Steering control method for a tractor capable of bending and steering

Abstract

The present invention relates to a wheeled, folding-back steering tractor, and more specifically, to a steering control method for a folding-back steering tractor. Three operating modes are defined: one for performing folding-back steering only; a second for performing rear-wheel assisted, in-phase steering simultaneously with folding-back steering; and a third for performing rear-wheel assisted, in-phase steering simultaneously with folding-back steering. The principle of the control method is to determine the steering mode based on different operating conditions. Using the control method provided by the present invention, the tractor has a smaller turning radius during steering than conventional tractors, thereby improving the vehicle's maneuverability in narrow spaces and providing greater stability when traveling at high and medium speeds.

Description

Technical Field

[0001] The invention relates to a wheel-type 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 tackling tractors have garnered widespread attention and adoption in China in recent years. Their defining feature is their unique steering method. While conventional tractors rely on friction between the steering wheels and the ground for steering, tackling technology achieves fast and precise steering by shifting the relative position of the wheels and frame. This steering method not only reduces the turning radius but also allows for flexible operation in confined spaces, significantly improving the efficiency and quality of farmland operations.

[0003] With the continuous improvement of agricultural mechanization in China, truncation-steer tractors, due to their superior performance and high operating efficiency, have gradually become more commonplace on more farmland and small farms. This places higher demands on the steering performance of truncation-steer tractors. In the existing technology, rear-wheel assisted steering and hydraulic power steering have been used in some agricultural machinery and engineering vehicles. However, due to the unique structure of truncation-steer tractors, these technologies have not yet been fully integrated into truncation-steer tractors. Summary of the Invention

[0004] In response to the problems raised in the background technology, the purpose of the present invention is to provide a steering control method for a tuck-in steering tractor. According to the structure of the tuck-in steering tractor, the method adopts hydraulic power steering technology and combines it with rear-wheel auxiliary steering technology to effectively reduce the turning radius, making the vehicle more flexible and convenient during driving and improving the maneuverability of the vehicle in narrow spaces.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A steering control method for a bending steering tractor, comprising the following steps:

[0007] Step S1: When the tractor is driving, when the control system receives a steering command, the control system obtains the current road surface bumpiness in real time. If the current road surface 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.

[0008] 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, step S3 is executed; otherwise, step S5 is executed.

[0009] Step S3: The control system obtains the current speed, lateral acceleration, and yaw rate of the tractor in real time. If the current speed is greater than a preset speed value, step S4 is executed; otherwise, step S5 is executed.

[0010] Step S4: The control system sets the rear wheel in-phase deflection angle and the camber steering angle according to the steering wheel speed, steering angle, current vehicle speed, lateral acceleration, yaw rate, and current road roughness, and then executes step S6.

[0011] Step S5: The control system sets the rear wheel counter-phase deflection angle and the camber steering angle according to the steering wheel speed, steering angle, current vehicle speed, lateral acceleration, yaw rate, and current road roughness, and then executes step S6;

[0012] 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;

[0013] Step S7: Turning ends.

[0014] 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 mounted on the front axle housing of the tractor, and the rotation angle sensor, the speed sensor, and the steering control valve are all mounted on the steering wheel and connected to the controller; the vehicle speed sensor is mounted on the suspension of the rear axle housing, and the rollover sensor is mounted on the tractor with a bent-back steering mechanism, and the vehicle speed sensor and the rollover sensor are both connected to the controller.

[0015] 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 will return 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 waist steering mechanism and the rear wheel auxiliary steering mechanism respectively, and then returns to the hydraulic oil tank 13.

[0016] The described 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.

[0017] 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 is controlled by the electromagnetic reversing valve to control the oil flow direction, thereby driving the rear wheel to reverse.

[0018] In step S1, the current road bumpiness is collected by a rollover sensor installed on the bending steering tractor. The current road bumpiness is defined as the change in the vehicle body tilt angle per unit time.

[0019] In step S3, the preset vehicle speed value is 20 km / h.

[0020] In step S3, the absolute value of the rear wheel counter-phase deflection angle is not greater than 5 degrees; in step S4, the absolute value of the rear wheel counter-phase deflection angle is also not greater than 5 degrees.

[0021] Beneficial effects of the present invention:

[0022] (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.

[0023] (2) Improved stability: Rear-wheel assisted steering can improve the stability of the tractor when driving at medium and high speeds or under the influence of side wind by controlling the steering angle of the rear wheels. 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.

[0024] (3) Improved response speed: Rear-wheel assisted steering can quickly respond to the driver's steering input, thereby optimizing the vehicle's reaction rate to steering operations and enabling the driver to more accurately control the vehicle's driving trajectory.

