Steering system capable of being switched between drive-by-wire mode and power assisting mode and control method

Abstract

According to the steering system capable of being switched between the drive-by-wire mode and the power-assisted mode and the control method, a mechanical connection subsystem and an electric control subsystem are integrated, a torque weight gradual change control strategy is introduced, the problems of torque impact and incoherence in the mode switching process are solved, really smooth and non-inductive mode switching is achieved, and the steering efficiency is improved. According to the method and the system, vehicle deviation or steering wheel shaking caused by mode switching is avoided, driving comfort and safety are greatly improved, when an electric control system (SBW) mode breaks down, the electric control system can rapidly and reliably return to a rack type electric power steering (REPS) mode, the basic steering function of the vehicle is guaranteed, the strict requirement of high-level automatic driving for functional safety is met, and the driving safety is improved. The flexible and adjustable steering hand feeling can be provided in the SBW mode, an interface is provided for intelligent driving, and the most direct and reliable mechanical feedback can be provided in the REPS mode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steering system control, in particular to a steering system switchable between SBW and EPS modes and a control method. BACKGROUND

[0002] Steer-by-wire (SBW) is one of the core technologies of the next generation of intelligent vehicles, which completely cancels the mechanical connection between the steering wheel and the steering wheel, and transmits the driving command through the electrical signal, and the motor executes the steering action. This system brings revolutionary advantages to vehicle design, including but not limited to: eliminating the limitations of the steering column on the interior layout, providing a more flexible execution interface for advanced autonomous driving, and being able to freely design and adjust the steering feel (i.e. "road feel") through algorithms.

[0003] However, the pure steer-by-wire system also introduces a fatal safety and reliability problem. Since it completely relies on the electrical control system to work, once one or several key components in the system, such as the angle sensor, torque sensor, main control ECU or assist motor, fails, the steering function will be completely lost, causing serious safety accidents. This reliability bottleneck seriously restricts the popularization and application of steer-by-wire technology in mass-produced passenger cars. In order to ensure basic safety, the existing technical solutions usually adopt redundant design, for example, setting up backups for key sensors and ECUs, but this greatly increases the cost and complexity of the system, and still belongs to the category of "electrical redundancy", which cannot cope with extreme situations such as global power failure.

[0004] On the other hand, the traditional rack-type electric power steering system (REPS) ensures the lower limit of safety through mechanical connection, and is mature in technology and low in cost, but its steering feel is fixed, the adjustment range is limited, and it cannot meet the needs of L3 and above level autonomous driving for steering wheel folding and decoupling control. SUMMARY

[0005] In view of the above technical problems, the present application provides a steering system switchable between SBW and EPS modes and a control method, which overcomes at least one deficiency.

[0006] The technical scheme adopted by the present application is as follows: a steering system switchable between SBW and EPS modes, comprising a mechanical connection subsystem, an electrical control subsystem and a main controller,

[0007] The mechanical connection subsystem comprises a steering wheel, an upper steering column, an electromagnetic clutch, an intermediate shaft and a lower steering assembly connected in sequence;

[0008] The electrical control subsystem comprises a road feel motor connected with the upper steering column, an assist motor connected with the lower steering assembly and a sensor group, the road feel motor is used to provide a feedback torque to the steering wheel; the assist motor is used to drive the steering wheel;

[0009] The main controller receives signals from the sensor group and generates instructions according to a preset control strategy, which are then sent to the road feel motor driver, the power steering motor driver, and the electromagnetic clutch driver to switch between steer-by-wire mode and rack-and-pinion electric power steering mode. During mode switching, the main controller executes a torque weighting gradual control strategy. During the engagement or disengagement of the electromagnetic clutch, the output torque is expressed as:

[0010]

[0011] Among them, T out (t) represents the output torque, α(t) is a weighting coefficient that varies continuously from 0 to 1, and T mech (t) represents the mechanical path torque transmitted through the electromagnetic clutch, T elec (t) is the electronically controlled path torque output by the booster motor and applied to the downswing assembly.

[0012] Optionally, the sensor group includes a steering wheel angle sensor mounted on the upper steering column, a torque sensor mounted on the road feel motor, a vehicle speed sensor, a yaw rate sensor, and a center of gravity sideslip angle sensor. The steering wheel angle sensor detects the steering wheel angle, the vehicle speed sensor detects the vehicle speed, the yaw rate sensor detects the vehicle yaw rate, and the center of gravity sideslip angle sensor detects the vehicle's center of gravity sideslip angle. The main controller is electrically connected to the steering wheel angle sensor, the torque sensor, the vehicle speed sensor, the yaw rate sensor, the road feel motor, the power steering motor, and the electromagnetic clutch.

