A Steering System Control Strategy

Abstract

The present invention relates to a steering system control strategy, which is used to solve the problem of stability and safety of the steering system. Specifically, during the system adjustment process, the vehicle driving speed signal, steering wheel angle signal, wheel angle signal, pressure signals of various parts of the system, etc. are first monitored to determine whether the system is working normally. If normal, check whether the speed of the motor or engine power take-off port has reached the use requirements. If it has reached the standard, the control valve group will charge and discharge the steering cylinder, and collect the wheel angle signal and the working pressure signal of each position in real time; if the speed of the motor or engine power take-off port does not meet the use requirements, the emergency steering system will be started, and the accumulator will be used to provide compensation pressure to the system to ensure normal operation, and further determine whether the working pressure and wheel angle meet the use requirements. If the target position is reached, the automatic centering function is executed and the steering is completed. If the target position is not reached, the steering cylinder is continuously adjusted by charging and discharging oil until the requirements are met.

Description

Technical Field

[0001] The invention relates to a steering system control strategy and belongs to the application field of hydraulic machinery and motor vehicles. Background Art

[0002] With the increasing requirements for vehicle transportation capacity and vehicle stability, safety and comfort, how to ensure the reliability of vehicle steering, how to ensure that the vehicle can maintain stable steering until it stops when the system power source fails, how to achieve system high efficiency and energy saving and reduce efficiency loss, etc., have become technical difficulties that domestic vehicle manufacturers are currently facing and have never been able to effectively solve. Therefore, it is particularly necessary to develop a proportional steering control system with automatic centering and emergency start functions.

[0003] In addition, the formulation of the steering system control strategy is crucial. Its rationality directly determines the stability and safety of the system operation. Especially for systems with rear-wheel steering function, it is even more important to ensure the stability of the vehicle during high-speed driving. Summary of the invention

[0004] In order to solve the problem of working stability and safety of the steering system, the present invention proposes a steering system control strategy. The system uses a high-pressure pump driven by a motor or an engine power take-off port as a power source to provide high-pressure power, uses a steering cylinder as an actuator, controls the steering cylinder piston rod to extend or retract through a functional valve group to realize vehicle steering, and realizes steering angle detection and closed-loop control through a sensor system. In the system adjustment process, the vehicle driving speed signal, the steering wheel angle signal, the wheel angle signal, the pressure signals of various parts of the system, etc. are first monitored to determine whether the system is working normally. If it is working normally, check whether the speed of the motor or the engine power take-off port meets the use requirements. If it meets the use requirements, the control valve group is used to charge and discharge the steering cylinder, and the wheel angle signal and the working pressure signal of each position are collected in real time. If the speed of the motor or the engine power take-off port does not meet the use requirements, the emergency steering system is started, and the accumulator is used to provide compensation pressure to the system to ensure normal operation. It is further determined whether the working pressure and the wheel angle meet the use requirements. If the target position is reached, the automatic centering function is executed and the steering ends. If the target position is not reached, the steering cylinder is continuously adjusted by charging and discharging oil until the requirements are met.

[0005] A tilt sensor is arranged near the center of mass of the vehicle body to monitor the body roll angle when the vehicle turns. It serves as a feedback signal for the rear wheel steering angle. The rear wheel steering angle decreases as the body roll angle increases. The threshold of the body roll angle should not be greater than 6°.

[0006] The system is used for rear-wheel steering when the vehicle speed does not exceed 25km / h. If the speed exceeds 25km / h, the system will be locked and the rear-wheel steering operation will not be performed to ensure vehicle driving safety.

