Rear wheel steering system with lock device and control method thereof

Abstract

The application relates to a rear wheel steering system with a locking device and a control method thereof, and relates to the technical field of vehicles. The rear wheel steering system comprises a steering gear, the steering gear comprises a shell, a screw rod shaft, an end cover and a locking device; an installation cavity is arranged in the shell; an opening is arranged at the end of the shell and communicates with the installation cavity; the screw rod shaft is rotatably arranged in the installation cavity; the end cover is fixedly arranged at the opening; the locking device is arranged between the screw rod shaft and the end cover, the locking device is used for realizing mutual locking or unlocking of the screw rod shaft and the end cover, thereby realizing rear wheel steering locking under a specified working condition, and thus the problems of low system rigidity and insufficient locking torque of the self-locking mode of the steering gear are overcome, and the safety and reliability of the steering gear are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of vehicle technology, and in particular to a rear-wheel steering system with a locking device and its control method. Background Technology

[0002] The rear-wheel steering system controls the steering of the vehicle's rear wheels to reduce the vehicle's sideslip angle during steering, decrease the steady-state overshoot of the yaw rate, and achieve smooth steering. It is an important component of the vehicle's steering system. The main functions of the rear-wheel steering system include: controlling the rear wheels to steer in the opposite direction to the front wheels when the vehicle is turning at low speeds, thereby reducing the turning radius; controlling the rear wheels to steer in the same direction as the front wheels when the vehicle is changing lanes at high speeds, thereby reducing the vehicle's yaw rate; and limiting the rear-wheel steering when the vehicle is traveling straight or making a steady turn, thereby ensuring normal vehicle operation.

[0003] When a vehicle is traveling at high speed in a straight line, the impact of uneven road surfaces on the tires and the lateral forces exerted on the tires by crosswinds are all applied to the steering system in the opposite direction through the tires. Therefore, if the stiffness of the rear wheel steering system is too small, it will be impossible to lock the rear wheel steering under specified working conditions, causing the rear wheels to deflect at an angle and vibrate at high frequency, thus affecting the vehicle's high-speed driving safety.

[0004] Existing rear-wheel steering systems typically use EPS (Electric Power Steering) or EHPS (Electronic High-Speed ​​Power Steering) systems as the core actuators to achieve speed reduction and torque increase in rear-wheel steering. EPS systems utilize the self-locking function of ball screws or worm gears to lock the rear wheels, while EHPS systems use a pneumatic locking principle. However, both of these locking methods suffer from low system rigidity and insufficient locking torque, making them unable to withstand the instantaneous impact of lateral forces generated during high-speed vehicle operation. Therefore, they are extremely detrimental to driving safety. Summary of the Invention

[0005] This invention provides a rear wheel steering system with a locking device and its control method, the main purpose of which is to solve the problems existing in the prior art.

[0006] The present invention adopts the following technical solution: A rear-wheel steering system with a locking device includes a steering gear, which comprises a housing, a lead screw shaft, an end cap, and a locking device. The housing has an internal mounting cavity, and an opening at one end of the housing communicating with the mounting cavity. The lead screw shaft is rotatably disposed within the mounting cavity. The end cap is fixedly disposed at the opening. The locking device is disposed between the lead screw shaft and the end cap, and is used to lock or unlock the lead screw shaft and the end cap.

[0007] Furthermore, the locking device includes a locking member, a mating member, and a driving member. The locking member is disposed on the lead screw shaft, the mating member is disposed on the end cap, and the driving member is used to drive the locking member and the mating member to lock or unlock each other.

[0008] Furthermore, the driving component includes an electromagnetic coil and a return spring. The electromagnetic coil is disposed within the mounting cavity, and the return spring is disposed between the electromagnetic coil and the locking component or the mating component.

[0009] Furthermore, the locking member is axially movable on the lead screw shaft via the driving member, and the locking member is provided with a plurality of locking teeth; the mating member is fixedly disposed on the end cover, and the mating member is provided with a plurality of mating teeth that mesh with the locking teeth.

[0010] Furthermore, the locking component is a locking end ring sleeved on the outer wall of the lead screw shaft, and the mating component and the end cap are integrally formed.

[0011] Furthermore, the locking tooth is a convex tooth disposed at the end of the locking end ring, and the mating tooth is a concave tooth disposed at the end of the end cap.

[0012] Furthermore: the outer wall of the lead screw shaft is provided with an axially extending guide key, and the locking member is provided with a keyway that cooperates with the guide groove.

