An automatic wheel alignment control system for the rear wheels of a multi-wheel steering system

Abstract

The present invention relates to an automatic centering control system for the rear wheels of a multi-wheel steering system, aiming to solve the problem that when the vehicle speed exceeds the limit in the multi-group mode, the steering system can automatically switch to the front-group mode, or when the steering mode switch is turned off to return to the front-group mode in the multi-group mode, the rear axle wheels can smoothly and stably return to the middle position and be completely locked to avoid the phenomenon of deviation. At the same time, a method study is also carried out on the situation of automatic centering of the rear axle when a fault occurs.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-disciplinary intersections such as automotive electrical appliances, automatic control, and hydraulic transmission, and specifically relates to an automatic centering control system for the rear wheels of a multi-wheel steering system. Background Art

[0002] Multi-wheel steering systems are usually applied to off-road vehicles with large body sizes that need to travel on narrow roads and in conditions where the turning space is limited. However, too high a vehicle speed will increase the risk coefficient of using a multi-wheel steering system, especially rear axle steering, which affects driving safety. Therefore, it is necessary to consider the safety of its operating conditions, especially when the rear wheels need to be centered and how to control their centering.

[0003] Multi-wheel steering systems generally include two working modes: the front group mode and the multi-group mode. In the front group mode, only the front axle steers, and the rear axle tires are always in the centered state. The centering function is achieved by controlling the hydraulic centering cylinder with a centering cylinder electromagnetic directional valve; in the multi-group mode, the rear axle hydraulic booster cylinder is controlled by an electro-hydraulic proportional valve and a booster cylinder electromagnetic directional valve to make the rear axle tires follow the front axle steering. However, considering system reliability and driving safety, it is necessary to reasonably distinguish the operating conditions of the two modes, that is, when the rear axle tires need to follow and when they need to be centered. These situations include: when the vehicle speed is lower than the limit value V and in the multi-group mode, the rear axle tires follow the front axle steering; when the vehicle speed exceeds the limit value V, to avoid unsafe situations such as the rear axle having a large angle and causing tail swing and side slip during high-speed movement of the vehicle, the system will forcibly switch the working mode from the multi-group mode to the front group mode, that is, the rear axle returns to the centered position; when the vehicle speed is lower than the limit value V and the working mode is switched to the front group mode, the rear axle returns to the centered position; it also includes when an electronic control failure occurs in the system, the rear axle returns to the centered position to meet the basic driving requirements of the system. As for how to control the centering of the rear axle tires, it needs to be considered from aspects such as safety, reliability, and driving comfort. First of all, the system cannot directly center through the hydraulic centering cylinder because when the centering pressure is released into the centering cylinder, an instantaneous impact will occur, which will have a certain impact on the steering system and affect driving comfort; secondly, the centering pressure comes from the front axle, is controlled by the steering wheel, and is affected by the accumulator. When the pressure is insufficient or not fully established, the centering cylinder cannot completely lock the rear axle tires in the middle position, and when encountering ground resistance during driving, it will cause the rear axle tires to deviate, affecting driving safety.

[0004] Based on the above considerations, the present invention proposes a method for controlling the centering of the rear axle wheels of a multi-wheel steering system, aiming to solve when the rear axle is centered and how to control the centering to ensure that the rear axle can smoothly and stably return to the middle position and be completely locked to avoid deviation. Summary of the Invention

[0005] In order to solve the problems existing in the background technology, the present invention aims to provide an automatic centering control system for the rear group of wheels of a multi-wheel steering system to solve the above situation.

