Tractor electro-hydraulic control steering system and steering control method thereof

Abstract

The application discloses a tractor electro-hydraulic control steering system and a steering control method thereof, and belongs to the field of tractor steering systems. The tractor electro-hydraulic control steering system comprises a steering oil cylinder, a shuttle valve, an oil supply unit, a steering gear unit, a manual steering unit and an electric control steering unit. The outlet of the oil supply unit is divided into two branches, and the two branches are connected with the oil lines of the manual steering unit and the electric control steering unit respectively. The electric control steering unit comprises a controller and an adjustable through valve, the controller is connected with the adjustable through valve in a signal mode, and the oil inlet end of the adjustable through valve is connected with the oil outlet of the oil supply unit. The manual steering unit comprises a pressure reducing valve, and the oil inlet end of the pressure reducing valve is connected with the oil outlet of the oil supply unit. The E port of the shuttle valve is connected with the oil outlet end of the adjustable through valve, the F port of the shuttle valve is connected with the oil outlet end of the pressure reducing valve, and the G port of the shuttle valve is connected with the oil inlet of the steering gear unit. The device has the advantages of reasonable structure, good controllability and fast response speed.

Description

Technical Field

[0001] This invention belongs to the field of tractor technology, specifically relating to a tractor electro-hydraulic steering system and its steering control method. Background Technology

[0002] Tractors are important agricultural machines used for plowing, irrigation, fertilizing, harvesting, and other agricultural operations. They also reduce the burden on agricultural laborers, decrease labor intensity, and improve the quality and efficiency of agricultural production. However, due to their large size and heavy steering load, tractors typically use a fully hydraulic steering system, which is complex, has many components, and suffers from poor reliability. When switching from automatic to manual driving mode, the system relies primarily on changes in hydraulic pressure, resulting in a slow response and poor controllability. In emergencies, this can make it difficult to ensure the safety of the vehicle and its occupants. Summary of the Invention

[0003] The purpose of this invention is to solve the problems existing in the prior art and provide a tractor electro-hydraulic steering system and its steering control method. This device has the advantages of reasonable structure, good controllability and fast response speed.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a tractor electro-hydraulic steering system, comprising a steering cylinder, a shuttle valve, an oil supply unit, a steering gear unit, a manual steering unit, and an electronically controlled steering unit; the outlet of the oil supply unit is divided into two branches, which are respectively connected to the oil circuits of the manual steering unit and the electronically controlled steering unit; the electronically controlled steering unit includes a controller and an adjustable through valve, the controller being signal-connected to the adjustable through valve, and the oil inlet of the adjustable through valve being connected to the oil outlet of the oil supply unit; the manual steering unit includes a pressure reducing valve, the oil inlet of the pressure reducing valve being connected to the oil outlet of the oil supply unit; the E port of the shuttle valve is connected to the oil outlet of the adjustable through valve, the F port of the shuttle valve is connected to the oil outlet of the pressure reducing valve, and the G port of the shuttle valve is connected to the oil inlet of the steering gear unit.

[0005] As a preferred embodiment, the oil supply unit includes an oil tank, a filter, a bypass valve, and an oil pump;

[0006] The oil outlet of the oil tank is divided into at least two branches. One branch is equipped with a filter, and the other branch is equipped with a bypass valve. The outlets of the filter and the bypass valve are connected to the inlet of the oil pump.

[0007] As a preferred embodiment, the steering unit includes a steering gear.

[0008] The steering gear has four ports, wherein the first port is connected to the G port of the shuttle valve, the second port of the steering gear is connected to the left chamber oil circuit of the steering cylinder, the third port of the steering gear is connected to the right chamber oil circuit of the steering cylinder, and the fourth port of the steering gear is connected to the return oil circuit.

[0009] As a preferred embodiment, the manual steering unit further includes a steering wheel, which is connected to the steering gear.

[0010] As a preferred embodiment, the electronically controlled steering unit further includes a steering angle sensor and a drive motor. The steering angle sensor and the drive motor are respectively connected to the controller signal. The drive motor is connected to the steering wheel. The steering angle sensor is used to detect the steering angle signal of the steering wheel and send it to the controller. The controller determines that the rate of change of steering angle has changed abruptly and stops inputting control current to the drive motor and the adjustable valve.

