A four-station double closed-loop electrically-controlled hydraulic steering system based on fork feedback and a control method thereof

Abstract

The present application relates to the technical field of vehicle steering system, and particularly relates to a four-station double closed loop electric hydraulic steering system based on feedback of a fork and a control method, through cooperation of a pressure inner ring and a rotation angle outer ring, double closed loop collaborative control is realized. The pressure inner ring ensures stable hydraulic pressure without fluctuation, and the rotation angle outer ring relies on feedback of a terminal fork posture to realize accurate correction of wheel rotation angle and dynamic compensation of four-wheel positioning parameters, synchronous linkage work of two control loops effectively compensates steering errors caused by hydraulic hysteresis, mechanical clearance and component wear, and improves angle control precision and dynamic response speed in the vehicle steering process. The structure can adapt to various driving conditions such as low-speed steering of the vehicle, high-speed straight driving fine adjustment, curve steering, intelligent auxiliary lane centering, fault emergency driving and the like, effectively reduces steering following errors, suppresses vehicle deviation and abnormal tire wear, and significantly improves vehicle steering stability, chassis posture consistency and steering comfort.

Description

Technical Field

[0001] This invention relates to the field of vehicle steering system technology, and in particular to a four-position dual closed-loop electro-hydraulic steering system and control method based on shift fork feedback. Background Technology

[0002] Electro-hydraulic steering, with its advantages of high output torque and strong load-bearing capacity, is widely used in heavy-duty vehicles such as commercial vehicles and engineering vehicles. Existing electro-hydraulic steering systems use an electronic controller to control a servo proportional solenoid valve based on vehicle speed, steering wheel torque, and steering angle signals to achieve adjustable control of the power steering hydraulic pressure. Most of these solutions only use pressure sensors to form a single closed-loop hydraulic pressure system, providing feedback adjustment only for the hydraulic power steering pressure. Due to factors such as steering mechanism clearance, friction, and hydraulic pressure hysteresis, relying solely on the pressure closed loop cannot obtain the true output posture of the wheels. This not only results in a large deviation between the target steering wheel angle and the actual wheel angle, leading to poor tracking performance, but also fails to simultaneously calculate the four wheel alignment parameters: camber, toe, caster, and kingpin inclination. Furthermore, it cannot monitor and dynamically compensate for alignment parameter offsets caused by chassis wear in real time. Long-term use can easily lead to vehicle pulling to one side, uneven tire wear, and decreased steering return performance.

[0003] Currently, while some technologies incorporate steering feedback, the acquired signals are all taken from the steering wheel input, only obtaining the input-side steering angle. This fails to reflect the actual wheel steering angle at the end of the steering gear and linkage transmission, cannot eliminate accumulated transmission chain errors, and cannot achieve precise closed-loop correction at the wheel end. Furthermore, existing solenoid valves often lack a complete four-position four-way structure, lacking independent straight-line center unloading lockout and fail-safe protection positions, resulting in high system energy consumption, poor straight-line stability, and insufficient fault redundancy. In addition, traditional electro-hydraulic steering is only compatible with manual steering operation, unable to continuously output smooth, small-amplitude active steering torque, making it difficult to match the lateral assistance requirements of Lane Centering Control (LCC) intelligent driving, thus limiting its adaptability to intelligent scenarios.

[0004] Therefore, there is an urgent need to develop a four-position dual closed-loop electro-hydraulic steering system and control method based on shift fork feedback, so as to effectively improve steering control accuracy, vehicle straight-line stability, fault safety and intelligent driving adaptability. Summary of the Invention

[0005] The main objective of this invention is to provide a four-position dual closed-loop electro-hydraulic steering system and control method based on shift fork feedback. This electro-hydraulic steering system and control method effectively solve the problems mentioned in the background technology, such as low steering angle control accuracy, inability to eliminate transmission errors, inability to perceive and compensate four-wheel alignment parameters in real time, difficulty in balancing stability and response speed in straight driving conditions, insufficient fault safety redundancy, and poor adaptability to active steering in intelligent driving.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A four-position dual closed-loop electro-hydraulic steering system based on shift fork feedback includes a steering wheel, steering column, angle and torque sensors, feedback shift fork, angle detection element, recirculating ball steering gear, first pressure sensor, second pressure sensor, steering linkage, wheel, electronic controller, accumulator, one-way valve, hydraulic pump, relief valve, servo proportional solenoid valve, and vehicle speed signal acquisition unit. The steering wheel is fixedly mounted on the top of the steering column, and the angle and torque sensors are mounted on the outside of the steering column to collect the angle and torque signals of the driver's steering operation in real time. The vehicle speed signal acquisition unit is used to obtain the real-time vehicle speed. The angle and torque sensors and the vehicle speed signal acquisition unit are electrically connected to the electronic controller through the vehicle's CAN bus, transmitting the operating condition signals to the electronic controller in real time for processing. The electronic controller can be connected to the vehicle's intelligent driving system to receive lane centering control commands and lane departure parameters. The hydraulic pump provides pressurized oil to the entire hydraulic circuit. The hydraulic pump is connected in sequence to a check valve and an accumulator. The check valve is used to prevent hydraulic oil from flowing back and protect the hydraulic pump from reverse impact. The accumulator adopts a bladder-type structure with a rated pressure matched to the system. It is used to store pressurized oil, absorb oil pressure pulsations in the circuit, and ensure a continuous and stable oil supply pressure. The relief valve is arranged in parallel on the main hydraulic oil supply line to monitor the system oil pressure in real time. When the oil pressure exceeds the safety threshold, it automatically overflows to release pressure, limiting the maximum working oil pressure of the system and realizing overload protection. The pressure port P of the servo proportional solenoid valve is connected to the end of the main hydraulic oil supply line. The servo proportional solenoid valve has four independent working positions, corresponding to the left steering working position, right steering working position, straight driving center position and fail-safe position respectively. The working ports A and B of the servo proportional solenoid valve are respectively connected to the first power steering chamber and the second power steering chamber of the circulating ball steering gear through high-pressure oil pipes.

[0007] The recirculating ball steering gear is equipped with a screw-ball transmission pair and a rocker arm shaft. The output end of the rocker arm shaft is hinged to the steering linkage through a ball joint structure. The two ends of the steering linkage are respectively connected to the steering knuckles of the two wheels. After the pressurized oil is introduced into the corresponding power steering oil chamber, it pushes the piston and screw mechanism inside the steering gear to move, causing the rocker arm shaft to swing back and forth around its own axis. In turn, the steering linkage pushes and pulls the wheel to deflect around the kingpin axis, thus completing the vehicle steering action.

[0008] The outer end of the recirculating ball steering gear is provided with a shoulder and a flat keyway. The feedback shift fork is circumferentially positioned by the flat key and achieves backlash-free transmission with interference fit. The outer side of the feedback shift fork is axially pressed and fixed by a lock nut to ensure that there is no relative rotation or axial movement between the two under long-term driving and repeated impact of the vehicle. The corner detection element is arranged on the side of the feedback shift fork and adopts the magnetoelectric non-contact detection principle. The sensor housing is fixedly installed on the end cover of the steering gear housing. A high-performance permanent magnet is embedded in the free end of the feedback shift fork. The permanent magnet swings synchronously with the shift fork. The sensor outputs an absolute angular displacement signal by sensing the change in the angle of the spatial magnetic field.