[0025] (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

[0026] Figure 1 It is a flow chart of the present invention.

[0027] Figure 2 It is a schematic diagram of the electrical principle of the present invention.

[0028] Figure 3 It is a structural block diagram of the control system of the present invention.

[0029] Figure 4 It is a schematic diagram of the top structure of the present invention.

[0030] Figure 5 It is the pid control flow chart of the present invention.

[0031] 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. Angle sensor, 22. Speed ​​sensor, 23. Oil filter, 25. Engine, 26. Rollover sensor. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings of this specification. It should be noted that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] like Figure 1-3 As shown, the present invention provides a steering control method for a bending steering tractor, comprising the following steps:

[0034] Step S1: When the tractor is driving, when the control system receives a steering command, the control system obtains the current road surface bumpiness in real time. If the current road surface 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.

[0035] 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, step S3 is executed; otherwise, step S5 is executed.

[0036] Step S3: The control system obtains the current speed, lateral acceleration, and yaw rate of the tractor in real time. If the current speed is greater than a preset speed value, step S4 is executed; otherwise, step S5 is executed.

[0037] Step S4: The control system sets the rear wheel in-phase deflection angle and the camber steering angle according to the steering wheel speed, steering angle, current vehicle speed, lateral acceleration, yaw rate, and current road roughness, and then executes step S6.

[0038] Step S5: The control system sets the rear wheel counter-phase deflection angle and the camber steering angle according to the steering wheel speed, steering angle, current vehicle speed, lateral acceleration, yaw rate, and current road roughness, and then executes step S6;

[0039] 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;

[0040] Step S7: Turning ends.

[0041] 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 left and right sides of the front axle box 14 are respectively provided with front wheels, and the left and right sides of the rear side of the rear axle box 19 are respectively provided with rear wheels 12. 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. The above belong to the existing technology.

[0042] 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.

[0043] 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 integrates a hydraulic steering assist mechanism, which provides power to 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. The steering hydraulic pump 1 outputs oil. When the oil passes through the flow distribution valve 2 and the solenoid valve 3, if no steering is performed, the oil is directly returned 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 enters the folding steering mechanism and the rear wheel auxiliary steering mechanism respectively, and then returns to the hydraulic oil tank 13.

[0044] 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 waist 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.

[0045] 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, and 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 the telescopic movement, so that they can fold and rotate at the articulation 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.

[0046] The present invention sets three working modes, one is to only perform waist-turning steering, the second is to perform rear wheel assisted same-phase steering while performing waist-turning steering, and the third is to perform rear wheel assisted 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 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 assisted steering are automatically adopted or the mode is selected according to the driver's wishes; wherein, according to the correspondence between the steering wheel rotation angle preset 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 of the rear wheel reverse-phase deflection, the target steering wheel 4 rotation angle value and the corresponding deflection angle of the front axle box 14 and the rear axle box 19 at the hinge and the rear wheel reverse-phase deflection are determined. Angle; when the tractor is unloaded or lightly loaded, 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 20 km / h, the same-phase rear-wheel auxiliary steering is adopted, and when the speed is less than 20 km / h, the opposite-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, as well as the corresponding relationship between the angle of the rear wheel anti-phase or in-phase deflection, the target steering wheel 4 rotation angle value and the corresponding angle of the front axle box 14 and the rear axle box 19 at the hinge and the angle of the rear wheel anti-phase or in-phase deflection are determined.

[0047] The steering hydraulic pump 1 can be mounted on the engine 25 and driven by the crankshaft via a belt to deliver hydraulic fluid. The hydraulic oil tank 13 has inlet and outlet pipe connections, connected to the steering hydraulic pump 1 and flow distribution valve 2 via oil pipes. The flow distribution valve 2 changes the oil flow path. When the vehicle is traveling in a straight line, the flow distribution valve 2 connects the hydraulic fluid pumped from the steering hydraulic pump 1 to the hydraulic oil tank 13, unloading the steering hydraulic pump 1 and preventing the steering gear 11 from assisting. To turn right, the driver turns the steering wheel 4 to the right. The flow distribution valve 2 connects the hydraulic fluid pumped from the steering hydraulic pump 1 to the steering control valve 5, which, through the transmission mechanism, causes the left and right rear wheels 12 to steer right, thus achieving right steering. The reverse occurs when turning left.

[0048] The rollover sensor 26 located on the vehicle body detects the ground environment in which the tractor is located. When the ground bumpiness reaches a certain level, the tractor can only complete the steering by extending and shortening the left hydraulic cylinder 8 and the right hydraulic cylinder 9, regardless of whether the mode is automatically selected by the driver or the controller 6.