[0011] As a preferred embodiment, the electronic steering unit includes an overflow valve one, an overflow valve two, a check valve one, and a check valve two. The inlet of the overflow valve one is connected to the left chamber oil circuit of the steering cylinder, the outlet of the overflow valve one is connected to the inlet and return oil line of the check valve two, the outlet of the check valve two is connected to the right chamber oil circuit of the steering cylinder, the inlet of the overflow valve two is connected to the right chamber oil circuit of the steering cylinder, the outlet of the overflow valve two is connected to the inlet and return oil line of the check valve one, and the outlet of the check valve one is connected to the left chamber oil circuit of the steering cylinder.

[0012] As a preferred embodiment, the electronic steering unit further includes a piston displacement sensor connected to the controller. The piston displacement sensor is connected to the steering cylinder and is used to detect the piston displacement of the steering cylinder and send the piston displacement signal of the steering cylinder to the controller.

[0013] As a preferred embodiment, the oil supply unit further includes a pressure switch connected in parallel across the filter to detect whether the filter is clogged and to control the bypass valve to open if clogged.

[0014] The second objective of this invention is to provide a control method for a tractor electro-hydraulic steering system, including a manual driving mode and an automatic driving mode; the specific steps of the manual driving mode are as follows:

[0015] When turning left, the operator turns the steering wheel to the left, causing the steering gear to rotate and the first and second ports of the steering gear to connect. At this time, the adjustable through valve defaults to a pressure greater than the safety valve pressure, so the adjustable through valve cannot be opened. Hydraulic oil flows from the oil tank through the pressure reducing valve into the shuttle valve, and then through the first and second ports of the steering gear into the left chamber of the steering cylinder. Part of the hydraulic oil in the right chamber of the steering cylinder is compensated to the left chamber through the relief valve and the check valve, while the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the right, driving the steering axle and steering wheel light components to achieve left turning.

[0016] When turning right, the operator turns the steering wheel to the right, causing the steering gear to rotate. The first and third ports of the steering gear are connected. At this time, the adjustable through valve defaults to a pressure greater than the safety valve pressure, so the adjustable through valve cannot be opened. Hydraulic oil flows from the oil tank through the pressure reducing valve into the shuttle valve, and then through the first and third ports of the steering gear into the right chamber of the steering cylinder. Part of the hydraulic oil in the left chamber of the steering cylinder is compensated to the right chamber through the relief valve and the check valve, while the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the left, driving the steering axle and steering wheel light components to achieve right turn.

[0017] The specific steps for the autonomous driving mode are as follows:

[0018] When the start switch is turned on, the controller determines whether steering is required based on the path information. If steering is required, the controller outputs current to adjust the through pressure of the adjustable valve to equal the safety pressure. Hydraulic oil flows into the shuttle valve E port through the adjustable through valve and into the shuttle valve F port through the pressure reducing valve. Since the pressure at port F is reduced to less than the safety pressure by the pressure reducing valve, the pressure at port E of the shuttle valve equals the safety pressure. The shuttle valve will select the larger of the two pressures for output. At this time, ports E and G of the shuttle valve are connected, and hydraulic oil enters the first port of the steering gear.

[0019] When turning left, the controller controls the drive motor to turn left, causing the steering gear to rotate. The first and second ports of the steering gear are connected, and hydraulic oil flows out from the oil tank through the adjustable through valve and shuttle valve G port. It then flows into the left chamber of the steering cylinder through the first and second ports of the steering gear. Part of the hydraulic oil in the right chamber of the steering cylinder is compensated to the left chamber through the relief valve 2 and the check valve 1, while the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the right, driving the steering axle and steering wheel light components to achieve left turning.

[0020] When turning right, the controller controls the drive motor to turn right, causing the steering gear to rotate, and the first and third ports of the steering gear are connected; hydraulic oil flows out from the oil tank through the adjustable through valve and shuttle valve G port, and flows into the right chamber of the steering cylinder through the first and third ports of the steering gear. Part of the hydraulic oil in the left chamber of the steering cylinder is compensated to the right chamber through the relief valve and the one-way valve, and the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the left, driving the steering axle and steering wheel light components to achieve right turn.

[0021] As a preferred embodiment, the system also includes a driving mode switching mode, which is used to switch from automatic driving mode to manual driving mode in case of an emergency. The operator turns the steering wheel to the left or right, and the steering angle sensor inputs a steering angle signal to the controller. The controller determines that the rate of change of steering angle has changed abruptly, stops inputting control current to the drive motor and the adjustable through valve, and the adjustable through valve resumes its default through pressure being greater than the safety pressure, thus preventing it from opening. At this time, hydraulic oil flows out from the pressure reducing valve.