[0009] The electronic controller has a built-in steering suspension kinematic coupling model calibrated on a vehicle bench. It pre-stores parameters such as rocker arm shaft length, steering link length, steering knuckle kingpin axis spatial coordinates, and suspension hardpoint position parameters. Based on a single angle signal from the feedback shift fork, it simultaneously calculates the actual wheel angle and four positioning parameters. The specific calculation logic is as follows: First, the actual steering angle of the wheel is calculated. After the electronic controller obtains the absolute angle signal of the feedback shift fork, it first subtracts the initial zero position offset to obtain the actual swing angle of the rocker arm shaft. Combined with the arm length from the center of rotation of the rocker arm shaft to the hinge point of the tie rod, the axial push-pull displacement of the steering tie rod is calculated using the arc length formula. Then, based on the geometric dimensions of the steering trapezoidal mechanism and combined with the Ackermann steering characteristics, the actual steering wheel angles of the left and right wheels around the kingpin are calculated respectively. The rationality of the difference in steering angles between the left and right wheels is verified, and abnormal values ​​caused by signal interference are eliminated. Secondly, wheel camber angle calculation: Based on the geometric coupling characteristics of kingpin inclination, the wheel camber angle will change sinusoidally with the steering angle during the wheel deflection around the kingpin. The electronic controller combines the kingpin inclination angle calibration value with the real-time wheel angle and calculates the real-time change of camber angle during the steering dynamic process through spatial projection relationship. The static camber reference value under straight driving state is superimposed to obtain the actual wheel camber angle under the current working condition. Third, toe angle calculation; the toe angle is determined by the difference in steering angle between the left and right wheels and the included angle of the steering trapezoidal arm. The electronic controller calculates the real-time toe angle under the current steering state by combining the difference in the actual steering angle of the left and right wheels with the design length and installation angle of the steering trapezoidal arm; in straight driving state, the system accurately monitors the offset of the static toe value by capturing the small angle fluctuations near the zero position of the shift fork. Fourth, the calculation of the caster angle and the kingpin inclination angle: the electronic controller combines the steering torque feedback and the wheel angle change rate, and based on the return torque characteristics generated by the caster angle, it back-derives the real-time value of the equivalent caster angle; at the same time, by decomposing the steering knuckle space angle in the longitudinal and lateral planes and combining the suspension hard point coordinates, the actual value of the kingpin inclination angle is calculated.

[0010] The electronic controller compares the four positioning parameters calculated in real time with the standard parameter range calibrated at the vehicle's factory, and calculates the parameter deviation. When the vehicle is in a straight-line state, and the positioning parameters show a static offset that is within the hydraulically correctable range, the electronic controller controls the servo proportional solenoid valve to perform micro-amplitude high-frequency switching between the left and right positions, outputting a small pressure difference to the first and second power steering chambers. This outputs a micro-level deflection to the steering knuckle via the steering linkage, dynamically compensating for the static offset of the toe angle and camber angle, and correcting the positioning deviation caused by mechanism wear and tire deformation. When the vehicle is in a steering condition, the electronic controller dynamically adjusts the power steering hydraulic pressure amplitude based on the real-time values ​​of the caster angle and kingpin inclination angle to compensate for the steering torque fluctuations caused by the kingpin geometry and optimize the steering feel; at the same time, it corrects the dynamic camber and toe-in changes during the steering process to ensure that the tire contact area is always in the optimal state and reduce abnormal tire wear.

[0011] The first pressure sensor and the second pressure sensor are respectively installed on the oil inlet lines of the first power steering oil chamber and the second power steering oil chamber. They collect the working oil pressure of the first power steering oil chamber and the second power steering oil chamber in real time and feed it back to the electronic controller to form a pressure inner closed-loop control. Combined with the wheel angle feedback from the shift fork and the four positioning parameters, they form a steering attitude outer loop, thus forming a dual closed-loop collaborative control system.

[0012] The four working positions and corresponding operating conditions of the servo proportional solenoid valve are as follows: Operating Condition 1: Torque > 0, left steering position; When the electronic controller outputs a positive control current, and the current value is greater than the mid-position dead zone threshold, the valve core overcomes the return spring force and moves to the left, switching to the left steering position; In this position, the pressure port P and the working port A are connected, and high-pressure oil flows through the pipeline into the first power steering chamber of the recirculating ball steering gear; the working port B and the return port T are connected, and the oil in the second power steering chamber flows back to the oil tank to complete the pressure relief; the high-pressure oil pushes the screw ball mechanism inside the steering gear to drive the rocker arm to swing to the left, and drives the wheel to turn to the left through the steering linkage. The steering angle detection element collects the deflection angle of the shift fork in real time and sends the signal back to the electronic controller to calculate the actual left turning angle of the wheel; the first pressure sensor collects the real-time oil pressure of the first power steering chamber and feeds it back to the electronic controller, forming a pressure inner loop, which is then processed by the PID controller. The system adjusts the algorithm to stabilize the power steering output pressure; the outer ring of the steering wheel compares the target left-turn angle with the actual left-turn angle fed back by the shift fork, calculates the steering angle deviation, dynamically corrects the solenoid valve control current and valve opening, and compensates for steering errors caused by mechanical backlash and hydraulic lag; throughout the steering process, the system simultaneously calculates the camber angle, toe angle, caster angle, and kingpin inclination angle under left-turn conditions, and fine-tunes the power steering oil pressure based on the dynamic values ​​of the positioning parameters to optimize steering feel and tire contact with the ground.

[0013] Operating Condition 2: Torque = 0, the solenoid valve spool returns to the center position, the vehicle maintains straight-line driving without steering input; the driver holds the steering wheel with no steering input, the torque sensor output signal returns to zero, the electronic controller outputs zero drive current, and the solenoid valve is stably held in the straight-line center position under the action of the return springs on both sides; this straight-line center position uses an O-type function, with pressure port P, return port T, working port A, and working port B all completely sealed and isolated, the oil inside the first and second power steering oil chambers is completely locked and sealed, the oil chambers always maintain residual oil pressure, and the steering piston is hydraulically locked and constrained; this structure can completely block the road surface. The reverse impact load generated by bumps prevents irregular wheel swaying and slight wobble, significantly improving the vehicle's high-speed straight-line stability. At the same time, with the pressure port P closed, the hydraulic pump continuously maintains the system's preset oil pressure reserve. Once a steering control command is received, the oil circuit can instantly establish a working pressure difference, significantly improving the assist response speed. During the vehicle's constant-speed straight-line movement, the system continuously reads the shift fork zero-position angle signal and monitors the static values ​​of the four-wheel alignment. When a slight deviation in the toe angle or camber angle is detected, the controller controls the solenoid valve to output a small oil pressure difference to dynamically calibrate the alignment parameters, always maintaining the chassis's standard posture.