[0013] A control method for a rear-wheel steering system with a locking device includes the following steps: Step S1: Based on the vehicle's two-degree-of-freedom model and according to the dynamic equilibrium logic, establish the dynamic equations of the rear-wheel steering system that characterize the influence of the locking device on the system's stiffness and damping. The specific expression is as follows:

[0014] In the formula: This represents the total moment of inertia of the output shaft. This refers to the acceleration of the rear wheels; For the system's equivalent damping; The angular velocity of the rear wheel; The equivalent stiffness of the system; This refers to the angular displacement of the rear wheel; This refers to the motor torque of the rear wheel steering motor; External disturbance torque; The locking torque of the locking device; Step S2: Construct a standard second-order system model of the locking device and calculate the driving voltage of the electromagnetic coil. The transfer function formula for a standard second-order system model is:

[0015] In the formula: The transfer function for a standard second-order system model; For the Laplace transform of the locking end ring displacement; This is the Laplace transform of the driving voltage of the electromagnetic coil; This represents the system's steady-state gain. It is the undamped natural frequency; The system damping ratio; Step S3: Integrate the stiffness adjustment of the locking device, the electromagnetic drive, and the dynamic characteristics of the rear wheel steering system into a state-space model. Optimize the control input using an LQR controller to achieve the equivalent stiffness of the locking device. The operating conditions are adaptively adjusted; the state equation of the state-space model is:

[0016] In the formula: This refers to the armature voltage of the steering motor; The voltage of the electromagnetic coil; The torque constant of the steering motor; For the armature resistance of the steering motor; External disturbance torque; The output equation of the state-space model is:

[0017] In the formula: This represents the measured angular displacement. For actual measurement of motor current ; This is the back EMF / current coefficient; Voltage coefficient; The expression for the LQR controller is:

[0018] In the formula: The objective function is... This is the system state vector; To control the input vector; The state weighting matrix; To control the weighting matrix.

[0019] Furthermore, the control method also includes the following steps: Step S4, constructing a Luneburg state observer based on the state-space model in step S3, and predicting the current by observing the steering motor. Compared with the measured current residual This enables fault diagnosis of the locking device.

[0020] Furthermore, in step S2, the system steady-state gain Undamped natural frequency And system damping ratio The calculation formula is:

[0021]

[0022]

[0023] In the formula: The current-force coefficient; This is the stiffness coupling coefficient; The coil resistance; The radius of the lead screw shaft.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The locking device provided by the present invention can realize the mutual locking or unlocking of the lead screw shaft and the end cover, thereby realizing the rear wheel steering lock under specified working conditions. This overcomes the problems of low system rigidity and insufficient locking torque in the steering gear's own locking method, and effectively improves the safety and reliability of the steering gear.

[0025] 2. The locking device provided by the present invention has the advantages of compact structure, small size, high locking rigidity, high reliability and strong compatibility. It can be integrated into the steering gear without occupying extra space in the vehicle, and is especially suitable for new energy vehicles.

[0026] 3. The control method provided by this invention quantifies the "voltage-displacement" relationship and optimizes parameters through a standard second-order system model to improve motion accuracy. It dynamically adjusts parameters based on the LQR control model to achieve stiffness adaptation, and uses the Luneburg state observer to diagnose faults reliably and at low cost without additional sensors. In addition, the model parameters can be correlated with the actual working conditions of the rear wheel steering system to improve control matching. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the steering mechanism in this invention.

[0028] Figure 2 This is an exploded view of the steering mechanism in this invention.

[0029] Figure 3 This is an overall cross-sectional view of the steering mechanism in this invention.

[0030] Figure 4 This is a partial cross-sectional view of the steering gear when locked in this invention.

[0031] Figure 5 This is a partial cross-sectional view of the steering mechanism when it is unlocked in this invention.

[0032] Figure 6This is a schematic diagram of the rear wheel steering system in this invention.

[0033] Figure 7 This is a diagram showing the overall architecture of the rear-wheel steering system in this invention.

[0034] Figure 8 This is a control flowchart of the rear wheel steering system in this invention.

[0035] In the diagram: 1-Steering gear; 11-Housing; 12-Lead screw shaft; 121-Guide key; 13-End cover; 14-Steering motor; 15-Steering input shaft; 16-Lead screw nut; 17-Sector tooth; 18-Output shaft; 2-Locking device; 21-Locking element; 211-Protruding tooth; 212-Keyway; 22-Matching part; 221-Concave tooth; 23-Electromagnetic coil; 24-Return spring; 3-Steering mechanism; 31-Steering tie rod connector; 32-Left steering tie rod; 33-Right steering tie rod; 34-Left rear wheel; 35-Right rear wheel. Detailed Implementation

[0036] Specific embodiments of the present invention will now be described with reference to the accompanying drawings. Many details are described below to provide a comprehensive understanding of the invention; however, those skilled in the art will be able to implement the invention without these details.