[0006] Solutions for solving problems

[0007] An automatic centering control system for the rear group of wheels of a multi-wheel steering system, comprising: a steering wheel, a front axle and a rear axle; the system further comprises:

[0008] A front axle displacement sensor, a rear axle displacement sensor, a steering mode switch, a controller, an electro-hydraulic proportional valve, a booster cylinder solenoid valve, a centering cylinder solenoid valve, a booster cylinder and a centering cylinder;

[0009] The front axle responds to the steering wheel. The front axle displacement sensor collects information about the front axle, and the rear axle displacement sensor collects information about the rear axle. The controller is used to process the information collected by the sensors and the real-time input vehicle speed information. The controller is electrically connected to the steering mode switch, the electro-hydraulic proportional valve, the booster cylinder solenoid valve and the centering cylinder solenoid valve;

[0010] The booster cylinder responds to the electro-hydraulic proportional valve and the booster cylinder solenoid valve, and the centering cylinder responds to the centering cylinder solenoid valve. The booster cylinder and the centering cylinder control the steering or centering of the rear axle.

[0011] Furthermore, the system includes: a front group mode and a multi-group mode; the front group mode: the final state of the rear axle is fully centered, and only the front axle steers; the multi-group mode: the rear axle follows the front axle to steer.

[0012] Furthermore, the controller first determines whether the steering mode switch is turned on. If it is not turned on, the system is in the front group mode; if it is turned on, the controller determines whether the received vehicle speed information exceeds a first threshold. If it exceeds, the system is in the front group mode; if it does not exceed the first threshold, the controller switches to the multi-group mode. In the multi-group mode, if it exceeds the first threshold, it enters the front group mode. After that, if it is lower than the first threshold again, the system still remains in the front group mode, and this process is irreversible.

[0013] Furthermore, when the controller switches to the multi-group mode, the controller controls the output of the electro-hydraulic proportional valve, energizes the booster cylinder solenoid valve and the centering cylinder solenoid valve, indirectly controls the operation of the booster cylinder, and the centering cylinder does not operate, and the rear axle follows the front axle to steer.

[0014] Furthermore, when the system is in the front group mode, the controller continues to determine whether the rear axle is close to the middle position according to the information sent by the rear axle displacement sensor; if it is not close to the middle position, the controller controls the output of the electro-hydraulic proportional valve, energizes the booster cylinder solenoid valve and the centering cylinder solenoid valve, indirectly controls the operation of the booster cylinder, and the centering cylinder does not operate, and the rear axle follows the front axle back to the middle position.

[0015] Further, if approaching the middle position, the controller records the data L0 of the displacement sensor of the front axle boost cylinder when the rear axle approaches the middle position. Within N consecutive times, it is determined whether the change amount of the acquisition value L of the displacement sensor of the front axle boost cylinder relative to L0 is greater than the preset threshold δ. If it is not greater, the controller controls the output of the electro-hydraulic proportional valve, energizes the boost cylinder solenoid valve, and energizes the centering cylinder solenoid valve, indirectly controls the operation of the boost cylinder and the centering cylinder, and the centering cylinder of the rear axle builds pressure.

[0016] Further, if it is greater, the controller starts a delay T, and then determines whether the delay time has ended. If it has not ended, the controller controls the output of the electro-hydraulic proportional valve, energizes the boost cylinder solenoid valve, and energizes the centering cylinder solenoid valve, indirectly controls the operation of the boost cylinder and the centering cylinder, and the centering cylinder of the rear axle builds pressure.

[0017] Further, if it has ended, the controller controls the electro-hydraulic proportional valve not to output, de-energizes the boost cylinder solenoid valve, and de-energizes the centering cylinder solenoid valve, indirectly controls the boost cylinder not to operate and the centering cylinder to operate, and the rear axle completes mechanical centering.

[0018] Further, when the controller detects a fault in one of the front axle displacement sensor, the rear axle displacement sensor, and the electro-hydraulic proportional valve, the controller directly controls the boost cylinder solenoid valve and the centering cylinder solenoid valve to be de-energized, which can ensure the pressure building operation of the centering cylinder and the unloading and follow-up of the boost cylinder.

[0019] Further, the controller adopts a PLC steering controller.