[0014] Operating Condition 3: Torque < 0, right steering position; when the electronic controller outputs reverse control current, the valve core moves to the right to switch to the right steering position; in this position, the pressure port P and the working port B are connected, and high-pressure oil enters the second power steering chamber; the working port A is connected to the return port T, and the first power steering chamber is connected to the return oil circuit for pressure relief; the high-pressure oil pushes the internal mechanism of the steering gear to drive the rocker arm to swing to the right axially, and drives the wheel to turn to the right through the steering linkage. The angle detection element collects the fork swing angle and transmits it back to calculate the actual right turning angle of the wheel; the second pressure sensor collects the oil pressure signal of the second power steering chamber and feeds it back to the electronic controller, and the pressure inner loop stabilizes the power steering oil pressure; the angle outer loop corrects the output current of the solenoid valve according to the right turning angle deviation to compensate for the right turning angle error caused by mechanical clearance and hydraulic hysteresis; during the right turn, the system synchronously calculates the dynamic values ​​of the four positioning parameters, corrects the power steering characteristics as needed, and ensures that the positioning parameters are optimal during the steering process.

[0015] Operating Condition 4: Fail-Safe Position; When the electronic controller fails, the control circuit is broken, or the vehicle loses power, the solenoid valve control current disappears, and the reset spring pushes the valve core to switch to the fail-safe position. In this position, the pressure port P is completely closed, cutting off the high-pressure oil supply. Working ports A and B are simultaneously connected to the return port T. The first and second power steering chambers of the recirculating ball steering gear are all connected to the oil tank for pressure relief, releasing the hydraulic lock and entering a floating state. The hydraulic power steering is completely disabled. At this time, the driver can manually control the vehicle steering through the pure mechanical transmission link of the steering wheel, steering column, and recirculating ball steering gear. The accumulator briefly releases the stored pressure oil, providing emergency assistance for tens of seconds to help the driver smoothly pull over to the side of the road. In the fault state, the feedback shift fork, angle detection element, and the first and second pressure sensors can still continuously collect signals. The backup power supply of the electronic controller can maintain fault monitoring and fault code reporting for a short time, reminding the driver to have it repaired in time.

[0016] Furthermore, when the vehicle activates the intelligent driving lane centering control function, the vehicle's intelligent driving system identifies lane markings through the onboard sensing unit, calculates the vehicle's lateral offset and heading deviation relative to the lane centerline, and sends correction commands to the electronic controller; the electronic controller employs a closed-loop PID controller. The control algorithm takes lane departure and heading deviation as inputs and the actual wheel angle collected by the feedback shift fork as feedback quantity to calculate the required active correction steering torque and corresponding control current. During the control process, the electronic controller controls the servo proportional solenoid valve to make high-frequency micro-adjustments between the left and right steering positions. By adjusting the duty cycle, it outputs a continuous and stable small hydraulic assist torque, actively driving the steering linkage to fine-tune the wheel deflection angle, counteracting the lane departure tendency caused by road cross slope and crosswind, so that the vehicle continues to drive in the center of the lane. During the lane centering correction process, the system simultaneously calculates and dynamically corrects four positioning parameters to ensure optimal wheel posture during active steering and improve stability during centering. When the steering angle and torque sensors detect that the driver intervenes in steering and the operating torque exceeds the set threshold, the system immediately stops the active correction torque output, and the solenoid valve switches back to the normal assist mode. The entire switching process is smooth and shock-free, ensuring driving safety.

[0017] Furthermore, the vehicle speed signal acquisition unit is installed at the output shaft of the vehicle's transmission. It calculates the real-time vehicle speed by acquiring the output shaft rotation speed pulse signal, achieving high detection accuracy and strong adaptability.

[0018] Furthermore, the corner detection element adopts a magnetoelectric non-contact angular displacement sensor, which has the characteristics of being resistant to vibration and oil interference, and can work stably for a long time in the harsh environment of the vehicle chassis.

[0019] Furthermore, the steering suspension kinematic coupling model built into the electronic controller is generated through vehicle bench calibration, and can adaptively switch parameter mapping tables according to vehicle load conditions to ensure the calculation accuracy under different loads.

[0020] The present invention also provides a control method for the above-mentioned electro-hydraulic steering system, the specific steps of which are as follows: The first step is multi-source signal synchronous acquisition: When the system is running, the angle and torque sensors acquire the angle and torque signals of the driver's steering operation in real time, the vehicle speed signal acquisition unit acquires the real-time vehicle speed, the angle detection element acquires the feedback shift fork's absolute swing angle, the first pressure sensor and the second pressure sensor acquire the working oil pressure of the corresponding power steering chamber, the lane centering control command and lane departure parameters are input by the vehicle's intelligent driving system, and all signals are synchronously transmitted to the electronic controller via the CAN bus with timestamps to ensure that the signal time deviation is within the allowable range; The second step is to calculate the wheel angle and positioning parameters: Based on the angular displacement signal of the feedback shift fork, the electronic controller, combined with the pre-calibrated steering suspension kinematic coupling model, calculates the real-time values ​​of the actual wheel steering angle, wheel camber angle, toe angle, kingpin caster angle, and kingpin inclination angle in sequence, and verifies the rationality of the calculation results and removes abnormal interference data. The third step is working condition identification and work position switching: The electronic controller determines the current steering working condition based on the steering operation signal, system operating status, and lane centering function start / stop status, and controls the servo proportional solenoid valve to smoothly switch to the corresponding working position, outputting basic hydraulic power assist that matches the working condition. The fourth step is dual closed-loop dynamic correction: relying on the feedback of oil pressure on both sides to complete the pressure inner loop stabilization and control, ensuring stable output of power assist oil pressure; comparing the target angle with the standard positioning parameters to complete the angle attitude outer loop correction, fine-tuning the output pressure difference of the solenoid valve, and compensating for mechanical transmission errors and positioning parameter offsets. Step 5, Lane Centering Cooperative Control: When the lane centering function is activated, based on the lane lateral offset and heading deviation, the solenoid valve is controlled to make high-frequency micro-adjustments between the left and right steering positions, outputting continuous micro-assistance to maintain the vehicle's lane-centered driving; when the driver's active steering operation is detected and the torque exceeds the threshold, the system actively corrects and automatically exits, returning to the normal manual assist mode. The sixth step involves the system continuously executing the complete process of signal acquisition, parameter calculation, workstation switching, and closed-loop correction, adapting to various driving scenarios including manual steering, straight-line driving, emergency response, and intelligent assisted driving.

