Steering control method of bowing steering tractor

Abstract

The invention relates to a wheel type bowing steering tractor, in particular to a steering control method of a bowing steering tractor, which sets three working condition modes: firstly, only bowing steering is executed, secondly, rear wheel auxiliary in-phase steering is executed while bowing steering is executed, and thirdly, rear wheel auxiliary reverse-phase steering is executed while bowing steering is executed. The principle of the control method is that steering modes are determined according to different working conditions. By means of the control method, the tractor has the smaller steering radius in the steering process compared with a traditional tractor, the maneuverability of the tractor in a narrow space is improved, and the tractor has higher stability during high-speed and medium-speed driving.

Description

Technical Field

[0001] The invention relates to a wheeled bending steering tractor, in particular to a steering control method for the bending steering tractor. Background Art

[0002] As a new type of agricultural machinery, wheeled folding steering tractors have received extensive attention and application in China in recent years. The biggest feature of wheeled folding steering tractors is their unique steering method. Traditional tractor steering requires friction between the steering wheel and the ground, while folding steering technology achieves fast and precise steering by changing the relative position between the wheel and the frame. This steering method not only reduces the turning radius, but also enables flexible operation in a small space, greatly improving the efficiency and quality of farmland operations.

[0003] With the continuous improvement of the degree of agricultural mechanization in China, the bending steering tractor has gradually been popularized in more farmlands and small farms due to its superior performance and high operating efficiency. This puts higher requirements on the steering performance of the bending steering tractor. In the prior art, there are precedents for the use of rear wheel auxiliary steering and hydraulic power steering on some agricultural machinery and engineering vehicles, but due to the unique structure of the bending steering tractor, these technologies have not yet been comprehensively applied on the bending steering tractor. Summary of the invention

[0004] In view of the problems raised by the background technology, the purpose of the present invention is to provide a steering control method for a folding steering tractor, which adopts hydraulic power steering technology according to the structure of the folding steering tractor and combines it with rear-wheel auxiliary steering technology to effectively reduce the turning radius, make the vehicle more flexible and convenient during driving, and improve the maneuverability of the vehicle in a narrow space.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A steering control method for a bending steering tractor comprises the following steps: Step S1, when the tractor is driving, when the control system receives a steering command, the control system obtains the current road bumpiness in real time. If the current road bumpiness is less than a preset bumpiness value, step S2 is executed. Otherwise, the control system only controls the bending steering mechanism to perform bending steering and directly proceeds to step S7; Step S2, the control system obtains the current load of the tractor in real time, if the current load of the tractor is less than the preset load value, execute step S3, otherwise execute step S5; Step S3, the control system acquires the current speed, lateral acceleration and yaw angular velocity of the tractor in real time, and if the current speed is greater than the preset speed value, executes step S4, otherwise executes step S5; Step S4, the control system sets the rear wheel in-phase deflection angle and the waist-bending steering angle according to the steering wheel speed, the steering angle, the current vehicle speed, the lateral acceleration, the yaw rate, and the current road bumpiness, and then executes step S6; Step S5, the control system sets the rear wheel reverse phase deflection angle and the bending steering angle according to the steering wheel speed, the steering angle, the current vehicle speed, the lateral acceleration, the yaw rate, and the current road bumpiness, and then executes step S6; Step S6, the control system controls the bending steering mechanism to perform bending steering, and also controls the rear wheel auxiliary steering mechanism to perform rear wheel auxiliary steering; during the tractor steering process, the control system calculates in real time the difference between the actual bending steering angle and the predetermined bending angle, as well as the difference between the actual rear wheel deflection angle and the predetermined rear wheel deflection angle, and uses fuzzy PID control to adjust the bending steering angle and the rear wheel deflection angle in real time; Step S7: Turning ends.