[0007] The existing steering system usually calculates the steering angle of each wheel position according to the Ackerman angle, so as to formulate a control strategy to realize the function of multi-wheel steering. In addition, when the system fails, it cannot perform emergency response to ensure the normal driving of the vehicle. The present invention proposes a new control strategy to address the hidden dangers and shortcomings of the prior art, adds closed-loop control of emergency steering activation, and proposes a strategy for adjusting the rear wheel steering angle in real time by monitoring the body roll angle as feedback, as well as limiting the maximum vehicle speed of all-wheel steering through actual vehicle testing. This is of great significance to reducing tire wear and improving vehicle handling stability and driving safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is the composition and principle diagram of the proportional steering control system with multi-cylinder automatic centering and emergency start functions;

[0009] Figure 2 It is the composition and principle diagram of the proportional steering control system with multi-cylinder automatic centering function only;

[0010] Figure 3 It is the composition and principle diagram of the proportional steering control system with single cylinder and automatic centering and emergency start function;

[0011] Figure 4 It is the schematic diagram of the power source;

[0012] Figure 5 It is the composition and principle diagram of the control valve group of the centering accumulator;

[0013] Figure 6 This is the schematic diagram of the proportional steering control valve group;

[0014] Figure 7 This is the schematic diagram of the emergency energy storage valve group;

[0015] Figure 8 It is the overall control logic of the system;

[0016] Fig. 9 For the system workflow.

[0017] In the figure: 1-power source, 2-centering accumulator control valve group, 3-centering pressure sensor, 4-centering accumulator, 5-cylinder one proportional steering control valve group, 6-nested steering cylinder one, 7-cylinder one angular displacement sensor, 8-cylinder two angular displacement sensor, 9-nested steering cylinder two, 10-cylinder two proportional steering control valve group, 11-system pressure sensor, 12-stop valve, 13-emergency pressure sensor, 14-emergency accumulator valve group , 15-emergency accumulator, 16-pump system, 17-pump non-return valve, 18-main oil filter, 19-oil circuit control valve, 20-overflow valve, 21-return oil filter, 22-accumulator connecting valve, 23-centering pressure control valve, 24-proportional flow control valve, 25-three-position four-way liquid replenishment valve, 26-liquid replenishment valve non-return valve, 27-control valve non-return valve, 28-non-return valve, 29-pressure relief safety valve, 30-safety overflow valve, 31-emergency stop valve. DETAILED DESCRIPTION

[0018] The following is a detailed description of the vehicle posture adjustment system in conjunction with the accompanying drawings:

[0019] The hydraulic steering system is composed of a system power source 1, a long-time working hydraulic system, a nested steering cylinder 1 6, a nested steering cylinder 2 8, an emergency energy storage system, an electronic control device, sensors, pipelines, joints, etc. The long-time working hydraulic system is composed of a centering accumulator control valve group 2, a centering pressure sensor 3, a centering accumulator 4, a cylinder 1 proportional steering control valve group 5, a cylinder 1 angular displacement sensor 7, a cylinder 2 angular displacement sensor 8, a cylinder 2 proportional steering control valve group 10, a system pressure sensor 11 and corresponding pipelines and joints; the emergency energy storage system is composed of a stop valve 12, an emergency pressure sensor 13, an emergency energy storage valve group 14, an emergency accumulator 15 and corresponding pipelines and joints. The internal valve groups of the long-time working hydraulic system and the emergency energy storage system and the system power source 1, the nested steering cylinder 1 6, and the nested steering cylinder 2 8 are connected by high-pressure hard pipes (or hoses), and the electronic control device is connected to the hydraulic system solenoid valve group through cables to provide control signals. In this system, the number of steering cylinders can be increased or decreased according to the actual vehicle steering needs, and technicians in this field can arbitrarily combine multiple integrated control valves according to actual needs to achieve steering adjustment.

