Four-wheel steering system for vehicle and control method thereof

Abstract

The invention discloses a vehicle four-wheel steering system and a control method thereof. The steering system comprises an oil tank, a hydraulic pump, a first overflow valve, a steering gear, a front axle working cylinder, a front axle drag cylinder and a rear axle control circuit. The control method is that each component of the steering system is actuated so that the vehicle can complete front-wheel steering / four-wheel steering / crab-shaped steering movements. The invention solves the technical problems of inconvenient steering and poor maneuverability of large vehicles in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle steering, and in particular to a vehicle four-wheel steering system and a control method thereof. Background Art

[0002] With the rapid development of modern society and the improvement of people's living standards, the number of vehicles is increasing rapidly, such as cars, trucks and some large vehicles. Each large vehicle has high requirements for steering. For example, on snowy days, the roads will be affected by snow accumulation, which will affect the passage of other vehicles. At this time, snowplows are needed for clearing. The existing snowplows have large blind spots due to steering restrictions, which will affect the cleaning effect.

[0003] The patent with authorization announcement number CN 202098457U discloses an electronically controlled hydraulic four-wheel steering system for a two-axle or three-axle vehicle. However, the front wheel steering mechanism of the steering system adopts a rack and pinion steering mechanism, and the rear wheels adopt a double-rod hydraulic cylinder to produce a certain degree of deflection, but such steering has certain limitations. Summary of the invention

[0004] The purpose of the present invention is to provide a vehicle four-wheel steering system and a control method thereof, which solves the technical problems of inconvenient steering and poor maneuverability of large vehicles in the prior art.

[0005] A vehicle four-wheel steering system comprises a fuel tank, a hydraulic pump, a first relief valve, a steering gear, a front axle working cylinder and a front axle dragging cylinder, the steering gear comprises a first steering oil inlet, a first steering oil outlet, a second steering oil outlet, a second steering oil inlet, a hydraulic oil inlet and a hydraulic oil return port, and two independent pipelines are arranged inside the steering gear, the front axle working cylinder is connected to one of the independent pipelines inside the steering gear through the first steering oil inlet and the first steering oil outlet, the front axle dragging cylinder is connected to the other pipeline inside the steering gear through the second steering oil outlet and the second steering oil inlet, the front axle working cylinder controls the rotation of the left front wheel of the vehicle, the front axle dragging cylinder controls the rotation of the right front wheel of the vehicle, the hydraulic oil inlet and the hydraulic oil return port are respectively connected to the hydraulic pump, the hydraulic pump is driven by the engine of the vehicle, and the hydraulic pump is connected to the fuel tank in parallel with the first relief valve.

[0006] The beneficial effects of adopting the above technical solution are: the present invention can rotate a single wheel through two hydraulic cylinders, so that the vehicle steering adjustment is convenient and the steering blind area of ​​large vehicles can be effectively reduced;

[0007] The present invention improves the low-speed maneuverability of the large vehicle by reducing the turning radius of the large vehicle, thereby improving the operating effect of the steering operation condition.

[0008] On the basis of the above technical solution, the present invention can also be improved as follows:

[0009] Furthermore, the front axle drag cylinder is a four-chamber hydraulic cylinder, and is divided into a first front axle chamber, a second front axle chamber, a third front axle chamber and a fourth front axle chamber from left to right, the first front axle chamber is connected to the second steering oil outlet, and the fourth front axle chamber is connected to the second steering oil inlet.

[0010] Furthermore, it also includes a rear axle control circuit, which is connected to the second front axle chamber and the third front axle chamber, and controls the rotation and centering of the rear wheels of the vehicle.

[0011] Furthermore, the rear axle control circuit includes a reversing valve, a rear axle working hydraulic cylinder and an accumulator, the reversing valve is a three-position four-way reversing valve, the two actuator oil ports of the reversing valve are respectively connected to the second front axle chamber and the third front axle chamber, the rear axle working hydraulic cylinder is a four-chamber hydraulic cylinder, and is divided into the first rear axle chamber, the second rear axle chamber, the third rear axle chamber and the fourth rear axle chamber from left to right, the first rear axle chamber is connected to the pressure oil port of the reversing valve to form a first circuit, the second rear axle chamber is connected to the return oil port of the reversing valve to form a second circuit, and the accumulator is respectively connected to the third rear axle chamber and the fourth rear axle chamber to form a third circuit.