[0022] Compared with existing technologies, this solution has at least the following beneficial effects:

[0023] Firstly, this invention achieves automatic vehicle steering by controlling the steering gear through structural improvements and simplifying control. In both automatic and manual steering, manual steering is prioritized. Even if the controller suddenly fails, the electronic control circuit can be shut down promptly to ensure vehicle safety in emergencies. Furthermore, it eliminates the need for a reversing valve in existing technologies (which rely on the movement of an electromagnetic reversing valve core to change the flow direction of the oil circuit, determining whether to connect to the left chamber or the oil chamber of the reversing cylinder. In existing technologies, the manual and intelligent control circuits are separate, requiring the electromagnetic reversing valve in the manual steering circuit to be closed before the electromagnetic reversing valve in the automatic steering circuit is activated for mode switching). Additionally, this solution eliminates the complex oil circuits and valve blocks in the electronic steering unit, resulting in a simpler overall structure that facilitates installation and maintenance.

[0024] Secondly, this invention optimizes the control method of the steering system. During the switching from automatic driving mode to manual driving mode, the controller only needs to determine whether the rate of change of the steering angle of the steering gear changes abruptly. By electrically connecting the drive motor and the adjustable valve, the driving mode can be switched quickly, and the response speed is faster. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the electro-hydraulic control steering system of the present invention;

[0027] Figure 2 This is a schematic diagram of the steering gear oil port of the present invention;

[0028] Figure 3 This is a schematic diagram of the shuttle valve port of the present invention;

[0029] Figure 4 This is a schematic diagram illustrating the principle of switching from automatic driving to manual driving steering in this invention.

[0030] The markings in the diagram are: 1. Oil tank, 2. Safety valve, 3. Pressure switch, 4. Start switch, 5. Controller, 6. Drive motor, 7. Steering angle sensor, 8. Check valve one, 9. Relief valve one, 10. Steering cylinder, 11. Piston displacement sensor, 12. Relief valve two, 13. Check valve two, 14. Steering wheel, 15. Steering gear, 16. Shuttle valve, 17. Pressure reducing valve, 18. Adjustable through valve, 19. Oil pump, 20. Radiator, 21. Spring-loaded check valve three, 22. Filter. Detailed Implementation

[0031] The present invention will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0032] It should be noted that, unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "a," "an," or "the," and similar words used in the specification and claims of this patent application do not express a limitation of quantity, but rather indicate the presence of at least one. Terms such as "comprising" or "including" indicate that the elements or objects preceding "comprising" encompass the elements or objects listed following "comprising" or "including" and their equivalents, but do not exclude other elements or objects having the same function.

[0033] This embodiment provides a tractor electro-hydraulic steering system, including an oil supply unit, a steering gear unit, an electronically controlled steering unit, a manual steering unit, a steering cylinder 10, and a shuttle valve 16. The oil supply unit has two branches, one of which is connected to the oil circuit of the manual steering unit, and the other is connected to the oil circuit of the electronically controlled steering unit. The shuttle valve 16 includes ports E, F, and G. The inlet of the pressure reducing valve 17 in the manual steering unit is connected to the oil supply port of the oil supply unit, and the outlet of the pressure reducing valve 17 is connected to port F of the shuttle valve. Port G of the shuttle valve 16 is connected to the inlet of the steering gear unit. The steering cylinder 10 includes a left-chamber oil circuit and a right-chamber oil circuit. The steering gear unit is connected to the left-chamber oil circuit, the right-chamber oil circuit, and the return oil circuit of the oil tank 1, respectively.