[0013] Optionally, the dynamic equation of the road sensor motor is:

[0014]

[0015]

[0016] Among them, T hw J is the steering torque of the steering wheel. hw J is the moment of inertia of the steering wheel. m B is the moment of inertia of the induction motor; hw B is the damping coefficient of the steering wheel. m f is the damping coefficient of the induction motor; hw τ is the frictional torque of the steering wheel. m I is the torque of the road-sensing motor; K is the torsional stiffness; I s θ is the reduction ratio; hw For steering wheel angle, The angular velocity of the steering wheel. hw θ is the angular acceleration of the steering wheel. m For the rotation angle of the road sensor motor; m The angular velocity of the road sensor motor; m This refers to the angular acceleration of the road sensor motor.

[0017] Optionally, in the online steering mode, the main controller calculates the target steering feedback torque based on the received vehicle status signal and controls the road feel motor to generate the feedback torque. The dynamic relationship equation of the target steering feedback torque is:

[0018]

[0019]

[0020]

[0021] Where T is the target steering feedback torque, T1 is the upper steering wheel return torque, and T2 is the lower road feel torque; B is the viscous friction coefficient, and K is the road feel torque gain; T da The equivalent damping moment; T in For the equivalent inertial torque; T al This is the self-correcting torque; T ja This is the lifting torque.

[0022] Optionally, in the online steering mode, the control signal u(t) generated and output to the power assist motor by the main controller is derived from the feedforward control signal u. ff (t) and PID feedback control signal u PID (t) is formed by adding together:

[0023]

[0024] The feedforward control signal u ff The model equation for (t) is:

[0025]

[0026] Where: θ ref (t) represents the rotation angle of the road sensor motor. ref (t) represents the angular velocity of the road sensor motor. ref (t) represents the angular acceleration of the road sensor motor; K f B is the equivalent stiffness coefficient. f J is the equivalent damping coefficient. f This is the equivalent moment of inertia compensation coefficient;

[0027] The PID feedback control signal uPID The equation for calculating (t) is:

[0028]

[0029]

[0030] Where: θ act (t) is the actual front wheel steering angle, e(t) is the angle error, and K p For proportional gain, K i For integral gain, K d This is the differential gain.

[0031] Optionally, the mode switching judgment logic of the main controller includes:

[0032] If any of the following faults are detected: abnormal torque sensor signal, abnormal steering angle sensor signal, road feel motor self-test status feedback is faulty, power assist motor self-test status feedback is faulty, power supply voltage is continuously lower than the first voltage threshold for a first preset time, communication timeout, or motor overheating, then the system will be forcibly reverted to rack and pinion electric power steering mode.

[0033] Determine if all of the following conditions are met, and if all of the following conditions are met, then enter the steer-by-wire mode:

[0034] The sensor group, road sensor motor, power assist motor, electromagnetic clutch, and main controller are all functioning correctly.

[0035] The absolute value of the steering wheel angle is less than the first angle threshold;

[0036] The absolute value of the steering wheel torque is less than a first torque threshold.

[0037] When both the road feel motor and the assist motor are functioning normally.

[0038] Optionally, the main controller executes the following control priority strategy: during normal operation, the control and status monitoring of the road sensor motor are given the highest priority; the start of the power steering motor is premised on the road sensor motor providing normal feedback and a valid target steering angle signal; when the road sensor motor is detected to be malfunctioning or its feedback signal is abnormal, the control priority is immediately switched to the fault-tolerant control of the power steering motor, and the electromagnetic clutch is triggered to engage, so as to maintain the basic steering function of the vehicle in the rack and pinion electric power steering mode.

[0039] Optionally, the main controller performs adaptive adjustment of the road feel curve, which can be achieved in the following ways:

[0040] Multiple road feel settings are pre-stored, and each road feel setting corresponds to a set of stiffness and damping parameters;

[0041] Based on the received vehicle speed signal and driving mode selection signal, select the current gear from the multiple road feel gears;

[0042] Based on real-time vehicle speed signals, the stiffness and damping parameters corresponding to the selected gear are continuously adjusted.

[0043] When the yaw rate or center of gravity sideslip angle exceeds a preset threshold, a high dynamic road feel curve is invoked, which has increased damping parameters and decreased stiffness parameters.