[0020] Beneficial effects:

[0021] The beneficial effects of the above technical solution are as follows:

[0022] First, the rear-wheel automatic alignment control method avoids potential unsafe risks such as skew and fishtailing that may occur when a vehicle uses multi-wheel steering under high-speed conditions, improving driving safety. Second, on the basis of not changing the existing hydraulic system, only by optimizing the control strategy can the rear wheels be ensured to be fully aligned, saving costs. Third, the rear-axle wheel centering control method adopts a step-by-step centering method, controlling the operation of the centering cylinder and the booster cylinder in stages, ensuring the rapidity, smoothness, and stability of the rear-axle wheel alignment to the greatest extent, and effectively avoiding the instantaneous impact of the hydraulic system. Fourth, the rear-axle wheel centering control method uses the change in the rotation of the front-axle steering wheel as the basis for whether the pressure of the rear-axle centering cylinder is fully established, avoiding the drawback of incomplete centering caused by insufficient pressure of the rear-axle centering cylinder (internal leakage in the pipeline or insufficient pressure of the accumulator). Fifth, considering the hysteresis of the hydraulic system, the rear-axle wheel centering control method adds a delay function to ensure that the role of the booster cylinder is withdrawn after the pressure of the centering cylinder is fully established and stable, improving the reliability of the rear-wheel automatic alignment. Sixth, three possible alignment conditions of the rear axle are analyzed, and different automatic alignment control methods are formulated according to different conditions. Seventh, the situation of faults in the electronic control system is handled to avoid affecting driving when the rear-wheel steering system completely fails, ensuring the basic use function of the steering system. Brief Description of the Drawings

[0023] Figure 1 is the block diagram of the rear-wheel automatic alignment system;

[0024] Figure 2 is the flow chart of the rear-wheel automatic alignment control method;

[0025] Figure 3 is the schematic diagram of the multi-wheel steering hydraulic system.

[0026] Description of the Reference Numerals:

[0027] 1 - Rear pump; 2 - Emergency pump; 3 - Front pump; 4 and 5 - Front-axle booster cylinders; 6 - Front-axle displacement sensor; 7 - Centering cylinder solenoid valve; 8 and 9 - Centering cylinders; 10 and 11 - Electro-hydraulic proportional valves; 12 and 13 - Booster cylinder solenoid valves; 14 and 15 - Rear-axle displacement sensors; 16 and 17 - Booster cylinders; 18 - Accumulator; 19 - PLC steering controller; 20 - Steering mode switch; Detailed Embodiments

[0028] The following describes the specific embodiments of the present invention in conjunction with the embodiments:

[0029] It should be noted that the structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the implementation conditions of the present invention. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0030] At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear narration and are not used to limit the scope of implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope of implementation of the present invention.

[0031] Embodiment 1:

[0032] The present invention relates to a method for automatically straightening the rear group of wheels in a multi-wheel steering system. The system components on which the control method depends include: a PLC steering controller (PLC controller), an electro-hydraulic proportional valve (proportional flow control valve), a booster cylinder solenoid valve (booster cylinder electro-hydraulic reversing solenoid valve), a centering cylinder solenoid valve, a displacement sensor integrated inside the front and rear axle booster cylinder blocks, a steering mode switch, and the entire steering hydraulic system.

[0033] The multi-wheel steering system includes two working modes: the front group mode and the multi-group mode, which are switched through the steering mode switch. When the switch is closed, it is in the front group mode. The front pump provides power for it. The front axle is steered by the steering wheel through the hydraulic system, and at the same time, centering pressure is provided for the rear axle centering cylinder. At this time, the rear axle booster cylinder unloads and follows, the rear axle centering cylinder builds pressure, and the rear axle is locked in the middle position through an internal mechanical device. When the switch is open, it is in the multi-group mode. The rear pump provides continuous high pressure for it. The rear axle centering cylinder unloads and follows, the rear axle booster cylinder builds pressure, and the rear axle tires are pushed to follow the front axle steering in real time.