[0037] like Figures 1 to 3 As shown, this embodiment provides a rear wheel steering system with a locking device, including a steering gear 1. The steering gear 1 includes a housing 11, a steering motor 14, a steering input shaft 15, a lead screw nut 16, a sector gear 17, and an output shaft 18, etc. The housing 11 has an internal mounting cavity. The steering input shaft 15, lead screw 12, lead screw nut 16, sector gear 17, and output shaft 18 are mutually driven and disposed in the mounting cavity. The steering motor 14 is disposed outside the housing 11 and is driven and connected to the steering input shaft 15.

[0038] like Figures 1 to 3 As shown, the steering gear 1 also includes an end cap 13 and a locking device 2. The end of the housing 11 is provided with an opening that communicates with the mounting cavity. The end cap 13 is fixedly installed at the opening by means of snap-fit ​​connection or bolt connection. The locking device 2 is disposed between the lead screw shaft 12 and the end cap 13. The locking device 2 is used to realize the mutual locking or unlocking of the lead screw shaft 12 and the end cap 13, thereby realizing the rear wheel steering lock under specified working conditions. This overcomes the problems of low system rigidity and insufficient locking torque of the steering gear 1's own locking method, and effectively improves the safety and reliability of the steering gear.

[0039] like Figures 2 to 5As shown, the locking device 2 includes a locking element 21, a mating element 22, and a driving element. The locking element 21 is disposed on the lead screw shaft 12, the mating element 22 is disposed on the end cover 13, and the driving element is used to drive the locking element 21 and the mating element 22 to lock or unlock each other, thereby realizing the mutual locking or unlocking of the lead screw shaft 12 and the end cover 13. The locking device 2 has a simple and compact structure, small size, and can be integrated into the steering gear 1, and is compatible with various types of steering gears 1.

[0040] like Figures 2 to 5 As shown, in practical applications, the locking member 21 can be driven to move axially by the driving member, thereby locking or unlocking it with the fixed mating member 22. Alternatively, the mating member 22 can be driven to move axially by the driving member, thereby locking or unlocking it with the locking member 21. To fully utilize the mounting cavity space outside the lead screw shaft 12, this embodiment preferably adopts the first solution. Specifically, the locking member 21 is axially movable on the lead screw shaft 12 by the driving member, and the locking member 21 is provided with a plurality of locking teeth; the mating member 22 is fixedly disposed on the end cover 13, and the mating member 22 is provided with a plurality of mating teeth that mesh with the locking teeth.

[0041] like Figures 2 to 5 As shown, more specifically, the locking element 21 is a locking end ring sleeved on the outer wall of the lead screw shaft 12, and the mating element 22 and the end cover 13 are integrally formed. This makes the structure of the locking device 2 more compact and reasonable, avoiding taking up too much space and causing the steering gear 1 to be too large.

[0042] like Figures 2 to 5 As shown, preferably, the locking tooth is a convex tooth 211 located at the end of the locking end ring near the end cover 13, and the mating tooth is a concave tooth 221 located at the end of the end cover 13 near the locking end ring. The mutual engagement of the convex tooth 211 and the concave tooth 221 achieves a surface-locking effect, ensuring that the lead screw shaft 12 is firmly locked, thereby restricting its rotation and effectively improving the locking rigidity and reliability of the locking device 2. In other embodiments, the locking tooth can also be designed as an external spline on the outer wall of the locking end ring, and the mating tooth can be designed as an internal spline on the inner wall of the end cover 13.

[0043] like Figure 2 As shown, the outer wall of the lead screw shaft 12 is provided with an axially extending guide key 121, and the locking end ring is provided with a keyway 212 that cooperates with the guide groove. The radial limit can be achieved by the mutual cooperation of the guide key 121 and the keyway 212, so as to prevent the locking end ring and the lead screw shaft 12 from rotating relative to each other, thereby affecting the locking effect.

[0044] like Figures 2 to 5As shown, the driving component includes an electromagnetic coil 23 and a return spring 24. The electromagnetic coil 23 is disposed within the mounting cavity, and the return spring 24 is disposed between the electromagnetic coil 23 and the locking component 21. When unlocking is required, the electromagnetic coil 23 is energized to generate an axial attraction force, allowing the locking end ring to overcome the force of the return spring and move axially, thereby separating from the mating component 22 and allowing the lead screw shaft 12 to rotate. When locking is required, the electromagnetic coil 23 is de-energized, the axial attraction force disappears, and the locking end ring returns to its original position under the force of the return spring 24, thereby locking with the mating component 22 and restricting the rotation of the lead screw shaft 12. Therefore, the rapid driving response of the locking component 21 can be achieved through the cooperation of the electromagnetic coil 23 and the return spring 24.

