that the steering motor's compensation action accurately compensates for the shimmy, the amplitude of the periodic compensation torque output by the steering motor of the steer-by-wire system 70 is correlated with the axial motion state (velocity and acceleration) of the rack. The rack's motion state can be detected by sensors. When front wheel shimmy occurs while the electric vehicle 10 is traveling straight, the abnormal alternating excitation force forces the rack to undergo unexpected axial reciprocating motion. The speed and acceleration of the rack's axial motion are acquired in real time and used as a reference for adjusting the compensation torque amplitude. The compensation torque amplitude increases with the increase of the rack's axial motion speed. The motion speed represents transient kinetic energy, and applying a speed-related damping force can effectively suppress vibration. Therefore, when the rack's axial motion speed increases, it indicates that the front wheel is undergoing rapid and severe shimmy, and the steering motor is controlled to synchronously increase the amplitude of the output periodic compensation torque. This is equivalent to introducing active variable electronic damping into the rack, which quickly absorbs and dissipates the kinetic energy of the rack during rapid movement by outputting a larger counteracting torque. The compensation torque amplitude increases with the acceleration of the rack's axial movement. The rack's axial acceleration reflects the abruptness of the front wheel shimmy during reversal and the magnitude of the transient impact force. When the rack's axial acceleration increases, it indicates that the front wheel is experiencing a harsh, high-frequency vibration impact, and the rack tends to accelerate suddenly or reverse abruptly. The steering motor is then controlled to instantaneously increase the compensation torque amplitude. This provides active inertial compensation for the rack, utilizing the peak torque generated instantaneously by the steering motor to counteract the destructive mechanical impact caused by high acceleration, thereby coping with high-frequency, sudden vibration spikes.

[0100] In one embodiment, reference continues... Figure 5 The control method also includes, during the steering process in which the two front wheels of the electric vehicle 10 oscillate, after the steering wheel is turned, controlling the steering motor of the steer-by-wire system 70 to output periodic compensation torque while simultaneously superimposing the output steering torque.

[0101] In actual driving of the electric vehicle 10, front wheel shimmy can occur not only during straight-line driving but also during cornering, lane changing, or emergency obstacle avoidance. When the electric vehicle 10 experiences sudden shimmy in a curve, the front wheels, already bearing enormous lateral forces and load transfers, will experience extremely severe chassis mechanical shocks due to the shimmy. The lateral grip of the tires can easily exceed its limits, causing the electric vehicle 10 to lose control. Therefore, during the steering process where the two front wheels of the electric vehicle 10 shimmy, i.e., the driver inputs a steering command by turning the steering wheel, and the front wheels are simultaneously subjected to abnormal external vibrations, the steer-by-wire system 70 must balance steering and vibration suppression. In the steer-by-wire system 70, since the steering wheel and front wheels are physically decoupled, the output of the steering motor is no longer limited to a single mechanical transmission command but can receive and execute multi-dimensional composite electrical signals. After the steering wheel is turned, the steer-by-wire system 70 first calculates the basic steering torque used to drive the electric vehicle 10 to the target path based on the steering wheel's rotation state, including the angle and angular velocity. Simultaneously, the steer-by-wire system 70 monitors the shimmy state of the front wheels in real time and calculates the periodic compensation torque to counteract abnormal front wheel oscillations. Then, the steering motor controlling the steer-by-wire system 70 outputs the periodic compensation torque while simultaneously superimposing the output steering torque. This is equivalent to superimposing the low-frequency reference signal representing the steering intention with the high-frequency compensation signal representing the vibration damping intention in the time domain. Upon receiving this superimposed signal, the steering motor continuously outputs a steering force to smoothly drive the front wheels to one side, accompanied by a high-frequency alternating torque matching the shimmy frequency and amplitude, thereby achieving destructive interference between steering and vibration energy.

[0102] like Figure 5 As shown, at time t2, the driver begins to turn the steering wheel. The steering wheel angle signal smoothly rises to the target large angle. After the steering wheel turns, the steering motor outputs periodic compensation torque while simultaneously superimposing the output steering torque. The angle and speed PI control algorithm in the steering controller begins to respond to the steering wheel request, outputting an instruction for increased steering drive torque. At this time, the output of the steering motor exhibits a linear superposition of the basic steering torque and the periodic compensation torque. As the tire steering angle is established, the self-centering torque exerted by the ground on the front wheels increases, and the curve also shows residual vibrations suppressed by the steering motor output torque.