[0021] The beneficial effects of this invention are as follows: The four-position dual-closed-loop electro-hydraulic steering system and control method based on shift fork feedback provided by this invention have the following technical features and advantages in practical use: 1. This invention uses a feedback shift fork as the core feedback carrier. It can simultaneously calculate the actual wheel angle and the full set of four-wheel alignment parameters through a single end angle acquisition structure, without the need to add multiple sets of sensors. At the same time, it relies on the feedback data of the shift fork to realize dynamic compensation of positioning parameters, effectively alleviate the problems of deviation and uneven tire wear caused by mechanism wear, and extend the service life of steering suspension. 2. This invention utilizes a four-position servo proportional solenoid valve structure to fully cover all operating scenarios, including left and right steering, straight-line locking, and emergency response. The straight-line center position employs an O-type mechanism, with full oil port closure to achieve hydraulic locking of the power steering oil chamber. When the steering command is triggered, a working pressure differential can be quickly established, balancing high-speed straight-line stability with steering response speed. The fail-safe position can automatically switch to emergency mode in case of electronic control failure, and, in conjunction with the accumulator, ensures emergency steering capability through short-term oil supply. The system has high safety redundancy and strong operational reliability. 3. This invention relies on closed-loop feedback of the shift fork angle and high-frequency micro-adjustment of the solenoid valve to directly realize active steering control for lane centering. It can adapt to the lateral assistance requirements of intelligent driving without the need for additional electric power assist or other actuators. The active correction process uses the actual turning angle at the end as the feedback reference, resulting in high control accuracy and stable torque output. When the driver intervenes, the manual driving mode can be seamlessly switched, effectively expanding the application scenarios and functional boundaries of the electro-hydraulic steering system. 4. This invention adopts a dual closed-loop architecture of pressure inner ring + shift fork feedback steering angle attitude outer ring, which can simultaneously compensate for hydraulic hysteresis, mechanical backlash and positioning offset, significantly improving steering angle control accuracy and vehicle driving stability, and is suitable for commercial vehicles, engineering vehicles and intelligent driving models. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall hydraulic and control principle structure of the electro-hydraulic steering system with dual closed-loop feedback of the present invention; Figure 2 This is a logic block diagram of the four-position operation of the servo proportional solenoid valve of the present invention. Figure 3 This is a schematic diagram of the overall vehicle steering mechanism layout structure of the present invention; Explanation of reference numerals in the attached diagram: 1-Steering wheel; 2-Steering column; 3-Angle and torque sensor; 4-Feedback shift fork; 4-1-Angle detection element; 5-Recirculating ball steering gear; 5-1-First pressure sensor; 5-2-Second pressure sensor; 5-3-First power steering chamber; 5-4-Second power steering chamber; 6-Steering linkage; 7-Wheel; 8-Electronic controller; 9-Accumulator; 10-Check valve; 11-Hydraulic pump; 12-Relief valve; 13-Servo proportional solenoid valve; 13-1-Return port T; 13-2-Pressure port P; 13-3-Working port B; 13-4-Working port A; 14-Vehicle speed signal acquisition unit; 15-Rocker arm shaft. Detailed Implementation

[0023] Specific Embodiment 1: To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that: In the present invention, unless otherwise specified, all embodiments and preferred methods mentioned herein can be combined to form new technical solutions. In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions. The "scope" disclosed in the present invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively. Unless otherwise stated, the technical and scientific terms used herein have the same meaning as those skilled in the art.

[0024] As per the instruction manual Figure 1 Instruction manual attached Figure 3 As shown, this embodiment discloses a four-position dual closed-loop electro-hydraulic steering system based on shift fork feedback. The system mainly includes a steering wheel (1), a steering column (2), a steering angle and torque sensor (3), a feedback shift fork (4), a steering angle detection element (4-1), a recirculating ball steering gear (5), a steering linkage (6), a wheel (7), an electronic controller (8), an accumulator (9), a one-way valve (10), a hydraulic pump (11), a relief valve (12), a servo proportional solenoid valve (13), and a vehicle speed signal acquisition unit (14). The recirculating ball steering gear (5) has a first power assist oil chamber (5-3) and a second power assist oil chamber inside. The oil chamber (5-4) is equipped with a first pressure sensor (5-1) and a second pressure sensor (5-2) on its respective hydraulic circuit. The hydraulic oil supply unit is composed of a hydraulic pump (11), an accumulator (9), a check valve (10) and an overflow valve (12), which provides high-pressure oil to the entire steering hydraulic circuit. The electronic controller (8) communicates with the vehicle bus to obtain the real-time vehicle speed signal. It can also access the vehicle intelligent driving system signal to obtain the relevant working condition parameters of lane centering and lane departure, providing comprehensive working condition basis for graded adjustment of power assist, dynamic correction of four-wheel alignment parameters and intelligent active steering control.

[0025] The angle and torque sensor (3) is fixedly mounted on the steering column (2) and can collect the target angle signal and operating torque signal output by the driver operating the steering wheel (1) in real time. The rotation of the steering wheel (1) is transmitted to the input end of the recirculating ball steering gear (5) through the steering column (2). The signal output end of the angle and torque sensor (3) is electrically connected to the electronic controller (8) and transmits the angle signal and torque signal to the electronic controller (8) as the input signal for steering assist adjustment. The vehicle speed signal acquisition unit (14) is fixedly installed on the vehicle transmission output shaft housing. The vehicle speed signal acquisition unit (14) completes the conversion of the real-time driving speed of the whole vehicle by acquiring the rotation pulse signal of the transmission output shaft and transmits the vehicle speed electrical signal to the electronic controller (8) to provide real-time operating condition parameter support for system assist adjustment and steering accuracy correction.

[0026] In the hydraulic oil supply unit, the hydraulic pump (11) serves as the power supply component of the entire hydraulic system. Its inlet end is connected to the oil tank, and its outlet end is connected in sequence to the check valve (10) and the accumulator (9), and finally connected to the pressure port P (13-2) of the servo proportional solenoid valve (13), forming the main oil supply circuit of the system. Among them, the check valve (10) can effectively block the backflow of high-pressure hydraulic oil and avoid the high-pressure oil reverse impact damaging the hydraulic pump (11). The accumulator (9) is arranged in parallel in the main oil supply circuit. It can absorb the oil pressure pulsation generated during the operation of the hydraulic pump (11), stabilize the system oil supply reference pressure, and at the same time, it can provide pressure supplementation oil supply in the case of short-term insufficient pressure supply of the hydraulic pump or failure pressure loss. It can also release the stored oil in the case of system failure to provide emergency assistance, ensure the continuous output of hydraulic power of the steering system, and improve driving safety. The overflow valve (12) is connected in parallel between the main hydraulic oil supply circuit and the return oil line to limit the maximum working pressure of the hydraulic system and realize system overload protection.

[0027] The signal output terminal of the electronic controller (8) is electrically connected to the electrical control terminal of the servo proportional solenoid valve (13). The electronic controller (8) can output a continuously adjustable DC current signal, and the magnitude of the output current is linearly related to the flow area of ​​the valve port of the servo proportional solenoid valve (13). By precisely controlling the output current, the stepless adjustment of the valve port opening of the servo proportional solenoid valve (13) can be achieved. The hydraulic ports of the servo proportional solenoid valve (13) are connected to the first power steering chamber (5-3) and the second power steering chamber (5-4) of the recirculating ball steering gear (5). During vehicle steering, the servo proportional solenoid valve (13) switches the oil circuit on / off state according to the steering conditions. When the vehicle turns left, high-pressure oil enters the first power steering chamber (5-3) and the second power steering chamber (5-4) returns oil to relieve pressure. When the vehicle turns right, high-pressure oil enters the second power steering chamber (5-4) and the first power steering chamber (5-3) returns oil to relieve pressure. By precisely adjusting the valve port opening, the oil flow rate and working pressure difference of the power steering chamber can be changed, thereby achieving precise and adjustable output of steering power torque.