[0020] Figure 1It is the composition and principle diagram of the proportional steering control system with multi-cylinder automatic centering and emergency start functions, mainly including power source 1, centering accumulator control valve group 2, centering pressure sensor 3, centering accumulator 4, cylinder one proportional steering control valve group 5, nested steering cylinder one 6, cylinder one angular displacement sensor 7, cylinder two angular displacement sensor 8, nested steering cylinder two 9, cylinder two proportional steering control valve group 10, system pressure sensor 11, stop valve 12, emergency pressure sensor 13, emergency accumulator valve group 14, emergency accumulator 15. Power source 1 provides working pressure for the system, and system pressure sensor 11 is connected in parallel at the oil outlet A of power source 1 to measure the actual working pressure of the system. The P oil inlets of the proportional steering control valve group 5 of the cylinder one and the proportional steering control valve group 10 of the cylinder two are respectively connected to the A oil outlet of the power source 1, the control cylinder retraction port SS1 of the proportional steering control valve group 5 of the cylinder one is connected to the retraction control chamber of the nested steering cylinder one 6, and the control cylinder extension port SC is connected to the extension control chamber of the nested steering cylinder one 6, the control cylinder retraction port SS2 of the proportional steering control valve group 10 of the cylinder two is connected to the retraction control chamber of the nested steering cylinder two 9, and the control cylinder extension port SC is connected to the extension control chamber of the nested steering cylinder two 9, which respectively control the extension and retraction of the piston rods of the nested steering cylinder one 6 and the nested steering cylinder two 9 to achieve the purpose of controlling the steering of the vehicle. The centering pressure sensor 3 and the centering accumulator 4 are connected in parallel, and are respectively connected to the pressure measuring port CY1 port and the accumulator connecting port AC port of the centering accumulator control valve group 2. The oil inlet P of the centering accumulator control valve group 2 is connected to the oil outlet A of the power source 1, and the centering port DZ port is respectively connected to the centering oil ports DZ1 and DZ2 of the nested steering cylinder 1 6 and the nested steering cylinder 2 9. The purpose of automatic steering centering is achieved by the back pressure provided by the centering accumulator 4. The accumulator connecting valve 22 is arranged between the accumulator 4 and the centering port DZ end of the centering accumulator control valve group 2, and is usually a two-position, two-position normally open solenoid valve. The centering pressure sensor 3 is used to monitor whether the pressure of the centering accumulator 4 meets the pressure required for the vehicle's automatic centering. When the pressure is lower than the pressure required for centering, the centering pressure control valve 23 in the centering accumulator control valve group 2 opens, and the power source 1 is connected to charge the centering accumulator 4 until the pressure meets the vehicle's centering pressure. The centering pressure control valve 23 is usually a two-position, two-normally closed solenoid valve. The emergency pressure sensor 13 and the emergency accumulator 15 are connected in parallel, and are respectively connected to the pressure sensor connection port MP end and the accumulator connection port AC end of the emergency accumulator valve group 14. The oil inlet P of the emergency accumulator valve group 14 is connected to the oil outlet A of the power source 1 to provide high-pressure oil, and the oil return port T is connected to the oil return port T of the power source 1 to relieve pressure. The oil supply port P1 is connected to the oil inlet P of the cylinder 1 proportional steering control valve group 5 and the cylinder 2 proportional steering control valve group 10 to provide emergency steering pressure for the steering cylinder.The emergency pressure sensor 13 is used to monitor whether the pressure of the emergency accumulator 15 meets the pressure required for emergency steering of the vehicle. When the pressure is lower than the pressure required for emergency steering, the emergency stop valve 31 in the emergency accumulator valve group 14 opens, and the power source 1 is connected to charge the emergency accumulator 15 until the pressure meets the emergency steering pressure of the vehicle. It should be noted that when the system is working normally, the pressure relief safety valve 29 in the emergency accumulator valve group 14 is in an energized cut-off state.