[0103] In one embodiment, the control method specifically includes, during the process of controlling the steering motor of the steer-by-wire system 70 to output periodic compensation torque, when the opening of the brake pedal increases, controlling the frequency of the output periodic compensation torque to decrease, and the amplitude of the periodic compensation torque to increase.

[0104] In actual driving of the electric vehicle 10, front wheel shimmy is affected not only by constant vehicle speed but also by longitudinal acceleration and deceleration, especially braking conditions. When the driver depresses the brake pedal during front wheel shimmy in the electric vehicle 10, the dynamic state of the electric vehicle 10 undergoes a drastic transient change. In order to maintain shimmy suppression under braking conditions, the output of the steering motor of the steer-by-wire system 70 is adjusted according to the brake pedal opening during the periodic compensation torque output.

[0105] When the brake pedal opening increases, the driver is applying or increasing braking force, and the electric vehicle 10 is decelerating. At this time, the periodic compensation torque output by the steer-by-wire system 70 is adjusted synchronously. The frequency of the periodic compensation torque output decreases. The excitation frequency of front wheel shimmy, especially the forced vibration frequency, is usually positively correlated with the driving speed and wheel speed of the electric vehicle 10. When the brake pedal opening increases, causing the vehicle speed and wheel speed to decrease, the actual mechanical shimmy frequency of the front wheels will also decrease synchronously. Therefore, the steer-by-wire system 70 actively controls the frequency of the periodic compensation torque output by the steering motor to decrease accordingly, to ensure that the compensation frequency of the steering motor can match the actual shimmy frequency that decreases due to deceleration in real time, maintaining synchronization. The amplitude of the periodic compensation torque output increases. The deceleration caused by the increased brake pedal opening will cause a sharp forward shift of the center of gravity of the electric vehicle 10, i.e., longitudinal load transfer. This transient load transfer will cause a rapid and significant increase in the vertical load on the front axle and the two front wheels. The surge in vertical pressure not only significantly alters the tire's lateral stiffness but also instantaneously compresses all movement clearances of the steering transmission mechanism to their limits, easily inducing strong self-excited shimmy or causing a destructive surge in the original shimmy amplitude—that is, a sharp amplification of vibration energy. To counteract this sudden increase in mechanical excitation energy due to the transfer of braking load, the steer-by-wire system 70 controls the steering motor to instantaneously increase the amplitude of its output periodic compensation torque, using a stronger, opposite-phase physical torque to offset the enormous shimmy impact force generated during braking.

[0106] In one embodiment, the control method further includes increasing the frequency of the output periodic compensation torque as the opening of the accelerator pedal increases during the process of controlling the steering motor of the steer-by-wire system 70 to output periodic compensation torque.

[0107] During actual driving of the electric vehicle 10, the front wheel shimmy, as a complex mechanical vibration, does not have a constant excitation frequency, but is related to the driving speed of the electric vehicle 10 and the rotation state of the wheels. In order to accurately cancel the shimmy without delay during the acceleration of the electric vehicle 10, the steering motor of the steer-by-wire system 70 is adjusted based on the accelerator pedal opening during the periodic compensation torque output process.

[0108] When the accelerator pedal opening increases, it indicates that the driver has input a clear acceleration intention. The longitudinal driving force of the electric vehicle 10 increases, and the vehicle speed and the rotational speed of the two front wheels will increase accordingly. The forced shimmy of the front wheels caused by factors such as wheel imbalance and tire radial force fluctuations has an excitation frequency that is directly proportional to the wheel's rotational angular velocity. Therefore, as the wheel speed increases due to the increased accelerator pedal opening, the actual physical shimmy frequency of the front wheels will also increase. To cope with the change, the frequency of the periodic compensation torque output by the steer-by-wire system 70 actively increases accordingly. The steer-by-wire system 70 uses the increase in accelerator pedal opening as a feedforward prediction signal, and simultaneously and in advance controls the steering motor to increase the frequency of the output compensation torque as the vehicle speed and physical shimmy frequency actually increase.