[0012] Furthermore, a first branch is connected between the first circuit and the third circuit, and a second branch is connected between the second circuit and the third circuit. The first branch is composed of a first one-way valve and a second overflow valve in parallel, and the second branch is composed of a second one-way valve and a second overflow valve in parallel. The conduction direction of the first one-way valve is opposite to that of the second one-way valve. The beneficial effect of adopting this step is that the extension and retraction of the hydraulic cylinder can be controlled by multiple one-way valves and overflow valves, thereby completing the transition of various steering modes.

[0013] The present invention also discloses a control method for a vehicle four-wheel steering system, which uses the vehicle four-wheel steering system to control the vehicle to perform front-wheel steering / four-wheel steering / crab steering.

[0014] The beneficial effect of adopting the above technical solution is that the present invention can achieve front-wheel steering / four-wheel steering / crab steering, so that the vehicle can be turned freely and the maneuverability of the vehicle can be improved.

[0015] On the basis of the above technical solution, the present invention can also be improved as follows:

[0016] Furthermore, when the vehicle is steering the front wheels, the hydraulic pump draws hydraulic oil from the oil tank and sends it into the steering gear. Part of the hydraulic oil enters a pipeline in the steering gear to control the extension and retraction of the front axle working cylinder, thereby realizing the rotation of the left front wheel of the vehicle, and the other part enters the remaining pipeline in the steering gear to control the movement of the front axle drag cylinder, thereby realizing the rotation of the right front wheel of the vehicle.

[0017] Furthermore, when the vehicle performs four-wheel steering, the hydraulic pump draws hydraulic oil from the oil tank and sends it to the steering gear. A part of the hydraulic oil enters a pipeline in the steering gear to control the extension and retraction of the front axle working cylinder, thereby realizing the rotation of the left front wheel of the vehicle, and the other part enters the remaining pipeline in the steering gear to control the movement of the front axle drag cylinder, thereby realizing the rotation of the right front wheel of the vehicle;

[0018] The reversing valve is started, so that the rear axle control circuit starts to work, and the piston rod inside the front axle drag cylinder moves, so that the hydraulic oil flows to the rear axle working hydraulic cylinder, and the rear axle working hydraulic cylinder is controlled to perform telescopic movement in the opposite direction of the telescopic direction of the front axle working cylinder, so as to realize rear wheel steering;

[0019] When the wheel needs to be straightened, the floating piston of the rear axle working hydraulic cylinder is squeezed by the high-pressure oil, and the piston rod between the floating pistons is constrained to the position when the vehicle is moving straight, that is, the centering of the rear axle wheels is achieved. At this time, the accumulator squeezes part of the hydraulic oil according to actual needs. This part of the hydraulic oil will enter the rear axle working hydraulic cylinder and the front axle towing cylinder through the first one-way valve, the second overflow valve, the second one-way valve, and the second overflow valve to replenish the oil to make up for the leakage of the hydraulic oil.

[0020] Furthermore, when the vehicle performs crab-turning, the hydraulic pump draws hydraulic oil from the oil tank and sends it into the steering gear. A portion of the hydraulic oil enters a pipeline in the steering gear to control the extension and retraction of the front axle working cylinder, thereby realizing the rotation of the left front wheel of the vehicle, and another portion enters the remaining pipeline in the steering gear to control the movement of the front axle drag cylinder, thereby realizing the rotation of the right front wheel of the vehicle.

[0021] The reversing valve is started, so that the rear axle control circuit starts to work, and the piston rod inside the front axle drag cylinder moves, so that the hydraulic oil flows to the rear axle working hydraulic cylinder, and the rear axle working hydraulic cylinder is controlled to perform telescopic movement in the same direction as the front axle working cylinder, so as to realize rear wheel steering;

[0022] When the wheel needs to be straightened, the floating piston of the rear axle working hydraulic cylinder is squeezed by the high-pressure oil, and the piston rod between the floating pistons is constrained to the position when the vehicle is moving straight, that is, the centering of the rear axle wheels is achieved. At this time, the accumulator squeezes part of the hydraulic oil according to actual needs. This part of the hydraulic oil will enter the rear axle working hydraulic cylinder and the front axle towing cylinder through the first one-way valve, the second overflow valve, the second one-way valve, and the second overflow valve to replenish the oil to make up for the leakage of the hydraulic oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of a vehicle four-wheel steering system according to a specific embodiment 1 of the present invention;