[0049] When the ground conditions are suitable, the steering mode is automatically selected by the driver or by controller 6. A load sensor (known technology, not shown) detects the tractor's load. Under moderate or heavy loads, the rear wheels are restricted to counter-steering. However, during operation, if the rollover sensor 26 detects excessive road roughness, the rear wheels 12 automatically return to the normal position until the road conditions return to a suitable state, at which point rear-wheel assisted steering is reactivated.

[0050] When the driver turns the tractor, the steering wheel 4 rotates a certain angle. When the steering wheel 4 moves at a high speed and a large angle, the turning radius is small; conversely, the turning radius is large. During the turning process, the rear wheel steering is in the opposite direction of the waist steering, i.e., counter-phase steering. This can effectively reduce the turning radius, but it reduces stability 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 steering, i.e., in-phase steering, to enhance driving stability.

[0051] like Figure 5 As shown, when the steering wheel 4 inputs the speed and angle, the controller 6 calculates the target angle based on 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 calculate a better steering angle, and then inputs the signal to the solenoid valve 3 to control the flow of hydraulic oil.

[0052] In one embodiment of the present invention, the corresponding relationship between the rotation angle of the steering wheel 4 and the articulation angle and rear wheel turning angle during the bending steering is as follows:

[0053] When the tractor is only in the bending steering position, the angle of the steering wheel 4 and the corresponding articulation angle during bending steering are shown in Table 1 below. (540° means the steering wheel is fully engaged)

[0054] Table 1:

[0055]

[0056] When the tractor is in the middle or high load or low speed mode and uses the tuck-in steering and rear wheel auxiliary steering, the angle of the steering wheel 4, the articulation angle during tuck-in steering, and the rear wheel steering angle are shown in Table 2 below. (The maximum rear wheel steering angle is 5°)

[0057] Table 2:

[0058]

[0059] When the tractor is driving at medium and high speeds and using the tuck-in and rear-wheel assisted steering, the rate of change in the steering wheel 4 rotation angle is small. The corresponding steering wheel 4 rotation angle, the articulation angle during tuck-in steering, and the rear wheel rotation angle are shown in Table 3 below. (The maximum rear wheel rotation angle is 5°)

[0060] Table 3:

[0061]

[0062] Because different steering wheel rotation speeds and vehicle speeds correspond to different real-world situations, the relationship between the steering wheel angle, vehicle speed, and rear wheel angle per unit time must be considered when considering rear-wheel assisted steering. If the steering wheel angle is greater than 90° and the vehicle speed is greater than 35°, the rear wheels will deflect by 5°. This is shown in Table 4 below:

[0063] Table 4:

[0064]

[0065] The above mapping relationships are merely illustrative for a hard, level surface. When the tractor operates under different road conditions and loads, the control system should be adjusted accordingly. Different mapping relationships can be developed based on the actual conditions of different vehicles and the target user.

[0066] 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 principles of the present invention should be included in the scope of protection of the present invention.

[0067] The parts not described in detail in this invention are prior art.

Claims

1. A steering control method for a tractor with a bent-back steering mechanism, characterized by: 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 surface bumpiness in real time. If the current road surface 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, step S3 is executed; otherwise, step S5 is executed. Step S3: The control system obtains the current speed, lateral acceleration, and yaw rate of the tractor in real time. If the current speed is greater than a preset speed value, step S4 is executed; otherwise, step S5 is executed. Step S4: The control system sets the rear wheel in-phase deflection angle and the camber steering angle according to the steering wheel speed, steering angle, current vehicle speed, lateral acceleration, yaw rate, and current road roughness, and then executes step S6. Step S5: The control system sets the rear wheel counter-phase deflection angle and the camber steering angle according to the steering wheel speed, steering angle, current vehicle speed, lateral acceleration, yaw rate, and current road roughness, 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 for a bending steering tractor according to claim 1, characterized in that: In step S1, the control system includes 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 the front axle housing (14) of the 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 the suspension of the rear axle housing (19); the rollover sensor (26) is mounted on the tractor with a bent-back 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, the oil is directly returned 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) enters the bending steering device and the rear wheel auxiliary steering device respectively, and then returns to the hydraulic oil tank (13).

3. The steering control method for a bending steering tractor according to claim 2, characterized in that: 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 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 for 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 the suspension of the rear axle box (19). The electromagnetic reversing valve (10) is connected to the steering control valve (5) through a third oil circuit. The electromagnetic reversing valve (10) is connected to the flow distribution valve (2) through 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 for 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 a bending steering tractor, and the current road bumpiness is defined as a change in the vehicle body tilt angle per unit time.

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

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