[0028] A first pressure sensor (5-1) and a second pressure sensor (5-2) are installed on the hydraulic circuit. The first pressure sensor (5-1) is arranged on the oil line connecting the first power steering chamber (5-3) to collect the oil pressure of one side of the steering condition. The second pressure sensor (5-2) is arranged on the oil line connecting the second power steering chamber (5-4) to collect the oil pressure of the other side of the steering condition. The oil pressure analog signals collected by the two sets of pressure sensors are continuously transmitted to the electronic controller (8) to provide real-time oil pressure data for the closed-loop control of the hydraulic pressure inner loop.

[0029] The recirculating ball steering gear (5) uses a triple fixing method of circumferential positioning with a flat key, nested interference fit, and axial clamping with a locking nut to rigidly assemble the feedback shift fork (4). There is no relative rotation, axial movement, or assembly gap between the feedback shift fork (4) and the input shaft. An angle detection element (4-1) is provided on the feedback shift fork (4). The angle detection element (4-1) adopts a magnetoelectric non-contact detection structure, which has no mechanical wear, strong anti-interference ability, and can stably detect the deflection angle of the feedback shift fork (4). The angle detection element (4-1) is electrically connected to the electronic controller (8) and transmits the collected shift fork swing angle signal to the electronic controller (8) in real time. The rocker arm shaft (15) at the output end of the recirculating ball steering gear (5) is connected to the steering linkage (6) through a ball joint structure. The two ends of the steering linkage (6) are connected to the steering knuckles of the wheels (7). The recirculating ball steering gear (5) drives the rocker arm shaft (15) to swing, which drives the wheels (7) through the steering linkage (6) to achieve deflection and steering.

[0030] Specifically, the electronic controller (8) has a pre-embedded steering-suspension kinematic coupling model calibrated on a vehicle bench. The model contains core calibration data such as rocker arm shaft rotation radius, steering link length, steering trapezoidal parameters, kingpin spatial coordinates, and suspension hardpoint positions. The electronic controller (8) can rely on the original signal of a single shift fork angle collected by the steering angle detection element (4-1) and combine it with the kinematic coupling relationship to calculate in real time the five core attitude parameters: actual wheel steering angle, wheel camber angle, vehicle toe angle, kingpin caster angle, and kingpin inclination angle. At the same time, it compares the real-time calculated four-wheel alignment parameters with the factory standard calibration range to accurately calculate parameter offset deviations, providing data support for subsequent steering error compensation and dynamic correction of alignment parameters.

[0031] When the car needs to turn, the steering system of the present invention starts to work. The driver operates the steering wheel (1) to turn. The angle and torque sensor (3) converts the angle and direction of the steering wheel (1) into corresponding electrical signals and sends them to the electronic controller (8). The electronic controller (8) also receives the vehicle speed signal. After processing the received signal, the electronic controller (8) outputs a current signal to control the servo proportional solenoid valve (13). The servo proportional solenoid valve (13) adjusts the pressure and flow of the output hydraulic oil. The pressurized oil enters the first power assist chamber (5-3) or the second power assist chamber (5-4) of the recirculating ball steering gear (5), driving the internal mechanism of the recirculating ball steering gear (5) to move, causing the rocker arm shaft (15) to swing. The rocker arm shaft (15) drives the wheel (7) through the steering linkage (6) to complete the steering action.

[0032] While the feedback fork (4) feeds back the wheel angle and four-wheel alignment posture parameters to the electronic controller (8), the first pressure sensor (5-1) and the second pressure sensor (5-2) collect the oil pressure signals of the corresponding recirculating ball steering gear (5) power steering oil chamber and feed them back to the electronic controller (8). The angle and posture signal feedback formed by the feedback fork (4) and the angle detection element (4-1) constitute the outer loop of the angle; the oil pressure feedback from the pressure sensors (5-1) and (5-2) constitutes the inner loop of the pressure, forming a dual closed-loop collaborative control architecture.

[0033] The servo proportional solenoid valve (13) is a shared hydraulic actuator in the dual closed-loop control system of pressure inner loop and angle outer loop. It can synchronously respond to oil pressure stabilization and adjustment commands, angle deviation correction commands, and four-wheel alignment parameter correction commands to achieve dual closed-loop coordinated control. This allows the hydraulic power assist torque to be precisely coupled with the mechanical torque manually input by the driver, smoothly and accurately driving the steering linkage and wheels to complete the steering action. At the same time, the electronic controller (8) reserves an intelligent driving signal interface, which can stably connect to the vehicle lane centering control working signal and lane departure parameters to realize intelligent active steering assistance function.

[0034] The target power assist pressure required for the current working condition is calculated based on the real-time vehicle speed, steering torque and target angle. It is then compared in real time with the actual oil pressure collected by the first pressure sensor (5-1) and the second pressure sensor (5-2). When the actual oil pressure is lower than the target oil pressure, the electronic controller (8) increases the output current of the servo proportional solenoid valve (13) and increases the valve opening to increase the oil supply flow and power assist pressure. When the actual oil pressure is higher than the target oil pressure, the output current is reduced and the valve opening is closed to reduce the power assist pressure, thereby ensuring that the hydraulic power assist output is stable and without vibration.

[0035] At the same time, the outer ring of the steering angle synchronously completes the high-precision deviation correction work. The electronic controller (8) compares the target steering angle input by the steering wheel (1) with the actual steering angle of the wheel fed back by the steering angle detection element (4-1) to accurately calculate the steering angle deviation value between the two. The electronic controller (8) can correct the current to the servo proportional solenoid valve (13) according to the magnitude, direction and rate of change of the steering angle deviation, combined with the real-time four-wheel alignment parameter deviation, and perform fine secondary adjustment of the power assist pressure and power assist torque to compensate for the steering angle error in real time.

[0036] When the vehicle activates the lane centering intelligent assist function, the electronic controller (8) receives the lane lateral offset and heading deviation signals sent by the vehicle's intelligent driving system and dynamically calculates the steering torque required for active correction. By controlling the servo proportional solenoid valve (13) to switch between left and right steering positions at high frequency and small amplitude, it outputs a continuous and shock-free small hydraulic assist torque, actively driving the steering linkage to finely adjust the wheel deflection angle, counteracting external interference such as crosswinds and road cross slopes, and maintaining the vehicle's centered driving. When the steering angle and torque sensor (3) detects that the driver has actively steered and the operating torque exceeds the preset threshold, the system immediately terminates the active steering correction and automatically switches back to the manual assist mode, realizing a seamless switch between intelligent assistance and manual control.