[0109] In one embodiment, the control method specifically includes controlling the steering motor of the steer-by-wire system 70 to output a periodic first compensation torque during straight-line travel of the electric vehicle 10 at a first speed and with both front wheels shimming, before the steering wheel is turned. During straight-line travel of the electric vehicle 10 at a second speed greater than the first speed and with both front wheels shimming, controlling the steering motor of the steer-by-wire system 70 to output a periodic second compensation torque before the steering wheel is turned, wherein the frequency of the second compensation torque is greater than the frequency of the first compensation torque.

[0110] During the actual operation of the electric vehicle 10, the excitation characteristics of front wheel shimmy are not statically constant, but rather related to the vehicle speed. Especially for shimmy caused by rotational excitation sources such as wheel mass imbalance and tire radial force fluctuations, its excitation frequency is limited by the wheel's rotational angular velocity. To achieve precise cancellation interference against front wheel shimmy across the entire speed range, the output of the steering motor of the steer-by-wire system 70 is adjusted based on the vehicle speed when controlling the periodic compensation torque. The physical frequencies of shimmy in the electric vehicle 10 at low and high speeds are drastically different. If the steer-by-wire system 70 only uses a fixed-frequency compensation strategy, frequency misalignment is easily generated when the vehicle speed changes, meaning the compensation torque frequency cannot keep up with the shimmy frequency at high speeds.

[0111] When the electric vehicle 10 experiences front wheel shimmy while driving straight, and the driver does not intervene before the steering wheel is turned, the steer-by-wire system 70 acquires the current speed of the electric vehicle 10 in real time and outputs compensation torque with differentiated frequency characteristics based on the speed. When the electric vehicle 10 is at a first speed, such as a low cruising speed, and both front wheels shimmy, the mechanical excitation frequency caused by the slow wheel rotation speed is relatively low. At this time, the steering motor of the steer-by-wire system 70 outputs a periodic first compensation torque. The alternating frequency of this first compensation torque is set to match the current low shimmy frequency to achieve vibration offsetting at low speeds. When the electric vehicle 10 accelerates or travels at a second speed greater than the first speed, such as a high-speed driving state, and both front wheels shimmy, as the speed increases, the wheel rotational angular velocity increases, causing the physical shimmy frequency of the front wheels to rise to a higher frequency range. The steer-by-wire system 70 controls the steering motor to output a periodic second compensation torque. The frequency of the second compensation torque is controlled to be greater than the frequency of the first compensation torque. Vehicle speed is used as a feedforward reference for the shimmy frequency. The higher the vehicle speed, the higher the frequency of the alternating counter-torque output by the steering motor.

[0112] In one embodiment, when the second vehicle speed is less than a preset vehicle speed, the amplitude of the second compensation torque is greater than the amplitude of the first compensation torque. When the first vehicle speed is greater than the preset vehicle speed, the amplitude of the second compensation torque is less than the amplitude of the first compensation torque.

[0113] Although the frequency of shimmy increases linearly with vehicle speed, the amplitude of shimmy exhibits a non-monotonic resonant relationship with vehicle speed. Specifically, the steering and suspension systems have their inherent natural resonant frequencies. When the excitation frequency of wheel rotation approaches this natural frequency, the shimmy amplitude increases sharply; however, as the vehicle speed continues to increase and the excitation frequency deviates from the natural frequency, the shimmy amplitude decreases. To ensure that the compensation torque output by the steering motor conforms to this pattern, when controlling the periodic compensation torque output of the steering motor in the steer-by-wire system 70, a segmented amplitude adjustment is implemented with a preset vehicle speed reflecting the resonance critical point of the electric vehicle 10 as the dividing line.

[0114] When the second vehicle speed is less than the preset speed, it indicates that the electric vehicle 10 is accelerating towards the resonance point of the steering system, meaning the wheel excitation frequency is approaching the system's natural frequency. At this time, the actual mechanical shimmy amplitude of the front wheels will continuously increase with increasing vehicle speed. Therefore, the amplitude of the second compensation torque output by the control is greater than the amplitude of the first compensation torque. Before crossing the preset resonance speed, the amplitude of the compensation torque output by the steering motor increases synchronously with increasing vehicle speed. When the first vehicle speed is greater than the preset speed, it indicates that the electric vehicle 10 has accelerated past the resonance sensitive zone and entered a higher speed range. At this time, because the excitation frequency has deviated from the natural frequency, the physical resonance effect disappears, and the actual mechanical shimmy amplitude of the front wheels will decrease and attenuate with further increases in vehicle speed. Therefore, the amplitude of the second compensation torque output by the control is less than the amplitude of the first compensation torque. After crossing the preset speed, the amplitude of the compensation torque output by the steering motor decreases accordingly with continued increases in vehicle speed, conforming to the trend of vibration attenuation.