[0006] In step S1, the control system includes a controller, a steering wheel, a rotation angle sensor, a speed sensor, a load sensor, a vehicle speed sensor, a rollover sensor, a steering hydraulic pump, a hydraulic oil tank, a steering control valve, a flow distribution valve and a solenoid valve. The steering wheel is installed on the front axle box of the tractor, and the rotation angle sensor, the speed sensor and the steering control valve are all installed on the steering wheel and connected to the controller; the vehicle speed sensor is installed on the suspension of the rear axle box, and the rollover sensor is installed on the tractor with a bent waist steering, and the vehicle speed sensor and the rollover sensor are all connected to the controller; The steering hydraulic pump is connected to the hydraulic oil tank. The steering hydraulic pump outputs oil. When the oil passes through the flow distribution valve and the solenoid valve, if steering is not performed, all the oil returns directly to the hydraulic oil tank; if steering is performed, part of the oil enters the steering control valve, and part of the oil returns directly to the hydraulic oil tank; the oil entering the steering control valve 5 enters the bending steering mechanism and the rear wheel auxiliary steering mechanism respectively, and then returns to the hydraulic oil tank 13.

[0007] The folding steering mechanism includes a front articulated seat, a rear articulated seat, a left hydraulic cylinder and a right hydraulic cylinder. The front end of the front articulated seat is connected to the front axle box, and the rear end is rotatably articulated with the front end of the rear articulated seat through an articulated shaft. The rear end of the rear articulated seat is connected to the rear axle box. The left hydraulic cylinder is arranged on the left side of the articulated shaft, and the left hydraulic cylinder is respectively connected to the front articulated seat and the rear articulated seat. The right hydraulic cylinder is arranged on the right side of the articulated shaft, and the right hydraulic cylinder is respectively connected to the front articulated seat and the rear articulated seat; the left hydraulic cylinder and the right hydraulic cylinder are connected to the steering control valve through a first oil circuit, and the left hydraulic cylinder and the right hydraulic cylinder are connected to the flow distribution valve through a second oil circuit.

[0008] The rear wheel auxiliary steering mechanism includes an electromagnetic reversing valve and a steering gear. The steering gear is arranged on the suspension of the rear axle box. The electromagnetic reversing valve is connected to the steering control valve through the third oil circuit. The electromagnetic reversing valve is connected to the flow distribution valve through the fourth oil circuit. The steering gear controls the oil flow direction by the electromagnetic reversing valve, thereby driving the rear wheel to reverse.

[0009] In the step S1, the current road bumpiness is collected by a rollover sensor installed on the bending steering tractor, and the current road bumpiness is defined as the change value of the vehicle body tilt angle per unit time.

[0010] In step S3, the preset vehicle speed value is 20 km / h.

[0011] In step S3, the absolute value of the rear wheel reverse phase deflection angle is not greater than 5 degrees; in step S4, the absolute value of the rear wheel reverse phase deflection angle is also not greater than 5 degrees.

[0012] Beneficial effects of the present invention: (1) Reduced turning radius: Since the rear wheels also have a certain steering function and work together with the front wheels, the turning radius of the tractor can be significantly reduced, thereby improving the maneuverability of the vehicle in narrow spaces.

[0013] (2) Improved stability: Rear-wheel assisted steering can control the steering angle of the rear wheels and work in conjunction with the front wheels to improve the stability of the tractor when driving at medium and high speeds or under lateral wind force. In addition, when the road adhesion coefficient changes suddenly, the rear-wheel following technology can enable the vehicle to maintain a high adhesion capacity, thereby enhancing the vehicle's stability against external interference.

[0014] (3) Improved response speed: Rear-wheel assisted steering can respond quickly to the driver's steering input, thereby optimizing the vehicle's reaction rate to steering operations and enabling the driver to control the vehicle's driving trajectory more accurately.

[0015] (4) Good operability: The driver can flexibly select the most suitable steering mode according to different road conditions. Compared with traditional steering technology, it has the following advantages: reduced turning radius, enhanced stability when driving at medium and high speeds, and better road feel, thus ensuring driving safety and comfort. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of the present invention.

[0017] Figure 2 It is a schematic diagram of the electrical principle of the present invention.

[0018] Figure 3 It is a structural block diagram of the control system of the present invention.

[0019] Figure 4 It is a schematic diagram of the top structure of the present invention.

[0020] Figure 5 It is the pid control flow chart of the present invention.