[0021] Figure 2 This is the composition and principle diagram of the proportional steering control system with multiple cylinders and automatic centering function. Figure 1 The multi-cylinder proportional steering control system with automatic centering and emergency start functions shown is the same, mainly including power source 1, centering accumulator control valve group 2, centering pressure sensor 3, centering accumulator 4, cylinder one proportional steering control valve group 5, nested steering cylinder one 6, cylinder one angular displacement sensor 7, cylinder two angular displacement sensor 8, nested steering cylinder two 9, cylinder two proportional steering control valve group 10, system pressure sensor 11, stop valve 12, emergency pressure sensor 13, emergency accumulator valve group 14, emergency accumulator 15. Power source 1 provides working pressure for the system, and system pressure sensor 11 is connected in parallel at the oil outlet A of power source 1 to measure the actual working pressure of the system. The oil inlet P of the cylinder one proportional steering control valve group 5 and the cylinder two proportional steering control valve group 10 are respectively connected to the oil outlet A of the power source 1, the control cylinder contraction port SS of the cylinder one proportional steering control valve group 5 is respectively connected to the contraction control chamber of the nested steering cylinder one 6 and the nested steering cylinder two 9, and the control cylinder extension port SC is respectively connected to the extension control chamber of the nested steering cylinder one 6 and the nested steering cylinder two 9, so as to control the extension and contraction of the piston rods of the nested steering cylinder one 6 and the nested steering cylinder two 9 respectively to achieve the purpose of controlling the steering of the vehicle. The centering pressure sensor 3 and the centering accumulator 4 are connected to the pressure measuring port CY1 and the accumulator connection port AC of the centering accumulator control valve group 2. The oil inlet port P of the centering accumulator control valve group 2 is connected to the oil outlet port A of the power source 1. The centering port DZ port is respectively connected to the centering oil ports DZ1 and DZ2 of the nested steering cylinder 1 6 and the nested steering cylinder 2 9, so as to achieve the purpose of automatic steering centering. The centering pressure sensor 3 is used to monitor whether the pressure of the centering accumulator 4 meets the pressure required for automatic vehicle centering. When the pressure is lower than the pressure required for centering, the centering pressure control valve 22 in the centering accumulator control valve group 2 is opened, and the power source 1 is connected to charge the centering accumulator 4 until the pressure meets the vehicle centering pressure.

[0022] Figure 3The composition and principle diagram of the proportional steering control system with automatic centering and emergency start function for a single cylinder are shown in the figure. The power source 1 is connected in series with the cylinder-proportional steering control valve group 5, the system pressure sensor 11 is connected in parallel at the oil outlet A of the power source 1, the centering accumulator control valve group 2 is connected with the centering pressure sensor 3 and the centering accumulator 4, and then connected with the centering oil port DZ1 of the nested steering cylinder 6, which is used to control the automatic centering of the cylinder, and the emergency accumulator valve group 14 is connected with the emergency pressure sensor 13 and the emergency accumulator 15, and then connected in parallel at the oil inlet P of the cylinder-proportional steering control valve group 5, which is used to provide emergency steering pressure. It should be noted that the principle of the proportional steering control system with automatic centering and emergency start function for single cylinder and multi-cylinder is the same, each cylinder can independently control the steering of one axle, and for multi-axle vehicles, it is only necessary to increase the number of proportional steering control valve groups and steering cylinders to meet the use requirements.

[0023] like Figure 4 The figure shows the schematic diagram of the power source composition. The valve group oil outlet A and the oil return port T are respectively connected to the oil inlet P and the oil return port T of other valve groups in the system, which are used to provide high-pressure working oil and system oil return connection. The power source 1 includes a pump system 16, a pump check valve 17, a main oil filter 18, an oil circuit control valve 19, and a relief valve 20. The pump system 16 can be an electric pump system in which a high-pressure oil pump is driven by a motor, or the high-pressure pump can be connected to the power take-off port of the vehicle engine or transmission box as the power drive of the system. The oil circuit control valve 19 is connected in series with the main oil filter 18 and then connected in parallel with the relief valve 20, and then connected in series with the pump system 16 and the return oil filter 21 to form a power source. The maximum working pressure of the system is controlled by the relief valve 20 to prevent the system from failing due to excessive pressure. The oil direction is switched by the oil circuit control valve 19. When the system is not working, the oil can be switched back to the oil tank to avoid excessive power loss.