[0115] In one embodiment, such as Figure 8 As shown, the waveform of the compensation torque is a sine wave.

[0116] Many external excitations that cause front wheel shimmy, such as forced vibrations caused by tire mass imbalance or radial force fluctuations, typically manifest as first-order or multiple harmonics related to the wheel rotation period, naturally exhibiting periodic fluctuations of sine or quasi-sine curves in the time domain. Simultaneously, when the two front wheels experience regular self-excited shimmy, the reciprocating oscillations of their mechanical system often exhibit near-sine waveform characteristics with stable amplitudes. Therefore, the shimmy frequency and amplitude are directly substituted into a sine function mathematical model or an equivalent sine expression to generate a sinusoidal waveform control signal. The steering motor is then controlled to output compensating torque according to this sinusoidal waveform. When the anti-phase sinusoidal compensating torque output by the steering motor meets the sinusoidal excitation torque transmitted from the front wheels at the mechanical actuator, the two can achieve smooth, continuous, and perfect waveform mirror cancellation at any transient point in time, thereby fundamentally neutralizing the abnormal shimmy energy of the front wheels.

[0117] When the front wheel shims, the abnormal high-frequency reciprocating vibration of the wheel around the kingpin is transmitted to the steering rack via the mechanical tie rod, causing the originally stable rack force to exhibit abnormal alternating fluctuations with a certain period. At this time, the downshift controller uses an algorithm to perform frequency domain or time domain analysis on the estimated rack force fluctuation signal, accurately extracting the signal frequency with the largest shimmy amplitude, thereby locking down the core excitation source that is dominating the current shimmy. In order to completely counteract this abnormal shimmy rack force from its physical source, an active control strategy based on the wave destructive interference principle is adopted. The downshift controller superimposes a periodic compensation motor torque signal specifically for vibration suppression on top of the conventional motor closed-loop control logic (such as steering drive control). The core setting principle of this compensation torque is to maintain "equal amplitude, same frequency, and opposite phase" with the abnormal rack force that causes the shimmy. The mathematical calculation model of the periodic compensation motor torque is set as follows:

[0118] in, This represents the compensation torque, which is the target suppressive torque command that the steering motor needs to output at the current moment. This represents the torque amplitude of the steering motor. The magnitude of this amplitude is set proportionally based on the maximum amplitude of the oscillating rack force extracted by the algorithm and the transmission ratio of the reduction mechanism. The frequency of the compensation signal is equal to the frequency of the signal corresponding to the maximum amplitude of the rack force oscillation (i.e., the aforementioned fd), to ensure that the counteracting torque output by the motor is synchronized with the actual oscillation of the wheel in terms of time. Represents a time variable. The phase representing the compensating motor torque is configured to be completely opposite to the fluctuation phase of the extracted front wheel shimmy rack force (i.e., 180 degrees out of phase).

[0119] The downshift controller generates the data in real time based on the above mathematical model. The signal drives the steering motor to output the periodic compensation torque. This torque is converted into a linear force through a reduction mechanism such as a synchronous belt and ball screw, which acts directly on the rack, forming an alternating counterforce that is equal in magnitude, has the same frequency, and is always opposite in direction to the shimmy force transmitted from the wheel end. This counter-phase compensation force can neutralize and absorb the abnormal oscillation energy that causes rack shimmy in real time, ultimately smoothing out the force on the rack and precisely eliminating front wheel shimmy at the bottom actuator end, thereby restoring the straight-line driving stability of the electric vehicle 10.

[0120] In one embodiment, the control method further includes increasing the damping torque of the road feel motor of the steer-by-wire system 70 during straight-line travel when the two front wheels of the electric vehicle 10 are shivering.