[0021] In the figure: 1. steering hydraulic pump, 2. flow distribution valve, 3. solenoid valve, 4. steering wheel, 5. steering control valve, 6. controller, 7. vehicle speed sensor, 8. left hydraulic cylinder, 9. right hydraulic cylinder, 10. solenoid reversing valve, 11. steering gear, 12. rear wheel, 13. hydraulic oil tank, 14. front axle box, 15. front articulated seat, 16. rear articulated seat, 18. articulated shaft, 19. rear axle box, 20. power output assembly, 21. rotation angle sensor, 22. speed sensor, 23. oil filter, 25. engine, 26. rollover sensor. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described clearly and completely below in conjunction with the drawings of this specification. It should be noted that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] like Figure 1-3 As shown, the present invention provides a steering control method for a bending steering tractor, comprising the following steps: Step S1, when the tractor is driving, when the control system receives a steering command, the control system obtains the current road bumpiness in real time. If the current road bumpiness is less than a preset bumpiness value, step S2 is executed. Otherwise, the control system only controls the bending steering mechanism to perform bending steering and directly proceeds to step S7; Step S2, the control system obtains the current load of the tractor in real time, if the current load of the tractor is less than the preset load value, execute step S3, otherwise execute step S5; Step S3, the control system acquires the current speed, lateral acceleration and yaw angular velocity of the tractor in real time, and if the current speed is greater than the preset speed value, executes step S4, otherwise executes step S5; Step S4, the control system sets the rear wheel in-phase deflection angle and the waist-bending steering angle according to the steering wheel speed, the steering angle, the current vehicle speed, the lateral acceleration, the yaw rate, and the current road bumpiness, and then executes step S6; Step S5, the control system sets the rear wheel reverse phase deflection angle and the bending steering angle according to the steering wheel speed, the steering angle, the current vehicle speed, the lateral acceleration, the yaw rate, and the current road bumpiness, and then executes step S6; Step S6, the control system controls the bending steering mechanism to perform bending steering, and also controls the rear wheel auxiliary steering mechanism to perform rear wheel auxiliary steering; during the tractor steering process, the control system calculates in real time the difference between the actual bending steering angle and the predetermined bending angle, as well as the difference between the actual rear wheel deflection angle and the predetermined rear wheel deflection angle, and uses fuzzy PID control to adjust the bending steering angle and the rear wheel deflection angle in real time; Step S7: Turning ends.

[0024] like Figure 4 As shown, the structure of the bending steering tractor includes a segmented chassis, which includes a front axle box 14 and a rear axle box 19. The front axle box 14 is provided with front wheels on the left and right sides, and the rear wheels 12 are provided on the left and right sides of the rear side of the rear axle box 19. A bending steering mechanism is connected between the rear axle box 19 and the front axle box 14, and a power output assembly 20 is provided at the rear end of the rear axle box 19. All of the above belong to the prior art.

[0025] The present invention arranges a hydraulically driven rear wheel auxiliary steering mechanism on the suspension of the rear axle box 19, and the rear wheel auxiliary steering mechanism includes a steering gear 11 and an electromagnetic reversing valve 10; the hydraulically driven rear wheel auxiliary steering mechanism also belongs to the prior art.

[0026] The control system provided by the present invention includes a controller 6 and a power output assembly controller. The controller 6 and the power output assembly control unit are both prior art and will not be described in detail. The innovation of the present invention is that the control system also incorporates a hydraulic steering assist mechanism, which provides power for the folding steering mechanism and the rear wheel auxiliary steering mechanism of the rear axle box respectively; the hydraulic steering assist mechanism includes a steering hydraulic pump 1, a hydraulic oil tank 13, a steering control valve 5, a flow distribution valve 2 and a solenoid valve 3, the steering hydraulic pump 1 is connected to the hydraulic oil tank 13, and the steering hydraulic pump 1 outputs oil. When the oil passes through the flow distribution valve 2 and the solenoid valve 3, if the steering is not performed, the oil is directly returned to the hydraulic oil tank 13; if the steering is performed, a part of the oil enters the steering control valve 5, and a part directly returns to the hydraulic oil tank 13; the oil entering the steering control valve 5 enters the folding steering mechanism and the rear wheel auxiliary steering mechanism respectively, and then returns to the hydraulic oil tank 13.

[0027] When the controller 6 controls the flow distribution valve 2 through the solenoid valve 3 according to the collected vehicle speed and steering wheel signal, the oil enters the bending steering mechanism and the rear wheel auxiliary steering mechanism respectively when passing through the steering control valve 5, and then returns to the hydraulic oil tank 13.