[0037] The servo proportional solenoid valve (13) is a four-position four-way servo proportional solenoid valve. The valve core has four independent working positions, from left to right: left turning position, straight-through center position, right turning position, and fail-safe position. A control solenoid is configured on the left side of the valve core, and a reset spring is configured on one side of the fail-safe position. The valve core position is precisely controlled by the dynamic balance between the electromagnetic force and the spring force on one side. See the attached instruction manual. Figure 2 As shown, the servo proportional solenoid valve (13) has the following four operating conditions: Condition 1: The steering angle and torque sensor (3) collects steering wheel angle and torque information. When the torque is >0, the solenoid valve is in the left steering position, that is, the solenoid valve is in the left position, and the vehicle turns to the left. The system is in normal power-on state, and the electronic controller (8) outputs positive control current to drive the servo proportional solenoid valve (13) to switch to the left steering position. The high pressure oil output by the hydraulic pump (11) enters the pressure oil port P (13-2) of the servo proportional solenoid valve (13) after being stabilized by the accumulator (9). The high pressure oil flows from the output port of the solenoid valve into the first power assist oil chamber (5-3) of the recirculating ball steering gear (5). The second power assist oil chamber (5-4) is connected to the return oil port T (13-1) of the solenoid valve, and the oil flows back to the oil tank to complete the pressure relief. The high-pressure oil enters the first power steering chamber (5-3), pushing the screw-ball mechanism inside the recirculating ball steering gear, causing the rocker arm shaft (15) to swing to the left; the rocker arm shaft (15) will transmit the mechanical motion to the steering linkage (6) to drive the wheel (7) to turn to the left. At the same time, the feedback fork (4) swings to the left synchronously, and the angle detection element (4-1) collects the fork deflection angle in real time, calculates the actual left turning angle of the wheel and feeds it back to the electronic controller (8). The outer ring of the angle completes the adjustment of the power steering and the calculation and correction of the four-wheel alignment parameters for the left turning condition. At the same time, the first pressure sensor (5-1) collects the real-time oil pressure of the first power steering chamber (5-3) and sends it to the electronic controller (8). The inner pressure ring of the pressure completes the adjustment of the power steering; the outer ring of the angle compares the target left turning angle of the steering wheel with the actual left turning angle of the wheel, calculates the angle deviation, dynamically corrects the control current of the solenoid valve, fine-tunes the valve opening, and corrects the steering error and dynamic positioning offset. Condition 2: The steering angle and torque sensor (3) collects steering wheel angle and torque information. The torque is 0, the solenoid valve is in the straight-line position, that is, the solenoid valve is in the middle position, the vehicle is going straight, and there is no steering operation. The driver holds the steering wheel (1) with both hands, there is no steering input action, the steering angle and torque signal output by the steering angle and torque sensor (3) is zero, the system is in normal power-on state, the drive current corresponding to the control command output by the electronic controller (8) is zero, and the servo proportional solenoid valve (13) is maintained in the straight-line position under the action of the return spring. The straight-line position is an O-type function, the pressure oil port P (13-2), the return oil port T (13-1), the working oil port A (13-4) and the working oil port B (13-3) are all closed, the oil inside the first power assist oil chamber and the second power assist oil chamber is sealed and locked, the two oil chambers maintain the residual pressure in the closed state, the steering gear rack piston is hydraulically locked, which can effectively isolate the impact load transmitted from the road surface, suppress the wheel deflection and sway, and improve the driving stability of the vehicle at high speed. At this time, the pressure port P (13-2) is closed, and the hydraulic pump (11) maintains a certain pressure. When the steering control command is received, the solenoid valve can quickly establish a working pressure difference to achieve a rapid response of the power assist. Under the steady-state working condition of straight driving, the system continuously monitors the static parameters of the four-wheel alignment based on the zero-position angle signal of the shift fork. For the small static offset of the toe angle and camber angle, the parameters are dynamically calibrated through the small pressure difference output of the solenoid valve to maintain the optimal attitude of the chassis. Condition 3: The steering angle and torque sensor (3) collects steering wheel angle and torque information. When the torque is <0, the solenoid valve is in the right steering position, that is, the solenoid valve is in the right position, and the vehicle turns to the right. The system is in normal power-on state, and the electronic controller (8) outputs reverse control current to drive the servo proportional solenoid valve (13) to switch to the right steering position. After the high-pressure oil enters the servo proportional solenoid valve (13), it is fed into the second power assist oil chamber (5-4), and the first power assist oil chamber (5-3) is connected to the return oil circuit to release pressure. The high-pressure oil pushes the internal screw-steel ball mechanism of the circulating ball steering gear to drive the rocker arm shaft (15) to swing to the right, which will transmit the mechanical motion to the steering linkage (6) to drive the wheel (7) to turn to the right; at the same time, the feedback shift fork (4) swings to the right, and the steering angle detection element (4-1) collects the shift fork deflection angle in real time, calculates the actual right turn angle of the wheel and feeds it back to the electronic controller (8). The outer ring of the steering angle completes the adjustment of the power assist size and the dynamic correction of the four-wheel alignment parameters in the right turn condition. Simultaneously, the second pressure sensor (5-2) collects the oil pressure signal from the second power steering chamber (5-4) and feeds it back to the electronic controller (8), stabilizing the power steering oil pressure in the inner pressure loop. The outer angle loop corrects the output current of the solenoid valve based on the right turn angle deviation, fine-tunes the valve opening, and corrects the steering error; Condition 4: Fail-safe position, i.e., the fourth position, is located on the far right of the valve. When the electronic controller (8) fails, the circuit is broken, or the vehicle's electronic control loses power, the electromagnet of the servo proportional solenoid valve (13) completely loses its driving current, the electromagnetic force disappears completely, the valve core is no longer electromagnetically constrained, and the valve-side reset spring directly pushes the valve core to the far right of the fail-safe position. At this time, the pressure port P (13-2) is completely closed, cutting off the system's high-pressure oil supply. The working port A (13-4) and the working port B (13-3) are simultaneously connected to the return port T (13-1). The first power assist chamber (5-3) and the second power assist chamber (5-4) of the recirculating ball steering gear (5) are all connected to the oil tank for depressurization. The first power assist chamber (5-3) and the second power assist chamber (5-4) are in a floating state, and the hydraulic power assist is completely ineffective. At this time, the driver can manually control the vehicle steering by relying on the steering wheel (1), steering column (2), and the pure mechanical transmission link inside the recirculating ball steering gear (5). In the fault state, the feedback shift fork (4), the angle detection element (4-1), the first pressure sensor (5-1) and the second pressure sensor (5-2) continue to collect signals and upload them to the electronic controller (8) to realize real-time fault monitoring and fault code retention and early warning.