[0034] In this scheme, the oil supply system I includes an oil tank 1, a safety valve 2, a pressure switch 3, an oil pump 19, a radiator 20, a check valve 21, and a filter 22. The inlet of filter 22 is connected to oil tank 1. Check valve 21 is a spring-loaded check valve, connected in parallel with pressure switch 3 across filter 22. Check valve 21 is connected in parallel to the hydraulic oil bypass of filter 22, and pressure switch 3 is connected in parallel to the detection bypass of filter 22. When filter 22 is clogged, pressure switch 3 will detect the blockage signal, illuminating its indicator light. Specifically, if filter 22 is clogged, the pressure difference between its inlet and outlet will surge, increasing the pressure difference. Pressure switch 3 will activate when the pressure difference exceeds a certain value, illuminating the indicator light. At this time, check valve 21 acts as a bypass valve. By controlling check valve 21 to open, hydraulic oil flows through the bypass connected to check valve 22, ensuring the normal operation of the hydraulic circuit. The outlet of filter 22 is connected to radiator 20, the outlet of radiator 20 is connected to oil pump 19, one end of safety valve 2 is connected to the outlet pipeline of oil pump 19, and the other end is connected to oil tank 1. The outlet of oil pump 19 is finally divided into two branches, the first branch of oil pump 19 outlet is connected to the oil circuit of electronic steering unit, and the second branch is connected to the oil circuit of manual steering unit.

[0035] In this embodiment, the system includes a start switch 4, a controller 5, a drive motor 6, a steering angle sensor 7, a piston displacement sensor 11, and an adjustable through valve 18. The start switch 4 and controller 5 are connected, and the start switch 4 is used to activate the automatic driving function. The signal output terminals of the steering angle sensor 7 and piston displacement sensor 11 are respectively connected to the controller 5, and the signal input terminal of the steering angle sensor 7 is connected to the steering gear 15. The steering angle sensor 7 detects the steering angle signal of the steering gear 15 and sends it to the controller 5. The controller 5 determines whether to terminate the automatic driving mode if a sudden change in the steering angle rate occurs. If a sudden change in the steering angle rate occurs, the controller stops inputting control current to the drive motor 6 and the adjustable through valve 18, and the automatic driving mode is quickly switched to manual driving mode. The piston displacement sensor 11 detects the piston displacement of the steering cylinder 10 and sends the piston displacement signal of the steering cylinder 10 to the controller 5.

[0036] In this embodiment, the drive motor 6 and the adjustable passage valve 18 are electrically connected to the controller 5. The drive motor 6 is connected to the steering gear 15 and receives electrical signals from the controller 5, enabling it to drive the steering gear 15 to rotate. The adjustable passage valve 18 is connected between the outlet branch of the oil pump 19 and the E port of the shuttle valve 16. The signal input terminal of the piston displacement sensor 11 is connected to the signal of the steering cylinder 10. The initial pressure of the adjustable passage valve 18 is greater than the relief valve safety pressure of the safety valve 2. The safety pressure referred to in this scheme refers to the safety pressure of the safety valve 2. The safety pressure of the safety valve 2 is the maximum pressure set for the entire circuit. When the system pressure exceeds the safety pressure, the safety valve 2 will open, and the oil will flow back to the oil tank 1 to ensure system safety.

[0037] In this scheme, the manual steering unit includes a steering wheel 14 and a pressure reducing valve 17. The steering wheel 14 is connected to the steering gear 15 and is used to manually control the rotation of the steering gear 15. The pressure reducing valve 17 is connected between the outlet branch of the oil pump 19 and the port of the shuttle valve 16F.

[0038] In this design, the steering unit includes a one-way valve 8, an overflow valve 9, an overflow valve 12, a one-way valve 13, and a steering gear 15. The inlets and outlets of one-way valve 8 and overflow valve 9 are connected to the left chamber oil circuit and return oil circuit of the steering cylinder 10, respectively. The inlets and outlets of overflow valve 12 and one-way valve 13 are connected to the right chamber oil circuit and return oil circuit of the steering cylinder 10, respectively. Specifically, the inlet of overflow valve 9 is connected to the left chamber oil circuit of the steering cylinder 10. The oil circuits of the two cylinders are connected. The outlet of the first overflow valve 9 is connected to the inlet and return oil line of the second check valve 13. The outlet of the second check valve 13 is connected to the right chamber oil circuit of the steering cylinder 10. The inlet of the second overflow valve 12 is connected to the right chamber oil circuit of the steering cylinder 10. The outlet of the second overflow valve 12 is connected to the inlet and return oil line of the first check valve 8. The outlet of the first check valve 8 is connected to the left chamber oil circuit of the steering cylinder 10.

[0039] In this scheme, the steering gear 15 includes port A, port B, port C and port D, which correspond to the first, second, third and fourth ports respectively. Port A of the steering gear 15 is connected to port G of the shuttle valve 16, port B is connected to the left chamber oil circuit of the steering cylinder 10, port C is connected to the right chamber oil circuit of the steering cylinder 10, and port D is connected to the return oil line of the oil tank 1. The hydraulic oil in the return oil line flows back to the oil tank 1.