[0028] The folding steering mechanism includes a front articulated seat 15, a rear articulated seat 16, a left hydraulic cylinder 8 and a right hydraulic cylinder 9. The front end of the front articulated seat 15 is connected to the front axle box 14, and the rear end is rotatably articulated with the front end of the rear articulated seat 16 through an articulated shaft 18. The rear end of the rear articulated seat 16 is connected to the rear axle box 19. The left hydraulic cylinder 8 is arranged on the left side of the articulated shaft 18, and the left hydraulic cylinder 8 is respectively connected to the front articulated seat 15 and the rear articulated seat 16. The right hydraulic cylinder 9 is arranged on the right side of the articulated shaft 18, and the right hydraulic cylinder 9 is respectively connected to the front articulated seat 15 and the rear articulated seat 16; the left hydraulic cylinder 8 and the right hydraulic cylinder 9 are respectively located on both sides of the articulated shaft 18, and the axes of the left hydraulic cylinder 8 and the right hydraulic cylinder 9 are symmetrical about the axis of the tractor; the control system can provide power and telescopic control to the two hydraulic cylinders in telescopic movement, so that they can fold and rotate at the hinge when turning. The angle of the bending steering mechanism is achieved by extending and shortening the left hydraulic cylinder 8 and the right hydraulic cylinder 9.

[0029] The present invention sets three working modes, one is to only perform waist-turning steering, the second is to perform rear wheel auxiliary same-phase steering while performing waist-turning steering, and the third is to perform rear wheel auxiliary reverse-phase steering while performing waist-turning steering. The principle of the control method is to determine the steering mode according to different working conditions. The present invention determines the selection order of working conditions. First, it is judged according to the road surface. When the road surface is highly bumpy, the tractor only performs waist-turning steering; when the tractor is under high and medium load, it is judged according to the vehicle speed, lateral acceleration, and yaw angular velocity at this time, and the waist-turning steering and rear wheel reverse-phase auxiliary steering are automatically adopted or the mode is selected according to the driver's wishes; wherein, according to the preset steering wheel rotation angle in the controller 6 and the deflection angle of the front axle box 14 and the rear axle box 19 at the hinge, and the angle correspondence of the rear wheel reverse-phase deflection, the target steering wheel 4 rotation angle value and the corresponding front axle box 14 and the rear axle box 19 hinge angle and the rear wheel reverse-phase deflection angle are determined. Angle; when the tractor is unloaded or under low load, the vehicle speed, lateral acceleration and yaw angular velocity are judged at this time, and the rear-wheel auxiliary steering module is automatically or manually selected according to the driver's wishes. When the speed is greater than 20km / h, the same-phase rear-wheel auxiliary steering is adopted, and when the speed is less than 20km / h, the reverse-phase rear-wheel auxiliary steering is adopted; according to the preset steering wheel rotation angle and the deflection angle of the front axle box 14 and the rear axle box 19 at the hinge, and the corresponding angle of the rear wheel reverse-phase or same-phase deflection, the target steering wheel 4 rotation angle value and the corresponding front axle box 14 and the rear axle box 19 at the hinge and the reverse-phase or same-phase deflection angle of the rear wheel are determined.

[0030] The steering hydraulic pump 1 can be installed on the engine 25, driven by the crankshaft through a belt and outputting hydraulic oil to the outside; the hydraulic oil tank 13 has inlet and outlet pipe joints, which are respectively connected to the steering hydraulic pump 1 and the flow distribution valve 2 through oil pipes. The flow distribution valve 2 is used to change the oil circuit. When the car is traveling in a straight line, the flow distribution valve 2 connects the working fluid pumped out by the steering hydraulic pump 1 to the hydraulic oil tank 13, the steering hydraulic pump 1 is in an unloading state, and the steering gear 11 does not play a power assist role. When the car needs to turn right, the driver turns the steering wheel 4 to the right, and the flow distribution valve 2 connects the working fluid pumped out by the steering hydraulic pump 1 to the steering control valve 5, and the left and right rear wheels 12 are deflected to the right through the transmission structure, thereby realizing right steering. When turning left, the situation is the opposite of the above.

[0031] The rollover sensor 26 located on the vehicle body detects the ground environment where the tractor is located. When the bumpiness of the ground reaches a certain level, regardless of whether the mode is automatically selected by the driver or the controller 6, the tractor can only complete the steering by extending and shortening the left hydraulic cylinder 8 and the right hydraulic cylinder 9.