[0045] like Figures 2 to 5 As shown, the return spring 24 is a laminated spring. Laminated springs have advantages such as compact structure, long service life, and good buffering and shock absorption effects. They can achieve large load and high stability in a small space, thus making the overall structure of the locking device 2 more stable and reliable.

[0046] like Figures 2 to 3 As shown, since the locking device 2 does not require significant modifications to other structures of the steering gear 1, it can be flexibly applied to EPS steering gears or EHPS steering gears. In this embodiment, the EPS steering gear is preferred.

[0047] like Figure 6 As shown, the rear-wheel steering system of this embodiment also includes a steering mechanism 3 that cooperates with the steering gear 1. The steering mechanism 3 includes components such as a steering tie rod connector 31, a left steering tie rod 32, a right steering tie rod 33, a left rear wheel 34, and a right rear wheel 35. The steering tie rod connector 31 is connected to the output shaft 18 of the steering gear 1, and is connected to the left rear wheel 34 and the right rear wheel 35 respectively through the left steering tie rod 32 and the right steering tie rod 33.

[0048] like Figures 1 to 6 As shown, the working principle of the rear wheel steering system is as follows: When driving straight, the rear wheel steering system needs to be locked. At this time, the electromagnetic coil 23 is de-energized, the axial attraction force disappears, and the locking end ring moves axially along the guide key 121 of the lead screw shaft 12 under the action of the return spring 24. The convex teeth 211 on its end face mesh with the concave teeth 221 of the end cover 13, thereby restricting the rotation of the lead screw shaft 12, thus realizing the locking of the rear wheel steering system.

[0049] When the vehicle control system determines that rear wheel steering is required (such as low-speed U-turn or high-speed lane change), the rear wheel steering system needs to be locked. At this time, the electromagnetic coil 23 is energized to generate an axial attraction force. The locking end ring overcomes the force of the return spring 24 and moves axially along the guide key 121 of the lead screw shaft 12. The convex tooth 211 on its end face disengages from the concave tooth 221 of the end cover 13, thereby allowing the lead screw shaft to rotate, thus unlocking the rear wheel steering. At the same time, the vehicle control system triggers the steering motor 14 to start. The power of the steering motor 14 is transmitted to the steering input shaft 15, which drives the lead screw shaft 12 to rotate. The rotational motion is converted into the axial linear motion of the lead screw nut 16 and the sector tooth 17 through the lead screw pair. The sector tooth 17 then meshes to drive the output shaft 18 to rotate. The output shaft 18 is linked to the steering tie rod connector 31 to push the left steering tie rod 32 and the right steering tie rod 33 to move laterally, thereby causing the left rear wheel 34 and the right rear wheel 35 to deflect around the steering knuckle, thus realizing rear wheel steering.

[0050] Real-vehicle testing has shown that installing a locking device 2 inside the steering gear 1 can effectively improve the overall performance of the rear-wheel steering system, as specifically demonstrated below: (1) After locking with the locking device 2 provided in this embodiment, the stiffness Ke of the rear wheel steering system is increased. It has been verified that the wheel angle fluctuation after locking is only 0.025°, a decrease of 70%, and the reverse rotation impact of the reverse wheel is reduced by 80%.

[0051] (2) The electromagnetic coil 23 of the locking device 2 has a pull force of about 200N, the axial travel of the locking end ring is 10-20mm, the locking execution time can reach the millisecond level, the response is sensitive, and it is far superior to the mechanical locking method of the traditional steering gear.

[0052] (3) Referring to the reduction ratio of the rear wheel steering system (commercial vehicle ig=15-22), the torque transmitted from the wheel end to the locking end ring is very small, which can make the outer end gear of the locking end ring smaller in module and more in number of teeth. The wheel angle corresponding to each tooth angle is <0.3°, which can meet the locking function under different steering angles of the vehicle.

[0053] (3) The locking device 2 provided in this embodiment can be integrated into the EPS steering gear or EHPS steering gear, without occupying extra space in the vehicle, and has low weight, making it especially suitable for new energy vehicles.

[0054] (4) The locking device 2 provided in this embodiment can be integrated into the EPS steering gear or EHPS steering gear, with strong compatibility, low torque requirement, and uses a ring disc return spring 24, which has high reliability and long service life.