[0040] Compared to existing technologies, this solution eliminates the electromagnetic directional valve in its steering system, and the electronic steering unit eliminates the complex oil circuits and valve blocks. It only requires the controller 5 to electrically control the drive motor 6 to rotate the steering gear 15, and the controller 5 to electrically control the oil pressure through the adjustable valve 17. This steering system can achieve both electro-hydraulic steering during automatic driving and manual mechanical hydraulic steering. It also allows for rapid switching between electro-hydraulic and manual hydraulic steering, making it particularly suitable for rapid handling in emergency situations. This solution achieves automatic vehicle steering by controlling the drive motor 6 to control the steering gear 15, simplifying control. In both automatic and manual steering, manual steering is prioritized. Even if the controller 5 suddenly fails, the electronic control circuit can be shut down promptly, ensuring vehicle safety in emergency situations.

[0041] This solution also provides a tractor electro-hydraulic steering control method, which includes a manual driving mode, an automatic driving mode, and a switching mode. The switching mode is used to switch from the automatic driving mode to the manual driving mode in case of an emergency.

[0042] Manual driving mode: When a manual turn requires a left turn, the operator turns the steering wheel 14 to the left, causing the steering gear 15 to rotate, connecting port A and port B of the steering gear 15. At this time, the adjustable passage valve 18 defaults to a pressure greater than that of the safety valve 2, preventing the adjustable passage valve 18 from opening. Hydraulic oil flows from the oil tank 1 through the pressure reducing valve 17 into the shuttle valve 16, and then through ports A and B (first and second ports) of the steering gear 15 into the left chamber of the steering cylinder 10. A portion of the hydraulic oil in the right chamber of the steering cylinder 10 is compensated to the left chamber through the overflow valve 12 and the check valve 8, while the other portion flows back to the oil tank 1. The piston rod of the steering cylinder 10 moves to the right, driving the steering axle and steering wheel light components to achieve a left turn. Similarly, when a manual turn requires a right turn, the operator turns the steering wheel 14 to the right, causing the steering gear 15 to rotate, connecting port A and port B (first and second ports) of the steering gear 15. At this time, the adjustable through valve 18 defaults to a pressure greater than the safety pressure of the safety valve 2, so the adjustable through valve 18 cannot be opened. The hydraulic oil flows from the oil tank 1 through the pressure reducing valve 17 into the shuttle valve 16, and then through the A and C ports (first and third ports) of the steering gear 15 into the right chamber of the steering cylinder 10. Part of the hydraulic oil in the left chamber of the steering cylinder 10 is compensated to the right chamber through the overflow valve 9 and the check valve 13, while the other part flows back to the oil tank 1. The piston rod of the steering cylinder 10 moves to the left, driving the steering axle and steering wheel light components to achieve right steering.

[0043] Autonomous driving mode:During autonomous driving, when the start switch 4 is turned on, the controller 5 determines whether steering is required based on the path information. If steering is required, the controller 5 outputs current to adjust the pressure through the adjustable valve 18 to equal the safety pressure. Hydraulic oil flows through the adjustable valve 18 into port E of shuttle valve 16, and through pressure reducing valve 17 into port F of shuttle valve 16. Since the pressure at port F of shuttle valve 16 is reduced by pressure reducing valve 17 to less than the safety pressure of safety valve 2, the pressure at port E of shuttle valve 16 equals the safety pressure of safety valve 2. Shuttle valve 16 will select the larger pressure for output. At this time, ports E and G of shuttle valve 16 are connected, and hydraulic oil enters port A of steering gear 15. When a left turn is required, the controller 5 controls the drive motor 6 to turn left, causing steering gear 15 to rotate. Ports A and B (first and second ports) of steering gear 15 are connected. Hydraulic oil flows from tank 1 through adjustable valve 18 and shuttle valve 16G, then flows through steering gear ports A and B into the left chamber of steering cylinder 10. Hydraulic oil in the right chamber of steering cylinder 10 is partially compensated for by overflow valve 12 and check valve 8, and partially flows back to tank 1. The piston rod of steering cylinder 10 moves to the right, driving the steering axle and steering wheel light components to achieve left steering. Similarly, when a right turn is needed, controller 5 controls drive motor 6 to turn right, driving steering gear 15 to rotate, connecting ports A and C (first and third ports) of steering gear 15. Hydraulic oil flows out from the oil tank 1 through the adjustable through valve 18 and shuttle valve 16 (G port), and flows into the right chamber of the steering cylinder 10 through the A and C ports (first and third ports) of the steering gear 15. Part of the hydraulic oil in the left chamber of the steering cylinder 10 is compensated to the right chamber through the relief valve 9 and the one-way valve 13, and part of it flows back to the oil tank 1. The piston rod of the steering cylinder 10 moves to the left, driving the steering axle and steering wheel light components to achieve right steering.