[0038] In summary, the four-position dual-closed-loop electro-hydraulic steering system and control method based on shift fork feedback of the present invention achieves dual-closed-loop coordinated control through the cooperation of the inner pressure loop and the outer angle loop. The inner pressure loop ensures stable and unfluctuating hydraulic power assist pressure, while the outer angle loop, relying on the end shift fork posture feedback, achieves precise wheel angle correction and dynamic compensation of four-wheel alignment parameters. The two control loops work synchronously and in conjunction, effectively compensating for steering errors caused by hydraulic hysteresis, mechanical clearance, and component wear, thereby improving the angle control accuracy and dynamic response speed during vehicle steering. This structure can adapt to various driving conditions such as low-speed steering, high-speed straight-line fine-tuning, cornering, intelligent lane centering assistance, and emergency driving, effectively reducing steering following errors, suppressing vehicle deviation and abnormal tire wear, and significantly improving vehicle steering stability, chassis posture consistency, and handling comfort. The basic principles, main features, and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback, characterized in that, It includes a steering wheel (1), steering column (2), angle and torque sensor (3), feedback shift fork (4), angle detection element (4-1), recirculating ball steering gear (5), first pressure sensor (5-1), second pressure sensor (5-2), steering linkage (6), wheel (7), electronic controller (8), accumulator (9), one-way valve (10), hydraulic pump (11), relief valve (12), servo proportional solenoid valve (13), and vehicle speed signal acquisition unit (14). The steering wheel (1) is fixedly mounted on the top of the steering column (2). The angle and torque sensor (3) is mounted on the outside of the steering column (2) and is used to collect the angle and torque signals of the driver's steering operation in real time. The vehicle speed signal acquisition unit (14) is used to obtain the real-time vehicle speed. The angle and torque sensor (3) and the vehicle speed signal acquisition unit (14) are electrically connected to the electronic controller (8) through the vehicle CAN bus and transmit the operating condition signal to the electronic controller (8) in real time to complete the calculation and processing. The electronic controller (8) can be connected to the vehicle intelligent driving system to receive lane centering control commands and lane departure parameters. The hydraulic pump (11) provides pressure oil to the entire hydraulic circuit. The hydraulic pump (11) is connected in sequence to the check valve (10) and the accumulator (9). The check valve (10) is used to prevent hydraulic oil from flowing back and to protect the hydraulic pump (11) from reverse impact. The accumulator (9) adopts a bladder structure with a rated pressure that matches the system. It is used to store pressure oil, absorb oil pressure pulsation in the oil circuit, and ensure that the oil supply pressure is continuous and stable. The relief valve (12) is arranged in parallel on the main hydraulic oil supply line to monitor the system oil pressure in real time. When the oil pressure exceeds the safety threshold, it automatically overflows and releases pressure to limit the maximum working oil pressure of the system and realize overload protection. The pressure port P (13-2) of the servo proportional solenoid valve (13) is connected to the end of the hydraulic oil supply main line. The servo proportional solenoid valve (13) is set with four independent working positions, which correspond to the left steering working position, the right steering working position, the straight driving center position and the fault safe position respectively. The working ports A (13-4) and B (13-3) of the servo proportional solenoid valve (13) are respectively connected to the first power assist oil chamber (5-3) and the second power assist oil chamber (5-4) of the circulating ball steering gear (5) through high pressure oil pipes.

2. The four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 1, characterized in that, The recirculating ball steering gear (5) is equipped with a screw steel ball transmission pair and a rocker arm shaft (15). The output end of the rocker arm shaft (15) is hinged to the steering linkage (6) through a ball joint structure. The two ends of the steering linkage (6) are respectively connected to the steering knuckles of the two wheels. After the pressure oil is introduced into the corresponding power assist oil chamber, it pushes the piston and screw mechanism inside the steering gear to move, causing the rocker arm shaft (15) to swing back and forth around its own axis. Then, through the steering linkage (6), the wheel is pushed and pulled to deflect around the kingpin axis, thus completing the vehicle steering action.

3. The four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 1, characterized in that, The recirculating ball steering gear (5) has a shoulder and a keyway at its outer end. The feedback shift fork (4) is circumferentially positioned by a key and is fitted with an interference fit to achieve backlash-free transmission. The feedback shift fork (4) is axially pressed and fixed by a locking nut on its outer side to ensure that there is no relative rotation or axial movement between the two under long-term driving and repeated impacts.

4. The four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 3, characterized in that, The corner detection element (4-1) is arranged on the side of the feedback fork (4). It adopts the magnetoelectric non-contact detection principle. The sensor housing is fixedly installed on the end cover of the steering gear housing. A high-performance permanent magnet is embedded in the free end of the feedback fork (4). The permanent magnet swings synchronously with the fork. The sensor outputs an absolute angular displacement signal by sensing the change in the angle of the spatial magnetic field.

5. A four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 1, characterized in that, The electronic controller (8) has a built-in steering suspension kinematic coupling model calibrated on the vehicle bench, and pre-stores the rocker arm shaft length, the length of each link of the steering linkage (6), the spatial coordinates of the steering knuckle kingpin axis, and the position parameters of the suspension hard points. Based on the single angle signal of the feedback shift fork (4), it synchronously calculates the actual wheel rotation angle and four positioning parameters. The calculation logic is as follows: First, the actual steering angle of the wheel is calculated; after the electronic controller (8) obtains the absolute angle signal of the feedback shift fork (4), it first subtracts the initial zero position offset to obtain the actual swing angle of the rocker arm shaft (15), and combines the arm length dimension from the rotation center of the rocker arm shaft (15) to the tie rod hinge point, and calculates the axial push-pull displacement of the steering tie rod through the arc length formula. Based on the geometric dimensions of the steering trapezoidal mechanism and the Ackermann steering characteristics, the actual steering wheel angles of the left and right wheels around the kingpin are calculated respectively, and the rationality of the difference in steering angles between the left and right wheels is verified, eliminating abnormal values ​​caused by signal interference. Secondly, the wheel camber angle is calculated. Based on the geometric coupling characteristics of the kingpin inclination, the wheel camber angle will change sinusoidally with the steering angle during the wheel deflection around the kingpin. The electronic controller (8) combines the kingpin inclination angle calibration value with the real-time wheel angle and calculates the real-time change of the camber angle during the steering dynamic process through the spatial projection relationship. The static camber reference value in the straight state is superimposed to obtain the actual wheel camber angle under the current working condition. Third, toe angle calculation; the toe angle is determined by the difference in the steering angle of the left and right wheels and the included angle of the steering trapezoidal arm. The electronic controller (8) calculates the real-time toe angle under the current steering state by combining the difference in the actual steering angle of the left and right wheels with the design length and installation angle of the steering trapezoidal arm. In straight driving mode, the system accurately monitors the offset of the static toe value by capturing minute angular fluctuations near the zero position of the shift fork. Fourth, the kingpin inclination angle and kingpin camber angle are calculated; the electronic controller (8) combines the steering torque feedback and the wheel angle change rate, and based on the return torque characteristics generated by the kingpin inclination, back-calculates the real-time value of the equivalent kingpin inclination angle; at the same time, by decomposing the steering knuckle space angle in the longitudinal and lateral planes and combining the suspension hard point coordinates, the actual value of the kingpin camber angle is calculated.

6. A four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 5, characterized in that, The electronic controller (8) compares the four positioning parameters calculated in real time with the standard parameter range calibrated by the vehicle factory and calculates the parameter deviation. When the vehicle is in a straight state, the positioning parameters show a static offset and the deviation is within the hydraulically correctable range, the electronic controller (8) controls the servo proportional solenoid valve (13) to perform a small-amplitude high-frequency switch between the left and right work positions, outputting a small pressure difference to the first power assist oil chamber (5-3) and the second power assist oil chamber (5-4), which drives the steering knuckle to generate a micron-level micro-deflection through the steering linkage (6), dynamically compensating for the static offset of the toe angle and camber angle, and correcting the positioning deviation caused by mechanism wear and tire deformation. When the vehicle is in a steering condition, the electronic controller (8) dynamically adjusts the power steering oil pressure amplitude according to the real-time values ​​of the kingpin caster angle and kingpin inclination angle to compensate for the steering torque fluctuation caused by the kingpin geometry; at the same time, it corrects the dynamic camber and toe-in changes during the steering process.