[0032] When the ground environment is suitable, the steering mode is automatically selected by the driver's will or the controller 6. At this time, the load sensor (known technology, not shown) detects the load of the tractor. In the case of medium or heavy load, the rear wheels can only perform reverse phase steering. However, during the operation, as long as the rollover sensor 26 detects that the road surface is too bumpy, the rear wheels 12 will automatically return to the normal state until the road surface is suitable, and the rear wheel auxiliary steering is reactivated.

[0033] When the driver drives the tractor to turn, the steering wheel 4 will turn a certain angle. When the steering wheel 4 moves at a high speed and a large angle, the turning radius is small, and vice versa. During the turning process, the rear wheel steering is opposite to the waist turning direction, that is, reverse phase steering, which can effectively reduce the turning radius, but the stability is weak at medium and high speeds. Therefore, when driving at medium and high speeds, the rear wheel steering is in the same direction as the waist turning direction, that is, in-phase steering, to enhance driving stability.

[0034] like Figure 5 As shown, when the steering wheel 4 inputs the rotation speed and the steering angle, the controller 6 calculates the target angle according to the input lateral acceleration, yaw angular velocity, vehicle speed, and road bumpiness. When the difference between the actual angle and the target angle is greater than 0, the controller 6 uses a fuzzy control algorithm to correct the proportional, integral, and differential coefficients of the PID regulation to obtain a better steering angle, and then inputs the signal to the solenoid valve 3 to control the flow of the hydraulic oil.

[0035] In one embodiment of the present invention, the corresponding relationship between the rotation angle of the steering wheel 4 and the articulation angle and the rear wheel turning angle during the bending steering is as follows: When the tractor is only used for bending and steering, the angle of the steering wheel 4 and the corresponding articulation angle during bending and steering are shown in Table 1 below. (540° means the steering wheel is fully turned) Table 1:

[0036] When the tractor is in the middle or high load or low speed, and uses the bending steering and rear wheel auxiliary steering, the steering wheel 4 rotation angle corresponds to the articulation angle and rear wheel turning angle during bending steering as shown in Table 2 below. (The maximum rear wheel turning angle is 5°) Table 2:

[0037] When the tractor is driving at medium and high speeds, the rate of change of the angle of the steering wheel 4 is small when the tractor is using the bending steering and rear wheel auxiliary steering. The corresponding angle of the steering wheel 4 rotation and the articulation angle and rear wheel turning angle during bending steering are shown in Table 3 below. (The maximum rear wheel turning angle is 5°) Table 3:

[0038] Since the actual situations corresponding to the different rotation speeds of the steering wheel 4 and the vehicle speed are different, the relationship between the steering wheel 4 angle, vehicle speed and rear wheel angle per unit time should be considered when considering rear wheel auxiliary steering. If the steering wheel 4 angle is greater than 90° and the vehicle speed is greater than 35°, the rear wheels are deflected by 5°. As shown in Table 4 below: Table 4:

[0039] The above correspondence is only an exemplary description under hard and level good road conditions. When the tractor is under different road conditions and different load conditions, it should be mainly adjusted according to the control system itself. Different correspondences can also be obtained according to the actual conditions of different vehicles, and different correspondences can also be determined according to the differences in target users.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

[0041] Parts of the present invention not described in detail are prior art.

Claims

1. A steering control method for a bending steering tractor, characterized in that: The following steps are involved: Step S1, when the tractor is driving, when the control system receives a steering command, the control system obtains the current road bumpiness in real time. If the current road bumpiness is less than a preset bumpiness value, step S2 is executed. Otherwise, the control system only controls the bending steering mechanism to perform bending steering and directly proceeds to step S7; Step S2, the control system obtains the current load of the tractor in real time, if the current load of the tractor is less than the preset load value, execute step S3, otherwise execute step S5; Step S3, the control system acquires the current speed, lateral acceleration and yaw angular velocity of the tractor in real time, and if the current speed is greater than the preset speed value, executes step S4, otherwise executes step S5; Step S4, the control system sets the rear wheel in-phase deflection angle and the waist-bending steering angle according to the steering wheel speed, the steering angle, the current vehicle speed, the lateral acceleration, the yaw rate, and the current road bumpiness, and then executes step S6; Step S5, the control system sets the rear wheel reverse phase deflection angle and the bending steering angle according to the steering wheel speed, the steering angle, the current vehicle speed, the lateral acceleration, the yaw rate, and the current road bumpiness, and then executes step S6; Step S6, the control system controls the bending steering mechanism to perform bending steering, and also controls the rear wheel auxiliary steering mechanism to perform rear wheel auxiliary steering; during the tractor steering process, the control system calculates in real time the difference between the actual bending steering angle and the predetermined bending angle, as well as the difference between the actual rear wheel deflection angle and the predetermined rear wheel deflection angle, and uses fuzzy PID control to adjust the bending steering angle and the rear wheel deflection angle in real time; Step S7: Turning ends.