[0055] Example 2: The control accuracy, adaptability to operating conditions, and fault handling capability of the locking device are crucial to the vehicle's handling stability. Therefore, based on the design concept of the locking device provided in Embodiment 1, this embodiment further provides a control algorithm for a rear-wheel steering system with a locking device. This control algorithm constructs a mathematical model based on the physical parameters of the locking device and controls the action of the locking device in real time. Specifically, it includes the following steps: Step S1: Based on the vehicle's two-degree-of-freedom model and according to the dynamic equilibrium logic, establish the dynamic equations of the rear-wheel steering system that characterize the influence of the locking device on the system's stiffness and damping. The specific expression is as follows:

[0056] The physical meanings of each parameter in the formula are as follows: The total moment of inertia of the output shaft includes the moment of inertia of components such as the locking end ring of the locking device and the lead screw shaft. For rear wheel acceleration, Represents the system's inertial torque; The equivalent damping of the system reflects the comprehensive damping characteristics of the locking device, including sliding friction and electromagnetic coil damping. The angular velocity of the rear wheel. Indicates the system's damping torque; The equivalent stiffness of the system is determined by the return spring stiffness of the locking device and the meshing stiffness of the convex / concave teeth. This refers to the angular displacement of the rear wheel. Indicates the system stiffness moment; The torque of the rear wheel steering motor is denoted as , and the active driving torque of the system is denoted as . External disturbance torques, such as road impacts and crosswind torques on the rear wheels; This refers to the locking torque of the locking device, a core performance indicator of the device, which is used when locking. Approaching infinity to limit the rotation of the rear wheels, when unlocked This allows the rear wheels to steer.

[0057] The dynamic equations of the rear-wheel steering system are used to define the mechanical relationship between the locking device and the rear-wheel steering system, quantify the impact of the locking device on the dynamic balance of the system, and provide basic parameters for subsequent control models. Step S2: Construct a standard second-order system model of the locking device and calculate the driving voltage of the electromagnetic coil.

[0058] Specifically, to further improve the dynamic control accuracy of the locking device, it is necessary to focus on its core action process of "electromagnetic drive - mechanical sliding". Therefore, this implementation abstracts the physical process of the locking device, namely "electromagnetic coil drive - locking end ring sliding - tooth engagement / disengagement", into a standard second-order system model, and quantifies the driving voltage of the electromagnetic coil through the transfer function. Displacement of the locking end ring The dynamic mapping relationship is used to calculate the optimal electromagnetic coil driving voltage, thereby ensuring that the locking end ring slides smoothly along the guide key and avoiding collision or misalignment between the convex and concave teeth. The specific steps are as follows: Step S21: Construct a standard second-order system model of the locking device, whose transfer function formula is:

[0059] The physical meanings of each parameter in the formula are as follows: The transfer function of a standard second-order system model describes the input in the complex frequency domain. With output The dynamic relationship; The Laplace transform of the locking end ring displacement reflects the mechanical action output of the locking device; The Laplace transform of the electromagnetic coil driving voltage is used as the control input for the locking device. The steady-state gain of the system reflects the static proportional relationship between the input voltage and the output displacement. It is the undamped natural frequency, reflecting the speed characteristics of the natural vibration of the locking device; The system damping ratio reflects the rate at which oscillations decay in the dynamic response of the locking device.

[0060] Step S22: Calculate the core parameters of the transfer function, specifically including: System steady-state gain The structural parameters of the locking device and the equivalent stiffness of the system in step S1 are used to determine the locking device's structure. The coupling calculation, its formula is:

[0061] In the formula: The current-force coefficient; This is the stiffness coupling coefficient; This is the coil resistance.

[0062] Undamped natural frequency Based on the total rotational inertia of the output shaft in step S1 System equivalent stiffness and the radius of the lead screw shaft The calculation is performed using the following formula:

[0063] In the formula: The radius of the lead screw shaft is used to convert system-level rotational parameters into linear parameters of the locking end ring.

[0064] System damping ratio Based on the total rotational inertia of the output shaft in step S1 System equivalent damping System equivalent stiffness and the radius of the lead screw shaft The calculation is performed using the following formula:

[0065] Step S23: Calculate the driving voltage of the electromagnetic coil: The target displacement of the locking end ring is determined based on the target action (locking / unlocking) of the locking device. ,right Perform Laplace transform to obtain Combined with transfer function Calculate the driving voltage of the electromagnetic coil :

[0066] When unlocking, via The control solenoid coil generates a driving force, causing the locking end ring to slide uniformly along the guide key against the force of the return spring; when locking, the control solenoid coil is de-energized, combined with... Predict the reset speed of the reset spring and fine-tune the low current pre-magnetization to reduce the impact of the locking end ring and avoid impact from the protruding teeth.