[0025] Reference numerals:

[0026] 1- oil tank; 2- hydraulic pump; 3- first overflow valve; 4- steering gear; 5- front axle working cylinder; 6- front axle drag cylinder; 7- rear axle control circuit; 8- first circuit; 9- second circuit; 10- third circuit; 11- first branch; 12- second branch; 13- first check valve; 14- second overflow valve; 15- second check valve; 16- third overflow valve;

[0027] 401 - first steering oil inlet; 402 - first steering oil outlet; 403 - second steering oil outlet; 404 - second steering oil inlet; 405 - hydraulic oil inlet; 406 - hydraulic oil outlet;

[0028] 601-first front bridge chamber; 602-second front bridge chamber; 603-third front bridge chamber; 604-fourth front bridge chamber;

[0029] 701 - reversing valve; 702 - rear axle working hydraulic cylinder; 703 - accumulator; 704 - first rear axle chamber; 705 - second rear axle chamber; 706 - third rear axle chamber; 707 - fourth rear axle chamber. DETAILED DESCRIPTION

[0030] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0031] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0032] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] Example 1

[0034] like Figure 1 As shown, a vehicle four-wheel steering system provided in this embodiment can realize the steering of the front wheels, and it includes a fuel tank 1, a hydraulic pump 2, a first overflow valve 3, a steering gear 4, a front axle working cylinder 5 and a front axle drag cylinder 6. The steering gear 4 includes a first steering oil inlet 401, a first steering oil outlet 402, a second steering oil outlet 403, a second steering oil inlet 404, a hydraulic oil inlet 405 and a hydraulic oil return port 406, and two independent pipelines are arranged inside the steering gear. The front axle working cylinder 5 is connected to one of the independent pipelines inside the steering gear 4 through the first steering oil inlet 401 and the first steering oil outlet 402, and the front axle drag cylinder 6 is connected to another pipeline inside the steering gear 4 through the second steering oil outlet 403 and the second steering oil inlet 404. The steering gear can be model SF100-03-07. The steering gear may also be other power steering gears with an independent pipeline inside. The front axle working cylinder 5 controls the rotation of the left front wheel of the vehicle, and the front axle drag cylinder 6 controls the rotation of the right front wheel of the vehicle. The hydraulic oil inlet 405 and the hydraulic oil return port 406 are respectively connected to the hydraulic pump 2. The hydraulic pump 2 is driven by the engine of the vehicle, and the hydraulic pump 2 is connected to the oil tank 1 in parallel with the first overflow valve 3. When working, the car engine is started, and the hydraulic pump is started by the car engine, and then the hydraulic pump 2 starts to supply oil to the steering gear 4. The steering gear controls the oil volume inside the front axle working cylinder 5 and the front axle drag cylinder 6 to complete the steering control, wherein the front axle working cylinder 5 controls the steering of the left front wheel, and the front axle drag cylinder 6 controls the steering of the right front wheel; in this embodiment, the first overflow valve 3 is used to control the maximum pressure output by the hydraulic pump 2; in this embodiment, there are two independent pipelines inside the steering gear 4, one pipeline transfers the high-pressure oil from the hydraulic pump to the front axle working cylinder 5 to realize the extension and retraction of the front axle hydraulic cylinder; the other pipeline transfers the oil from the hydraulic pump to the front axle drag cylinder 6 to drive the extension and retraction of the front axle drag cylinder.

[0035] Among them, Figure 1 As shown, the front axle towing cylinder 6 is a four-chamber hydraulic cylinder, and is divided into a first front axle chamber 601, a second front axle chamber 602, a third front axle chamber 603 and a fourth front axle chamber 604 from left to right, the first front axle chamber 601 is connected to the second steering oil outlet 403, and the fourth front axle chamber 604 is connected to the second steering oil inlet 404.

[0036] Among them, Figure 1 As shown, it also includes a rear axle control circuit 7, which is connected to the second front axle chamber 602 and the third front axle chamber 603, and the rear axle control circuit 7 controls the rotation and centering of the rear wheels of the vehicle; the rear axle control circuit 7 in this embodiment controls the rear wheels of the vehicle to change the steering mode of the vehicle.