[0044] Switch mode: In emergency situations requiring a switch from automatic to manual driving, the operator turns the steering wheel 14 left or right. The steering angle sensor 7 inputs a steering angle signal to the controller 5. The controller 5 detects a sudden change in the rate of change of the steering angle and stops inputting control current to the drive motor 6 and the adjustable valve 18. The adjustable valve 18 returns to its default state where it cannot open due to pressure exceeding the safety pressure, and hydraulic oil flows out from the pressure reducing valve 17. This switches to manual operation, prioritizing manual control. Traditional fully hydraulic steering systems, which rely on pressure differences, exhibit hysteresis and slow response when switching from automatic to manual driving. However, compared to existing technologies, this invention only requires the controller 5 to determine if there is a sudden change in the rate of change of the steering angle of the steering gear 15. By electrically controlling the drive motor 6 and the adjustable valve 18, the switch from automatic to manual driving is completed, resulting in faster response, higher safety, and effective protection for the vehicle and personnel in emergency situations.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A tractor electro-hydraulic steering system, characterized in that: It includes steering cylinders, shuttle valves, oil supply units, steering gear units, manual steering units, and electronic steering units; The outlet of the oil supply unit is divided into two branches, which are respectively connected to the oil circuits of the manual steering unit and the electronic steering unit. The electronic steering unit includes a controller and an adjustable through valve. The controller is signal-connected to the adjustable through valve, and the oil inlet of the adjustable through valve is connected to the oil outlet of the oil supply unit. The manual steering unit includes a pressure reducing valve, the oil inlet of which is connected to the oil outlet of the oil supply unit. The E port of the shuttle valve is connected to the oil outlet of the adjustable through valve, the F port of the shuttle valve is connected to the oil outlet of the pressure reducing valve, and the G port of the shuttle valve is connected to the oil inlet of the steering unit.

2. The tractor electro-hydraulic steering system according to claim 1, characterized in that: The oil supply unit includes an oil tank, a filter, a bypass valve, and an oil pump; The oil outlet of the oil tank is divided into at least two branches. One branch is equipped with a filter, and the other branch is equipped with a bypass valve. The outlets of the filter and the bypass valve are connected to the inlet of the oil pump.

3. A tractor electro-hydraulic steering system according to claim 1 or 2, characterized in that: The steering unit includes a steering gear. The steering gear has four ports, wherein the first port is connected to the G port of the shuttle valve, the second port of the steering gear is connected to the left chamber oil circuit of the steering cylinder, the third port of the steering gear is connected to the right chamber oil circuit of the steering cylinder, and the fourth port of the steering gear is connected to the return oil circuit.

4. A tractor electro-hydraulic steering system according to claim 3, characterized in that: The manual steering unit also includes a steering wheel, which is connected to the steering gear.

5. A tractor electro-hydraulic steering system according to claim 4, characterized in that: The electronically controlled steering unit also includes a steering angle sensor and a drive motor. The steering angle sensor and the drive motor are respectively connected to the controller signal. The drive motor is connected to the steering wheel. The steering angle sensor is used to detect the steering angle signal of the steering wheel and send it to the controller. The controller determines that the rate of change of steering angle has changed abruptly and stops inputting control current to the drive motor and the adjustable valve.

6. A tractor electro-hydraulic steering system according to claim 4, characterized in that: The electronic steering unit includes an overflow valve, an overflow valve, a check valve, and a check valve. The inlet of the overflow valve is connected to the left chamber oil circuit of the steering cylinder. The outlet of the overflow valve is connected to the inlet and return oil line of the check valve. The outlet of the check valve is connected to the right chamber oil circuit of the steering cylinder. The inlet of the overflow valve is connected to the right chamber oil circuit of the steering cylinder. The outlet of the overflow valve is connected to the inlet and return oil line of the check valve. The outlet of the check valve is connected to the left chamber oil circuit of the steering cylinder.