[0034] Considering system reliability and driving safety, when the vehicle speed exceeds the limit value V in the multi-group mode, or when the steering mode switch is turned off, the system needs to forcibly and automatically switch to the front-group mode, that is, the rear axle wheels return to the straight position. In particular, it is to prevent unsafe situations such as tail swing and side slip when the rear axle has a large angle under the condition of vehicle speeding. In either case, the switching process includes 4 stages: First, unload and follow the middle cylinder, and build pressure by the booster cylinder to pull the rear axle tire back to a position close to the middle position. At this time, the rear axle tire is basically in the middle position; then, let the middle cylinder intervene, that is, the middle cylinder and the booster cylinder act simultaneously. At this time, it is judged whether the change amount of the front axle steering angle (because the pressure of the middle cylinder on the rear axle is established by turning the steering wheel) is greater than the specified value δ within the set number of times N, and this is used as the basis for whether the pressure of the middle cylinder on the rear axle is fully established; after the condition is satisfied, considering the delay characteristic of the hydraulic system, delay for T seconds to make the pressure of the middle cylinder tend to be stable; finally, control the rear axle booster cylinder to unload and follow, and the middle cylinder mechanically locks the rear axle completely in the middle position, that is, the rear axle completes automatic return to the straight position.

[0035] In addition, when a fault occurs in the electronic control system (when the sensor / proportional flow control valve fails and the fault level is the highest), regardless of the working mode of the steering mode switch, the system must forcibly enter the front-group mode. At this time, the pressure is directly established by the middle cylinder, the booster cylinder unloads and follows, and the middle pressure mainly comes from the accumulator.

[0036] Specifically, the automatic return control method for the rear-group wheels is as follows:

[0037] In the front-group mode, the final state of the rear axle is completely returned to the straight position, and only the front axle steers; in the multi-group mode, the rear axle follows the front axle to steer. However, when the vehicle speed exceeds the limit value of V km / h, considering system and driving safety, the system will forcibly switch to the front-group mode, or when the vehicle speed is lower than the limit value of V km / h and in the multi-group mode, when the steering mode switch is turned off, the system will also switch to the front-group mode. In either case, this switch will go through the following 4 control processes:

[0038] In the first step, the booster cylinder works and the middle cylinder does not work. Considering the stability and smoothness of the steering system and preventing hydraulic impact force, it is necessary to pull the rear axle back to a position close to the middle position ΔL (the difference between the length of the rear axle booster cylinder close to the middle position and the theoretical designed middle position) through the booster cylinder. During this process, the booster cylinder builds pressure, the middle cylinder unloads and follows, and the rear axle is slowly returned to a position close to the middle through the electro-hydraulic proportional valve. At the same time, the PLC steering controller records the data L0 of the front axle booster cylinder displacement sensor at the moment when the rear axle reaches a position close to the middle.

[0039] In the second step, the power cylinder and the centering cylinder are activated. When the rear axle reaches a near-neutral position, the centering cylinder is also activated. However, since the cylinder pressure has not yet been established when the centering cylinder is first activated, and the centering cylinder pressure is completely determined by the front axle, it is necessary to turn the front axle steering wheel to build pressure in the centering circuit. At this time, the front axle angle threshold δ is set (the displacement value of the displacement sensor represents the size of the tire angle). At the same time, the front axle power cylinder displacement sensor data L is continuously collected according to the period T0 (the change in L indicates that the steering wheel is turning and the centering cylinder is building pressure). If the difference between L and L0 is greater than δ for N consecutive times, it can be determined that the rear axle centering cylinder pressure is fully established.

[0040] In the third step, the power cylinder and the centering cylinder continue to work simultaneously. When the centering cylinder pressure is fully established (the conditions in the second step are met), a certain delay time T needs to be set to ensure the stability of the pressure in the centering cylinder. During this process, the power cylinder and the centering cylinder continue to work simultaneously.

[0041] Step 4: The centering cylinder activates and the power cylinder deactivates. When the delay time T expires, the power cylinder is unloaded and deactivated, allowing the centering cylinder to lock the rear axle in neutral through its internal mechanism. This completes the automatic self-centering of the rear wheels.