[0067] Step S3: Integrate the stiffness adjustment of the locking device, the electromagnetic drive, and the dynamic characteristics of the rear wheel steering system into a state-space model. Optimize the control input using an LQR controller to achieve the equivalent stiffness of the locking device. The operating conditions are adaptively adjusted, and the specific steps are as follows: Step S31: Establish the state equations of the state-space model. The state equations are used to describe the system state (rear wheel angular displacement). and rear wheel angular velocity ) according to control input (electromagnetic coil voltage) and steering motor armature voltage ) and external disturbances (external disturbance torque) The dynamic change of ) is expressed as:

[0068] In the formula, the parameters are defined as follows: The state vector includes the rear wheel angular displacement. and rear wheel angular velocity ; To control the input vector, where This is the armature voltage of the steering motor. The voltage of the electromagnetic coil; The torque constant of the steering motor; For the armature resistance of the steering motor; This refers to the external disturbance torque.

[0069] It should be noted that in the locked state ( (Power off), the locking device's convex and concave teeth mesh tightly, locking torque Approaching infinity, rear wheel angular displacement Keep constant (i.e.) At this point, the state equations are not applicable, and there is no need to calculate the state through the model. This state-space model ignores motor inductance and complex friction, reducing the amount of computation while ensuring accuracy, and adapting to the real-time requirements of vehicle dynamic driving.

[0070] Step S32: Establish the output equations of the state-space model. The output equations are used to convert the system state into a signal that can be measured by sensors (measured rear wheel angular displacement). Actual measured motor current This provides feedback for control optimization, and the expression is:

[0071] In the formula, the parameters are defined as follows: Let be the system output vector, where For the measured angular displacement, This is the actual measured motor current; The back EMF / current coefficient, The voltage coefficient is determined by the hardware characteristics of the locking device and the motor, ensuring accurate measurement and inversion of the true state of the system.

[0072] Step S33: Design an LQR controller as the upper-level corner tracking controller by minimizing the objective function. Optimize control input electromagnetic coil voltage To achieve the equivalent stiffness of the locking device The adaptive adjustment, the objective function expression is:

[0073] In the formula, the parameters are defined as follows: The objective function reflects the balance between control accuracy and energy consumption; The system state vector, i.e. ; To control the input vector, i.e. ; The state weighting matrix is ​​increased under high-speed conditions. The corresponding weights are used to prioritize suppressing rear wheel shimmy (improving equivalent stiffness). Reducing weights at low speeds reduces steering resistance (and thus reduces equivalent stiffness). ); To control the weighting matrix, the electromagnetic coil voltage is increased under low-speed conditions. The corresponding weights are used to reduce energy consumption, and the weights are reduced under high-speed conditions to ensure locking stiffness.

[0074] Step S4: Construct a Luneburg state observer based on the state-space model from step S3, and predict the current by observing the steering motor. Compared with the measured current residual The following are the specific steps to diagnose locking device malfunctions: Step S41: Establish the Luneburg state observer model. The Luneburg state observer predicts the system state based on the system input and measured output. The model expression is:

[0075]

[0076] In the formula, the parameters are defined as follows: To predict the state vector, and Consistent dimensions; To predict the output vector, and Consistent dimensions; The actual measurement vector, i.e. ; The system state matrix, i.e. ; The input matrix is, i.e. ; The output matrix, i.e. ; For the front matrix, i.e. ; The observer gain matrix is ​​designed with pole placement to ensure that the predicted state quickly tracks the actual state.

[0077] Step S42: Calculate current residual and diagnose faults: from the predicted output vector Extract the estimated current of the steering motor (Right now ), and the measured motor current (Right now Calculate the residual :

[0078] The fault diagnosis threshold is calibrated based on the motor power and locking device characteristics. The fault diagnosis logic is as follows:

[0079] When a fault is diagnosed, the system triggers fail-safe strategies (such as increasing the voltage of the electromagnetic coil). (Attempt to escape from the predicament, switch to mechanical lock backup mode), to improve the functional safety level.

[0080] This control algorithm has the following beneficial effects: (1) Significantly improved action accuracy: The dynamic relationship between voltage and displacement is quantified by standard second-order system model, and the natural frequency and damping ratio are optimized to avoid overshooting or lag of the locking end ring. The engagement / disengagement accuracy of the convex teeth is controlled within ±0.1mm. (2) Stiffness adaptive adaptation condition: Based on the state-space model of LQR control, it can be dynamically adjusted according to vehicle speed and steering requirements. Balancing high-speed impact resistance with low-speed agility; (3) Low cost and reliable fault diagnosis: The Luneburger condition observer does not require additional sensors and can diagnose faults only through the motor current residual. The diagnostic accuracy is ≥99%, the response time is ≤50ms, and the hardware cost is reduced by more than 30%. (4) Deep coupling between model and system: From dynamic equations to state-space model, all parameters are related to the actual working conditions of rear wheel steering system, and the matching degree between control commands and system requirements is improved by 40%, avoiding control misalignment.