[0024] Figure 5The centering accumulator control valve group is composed of the accumulator connecting valve 22 and the centering pressure control valve 23. The accumulator connection port AC is connected to the centering accumulator 4. The pressure measuring port CY1 is connected to the centering pressure sensor 3 for testing the centering pressure. The centering port DZ oil port for connecting the steering centering mechanism is located between the accumulator connecting valve 22 and the centering pressure control valve 23. The centering pressure control valve 23 and the accumulator connecting valve 22 are arranged in sequence between the oil inlet P of the centering accumulator control valve group 2 and the accumulator connection port AC. When working normally, the system is The centering pressure is detected at the same time. When the centering pressure cannot meet the actual use requirements, the system controls the centering pressure control valve 23 to be energized, and the centering accumulator 4 is connected to the power source 1. After the centering accumulator 4 is pressurized until the system use requirements are met, the centering pressure control valve 23 loses power, and the accumulator connecting valve 22 is a two-position, two-normally open solenoid valve. Under normal circumstances, the centering accumulator 4 is connected to the steering cylinder centering structure through the solenoid valve, which can not only ensure timely and effective centering and resetting of the steering cylinder, but also provide hydraulic buffering when the cylinder pressure shock is large.

[0025] Figure 6 This is a schematic diagram of the composition of the proportional steering control valve group. A control valve check valve 27 is connected in series at the oil return port of the proportional flow control valve 24, and a check valve 26 is connected in series at the oil return port of the three-position four-way replenishment valve 25. The steering cylinder is controlled by controlling the reversing of the proportional flow control valve 24 to achieve the purpose of vehicle steering. The three-position four-way replenishment valve 25 is connected in parallel with the proportional flow control valve 24 to increase the system oil delivery channel and provide oil flow replenishment during emergency steering.

[0026] Figure 7It is a schematic diagram of the emergency accumulator valve group, including a one-way valve 28, a pressure relief safety valve 29, a safety overflow valve 30, and an emergency stop valve 31. The emergency stop valve 31 is arranged between the oil inlet P and the oil supply port P1. The parallel structure of the emergency stop valve 31, the pressure relief safety valve 29 and the safety overflow valve 30 is arranged in sequence between the oil supply port P1 and the oil return port T. The one-way valve 28, the oil supply port P1, the accumulator connection port AC, and the pressure measuring port MP are connected. When in use, the accumulator connection port AC is connected to the emergency accumulator 15, the oil supply port P1 is connected in series with the stop valve 12 and then connected to the main pressure oil channel of the system, and the pressure measuring port MP is connected to the emergency pressure sensor 13, and the safety relief valve 30 is set to a pressure equal to or slightly higher than the maximum working pressure required by the system. When the system is working, the pressure relief safety valve 29 is powered off and the emergency stop valve 31 is powered on. The system charges the emergency accumulator 15. When the pressure measured by the emergency pressure sensor 13 meets the system operating pressure, the emergency stop valve 31 loses power and locks, and the emergency system is pressurized. When the system power source 1 cannot work normally, or the system needs an emergency power source for steering, the stop valve 12 is powered on to connect the emergency accumulator 15 with the system main pressure oil channel to provide emergency pressure supplement for the system. The emergency stop valve 31 is usually a two-position, two-way normally closed solenoid valve, the pressure relief safety valve 29 is usually a two-position, two-way normally open solenoid valve, and the stop valve 12 is usually a two-position, two-way normally closed solenoid valve.

[0027] like Figure 8-9As shown, the system uses a high-pressure pump driven by a motor or engine power take-off port as a power source to provide high-pressure power, uses a steering cylinder as an actuator, controls the steering cylinder piston rod to extend or retract through a functional valve group to achieve vehicle steering, and realizes the detection and closed-loop control of the steering angle through a sensor system. During the system adjustment process, the vehicle speed signal, steering wheel angle signal, wheel angle signal, and pressure signals of various parts of the system are first monitored to determine whether the system is working normally. If it is working normally, check whether the speed of the motor or engine power take-off port meets the use requirements. If it meets the use requirements, the control valve group will charge and discharge the steering cylinder, and collect the wheel angle signal and the working pressure signal of each position in real time. If the speed of the motor or engine power take-off port does not meet the use requirements, the emergency steering system will be started, and the accumulator will be used to provide compensation pressure to the system to ensure normal operation. It is further determined whether the working pressure and wheel angle meet the use requirements. If the target position is reached, the automatic centering function is executed and the steering ends. If the target position is not reached, the steering cylinder is adjusted by charging and discharging oil until the requirements are met. The rear wheel steering angle and the front wheel steering angle need to be determined in accordance with the Ackerman turning angle theorem. In addition, since the rear wheel steering angle has a direct impact on the turning radius, and the turning radius of the vehicle is inversely proportional to the centrifugal force exerted on the vehicle body when turning, the greater the centrifugal force, the greater the roll angle of the vehicle body, which may cause dangerous situations such as rollover. In view of this situation, it is proposed to arrange a tilt sensor near the center of mass of the vehicle body to monitor the roll angle of the vehicle body when turning. As a feedback signal of the rear wheel steering angle, the rear wheel steering angle needs to decrease with the increase of the roll angle of the vehicle body. The threshold of the roll angle should not be greater than 6°. Closed-loop control of the rear wheel steering angle can effectively improve the safety and stability of the vehicle during driving.