[0044] This invention also discloses a control method for the steering system described above, which can switch between steer-by-wire and power-assisted modes, comprising the following steps:

[0045] S1. Collect steering wheel angle signal, steering wheel torque signal, vehicle speed signal, yaw rate signal, and center of gravity sideslip angle signal;

[0046] S2. Based on the mode switching judgment logic of the main controller, determine whether the system enters the steer-by-wire mode or the rack and pinion electric power steering mode;

[0047] S3. During mode switching, the electromagnetic clutch is engaged or disengaged, and the torque weight gradual control strategy is adopted to make the system output torque transition smoothly.

[0048] Optionally, the timing control for switching from rack-and-pinion electric power steering mode to steer-by-wire mode includes:

[0049] At time 1-1, the main controller issues a switchover preparation command;

[0050] During the first and second time periods, confirm that the system status meets the switching conditions;

[0051] During periods 1-3, the mechanical path torque is unloaded to near zero, and the torque is taken over by the electronically controlled path.

[0052] During periods 1-4, the electromagnetic clutch is disengaged.

[0053] During periods 1-5, the mechanical disconnection is completed and the closed-loop control of the electronic control path is fully activated;

[0054] The timing control for switching from steer-by-wire mode to rack-and-pinion electric power steering mode includes:

[0055] At time 2-1, the main controller issues a switchover preparation command;

[0056] During the 2-2 time period, confirm that the dynamic state allows for mechanical engagement;

[0057] Within 2-3 time periods, control the synchronous output shaft rotation angle of the power assist motor;

[0058] During time periods 2-4, the electromagnetic clutch is driven to engage softly with a low current.

[0059] During the 2-5 time period, torque weight gradual control is implemented to gradually transition the main output of steering torque from the electronic control path to the mechanical path.

[0060] During time intervals 2-6, the electromagnetic clutch is fully engaged and mechanically locked. After the main controller confirms the successful mechanical connection, it exits the active steering control of the electronically controlled path.

[0061] The beneficial effects of this invention are as follows: By integrating the mechanical connection subsystem and the electronic control subsystem, and introducing a torque weight gradual change control strategy, the problems of torque shock and discontinuity during mode switching are solved, achieving truly smooth and imperceptible mode switching. This avoids vehicle deviation or steering wheel vibration caused by mode switching, greatly improving driving comfort and safety. When the electronic control system (SBW) mode malfunctions, it can quickly and reliably revert to the rack and pinion electric power steering (REPS) mode, ensuring the vehicle's basic steering function and meeting the stringent functional safety requirements of high-level autonomous driving. It can provide flexible and adjustable steering feel and provide an interface for intelligent driving in SBW mode, and provide the most direct and reliable mechanical feedback in REPS mode. Attached Figure Description

[0062] Fig. 1 This is a block diagram illustrating the control logic principle of a steering system that can switch between steer-by-wire and power-assisted modes, as proposed in an embodiment of the present invention.

[0063] Fig. 2 This is a block diagram of the rack-and-pinion electric power steering and steer-by-wire mode switching strategy proposed in an embodiment of the present invention;

[0064] Fig. 3 This is a safety strategy block diagram of a steering system that can switch between steer-by-wire and power-assisted modes, as proposed in an embodiment of the present invention.

[0065] Fig. 4 This is a control priority block diagram of a steering system that can switch between steer-by-wire and power-assisted modes, as proposed in an embodiment of the present invention. Detailed Implementation

[0066] The present application will now be described in further detail with reference to the accompanying drawings and embodiments.

[0067] like Figs. 1 to 3As shown, this embodiment discloses a steering system switchable between drive-by-wire and power-assisted modes, including a mechanical connection subsystem, an electronic control subsystem, and a main controller (ECU). The mechanical connection subsystem includes a steering wheel, an upper steering column, an electromagnetically controllable clutch, an intermediate shaft, and a lower steering assembly, which are mechanically connected in sequence. The lower steering assembly is connected to the steering wheels. The electronic control subsystem includes a road feel motor, a power assist motor, and a sensor group. The road feel motor is coupled to the upper steering column via a gear or belt drive mechanism to provide feedback torque to the steering wheel. The power assist motor is coupled to the lower steering assembly via a gear mechanism to drive the steering wheels.