[0121] In the steer-by-wire system 70, the mechanical connection between the steering wheel and the front wheels is eliminated, and the resistance felt by the driver when turning the steering wheel is simulated by the road feel motor. During straight-line travel when the two front wheels of the electric vehicle 10 oscillate, the front wheels and chassis are in a state of violent dynamic fluctuation. At this time, any additional or improper steering input may exacerbate the lateral instability of the electric vehicle 10. In order to maximize the stability of the driving path, the damping torque of the road feel motor controlling the steer-by-wire system 70 is increased.

[0122] Damping torque is the force that resists the rotational motion of the steering wheel. When the electric vehicle 10 detects front wheel shimmy while driving straight, the steer-by-wire system 70 actively increases the damping torque of the road feel motor, significantly increasing the rotational resistance of the steering wheel, meaning the driver perceives the steering wheel as heavier. This increase in damping is equivalent to applying a constraint force to the steering wheel's rotation axis, making the steering wheel less light and easy to turn than usual. Through this change in physical resistance, the steer-by-wire system 70, without issuing warnings, provides intuitive tactile feedback to encourage the driver to keep their hands firmly on the steering wheel. Thus, during periods of chassis instability, the heavier steering wheel physically limits and guides the driver's potential steering maneuvers.

[0123] In one embodiment, the control method further includes controlling the damping torque of the road feel motor of the steer-by-wire system 70 to increase as the amplitude of the periodic compensation torque increases during straight-line travel when the two front wheels of the electric vehicle 10 oscillate.

[0124] In the steer-by-wire system 70, the amplitude of the periodic compensation torque output by the bottom-level steering motor is a direct and accurate quantitative indicator of the severity of transient shimmy in the front wheels. The more severe the shimmy, the greater the required compensation torque amplitude. Therefore, the steer-by-wire system 70 uses the compensation torque amplitude as a feedforward variable for the damping control of the upper-level road feel motor. During control execution, when severe shimmy occurs and the amplitude of the periodic compensation torque output by the bottom-level steering motor increases, the damping torque output by the upper-level road feel motor simultaneously increases, making the steering wheel feel exceptionally heavy and applying the strongest physical restraint to the driver's hands to prevent loss of control due to panicked sudden steering. When the shimmy energy begins to decay or is in a state of slight shimmy, the compensation torque amplitude of the steering motor decreases, and the damping torque of the road feel motor simultaneously decreases.

[0125] The vibration suppression process provided in this application embodiment is as follows: Figure 9As shown, the control loop includes an angle control loop, a speed control loop, and a current closed-loop control loop. The downshift controller receives the front wheel angle command sent from the chassis bus and simultaneously obtains the current front wheel angle feedback value. The front wheel angle command and feedback are used as inputs for proportional-integral calculation. The speed control loop inputs the speed command and the current motor speed feedback value to the speed regulator for closed-loop adjustment. The speed regulator calculates based on the speed deviation and outputs a reference torque command. When front wheel shimmy occurs, the shimmy suppression and compensation torque module is activated. This module dynamically extracts the signal frequency with the largest shimmy amplitude on the rack using software algorithms (such as Kalman filtering) and generates a periodic torque compensation signal with matched amplitude and opposite phase. This periodic torque compensation signal is added as a compensation term to the reference torque command output by the speed control loop, thereby correcting the torque command before it enters the current loop, synthesizing the final comprehensive torque command. The corrected comprehensive torque command is used as the target value and input to the motor current closed-loop control module. This module completes the vector control of the steering motor current and drives the motor output torque to be applied to the rack mechanism, ultimately achieving precise control of the front wheel angle.

[0126] According to the solution of this application, when the electric vehicle 10 experiences front wheel shimmy, the steering motor is controlled to output periodic compensation torque to counteract the periodic shimmy, quickly reducing the reciprocating vibration of the wheels and preventing the electric vehicle 10 from deviating from the lane due to shimmy loss of control. This greatly improves driving safety under extreme conditions, actively suppresses wheel shimmy, thereby significantly reducing the dynamic alternating load on various mechanical components of the system, effectively reducing abnormal tire wear, and significantly extending the overall service life of the chassis and steering actuator.