[0081] Example 3: After configuring the locking device provided in Embodiment 1, in order to deeply integrate the control algorithm provided in Embodiment 2 into the rear-wheel steering system, the overall architecture and control flow of the rear-wheel steering system should also be adaptively adjusted. Based on this, this embodiment further provides an overall architecture and control flow for a rear-wheel steering system with a locking device.

[0082] like Figure 7 As shown, the overall architecture of the rear-wheel steering system includes a signal input module, a processing and decision-making module, a drive output module, and actuators and the vehicle. The functions of each module are as follows: (1) Signal input module: integrates vehicle speed sensor, steering wheel angle sensor, yaw / acceleration sensor and driving mode selection unit, used to collect vehicle status signals and perform preprocessing such as filtering and reliability detection; (2) Processing and decision-making module: Based on the central domain controller, execute control algorithms (including dynamic modeling, second-order system analysis, LQR optimization, fault diagnosis, etc.) and output control commands; (3) Drive output module: includes the locking device electromagnetic coil drive circuit and the rear wheel steering motor drive circuit, used to convert control commands into drive parameters; (4) Actuator and vehicle: including locking device, rear wheel steering system and vehicle, used to perform driving actions and provide feedback status.

[0083] As shown in Figure 8, the control process of the rear wheel steering system includes the following steps: (1) Signal acquisition and preprocessing: Start the signal acquisition cycle, acquire steering trend signals such as vehicle speed, steering wheel angle, and yaw rate, and perform filtering and reliability detection; if the signal is lost or unreliable, the system enters a forced lockout state.

[0084] (2) Driving condition judgment and advanced function optimization: The driving condition (low-speed turning / high-speed lane change, high-speed driving / fine-tuning, etc.) is judged based on the collected signals, and advanced function optimization is performed. Advanced function optimization includes the following: a. Dynamic response preheating: When monitoring the turning trend, the electromagnetic coil of the locking device is pre-magnetized in milliseconds so that the coil has formed a stable magnetic field before the unlocking command takes effect. After the command is issued, the locking end ring is directly driven to slide. b. Adaptive driving mode: Sport or Comfort mode is selected; c. Adaptive to road conditions: Increase the locking threshold under adverse working conditions.

[0085] (3) Locking or unlocking control: In low-speed cornering or high-speed lane changing scenarios: an unlocking command is issued, and steering control is executed. The electromagnetic coil drive voltage is quantified by constructing a standard second-order system model of the locking device. Displacement of the locking end ring The dynamic relationship is used to calculate the optimal driving voltage, so that the locking end ring slides smoothly along the guide key and avoids impact from the protruding teeth.

[0086] For high-speed driving or other conditions requiring fine-tuning: a lock-up command is issued to execute lock-up control. A trial pulse is injected, and residual diagnosis is performed based on the Lumberjack state observer. If the lock-up is confirmed to be successful, the lock-up state is maintained. At this time, the drive output module immediately cuts off the power supply to the electromagnetic coil, and the lock-up is maintained only by the mechanical structure, thereby achieving zero-energy maintenance of the lock-up state. If the lock-up fails, a fault-tolerant control strategy is activated.

[0087] (4) Fault diagnosis and fault tolerance control: When locking fails, the fault code is recorded and the fault tolerance control mechanism is activated. a. Level 1 alarm: Restricts rear wheel steering function, maintains the locked state and prompts for maintenance. This step also relies on the preload of the return spring and does not consume power, thus achieving zero power consumption for static locking of the locking device. b. Level 2 alarm: Limits maximum speed and reminds drivers to drive cautiously; c. Fault codes are reported to the cloud via the CAN bus, and the system status is output.

[0088] The overall architecture and control process of the rear-wheel steering system provided in this embodiment have the following beneficial effects: (1) The system architecture is highly collaborative and energy efficient: Through the linkage mechanism of signal input, processing decision, drive output and actuator, the locking command is quickly responded to. The pre-magnetization technology reduces the unlocking delay to the millisecond level and the control delay is reduced by more than 30%. The normally closed design of the locking device achieves zero static power consumption.