7. A four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 6, characterized in that, The first pressure sensor (5-1) and the second pressure sensor (5-2) are respectively installed on the oil inlet lines of the first power-assisted oil chamber (5-3) and the second power-assisted oil chamber (5-4), respectively, to collect the working oil pressure of the first power-assisted oil chamber (5-3) and the second power-assisted oil chamber (5-4) in real time and feed it back to the electronic controller (8), forming a pressure inner loop closed-loop control; combined with the wheel rotation angle fed back by the shift fork and the four positioning parameters, a rotation attitude outer loop is formed, forming a dual closed-loop collaborative control system.

8. A four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 7, characterized in that, The four working positions and corresponding operating conditions of the servo proportional solenoid valve (13) are as follows: Condition 1: Torque > 0, left steering position; when the electronic controller (8) outputs a positive control current and the current value is greater than the mid-position dead zone threshold, the valve core moves to the left against the force of the reset spring, switching to the left steering position; in this position, the pressure port P (13-2) and the working port A (13-4) are connected, and the high-pressure oil is introduced into the first power assist oil chamber (5-3) of the recirculating ball steering gear (5) through the pipeline; the working port B (13-3) and the return port T (13-1) are connected, and the second power assist oil chamber (5-3) is connected. -4) The oil in the tank flows back to the oil tank to complete the pressure relief; the high pressure oil pushes the screw steel ball mechanism inside the steering gear to drive the rocker arm shaft (15) to swing to the left, and drives the wheel to turn to the left through the steering linkage (6). The angle detection element (4-1) collects the deflection angle of the shift fork in real time, and sends the signal back to the electronic controller (8) to calculate the actual left turn angle of the wheel; the first pressure sensor (5-1) collects the real-time oil pressure of the first power assist oil chamber (5-3) and feeds it back to the electronic controller (8) to form the pressure inner loop, and stabilizes the power assist output pressure through the PID adjustment algorithm; the angle outer loop compares the target left turn angle of the steering wheel (1) with the actual left turn angle fed back by the shift fork, calculates the angle deviation, dynamically corrects the control current of the solenoid valve and the valve opening, and compensates for the steering error caused by mechanical clearance and hydraulic lag; Condition 2: Torque = 0, the solenoid valve core returns to the middle position, the vehicle maintains straight driving without steering operation; the driver holds the steering wheel (1) without steering input, the angle torque sensor (3) outputs a signal of zero, the electronic controller (8) outputs a drive current of zero, and the solenoid valve is stably in the straight driving middle position under the action of the reset springs on both sides; Condition 3: Torque < 0, right steering working position; when the electronic controller (8) outputs reverse control current, the valve core moves to the right to switch to the right steering working position; in this position, the pressure port P (13-2) and the working port B (13-3) are connected, and the high pressure oil enters the second power assist oil chamber (5-4); the working port A (13-4) is connected to the return port T (13-1), and the first power assist oil chamber (5-3) is connected to the return oil circuit to release pressure; the high pressure oil pushes the internal mechanism of the steering gear to drive the rocker arm shaft (15) to swing to the right, and drives the wheel to turn to the right through the steering linkage (6). The angle detection element (4-1) collects the fork swing angle and transmits it back, and calculates the actual right turn angle of the wheel; the second pressure sensor (5-2) collects the oil pressure signal of the second power assist oil chamber (5-4) and feeds it back to the electronic controller (8), and the pressure inner ring stabilizes the power assist oil pressure; Condition 4: Fail-safe position; The pressure port P (13-2) under this position is completely closed, cutting off the high-pressure oil supply. Working ports A (13-4) and B (13-3) are simultaneously connected to the return port T (13-1). The first power assist chamber (5-3) and the second power assist chamber (5-4) of the recirculating ball steering gear (5) are all connected to the oil tank for pressure relief. The hydraulic lock is released and the vehicle is in a floating state, and the hydraulic power assist is completely ineffective. At this time, the driver can manually control the vehicle steering through the pure mechanical transmission link of the steering wheel (1), steering column (2), and recirculating ball steering gear (5). The accumulator (9) releases the stored pressure oil for a short time to provide emergency assistance.

9. A four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback according to claim 8, characterized in that, The vehicle speed signal acquisition unit (14) is installed at the output shaft of the vehicle transmission. The real-time vehicle speed is obtained by acquiring the output shaft rotation speed pulse signal. The corner detection element (4-1) adopts a magnetoelectric non-contact angular displacement sensor.

10. The control method for a four-position dual-closed-loop electro-hydraulic steering system based on shift fork feedback as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Multi-source signal synchronous acquisition: When the system is running, the angle and torque sensor (3) collects the angle and torque signals of the driver's steering operation in real time, the vehicle speed signal acquisition unit (14) collects the real-time driving speed of the vehicle, the angle detection element (4-1) collects the absolute swing angle of the feedback shift fork (4), the first pressure sensor (5-1) and the second pressure sensor (5-2) collect the working oil pressure of the corresponding power assist oil chamber, the lane centering control command and lane deviation parameters are input by the whole vehicle intelligent driving system, and all signals are synchronously transmitted to the electronic controller (8) through the CAN bus with timestamps to ensure that the signal time deviation is within the allowable range; S2. Calculation of wheel steering angle and positioning parameters: The electronic controller (8) calculates the real-time values ​​of the actual wheel steering angle, wheel camber angle, toe angle, kingpin caster angle and kingpin inclination angle in sequence based on the angular displacement signal of the feedback fork (4) and the pre-calibrated steering suspension kinematic coupling model, and verifies the rationality of the calculation results and removes abnormal interference data. S3, Working Condition Identification and Workstation Switching: The electronic controller (8) determines the current steering working condition based on the steering operation signal, system operating status, and lane centering function start / stop status, and controls the servo proportional solenoid valve (13) to smoothly switch to the corresponding working position and output basic hydraulic power assist that matches the working condition. S4, Dual Closed-Loop Dynamic Correction: Relying on dual-side oil pressure feedback to complete the pressure inner loop stabilization and control, ensuring stable output of power assist oil pressure; comparing the target angle with the standard positioning parameters to complete the angle attitude outer loop correction, fine-tuning the output pressure difference of the solenoid valve, and compensating for mechanical transmission errors and positioning parameter offsets; S5, Lane Centering Cooperative Control: When the lane centering function is activated, the solenoid valve is controlled to make high-frequency micro-adjustments between the left and right steering positions based on the lane lateral offset and heading deviation, and outputs continuous micro-assistance to maintain the vehicle's lane centering; when the driver's active steering operation is detected and the torque exceeds the threshold, the automatic correction is automatically disengaged and the vehicle returns to the normal manual assist mode. The S6 system cyclically executes the complete process of signal acquisition, parameter calculation, workstation switching, and closed-loop correction, adapting to various driving scenarios such as manual steering, straight-line driving, fault emergency response, and intelligent assisted driving.

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