[0068] The sensor group includes: a steering wheel angle sensor mounted on the upper steering column for detecting the steering wheel angle; a torque sensor mounted on the road feel motor for detecting the driver's input torque; a vehicle speed sensor mounted on the vehicle body for detecting the vehicle speed; a yaw rate sensor mounted on the vehicle body for detecting the vehicle's yaw rate; and a sensor or estimator module for detecting or estimating the vehicle's center of gravity sideslip angle.

[0069] The main controller (ECU) is electrically connected via the vehicle CAN bus or hardwired connections to the steering wheel angle sensor, torque sensor, vehicle speed sensor, yaw rate sensor, center of gravity sideslip angle sensor or estimator module, the driver of the road feel motor, the driver of the power steering motor, and the driver of the electromagnetically controllable clutch. The ECU is configured to receive signals from all sensors and generate commands according to a preset control strategy, sending them to the road feel motor driver, the power steering motor driver, and the electromagnetic clutch driver to control their actions and switch between steer-by-wire (SBW) mode and rack-and-pinion electric power steering (REPS) mode. During mode switching, the main controller executes a torque weighted gradual control strategy. During the engagement or disengagement of the electromagnetic clutch, the final output torque acting on the steering wheel is composed of a mixture of mechanical path torque and electronically controlled path torque based on a weighted function to ensure continuous output torque. The output torque is expressed as:

[0070]

[0071] Among them, T out (t) represents the output torque, α(t) is a weighting coefficient that varies continuously from 0 to 1 or from 1 to 0, and T mech (t) represents the mechanical path torque transmitted through the electromagnetic clutch, T elec (t) is the electronically controlled path torque output by the booster motor and applied to the downswing assembly.

[0072] 0 <t<t f

[0073] α(t) is the torque weighting curve gradient function, t is the engagement time, and t f The time it takes for the transition to complete.

[0074] The electromagnetic clutch is installed at the connection section between the upper steering column and the intermediate shaft. Its housing is fixed to the steering assembly bracket, and its internal clutch mechanism engages with the shaft through a spline. The ECU sends control commands to the electromagnetic clutch driver via the CAN bus to drive the electromagnetic clutch to engage or disengage.

[0075] The road-sensing motor is used to simulate the feedback of a virtual torsion bar in the online steering mode, and its dynamic equation is:

[0076]

[0077]

[0078] Among them, T hw J is the steering torque of the steering wheel. hw J is the moment of inertia of the steering wheel. m B is the moment of inertia of the induction motor; hw B is the damping coefficient of the steering wheel. m f is the damping coefficient of the induction motor; hw τ is the frictional torque of the steering wheel. m I is the torque of the road-sensing motor; K is the torsional stiffness; I s θ is the reduction ratio; hw For steering wheel angle, hw The angular velocity of the steering wheel. hw θ is the angular acceleration of the steering wheel. m For the rotation angle of the road sensor motor; m The angular velocity of the road sensor motor; m The angular acceleration of the road-sensing motor is used. By establishing a precise dynamic model of the road-sensing motor, a theoretical foundation and core algorithm are provided for generating realistic and natural steering feel in SBW mode. It can accurately simulate and reproduce the elastic force and damping feel of the torsion bar in the electric power steering system, allowing the driver to obtain familiar force feedback and avoiding discomfort caused by sudden changes in steering system characteristics. This model makes the steering torque T... hw and the torque τ of the road feel motor m This allows them to become precisely controllable variables, laying the foundation for subsequent personalized adjustments.

[0079] In online steering mode, the main controller calculates the target steering feedback torque based on the received vehicle status signal and controls the road feel motor to generate this feedback torque. The target steering feedback torque is composed of the upper-level return torque and the lower-level road feel torque, and its dynamic relationship is defined by the following equation:

[0080]

[0081]

[0082]

[0083] Where T is the target steering feedback torque, T1 is the upper steering wheel return torque, and T2 is the lower road feel torque; hw The angular velocity of the steering wheel. hw J is the angular acceleration of the steering wheel. hw Where is the moment of inertia of the steering wheel, B is the coefficient of viscous friction, K is the road feel torque gain, reflecting the transmission ratio of the lower-level road feel torque from the tires to the steering wheel; T da The equivalent damping moment; T in For the equivalent inertial torque; T al This is the self-correcting torque; T ja The upper-level return torque T1 simulates the inertial damping characteristics of the steering wheel itself, ensuring a realistic dynamic response. The lower-level road feel torque T2 efficiently transmits various force information generated by the contact between the tires and the road surface (such as return force, damping force, and inertial force), enabling the driver to clearly perceive the vehicle's status and road information, thus improving the driver-vehicle communication and driving confidence.