[0089] (2) The control process is adaptive and has strong fault tolerance: intelligent identification of working conditions and dynamic and precise adjustment of locking strategy according to working conditions; through multiple fault diagnosis and failure protection, the functional safety level of the system is significantly improved.

[0090] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A control method for a rear wheel steering system with a locking device, the rear wheel steering system comprising a steering gear and a steering motor, the steering gear comprising a housing, the housing having an internal mounting cavity, and the mounting cavity having a steering input shaft, a lead screw shaft and an output shaft that are connected in a transmission manner; The steering gear also includes an end cap and a locking device; the end of the housing is provided with an opening communicating with the mounting cavity, and the end cap is disposed at the opening; the locking device is disposed between the lead screw shaft and the end cap, and the locking device is used to realize the mutual locking or unlocking of the lead screw shaft and the end cap; The locking device includes a locking element, a mating element, and a driving element. The locking element is disposed on the lead screw shaft, the mating element is disposed on the end cover, and the driving element is used to drive the locking element and the mating element to lock or unlock each other. The driving element includes an electromagnetic coil and a return spring. The electromagnetic coil is disposed in the mounting cavity, and the return spring is disposed between the electromagnetic coil and the locking element or the mating element. Its features are: The control method for the rear-wheel steering system includes the following steps: Step S1: Based on the vehicle's two-degree-of-freedom model and according to the dynamic equilibrium logic, establish the dynamic equations of the rear-wheel steering system that characterize the influence of the locking device on the system's stiffness and damping. The specific expression is as follows: ； In the formula: This represents the total moment of inertia of the output shaft. This refers to the acceleration of the rear wheels; For the system's equivalent damping; The angular velocity of the rear wheel; The equivalent stiffness of the system; This refers to the angular displacement of the rear wheel; This refers to the motor torque of the rear wheel steering motor; External disturbance torque; The locking torque of the locking device; Step S2: Construct a standard second-order system model of the locking device and calculate the driving voltage of the electromagnetic coil. The transfer function formula for a standard second-order system model is: ; In the formula: The transfer function for a standard second-order system model; For the Laplace transform of the locking end ring displacement; This is the Laplace transform of the driving voltage of the electromagnetic coil; This represents the system's steady-state gain. It is the undamped natural frequency; The system damping ratio; Step S3: Integrate the stiffness adjustment of the locking device, the electromagnetic drive, and the dynamic characteristics of the rear wheel steering system into a state-space model. Optimize the control input using an LQR controller to achieve the equivalent stiffness of the locking device. The operating conditions are adaptively adjusted; the state equation of the state-space model is: ； In the formula: This refers to the armature voltage of the steering motor. The voltage of the electromagnetic coil; The torque constant of the steering motor; For the armature resistance of the steering motor; External disturbance torque; The output equation of the state-space model is: ； In the formula: This represents the measured angular displacement. For actual measurement of motor current ; This is the back EMF / current coefficient; Voltage coefficient; The expression for the LQR controller is: ; In the formula: The objective function is... This is the system state vector; To control the input vector; The state weighting matrix; To control the weighting matrix.

2. The control method for a rear wheel steering system with a locking device as described in claim 1, characterized in that: The locking member is axially movable on the lead screw shaft via the driving member, and the locking member is provided with a plurality of locking teeth; the mating member is fixedly disposed on the end cover, and the mating member is provided with a plurality of mating teeth that mesh with the locking teeth.

3. The control method for a rear wheel steering system with a locking device as described in claim 2, characterized in that: The locking component is a locking end ring sleeved on the outer wall of the lead screw shaft, and the mating component and the end cap are integrally formed.

4. The control method for a rear wheel steering system with a locking device as described in claim 3, characterized in that: The locking tooth is a convex tooth located at the end of the locking end ring, and the mating tooth is a concave tooth located at the end of the end cap.

5. The control method for a rear wheel steering system with a locking device as described in claim 2, characterized in that: The outer wall of the lead screw shaft is provided with an axially extending guide key, and the locking member is provided with a keyway that cooperates with the guide key.

6. The control method for a rear wheel steering system with a locking device as described in claim 1, characterized in that: The control method further includes the following steps: Step S4: Construct a Luneburg state observer based on the state-space model from step S3, and predict the current by observing the steering motor. Compared with the measured current residual This enables fault diagnosis of the locking device.

7. The control method for a rear wheel steering system with a locking device as described in claim 1, characterized in that: In step S2, the steady-state gain of the system Undamped natural frequency And system damping ratio The calculation formula is: ； In the formula: The current-force coefficient; This is the stiffness coupling coefficient; The coil resistance; The radius of the lead screw shaft.

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