[0127] 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 suppress the shimmy of the two front wheels of the electric vehicle through a steer-by-wire system during the operation of the electric vehicle. The control method includes: During normal straight-line driving when the steering wheel of the electric vehicle is not turned, the output torque of the steering motor controlling the steer-by-wire system remains constant; During the steering process after the steering wheel is turned, the steering motor of the steer-by-wire system outputs steering torque to drive the two front wheels to steer. During the straight-line movement of the electric vehicle when the two front wheels oscillate, before the steering wheel is turned, the steering motor of the steer-by-wire system is controlled to output periodic compensation torque.

2. The control method according to claim 1, characterized in that, The control method specifically includes: The frequency of the periodic compensation torque output by the steering motor of the steer-by-wire system varies with the shimmy frequency of the two front wheels, and the amplitude of the periodic compensation torque varies with the shimmy amplitude of the two front wheels.

3. The control method according to claim 1 or 2, characterized in that, The control method specifically includes: The frequency of the periodic compensation torque output by the steering motor of the steer-by-wire system is equal to the shimmy frequency of the two front wheels, and the phase of the compensation torque is opposite to the phase of the shimmy of the two front wheels.

4. The control method according to any one of claims 1-3, characterized in that, The steering motor adjusts the output torque to adjust the rack force on the two front wheels. The control method specifically includes: During normal straight-line driving when the steering wheel of the electric vehicle is not turned, the output torque of the steering motor is kept constant so that the rack force on the rack remains zero; During the steering process after the steering wheel is turned, the rack force on the rack is controlled to change with the rotation of the steering wheel to drive the two front wheels to turn to one side; During the straight-line movement of the electric vehicle, when the rack force on the rack periodically exceeds a preset value, before the steering wheel is turned, the steering motor of the steer-by-wire system is controlled to output periodic compensation torque to reduce the amplitude of the rack force.

5. The control method according to claim 4, characterized in that, The control method specifically includes: The magnitude of the periodic compensation torque output by the steering motor controlling the steer-by-wire system increases with the increase of the axial speed of the rack and with the increase of the acceleration of the axial movement of the rack.

6. The control method according to any one of claims 1-5, characterized in that, The control method further includes: During the steering process when the two front wheels of the electric vehicle wobble, after the steering wheel is turned, the steering motor controlling the steer-by-wire system outputs the steering torque while simultaneously superimposing the periodic compensation torque.

7. The control method according to any one of claims 1-6, characterized in that, The control method specifically includes: During the process of controlling the steering motor of the steer-by-wire system to output periodic compensation torque, when the opening of the brake pedal of the electric vehicle increases, the frequency of the periodic compensation torque output decreases, and the amplitude of the periodic compensation torque increases.

8. The control method according to any one of claims 1-7, characterized in that, The control method further includes: During the process of controlling the steering motor of the steer-by-wire system to output periodic compensation torque, when the opening of the accelerator pedal of the electric vehicle increases, the frequency of the periodic compensation torque output by the control increases.

9. The control method according to any one of claims 1-8, characterized in that, The control method specifically includes: During the straight-line driving process where the electric vehicle is traveling at a first speed and the two front wheels are wobbling, before the steering wheel is turned, the steering motor of the steer-by-wire system is controlled to output a periodic first compensation torque. During the process of the electric vehicle traveling straight at a second speed greater than the first speed and with the two front wheels oscillating, before the steering wheel is turned, the steering motor of the steer-by-wire system is controlled to output a periodic second compensation torque, wherein the frequency of the second compensation torque is greater than the frequency of the first compensation torque.

10. The control method according to claim 9, characterized in that, When the second vehicle speed is less than the preset vehicle speed, the amplitude of the second compensation torque is greater than the amplitude of the first compensation torque; When the first vehicle speed is greater than the preset vehicle speed, the amplitude of the second compensation torque is less than the amplitude of the first compensation torque.

11. The control method according to any one of claims 1-10, characterized in that, The control method further includes: During the straight-line movement of the electric vehicle when the two front wheels oscillate, the damping torque of the road feel motor controlling the steer-by-wire system increases.

12. The control method according to any one of claims 1-11, characterized in that, The control method further includes: During the straight-line movement of the electric vehicle when the two front wheels oscillate, the damping torque of the road feel motor controlling the steer-by-wire system increases as the amplitude of the periodic compensation torque increases.

13. The control method according to any one of claims 1-12, characterized in that, The waveform of the compensation torque is a sine wave.

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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