[0042] In addition, in the event of a failure in the electronic control system, the power cylinder system cannot provide centering power for the rear axle wheels due to a failure in the sensor / proportional flow control valve, and centering can only be performed by the centering cylinder. At this time, the centering pressure mainly comes from the accumulator and the front axle.

[0043] Example 2:

[0044] The following takes a 5-axle vehicle as an example (3 axles do not participate in steering), combined with the attached Figure 1 、 2 3. The present invention is further described in detail:

[0045] The electronically controlled hydraulic multi-wheel steering system includes two working modes: front group and multi-group. The steering mode switch 20 is closed by default, which is the front group mode. At this time, the final state of the rear axle wheels is fully returned to the center position. The rear axle is mechanically locked in the middle position by the centering cylinders 8 and 9. Only the front axle is steered by the steering wheel. The front pump 3 provides power for the front axle circuit and the rear axle centering circuit. When the steering mode switch 20 is turned on, it is the multi-group mode. At this time, the rear pump 1 provides power for the rear axle power-assisting circuit, which follows the steering of the front axle under the push of the power-assisting cylinders 16 and 17. However, when the vehicle speed exceeds the limit Vkm / h, considering the system and driving safety, the system will be forced to switch to the front group mode. Or, when the vehicle speed is lower than the limit Vkm / h and is in the multi-group mode, when the steering mode switch 20 is turned off, the system will also switch to the front group mode. In either case, the switch will go through the following four control processes:

[0046] In the first step, the power cylinders 16 and 17 build up pressure and the centering cylinders 8 and 9 are unloaded and do not work. Considering the stability and smoothness of the steering system and preventing hydraulic impact, the power cylinders 16 and 17 are needed to pull the rear axle back to a position close to the middle position ΔL (the difference between the near-mid-length of the rear axle power cylinder and the theoretically designed mid-length). During this process, the PLC steering controller 19 controls the power cylinder solenoid valves 12 and 13 and the centering cylinder solenoid valve 7 to be energized, and controls the output of the proportional solenoid valves 10 and 11. At this time, the power cylinders 16 and 17 build up pressure, and the centering cylinders 8 and 9 are unloaded and follow-up. The electro-hydraulic proportional valves 10 and 11 control the power cylinders 16 and 17 to push the rear axle back to the near-mid-position slowly. At the same time, the PLC steering controller 19 records the data L0 of the displacement sensor 6 on the front axle power cylinder 4 at the moment the rear axle reaches the near-mid-position.

[0047] In the second step, power cylinders 16 and 17 build pressure, and centering cylinders 8 and 9 also build pressure. When the rear axle reaches near neutral, centering cylinders 8 and 9 are activated. Centering cylinder solenoid valve 7 is de-energized, while the remaining solenoid valves remain in the same state as in the first step. However, since pressure in the cylinders of centering cylinders 8 and 9 has not yet been established when centering cylinders 8 and 9 begin to intervene, power cylinders 16 and 17 cannot be immediately removed. The pressure in centering cylinders 8 and 9 is completely determined by the front axle, so pressure must be built up in the centering circuit by turning the front steering wheel. At this point, a front axle angle threshold δ (the displacement value of the displacement sensor represents the wheel angle) is set. Simultaneously, data L from displacement sensor 6 on the front axle power cylinder 4 is continuously collected at a period T0 (a change in L indicates steering wheel rotation and pressure buildup in the centering cylinders). If the difference between L and L0 is greater than δ for N consecutive times, it can be determined that pressure in the rear axle centering cylinders 8 and 9 is fully established.

[0048] In the third step, booster cylinders 16 and 17 and centering cylinders 8 and 9 continue to operate simultaneously. After the pressure in centering cylinders 8 and 9 is fully established (the conditions in the second step are met), a delay time T is set to ensure the stability of the pressure in centering cylinders 8 and 9. During this process, all solenoid valves remain in the same state as in the second step, and booster cylinders 16 and 17 and centering cylinders 8 and 9 continue to operate simultaneously.