[0028] For multi-axle heavy-duty transport vehicles, the system is used for rear-wheel steering when the vehicle speed usually does not exceed 25km / h. When the speed exceeds 25km / h, the system is locked and the rear-wheel steering operation is not performed to ensure vehicle driving safety.

[0029] It should be noted that those skilled in the art can easily understand that the steering system device involved in the present invention can be installed on different types of vehicles in the above-mentioned manner, and the system can include one or more steering cylinders and corresponding hydraulic control valve groups according to the vehicle usage requirements, and various different forms of changes and modifications can be made to the present invention without departing from the spirit and scope of the present invention as defined by the attached claims.

Claims

1. A steering system control strategy, based on a steering system, wherein the steering system uses a high-pressure pump driven by a motor or an engine power take-off port as a power source to provide high-pressure power, uses a steering cylinder as an actuator, controls the extension or retraction of the steering cylinder piston rod through a functional valve group to achieve vehicle steering, and realizes the detection and closed-loop control of the steering angle through a sensor system, and is characterized by: During the steering system adjustment process, the vehicle speed signal, steering wheel angle signal, wheel angle signal, and pressure signals of various parts of the system are first monitored to determine whether the system is working normally. If it is working normally, check whether the speed of the motor or engine power take-off port has reached the use requirements. If it has reached the use requirements, the control valve group will charge and discharge oil from the steering cylinder, and collect wheel angle signals and working pressure signals at various positions in real time. If the speed of the motor or engine power take-off port does not meet the use requirements, the emergency steering system will be started, and the accumulator will be used to provide compensation pressure to the system to ensure normal operation. It will be further determined whether the working pressure and wheel angle meet the use requirements. If the target position is reached, the automatic centering function will be executed and the steering will end. If the target position is not reached, the steering cylinder will continue to be adjusted by charging and discharging oil until the requirements are met. The steering system is composed of a system power source (1), a long-time working hydraulic system, a nested steering cylinder 1 (6), a nested steering cylinder 2 (9), an emergency energy storage system, an electronic control device and sensors, pipelines and joints; the long-time working hydraulic system is composed of a centering accumulator control valve group (2), a centering pressure sensor (3), a centering accumulator (4), a cylinder 1 proportional steering control valve group (5), a cylinder 1 angular displacement sensor (7), a cylinder 2 angular displacement sensor (8), a cylinder 2 proportional steering control valve group (10), a system pressure sensor (11) and corresponding pipelines and joints; the emergency energy storage system is composed of a stop valve (12), an emergency pressure sensor (13) , an emergency energy storage valve group (14), an emergency energy storage device (15) and corresponding pipelines and joints; the long-term working hydraulic system, the internal valve group of the emergency energy storage system and the system power source (1), the nested steering cylinder 1 (6) and the nested steering cylinder 2 (9) are connected through high-pressure hard pipes or hoses, and the electronic control device is connected to the hydraulic system electromagnetic valve group through cables to provide control signals; the centering accumulator control valve group (2) includes an accumulator connecting valve (22) and a centering pressure control valve (23); the emergency energy storage valve group (14) includes a one-way valve (28), a pressure relief safety valve (29), a safety overflow valve (30) and an emergency stop valve (31); The power source (1) provides working pressure, and the system pressure sensor (11) is connected in parallel at the oil outlet A of the power source (1) for measuring the actual working pressure of the system; the P oil inlets of the oil cylinder one proportional steering control valve group (5) and the oil cylinder two proportional steering control valve group (10) are respectively connected to the A oil outlet of the power source (1); the control oil cylinder contraction port SS1 of the oil cylinder one proportional steering control