[0037] Among them, Figure 1 As shown, the rear axle control circuit 7 includes a reversing valve 701, a rear axle working hydraulic cylinder 702 and an accumulator 703. The reversing valve 701 is a three-position four-way reversing valve. The two actuator oil ports of the reversing valve 701 are respectively connected to the second front axle chamber 602 and the third front axle chamber 603. The rear axle working hydraulic cylinder 702 is a four-chamber hydraulic cylinder, and is divided into a first rear axle chamber 704, a second rear axle chamber 705, a third rear axle chamber 706 and a fourth rear axle chamber 707 from left to right. The first rear axle chamber 704 is connected to the pressure oil port of the reversing valve 701 to form a first circuit 8, the second rear axle chamber 705 is connected to the return oil port of the reversing valve 701 to form a second circuit 9, and the accumulator 703 is respectively connected to the third rear axle chamber 706 and the fourth rear axle chamber 707 to form a third circuit 10.

[0038] Among them, a first branch 11 is connected between the first circuit 8 and the third circuit 10, and a second branch 12 is connected between the second circuit 9 and the third circuit 10. The first branch 11 is composed of a first one-way valve 13 and a second overflow valve 14 in parallel, and the second branch 12 is composed of a second one-way valve 15 and a third overflow valve 16 in parallel. The conduction direction of the first one-way valve 13 is opposite to that of the second one-way valve 15.

[0039] In this embodiment, each time the rear axle wheels are centered, the accumulator 703 will replenish the oil in the front axle towing cylinder and the rear axle working and centering cylinder through the first one-way valve 13, the second one-way valve 15, the second overflow valve 14 and the third overflow valve 16 as needed to compensate for the leakage of hydraulic oil; when the rear axle needs to be centered, the accumulator 703 will squeeze the high-pressure oil into the third rear axle chamber 706 and the fourth rear axle chamber 707 of the rear axle working hydraulic cylinder 702, and the rear axle wheels will be centered by squeezing the floating piston with the high-pressure oil.

[0040] The working process of this embodiment:

[0041] This embodiment has three modes, namely, front-wheel steering mode, four-wheel steering mode and crab steering mode. When this embodiment is working, all pipelines are filled with oil;

[0042] Embodiment 2:

[0043] The present invention also discloses a control method for a vehicle four-wheel steering system, which uses the vehicle four-wheel steering system in Example 1 to control the vehicle to perform front-wheel steering / four-wheel steering / crab steering, and the conversion between the two modes of four-wheel steering and crab steering in this embodiment is achieved through a reversing valve 7.

[0044] Among them, when the vehicle performs front wheel steering, the hydraulic pump 2 draws hydraulic oil from the oil tank 1 and sends it into the steering gear 4. A part of the hydraulic oil enters a pipeline in the steering gear 4 to control the extension and retraction of the front axle working cylinder 5, thereby realizing the left front wheel rotation of the vehicle. At this time, this part of the hydraulic oil needs to pass through the first steering oil inlet 401 and the first steering oil outlet 402; the other part enters the remaining pipeline in the steering gear 4 to control the movement of the front axle drag cylinder 6, thereby realizing the right front wheel rotation of the vehicle. At this time, this part of the hydraulic oil needs to pass through the second steering oil outlet 403 and the second steering oil inlet 404.

[0045] When the vehicle performs four-wheel steering, the hydraulic pump 2 draws hydraulic oil from the oil tank 1 and sends it to the steering gear 4. A part of the hydraulic oil enters a pipeline in the steering gear 4 to control the extension and retraction of the front axle working cylinder 5, so as to realize the left front wheel rotation of the vehicle. At this time, this part of the hydraulic oil needs to pass through the first steering oil inlet 401 and the first steering oil outlet 402; the other part enters the remaining pipeline in the steering gear 4 to control the movement of the front axle drag cylinder 6, so as to realize the right front wheel rotation of the vehicle. At this time, this part of the hydraulic oil needs to pass through the second steering oil outlet 403 and the second steering oil inlet 404;

[0046] The reversing valve 701 is started, so that the rear axle control circuit 7 starts to work, and the piston rod inside the front axle drag cylinder 6 moves, so that the hydraulic oil flows to the rear axle working hydraulic cylinder 702, and the rear axle working hydraulic cylinder 702 is controlled to perform telescopic movement in the opposite direction of the telescopic direction of the front axle working cylinder 6, so as to realize rear wheel steering;

[0047] When the wheel needs to be straightened, the floating piston of the rear axle working hydraulic cylinder 702 is squeezed by the high-pressure oil, and the piston rod between the floating pistons is constrained to the position when the vehicle is moving straight, that is, the centering of the rear axle wheels is achieved. At this time, the accumulator 703 squeezes part of the hydraulic oil according to actual needs. This part of the hydraulic oil will enter the rear axle working hydraulic cylinder 702 through the first one-way valve 13, the second overflow valve 14, the second one-way valve 15, and the third overflow valve 16 to replenish the oil to make up for the leakage of the hydraulic oil.