[0084] In online steering mode, the control signal u(t) generated and output to the power assist motor by the main controller is derived from the feedforward control signal u. ff (t) and PID feedback control signal u PID (t) is formed by adding together:

[0085]

[0086] The feedforward control signal u ff The model equation for (t) is:

[0087]

[0088] Where: θ ref (t) represents the rotation angle of the road sensor motor. ref (t) represents the angular velocity of the road sensor motor. ref(t) represents the angular acceleration of the road sensor motor; K f B is the equivalent stiffness coefficient. f J is the equivalent damping coefficient. f This is the equivalent moment of inertia compensation coefficient.

[0089] The PID feedback control signal u PID The equation for calculating (t) is:

[0090]

[0091]

[0092] Where: θ act (t) is the actual front wheel steering angle, e(t) is the angle error, and K p For proportional gain, K i For integral gain, K d This is the differential gain.

[0093] The main controller executes the following control priority strategy: during normal operation, the control and status monitoring of the road sensor motor are given the highest priority; the start of the power steering motor is conditional on the road sensor motor providing normal feedback and a valid target steering angle signal; when the road sensor motor is detected to be malfunctioning or its feedback signal is abnormal, the control priority is immediately switched to the fault-tolerant control of the power steering motor, and the electromagnetic clutch is triggered to engage, so as to maintain the basic steering function of the vehicle in the rack and pinion electric power steering mode.

[0094] The main controller (ECU) internally stores multiple preset road feel curve levels, such as "Comfort," "Standard," and "Sport." Each level corresponds to a set of pre-calibrated parameters, including the equivalent stiffness coefficient K and the equivalent damping coefficient B. The level switching logic is as follows: the ECU determines the currently used level by reading the vehicle speed signal from the vehicle's CAN bus and the mode signal selected by the driver via a button. For example, when the vehicle speed is below 50 km / h and the driver selects "Comfort" mode, the ECU uses K and B as parameters in the feedforward control model.

[0095] Dynamic gain adjustment: Even in the same gear, the parameters are not fixed. The ECU continuously fine-tunes the stiffness and damping parameters based on the real-time vehicle speed. For example, in "standard" gear, the damping coefficient B changes with vehicle speed, thereby increasing damping at high speeds to suppress steering wheel vibration and decreasing damping at low speeds to make steering easier.

[0096] High Dynamic Adjustment: When the yaw rate (r) obtained by the ECU through the IMU or the estimated sideslip angle (β) exceeds a set threshold (e.g., |r| > 30 deg / s or |β| > 3 deg), the ECU determines that the vehicle is in a high dynamic driving state, such as an emergency lane change. At this time, the ECU temporarily calls a road feel curve designed specifically for high loads. This curve significantly increases the damping coefficient B and moderately reduces the stiffness coefficient K, transmitting a heavier and more stable force to the driver through the steering wheel, making the driver perceive that the vehicle is approaching its limits. Through multiple road feel curves and dynamic gain adjustment, adaptive matching of steering feel with driving scenarios and user preferences is achieved, significantly improving the subjective driving experience.

[0097] The specific steps for determining the mode switching of the main controller (ECU) are as follows:

[0098] Conditions for forcibly reverting to REPS mode (triggered if any condition is met):

[0099] (1) Sensor failure: The ECU detects that the signal value of the torque sensor or steering wheel angle sensor is continuously outside the physical reasonable range (such as torque >100 Nm or < -100 Nm), or the signal change rate is abnormal, or the CAN message is lost and timed out (>20ms).

[0100] (2) Driver failure: The "fault flag" is set in the status word received by the ECU from the road sensor motor driver or the power assist motor driver. This indicates that the driver's internal self-test has detected errors such as overcurrent, overtemperature, short circuit, or communication interruption.

[0101] (3) Power supply failure: The ADC module of the ECU detects a power supply voltage V bat The voltage remained below 9V for 50ms.

[0102] (4) Communication failure: CAN communication between ECU and driver or IMU timed out (>20ms without receiving a valid message).

[0103] (5) Over-temperature fault: The motor temperature T reported by the driver motor Temperatures remained above 120°C.

[0104] Any single point of failure will be detected and trigger the system to revert to a more reliable mechanical mode, maximizing the safety of passengers.