valve group (5) is connected to the contraction control chamber of the nested steering oil cylinder one (6); the control oil cylinder extension port SC1 is connected to the extension control chamber of the nested steering oil cylinder one (6); the control oil cylinder contraction port SS2 of the oil cylinder two proportional steering control valve group (10) is connected to the contraction control chamber of the nested steering oil cylinder two (9); the control oil cylinder extension port SC2 is connected to the extension control chamber of the nested steering oil cylinder two (9), respectively controlling the nested steering oil cylinders. The purpose of controlling the steering of the vehicle is achieved by extending and retracting the piston rods of the first steering cylinder (6) and the second nested steering cylinder (9); the centering pressure sensor (3) and the centering accumulator (4) are connected in parallel, and are respectively connected to the pressure measuring port CY1 of the centering accumulator control valve group (2) and the accumulator connection port AC port; the oil inlet P of the centering accumulator control valve group (2) is connected to the oil outlet A of the power source (1); the centering port DZ port is respectively connected to the centering ports DZ1 and DZ2 of the first nested steering cylinder (6) and the second nested steering cylinder (9); the purpose of automatic steering centering is achieved by the back pressure provided by the centering accumulator (4); the accumulator connecting valve (22) is arranged between the centering accumulator (4) and the centering port DZ end of the centering accumulator control valve group (2), and is usually a two-position, two-position normally open solenoid valve; The centering pressure sensor (3) is used to monitor whether the pressure of the centering accumulator (4) meets the pressure required for the vehicle's automatic centering. When the pressure is lower than the pressure required for centering, the centering pressure control valve (23) in the centering accumulator control valve group (2) is opened, and the power source (1) is connected to charge the centering accumulator (4) until the pressure meets the vehicle's centering pressure. The centering pressure control valve (23) is a two-position, two-position normally closed solenoid valve. The emergency pressure sensor (13) and the emergency accumulator (15) are connected in parallel and are respectively connected to the pressure sensor connection port MP end and the accumulator connection port AC end of the emergency accumulator valve group (14). The oil inlet P of the emergency accumulator valve group (14) is connected to the oil outlet A of the power source (1) to provide high-pressure oil. The oil return port T is connected to the oil return port T of the power source (1) to relieve pressure, and the oil supply port P1 is connected to the oil inlet port P of the oil cylinder one proportional steering control valve group (5) and the oil cylinder two proportional steering control valve group (10) to provide emergency steering pressure for the steering oil cylinder; the emergency pressure sensor (13) is used to monitor whether the pressure of the emergency accumulator (15) meets the pressure required for emergency steering of the vehicle. When the pressure is lower than the pressure required for emergency steering, the emergency stop valve (31) in the emergency accumulator valve group (14) is opened, and the power source (1) is connected to charge the emergency accumulator (15) until the pressure meets the emergency steering pressure of the vehicle; when the system is working normally, the pressure relief safety valve (29) in the emergency accumulator valve group (14) is in an energized stop state; According to the actual vehicle steering needs, the number of steering cylinders is increased or decreased, and multiple integrated control valves can be arbitrarily combined according to actual needs to achieve steering adjustment.

2. A steering system control strategy according to claim 1, characterized in that: A tilt sensor is arranged near the center of mass of the vehicle body to monitor the body roll angle when the vehicle turns. It serves as a feedback signal for the rear wheel steering angle. The rear wheel steering angle decreases as the body roll angle increases. The threshold of the body roll angle should not be greater than 6°.

3. A steering system control strategy according to claim 1, characterized in that: The system is used for rear-wheel steering when the vehicle speed does not exceed 25km / h. If the speed exceeds 25km / h, the system will be locked and the rear-wheel steering operation will not be performed to ensure vehicle driving safety.

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