7. A tractor electro-hydraulic steering system according to claim 4, characterized in that: The electronic steering unit also includes a piston displacement sensor connected to the controller. The piston displacement sensor is connected to the steering cylinder and is used to detect the piston displacement of the steering cylinder and send the piston displacement signal of the steering cylinder to the controller.

8. A tractor electro-hydraulic steering system according to claim 4, characterized in that: The oil supply unit also includes a pressure switch connected in parallel across the filter to detect whether the filter is clogged and to control the bypass valve to open if clogged.

9. A control method for a tractor electro-hydraulic steering system according to any one of claims 1-8, characterized in that: Includes manual driving mode and automatic driving mode; The specific steps for the manual driving mode are as follows: When turning left, the operator turns the steering wheel to the left, causing the steering gear to rotate and the first and second ports of the steering gear to connect. At this time, the adjustable through valve defaults to a pressure greater than the safety pressure, so the adjustable through valve cannot be opened. Hydraulic oil flows from the oil tank through the pressure reducing valve into the shuttle valve, and then through the first and second ports of the steering gear into the left chamber of the steering cylinder. Part of the hydraulic oil in the right chamber of the steering cylinder is compensated to the left chamber through the relief valve and the check valve, while the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the right, driving the steering axle and steering wheels to achieve left turning. When turning right, the operator turns the steering wheel to the right, causing the steering gear to rotate. The first and third ports of the steering gear are connected. At this time, the adjustable through valve defaults to a pressure greater than the safety pressure, so the adjustable through valve cannot be opened. Hydraulic oil flows from the oil tank through the pressure reducing valve into the shuttle valve, and then through the first and third ports of the steering gear into the right chamber of the steering cylinder. Part of the hydraulic oil in the left chamber of the steering cylinder is compensated to the right chamber through the relief valve and the check valve, while the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the left, driving the steering axle and steering wheels to achieve right turn. The specific steps for the autonomous driving mode are as follows: When the start switch is turned on, the controller determines whether steering is required based on the path information. If steering is required, the controller outputs current to adjust the through pressure of the adjustable valve to equal the safety pressure. Hydraulic oil flows into port E of the shuttle valve through the adjustable through valve and into port F of the shuttle valve through the pressure reducing valve. Since the pressure at port F is reduced to less than the safety pressure by the pressure reducing valve, the pressure at port E of the shuttle valve equals the safety pressure. The shuttle valve will select the larger of the two pressures for output. At this time, ports E and G of the shuttle valve are connected, and hydraulic oil enters the first port of the steering gear. When turning left, the controller controls the drive motor to turn left, causing the steering gear to rotate. The first and second ports of the steering gear are connected, and hydraulic oil flows out from the oil tank through the adjustable through valve and shuttle valve G port. It then flows into the left chamber of the steering cylinder through the first and second ports of the steering gear. Part of the hydraulic oil in the right chamber of the steering cylinder is compensated to the left chamber through the relief valve and the check valve, while the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the right, driving the steering axle and steering wheel to achieve left turning. When turning right, the controller controls the drive motor to turn right, causing the steering gear to rotate, and the first and third ports of the steering gear are connected; hydraulic oil flows out from the oil tank through the adjustable through valve and shuttle valve G port, and flows into the right chamber of the steering cylinder through the first and third ports of the steering gear. Part of the hydraulic oil in the left chamber of the steering cylinder is compensated to the right chamber through the relief valve and the one-way valve, and the other part flows back to the oil tank. The piston rod of the steering cylinder moves to the left, driving the steering axle and steering wheel to achieve right turn.

10. The control method for a tractor electro-hydraulic steering system according to claim 9, characterized in that: It also includes a switching mode, which is used to switch from automatic driving mode to manual driving mode in case of an emergency. When the operator turns the steering wheel to the left or right, the steering angle sensor inputs the steering angle signal to the controller. The controller determines that the rate of change of steering angle has changed abruptly, stops inputting control current to the drive motor and the adjustable through valve, and the adjustable through valve restores its default through pressure to be greater than the safety pressure, so that it cannot be opened. At this time, hydraulic oil flows out from the pressure reducing valve.

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