[0105] The following conditions must be met to allow entry into SBW mode:

[0106] (1) No system fault: All forced rollback conditions in the above judgment conditions for forced rollback to REPS mode are not met. That is, all sensors, road feel motor drivers, power assist motor drivers, electromagnetic clutch drivers and ECU itself report normal status.

[0107] (2) Driving state constraints: To avoid the risks caused by large-angle switching at high speeds, the absolute value of the steering wheel angle |θ is required to be within a certain range. hw | < 45° and the absolute value of steering wheel torque |T sw | < 5 Nm.

[0108] (3) Actuator ready: The road sensor motor can normally feed back torque, and the power assist motor can drive normally.

[0109] This embodiment also discloses a control method for the steering system described above, which can switch between steer-by-wire and power-assisted modes. The control method is implemented by the main loop task in the ECU, and its execution cycle is 1~2ms. The steps are as follows:

[0110] S1. Data Acquisition: The ECU periodically reads the steering wheel angle θ via the CAN interface and ADC interface. hw Steering wheel torque T hw Vehicle speed v, yaw rate r, center of gravity sideslip angle β, status words of each motor driver and power supply voltage V bat ;

[0111] S2. Safety Judgment and Decision: The ECU calls the mode switching judgment logic described above to process and analyze the collected data.

[0112] If it is determined that a forced reversal is required, the ECU immediately generates a command to control the electromagnetic clutch to engage and exit the SBW control algorithm;

[0113] If it is determined that entry into SBW is permitted and the current mode is REPS, the ECU initiates the timing process for switching to SBW mode.

[0114] If the system is fault-free but does not meet the SBW switching conditions, or is already in REPS mode, the ECU will maintain REPS mode operation.

[0115] S3. Torque Gradual Control: During mode switching, the ECU starts a timer and calculates a weighting coefficient α(t) based on the current time t (e.g., using a linear function, S-curve, etc.). The ECU estimates the mechanical path torque T in real time. mech (t) and the torque T of the electronic control path elec (t), and according to the formula The mixed output torque is calculated, and the output torque is ultimately achieved by controlling the boost motor to ensure smooth switching.

[0116] The specific timing control for switching from REPS mode to SBW mode is as follows:

[0117] t = 0 ms: The ECU determines that the switching conditions are met and broadcasts a "switching preparation" command to the system;

[0118] t = 0-10ms: The road feel motor driver and power steering motor driver are reporting normal status; the ECU rechecks the vehicle speed and yaw rate, which are within the safe range.

[0119] t = 100-120ms: The ECU controls the road feel motor to apply a small torque, unloading the load torque of the mechanical connection path (via torsion bar and electromagnetic clutch) to near zero. At the same time, the ECU controls the power assist motor to enter position servo mode, keeping its output shaft rotation angle synchronized with the rotation angle of the upper rotary column (after reduction ratio conversion);

[0120] t = 120-200ms: The ECU sends a command to the electromagnetic clutch driver to drive the electromagnetic clutch to disengage with a lower current, so that its splines smoothly slip out of the engagement state until it is completely disengaged;

[0121] t = 200-300ms: After the ECU confirms that the electromagnetic clutch has been fully disengaged, the road feel motor begins to calculate and generate virtual road feel feedback torque based on the vehicle status information, while the power assist motor executes steering actions entirely according to the steering wheel angle command.

[0122] The specific timing control for switching from SBW mode to REPS mode is as follows:

[0123] t = 0 ms: The ECU detects a fault or a driver request and decides to switch back to REPS mode, issuing a "switch preparation" command.

[0124] t = 0-10 ms: The ECU confirms that the current vehicle speed, yaw rate, and other dynamic states allow for mechanical engagement.

[0125] t = 10-150 ms: The ECU obtains the current steering wheel angle θ through the upper steering column angle sensor. hw The ECU then estimates the target rotation angle of the intermediate shaft. The ECU controls the power steering motor to operate in position control mode, ensuring its output shaft rotation angle precisely tracks this target angle, preparing for mechanical engagement.

[0126] t = 150-250 ms: The ECU sends a command to the electromagnetic clutch driver to engage the electromagnetic clutch with a low initial current, and monitors the feedback from the engagement stroke sensor or the change in motor current in real time to determine whether engagement has started.

[0127] t = 250-350 ms: ECU starts with a torque weighted gradual control strategy. During this phase, the weighting coefficient α(t) gradually increases from 0 to 1. The ECU controls the output torque T of the assist motor. elec (t) gradually decreases, while the torque T transmitted through the mechanical path... mech (t) gradually increases, eventually achieving a smooth transition in torque transmission.