[0048] When the vehicle performs crab-shaped steering, the hydraulic pump 2 draws hydraulic oil from the oil tank 1 and sends it into the steering gear 4. A part of the hydraulic oil enters a pipeline in the steering gear 4 to control the extension and retraction of the front axle working cylinder 5, so as to realize the left front wheel rotation of the vehicle. At this time, this part of the hydraulic oil needs to pass through the first steering oil inlet 401 and the first steering oil outlet 402; the other part enters the remaining pipeline in the steering gear 4 to control the movement of the front axle drag cylinder 6, so as to realize the right front wheel rotation of the vehicle. At this time, this part of the hydraulic oil needs to pass through the second steering oil outlet 403 and the second steering oil inlet 404;

[0049] The reversing valve 701 is started, so that the rear axle control circuit 7 starts to work, and the piston rod inside the front axle drag cylinder 6 moves, so that the hydraulic oil flows to the rear axle working hydraulic cylinder 702, and the rear axle working hydraulic cylinder 702 is controlled to perform a telescopic movement in the same direction as the front axle working cylinder 6, so as to realize rear wheel steering;

[0050] When the wheel needs to be straightened, the floating piston of the rear axle working hydraulic cylinder 702 is squeezed by the high-pressure oil, and the piston rod between the floating pistons is constrained to the position when the vehicle is moving straight, that is, the centering of the rear axle wheels is achieved. At this time, the accumulator 703 squeezes part of the hydraulic oil according to actual needs. This part of the hydraulic oil will enter the rear axle working hydraulic cylinder 702 through the first one-way valve 13, the second overflow valve 14, the second one-way valve 15, and the third overflow valve 16 for oil replenishment. At this time, the floating piston of the rear axle working hydraulic cylinder 702 squeezes the piston rod to achieve the centering of the rear axle wheels to compensate for the leakage of hydraulic oil.

[0051] In the description of the present invention, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0052] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A control method for a vehicle four-wheel steering system, characterized in that: The vehicle's four-wheel steering system is used to control the vehicle to perform front-wheel steering, four-wheel steering and crab steering; The vehicle four-wheel steering system includes a fuel tank, a hydraulic pump, a first relief valve, a steering gear, a front axle working cylinder, a front axle drag cylinder and a rear axle control circuit. The steering gear is connected with a first steering oil inlet, a first steering oil outlet, a second steering oil outlet, a second steering oil inlet, a hydraulic oil inlet and a hydraulic oil return port, and two independent pipelines are arranged inside the steering gear. The front axle working cylinder is connected with one of the independent pipelines inside the steering gear through the first steering oil inlet and the first steering oil outlet, and the front axle drag cylinder is connected with another pipeline inside the steering gear through the second steering oil outlet and the second steering oil inlet. The front axle working cylinder controls the rotation of the left front wheel of the vehicle, and the front axle drag cylinder controls the rotation of the right front wheel of the vehicle. The hydraulic oil inlet and the hydraulic oil return port are respectively connected with the hydraulic pump, and the hydraulic pump is driven by the engine of the vehicle. The hydraulic pump is connected in parallel with the first relief valve and then connected with the fuel tank; The front axle drag cylinder is a four-chamber hydraulic cylinder, and is divided into a first front axle chamber, a second front axle chamber, a third front axle chamber and a fourth front axle chamber from left to right, the first front axle chamber is connected to the second steering oil outlet, and the fourth front axle chamber is connected to the second steering oil inlet; The rear axle control circuit is connected to the second front axle chamber and the third front axle chamber, and the rear axle control circuit controls the rotation and centering of the rear wheels of the vehicle; The rear axle control circuit includes a reversing valve, a rear axle working hydraulic cylinder and an accumulator. The reversing valve is a three-position four-way reversing valve. The two actuator oil ports of the reversing valve are respectively connected to the second front axle chamber and the third front axle chamber. The rear axle working hydraulic cylinder is a four-chamber hydraulic cylinder, and is divided into a first rear axle chamber, a second rear axle chamber, a third rear axle chamber and a fourth rear axle chamber from left to right. The first rear axle chamber is connected to the pressure oil port of the reversing valve to form a first circuit, the second rear axle chamber is connected to the return oil port of the reversing valve to form a second circuit, and the accumulator is respectively connected to the third rear axle chamber and the fourth rear axle chamber to form a third circuit; A first branch is connected between the first circuit and the third circuit, and a second branch is connected between the second circuit and the third circuit. The first branch is composed of a first one-way valve and a second overflow valve in parallel, and the second branch is composed of a second one-way valve and a second overflow valve in parallel. The conduction direction of the first one-way valve is opposite to that of the second one-way valve.