[0049] In the fourth step, centering cylinders 8 and 9 build pressure, while booster cylinders 16 and 17 unload and follow. When delay time T expires, rear axle centering cylinders 8 and 9 fully meet the centering pressure. At this point, booster cylinder solenoid valves 12 and 13 are de-energized, electro-hydraulic proportional valves 10 and 11 are de-energized, and booster cylinders 16 and 17 unload and follow, effectively exiting operation. Centering cylinder solenoid valve 7 remains de-energized, and the internal mechanisms of centering cylinders 8 and 9 completely lock the rear axle wheels in neutral. Automatic wheel alignment is now complete.

[0050] Specifically, for the case where a fault occurs in the electronic control system (a fault occurs in one of the front axle displacement sensor 6, rear axle displacement sensors 14 and 15, and the electro-hydraulic proportional valve), the PLC steering controller 19 directly controls the solenoid directional control valves 12 and 13 of the boost cylinders and de-energizes the centering cylinder solenoid valve 7, which can ensure that the centering cylinders 8 and 9 build pressure and the boost cylinders 16 and 17 unload and follow up. At this time, the centering pressure mainly comes from the accumulator 18.

[0051] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing device produce a means for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0052] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction means that implements the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0053] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

Claims

1. A method for automatically straightening the rear group of wheels of a multi-wheel steering system, characterized in that, Applied to the automatic centering system of the rear group wheels in multi-wheel steering: The automatic centering system of the rear group wheels in multi-wheel steering includes: a controller, an electro-hydraulic proportional valve, a booster cylinder solenoid valve, a centering cylinder solenoid valve, a booster cylinder, a centering cylinder, a front axle displacement sensor, a rear axle displacement sensor, a steering mode switch, and the entire steering hydraulic system; The automatic centering system of the rear group wheels in multi-wheel steering includes two working modes: the front group mode and the multi-group mode, which are switched through the steering mode switch; when the switch is closed, it is the front group mode, and when the switch is open, it is the multi-group mode. In the front group mode: the final state of the rear axle is fully centered, and only the front axle steers; in the multi-group mode: the rear axle follows the front axle to steer; When the vehicle speed exceeds the limit value in the multi-group mode, or when the steering mode switch is closed, the system is forced to automatically switch to the front group mode; this switching process includes 4 stages: The first step, the booster cylinder works, and the centering cylinder does not work: the centering cylinder unloads and follows, and the booster cylinder builds pressure to pull the rear axle tires back to a position close to the middle position. At this time, the rear axle tires are basically in the middle position; The second step, the booster cylinder works, and the centering cylinder also works: let the centering cylinder intervene, that is, the centering cylinder and the booster cylinder act simultaneously. At this time, it is determined whether the change amount of the front axle steering angle is greater than the specified value within the set number of times as the basis for whether the pressure of the rear axle centering cylinder is fully established; The third step, the booster cylinder and the centering cylinder continue to work simultaneously: after the conditions are met, delay for T seconds to make the pressure of the centering cylinder tend to be stable; The fourth step, the centering cylinder works, and the booster cylinder exits: when the delay time T ends, control the rear axle booster cylinder to unload and follow, and the centering cylinder mechanically locks the rear axle completely in the middle position, that is, the rear axle completes automatic centering; when a fault occurs in the electronic control system, regardless of the working mode of the steering mode switch, the system must be forced to enter the front group mode. At this time, the pressure is directly established by the centering cylinder, the booster cylinder unloads and follows, and the centering pressure mainly comes from the accumulator.

2. The automatic return control method for the rear group wheels of the multi-wheel steering system according to claim 1, characterized in that: The front axle responds to the steering wheel. The front axle displacement sensor collects information about the front axle, and the rear axle displacement sensor collects information about the rear axle. The controller is used to process the information collected by the sensors and the real-time input vehicle speed information. The controller is electrically connected to the steering mode switch, the electro-hydraulic proportional valve, the booster cylinder solenoid valve, and the centering cylinder solenoid valve; The booster cylinder responds to the electro-hydraulic proportional valve and the booster cylinder solenoid valve, and the centering cylinder responds to the centering cylinder solenoid valve. The booster cylinder and the centering cylinder control the steering or centering of the rear axle.