[0128] t = 350-450 ms: The ECU controls the electromagnetic clutch driver to apply the maximum current, ensuring that the electromagnetic clutch is fully engaged and locked by the mechanical pin. After the ECU confirms that the mechanical connection is secure and reliable through sensor signals, it stops the active steering control of the power steering motor, and the system fully enters REPS mode.

[0129] It is understood that the specific embodiments described above are merely for explaining the relevant invention and not for limiting the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Multiple technical solutions in the same embodiment, as well as multiple technical solutions in different embodiments, can be arranged and combined to form new technical solutions that do not contradict or conflict with each other. Any equivalent structural transformations made based on the content of this specification and drawings, whether directly or indirectly applied to other related technical fields, are similarly included within the scope of protection of this invention.

Claims

1. A steering system switchable between steer-by-wire and power-assisted modes, characterized in that, This includes a mechanical connection subsystem, an electrical control subsystem, and a main controller. The mechanical connection subsystem includes a steering wheel, an upper steering column, an electromagnetic clutch, an intermediate shaft, and a lower steering assembly connected in sequence. The electronic control subsystem includes a road feel motor connected to the upper steering column, a power assist motor connected to the lower steering assembly, and a sensor group. The road feel motor is used to provide feedback torque to the steering wheel; the power assist motor is used to drive the steering wheels. The main controller receives signals from the sensor group and generates instructions according to the preset control strategy, which are then sent to the road feel motor driver, the power assist motor driver and the electromagnetic clutch driver to realize the switching between the steer-by-wire mode and the rack and pinion electric power steering mode. During mode switching, the main controller executes a torque weighted gradual control strategy. During the engagement or disengagement of the electromagnetic clutch, the output torque acting on the steering wheel is expressed as: ， Among them, T out (t) represents the output torque, α(t) is a continuously varying weighting coefficient, and T mech (t) represents the mechanical path torque transmitted through the electromagnetic clutch, T elec (t) is the electronically controlled path torque output by the booster motor and applied to the downswing assembly.

2. The steering system switchable between steer-by-wire and power-assisted modes according to claim 1, characterized in that, The sensor group includes a steering wheel angle sensor mounted on the upper steering column, a torque sensor mounted on the road feeler motor, a vehicle speed sensor, a yaw rate sensor, and a center of gravity sideslip angle sensor. The steering wheel angle sensor is used to detect the steering wheel angle, the vehicle speed sensor is used to detect the vehicle speed, the yaw rate sensor is used to detect the vehicle yaw rate, and the center of gravity sideslip angle sensor is used to detect the vehicle's center of gravity sideslip angle.

3. The steering system switchable between steer-by-wire and power-assisted modes according to claim 1, characterized in that, The dynamic equation of the road sensor motor is: ， ， Among them, T hw J is the steering torque of the steering wheel. hw J is the moment of inertia of the steering wheel. m B is the moment of inertia of the induction motor; hw B is the damping coefficient of the steering wheel. m f is the damping coefficient of the induction motor; hw τ is the frictional torque of the steering wheel. m I is the torque of the road-sensing motor; K is the torsional stiffness; I s θ is the reduction ratio; hw For steering wheel angle, hw The angular velocity of the steering wheel. hw θ is the angular acceleration of the steering wheel. m For the rotation angle of the road sensor motor; m The angular velocity of the road sensor motor; m This refers to the angular acceleration of the road sensor motor.

4. The steering system switchable between steer-by-wire and power-assisted modes according to claim 1, characterized in that, In online steering mode, the main controller calculates the target steering feedback torque based on the received vehicle status signal and controls the road-sensing motor to generate this feedback torque. The dynamic relationship equation of the target steering feedback torque is as follows: ， ， ， Where T is the target steering feedback torque, T1 is the upper steering wheel return torque, and T2 is the lower road feel torque; B is the viscous friction coefficient, and K is the road feel torque gain; T da The equivalent damping moment; T in For the equivalent inertial torque; T al This is the self-correcting torque; T ja This is the lifting torque.