2. The steering control method of a bending steering tractor according to claim 1, characterized in that: In step S1, the control system comprises a controller (6), a steering wheel (4), a rotation angle sensor (21), a rotation speed sensor (22), a vehicle speed sensor (7), a rollover sensor (26), a steering hydraulic pump (1), a hydraulic oil tank (13), a steering control valve (5), a flow distribution valve (2) and a solenoid valve (3); the steering wheel (4) is mounted on a front axle housing (14) of a tractor; the rotation angle sensor (21), the rotation speed sensor (22) and the steering control valve (5) are all mounted on the steering wheel (4) and connected to the controller (6); the vehicle speed sensor (7) is mounted on a suspension of a rear axle housing (19); the rollover sensor (26) is mounted on a tractor with a folding steering mechanism; and the vehicle speed sensor (7) and the rollover sensor (26) are both connected to the controller (6); The steering hydraulic pump (1) is connected to the hydraulic oil tank (13). The steering hydraulic pump (1) outputs oil. When the oil passes through the flow distribution valve (2) and the solenoid valve (3), if steering is not performed, all the oil directly returns to the hydraulic oil tank (13); if steering is performed, part of the oil enters the steering control valve (5) and part directly returns to the hydraulic oil tank (13); the oil entering the steering control valve (5) respectively enters the bending steering device and the rear wheel auxiliary steering device, and then returns to the hydraulic oil tank (13).

3. The steering control method of a bending steering tractor according to claim 2, characterized in that: The folding steering mechanism comprises a front articulated seat (15), a rear articulated seat (16), a left hydraulic cylinder (8) and a right hydraulic cylinder (9); the front end of the front articulated seat (15) is connected to the front axle box (14), and the rear end is rotatably articulated with the front end of the rear articulated seat (16) through an articulated shaft (18); the rear end of the rear articulated seat (16) is connected to the rear axle box (19); the left hydraulic cylinder (8) is arranged on the left side of the articulated shaft (18), and the left hydraulic cylinder (8) is respectively connected to the front articulated seat (15) and the rear articulated seat (16); the right hydraulic cylinder (9) is arranged on the right side of the articulated shaft (18), and the right hydraulic cylinder (9) is respectively connected to the front articulated seat (15) and the rear articulated seat (16); the left hydraulic cylinder (8) and the right hydraulic cylinder (9) are connected to the steering control valve (5) through a first oil circuit, and the left hydraulic cylinder (8) and the right hydraulic cylinder (9) are connected to the flow distribution valve (2) through a second oil circuit.

4. The steering control method of a bending steering tractor according to claim 2, characterized in that: The rear wheel auxiliary steering mechanism comprises an electromagnetic reversing valve (10) and a steering gear (11); the steering gear (11) is arranged on a suspension of a rear axle box (19); the electromagnetic reversing valve (10) is connected to a steering control valve (5) via a third oil circuit; the electromagnetic reversing valve (10) is connected to a flow distribution valve (2) via a fourth oil circuit; the electromagnetic reversing valve (10) controls the oil flow direction of the steering gear (11), thereby driving the rear wheel (12) to reverse direction.

5. The steering control method of a bending steering tractor according to claim 1, characterized in that: In step S1, the current road bumpiness is collected by a rollover sensor (26) installed on the bending steering tractor, and the current road bumpiness is defined as the change value of the vehicle body tilt angle per unit time.

6. The steering control method of a bending steering tractor according to claim 1, characterized in that: In step S3, the preset vehicle speed value is 20 km / h.

7. The steering control method of a bending steering tractor according to claim 1, characterized in that: In step S3, the absolute value of the rear wheel reverse phase deflection angle is not greater than 5 degrees; in step S4, the absolute value of the rear wheel reverse phase deflection angle is also not greater than 5 degrees.

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