3. The automatic centering control method for the rear group of wheels of the multi-wheel steering system according to claim 1, characterized in that, The controller first judges whether the steering mode switch is open. If it is not open, the system is in the front group mode; if it is open, the controller judges whether the received vehicle speed information exceeds the first threshold. If it exceeds, the system is in the front group mode; if it does not exceed the first threshold, the controller switches to the multi-group mode. In the multi-group mode, if it exceeds the first threshold, it enters the front group mode. After that, if it is lower than the first threshold again, the system still remains in the front group mode, and this process is irreversible.

4. The automatic wheel alignment control method for the rear set of wheels of the multi-wheel steering system according to claim 3, characterized in that, The controller switches to the multi-group mode. The controller controls the output of the electro-hydraulic proportional valve, energizes the booster cylinder solenoid valve, and energizes the centering cylinder solenoid valve, indirectly controls the booster cylinder to work, and the centering cylinder does not work, and the rear axle follows the front axle to steer.

5. The automatic wheel alignment control method for the rear group of wheels of the multi-wheel steering system according to claim 3, characterized in that, When the system is in the front group mode, the controller continues to determine whether the rear axle is approaching the middle position according to the information sent by the rear axle displacement sensor; if it is not approaching the middle position, the controller controls the output of the electro-hydraulic proportional valve, energizes the booster cylinder solenoid valve, and energizes the centering cylinder solenoid valve, indirectly controls the operation of the booster cylinder and the non-operation of the centering cylinder, and the rear axle follows the front axle back to the middle position.

6. The automatic centering control method for the rear group of wheels of the multi-wheel steering system according to claim 5, characterized in that, If it is approaching the middle position, the controller records the data L0 of the front axle booster cylinder displacement sensor when the rear axle is approaching the middle position. Within N consecutive times, whether the change amount of the acquisition value L of the front axle booster cylinder displacement sensor relative to L0 is greater than the preset threshold δ. If it is not greater, the controller controls the output of the electro-hydraulic proportional valve, energizes the booster cylinder solenoid valve, and energizes the centering cylinder solenoid valve, indirectly controls the operation of the booster cylinder and the operation of the centering cylinder, and the rear axle centering cylinder builds pressure.

7. The automatic wheel alignment control method for the rear set of wheels of the multi-wheel steering system according to claim 6, characterized in that, If it is greater, the controller starts the delay T, and then determines whether the delay time has ended. If it has not ended, the controller controls the output of the electro-hydraulic proportional valve, energizes the booster cylinder solenoid valve, and energizes the centering cylinder solenoid valve, indirectly controls the operation of the booster cylinder and the operation of the centering cylinder, and the rear axle centering cylinder builds pressure.

8. The automatic wheel alignment control method for the rear group of wheels of the multi-wheel steering system according to claim 7, characterized in that, If it has ended, the controller controls the electro-hydraulic proportional valve not to output, de-energizes the booster cylinder solenoid valve, and de-energizes the centering cylinder solenoid valve, indirectly controls the non-operation of the booster cylinder and the operation of the centering cylinder, and the rear axle completes mechanical centering.

9. The automatic wheel alignment control method for the rear group of wheels of the multi-wheel steering system according to claim 8, characterized in that, When the controller detects a fault in one of the front axle displacement sensor, rear axle displacement sensor, and electro-hydraulic proportional valve, the controller directly controls the de-energization of the booster cylinder solenoid valve and the centering cylinder solenoid valve, which can ensure the pressure building work of the centering cylinder and the unloading and follow-up of the booster cylinder.

10. The automatic wheel alignment control method for the rear set of wheels of the multi-wheel steering system according to claim 1, characterized in that, The controller adopts a PLC steering controller.

Images