5. The steering system switchable between steer-by-wire and power-assisted modes according to claim 1, characterized in that, In online steering mode, the control signal u(t) generated and output to the power assist motor by the main controller is derived from the feedforward control signal u. ff (t) and PID feedback control signal u PID (t) is formed by adding together: ， The feedforward control signal u ff The model equation for (t) is: ， Where: θ ref (t) represents the rotation angle of the road sensor motor. ref (t) represents the angular velocity of the road sensor motor. ref (t) represents the angular acceleration of the road sensor motor; K f B is the equivalent stiffness coefficient. f J is the equivalent damping coefficient. f This is the equivalent moment of inertia compensation coefficient; The PID feedback control signal u PID The equation for calculating (t) is: ， ， Where: θ act (t) is the actual front wheel steering angle, e(t) is the angle error, and K p For proportional gain, K i For integral gain, K d This is the differential gain.

6. The steering system switchable between steer-by-wire and power-assisted modes according to claim 2, characterized in that, The mode switching judgment logic of the main controller includes: If any of the following faults are detected: abnormal torque sensor signal, abnormal steering angle sensor signal, road feel motor self-test status feedback is faulty, power assist motor self-test status feedback is faulty, power supply voltage is continuously lower than the first voltage threshold for a first preset time, communication timeout, or motor overheating, then the system will be forcibly reverted to rack and pinion electric power steering mode. Determine if all of the following conditions are met, and if all of the following conditions are met, then enter the steer-by-wire mode: The sensor group, road sensor motor, power assist motor, electromagnetic clutch, and main controller are all functioning correctly. The absolute value of the steering wheel angle is less than the first angle threshold; The absolute value of the steering wheel torque is less than a first torque threshold. When both the road feel motor and the assist motor are functioning normally.

7. The steering system switchable between steer-by-wire and power-assisted modes according to claim 1, characterized in that, The main controller executes the following control priority strategy: During normal operation, the control and status monitoring of the road sensor motor are given the highest priority. The starting of the assist motor is contingent upon the road feel motor providing normal feedback and a valid target turning angle signal. When a failure of the road feel motor or an abnormality in its feedback signal is detected, the control priority is immediately switched to the fault-tolerant control of the power steering motor, and the electromagnetic clutch is triggered to engage, so as to maintain the basic steering function of the vehicle in rack and pinion electric power steering mode.

8. The steering system switchable between steer-by-wire and power-assisted modes according to claim 1, characterized in that, The main controller performs adaptive adjustment of the road feel curve, which is achieved in the following ways: Multiple road feel settings are pre-stored, and each road feel setting corresponds to a set of stiffness and damping parameters; Based on the received vehicle speed signal and driving mode selection signal, select the current gear from the multiple road feel gears; Based on real-time vehicle speed signals, the stiffness and damping parameters corresponding to the selected gear are continuously adjusted. When the yaw rate or center of gravity sideslip angle exceeds a preset threshold, a high dynamic road feel curve is invoked, which has increased damping parameters and decreased stiffness parameters.

9. A control method for a steering system switchable between steer-by-wire and power-assisted modes as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Collect steering wheel angle signal, steering wheel torque signal, vehicle speed signal, yaw rate signal, and center of gravity sideslip angle signal; S2. Based on the mode switching judgment logic of the main controller, determine whether the system enters the steer-by-wire mode or the rack and pinion electric power steering mode; S3. During mode switching, the electromagnetic clutch is engaged or disengaged, and the torque weight gradual control strategy is adopted to make the system output torque transition smoothly.

10. The control method according to claim 9, characterized in that, The timing control for switching from rack-and-pinion electric power steering mode to steer-by-wire mode includes: At time 1-1, the main controller issues a switchover preparation command; During the first and second time periods, confirm that the system status meets the switching conditions; During periods 1-3, the mechanical path torque is unloaded to near zero, and the torque is taken over by the electronically controlled path. During periods 1-4, the electromagnetic clutch is disengaged. During periods 1-5, the mechanical disconnection is completed and the closed-loop control of the electronic control path is fully activated; The timing control for switching from steer-by-wire mode to rack-and-pinion electric power steering mode includes: At time 2-1, the main controller issues a switchover preparation command; During the 2-2 time period, confirm that the dynamic state allows for mechanical engagement; Within 2-3 time periods, control the synchronous output shaft rotation angle of the power assist motor; During time periods 2-4, the electromagnetic clutch is driven to engage softly with a low current. During the 2-5 time period, torque weight gradual control is implemented to gradually transition the main output of steering torque from the electronic control path to the mechanical path. During time intervals 2-6, the electromagnetic clutch is fully engaged and mechanically locked. After the main controller confirms the successful mechanical connection, it exits the active steering control of the electronically controlled path.

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