2. A control method for a vehicle four-wheel steering system according to claim 1, characterized in that: When the vehicle is steering the front wheels, the hydraulic pump draws hydraulic oil from the oil tank and sends it into the steering gear. Part of the hydraulic oil enters a pipeline in the steering gear to control the extension and retraction of the front axle working cylinder, thereby realizing the rotation of the left front wheel of the vehicle, and the other part enters the remaining pipeline in the steering gear to control the movement of the front axle drag cylinder, thereby realizing the rotation of the right front wheel of the vehicle.

3. The control method of a vehicle four-wheel steering system according to claim 2, characterized in that: When the vehicle performs four-wheel steering, the hydraulic pump draws hydraulic oil from the oil tank and sends it to the steering gear. A part of the hydraulic oil enters a pipeline in the steering gear to control the extension and retraction of the front axle working cylinder, thereby realizing the rotation of the left front wheel of the vehicle, and the other part enters the remaining pipeline in the steering gear to control the movement of the front axle drag cylinder, thereby realizing the rotation of the right front wheel of the vehicle; The reversing valve is started, so that the rear axle control circuit starts to work, and the piston rod inside the front axle drag cylinder moves, so that the hydraulic oil flows to the rear axle working hydraulic cylinder, and the rear axle working hydraulic cylinder is controlled to perform telescopic movement in the opposite direction of the telescopic direction of the front axle working cylinder, so as to realize rear wheel steering; When the wheel needs to be straightened, the floating piston of the rear axle working hydraulic cylinder is squeezed by the high-pressure oil, and the piston rod between the floating pistons is constrained to the position when the vehicle is moving straight, that is, the centering of the rear axle wheels is achieved. At this time, the accumulator squeezes part of the hydraulic oil according to actual needs. This part of the hydraulic oil will enter the rear axle working hydraulic cylinder and the front axle towing cylinder through the first one-way valve, the second overflow valve, the second one-way valve, and the second overflow valve to replenish the oil to make up for the leakage of the hydraulic oil.

4. A control method for a vehicle four-wheel steering system according to claim 3, characterized in that: When the vehicle performs crab-turning, the hydraulic pump draws hydraulic oil from the oil tank and sends it into the steering gear. A part of the hydraulic oil enters a pipeline in the steering gear to control the extension and retraction of the front axle working cylinder, thereby realizing the rotation of the left front wheel of the vehicle, and the other part enters the remaining pipeline in the steering gear to control the movement of the front axle drag cylinder, thereby realizing the rotation of the right front wheel of the vehicle; The reversing valve is started, so that the rear axle control circuit starts to work, and the piston rod inside the front axle drag cylinder moves, so that the hydraulic oil flows to the rear axle working hydraulic cylinder, and the rear axle working hydraulic cylinder is controlled to perform telescopic movement in the same direction as the front axle working cylinder, so as to realize rear wheel steering; When the wheels need to be centered, the floating pistons of the rear axle hydraulic cylinders are squeezed by high-pressure oil, and the piston rods between the floating pistons are constrained to the position when the vehicle is moving straight, that is, the rear axle wheels are aligned. The accumulator squeezes part of the hydraulic oil according to actual needs, and this part of the hydraulic oil enters the rear axle working hydraulic cylinder and the front axle towing cylinder through the first one-way valve, the second overflow valve, the second one-way valve, and the second overflow valve to replenish the oil to make up for the leakage of the hydraulic oil.

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