Hydraulic variable frequency air suspension system and variable frequency leveling control method

Abstract

This invention provides a hydraulic variable frequency air suspension system and a variable frequency leveling control method, belonging to the field of air suspension technology. The system includes on-board sensors, a hydraulic adjustment system, and a vehicle frame. The hydraulic adjustment system includes a hydraulic pump, a hydraulic oil tank, a front axle control valve, a center and rear axle control valve, a front axle branch, a center and rear axle branch, a front wheel hydraulic variable frequency adjustment mechanism, and a center and rear wheel hydraulic variable frequency adjustment mechanism. The hydraulic pump input is connected to the hydraulic oil tank outlet, and the hydraulic pump output is connected to the front axle control valve and the center and rear axle control valve respectively. The front wheel hydraulic variable frequency adjustment mechanism is located between the front axle branch and the front axle control valve, and the center and rear wheel hydraulic variable frequency adjustment mechanism is located between the center and rear axle branch and the center and rear axle control valve. This invention can achieve precise release of different hydraulic frequencies in the front axle branch and the center and rear axle branch, improving the response speed and adjustment smoothness during the adjustment process of special vehicles and off-road vehicles, thereby improving ride comfort.

Description

Technical Field

[0001] This invention relates to the field of hydropneumatic suspension technology, specifically to a hydraulic variable frequency hydropneumatic suspension system and a variable frequency leveling control method. Background Technology

[0002] A hydropneumatic suspension is a general term for all force-transmitting connections between a vehicle's frame (or monocoque chassis) and axles (or wheels). It transmits pressure using hydraulic fluid, typically with nitrogen as the elastic medium, and consists of an accumulator (equivalent to a gas spring) and hydropneumatic springs that function as shock absorbers. Its function is to transmit forces and torques acting between the wheels and the frame, and to buffer the impact forces transmitted from uneven road surfaces to the frame or body, reducing the resulting vibrations to ensure a smooth vehicle ride.

[0003] CN105459748A discloses a hydraulic adjustment system for an air suspension, which sets up front, middle and rear air springs to lift synchronously, balance the suspension structure and load, and effectively solves the problem of asynchronous lifting from the design of the hydraulic adjustment system.

[0004] However, existing technologies have the following technical problems: for special vehicles and off-road vehicles, the vehicle's weight and load-bearing capacity are relatively large, and relying solely on a single-axle valve body flow-limiting adjustment mechanism and elastic unit to mitigate impacts is not very effective, resulting in relatively poor driving comfort and vehicle smoothness. There is an urgent need to provide a hydraulic variable frequency hydropneumatic suspension system and a variable frequency leveling control method to solve the above-mentioned technical problems. Summary of the Invention

[0005] In view of this, it is necessary to provide a hydraulic variable frequency air suspension system and a variable frequency leveling control method to solve the technical problem that the existing technology cannot be applied to special vehicles, off-road vehicles and other scenarios with relatively large vehicle weight and load, resulting in poor ride comfort and vehicle smoothness in the above scenarios.

[0006] On one hand, the present invention provides a hydraulic variable frequency air suspension system, including an on-board sensor, a hydraulic adjustment system, and a vehicle frame; the hydraulic adjustment system includes a hydraulic pump, a hydraulic oil tank, a front axle control valve, a center and rear axle control valve, a front axle branch, a center and rear axle branch, a front wheel hydraulic variable frequency adjustment mechanism, and a center and rear wheel hydraulic variable frequency adjustment mechanism. The input end of the hydraulic pump is connected to the outlet of the hydraulic oil tank, and the output end of the hydraulic pump is connected to the front axle control valve and the center and rear axle control valve respectively. The front wheel hydraulic variable frequency adjustment mechanism is disposed between the front axle branch and the front axle control valve, and the center and rear wheel hydraulic variable frequency adjustment mechanism is disposed between the center and rear axle branch and the center and rear axle control valve.

[0007] In one possible implementation, the front axle branch includes a left front locking valve, a right front locking valve, a left front pneumatic spring locking valve, a right front pneumatic spring locking valve, a left front suspension, and a right front suspension; the left front locking valve and the right front locking valve are connected in parallel and their input ends are connected to the oil outlet of the front axle control valve; both ends of the left front suspension are respectively connected to the input ends of the left front locking valve and the left front pneumatic spring locking valve; and both ends of the right front suspension are respectively connected to the input ends of the right front locking valve and the right front pneumatic spring locking valve.

[0008] The front wheel hydraulic frequency conversion adjustment mechanism includes a left front wheel hydraulic frequency conversion adjustment mechanism and a right front wheel hydraulic frequency conversion adjustment mechanism. The left front wheel hydraulic frequency conversion adjustment mechanism includes a first main control valve and a second main control valve connected in parallel, as well as a first hydraulic frequency conversion adjustment valve connected to the first main control valve and a second hydraulic frequency conversion adjustment valve connected to the second main control valve. The right front wheel hydraulic frequency conversion adjustment mechanism includes a third main control valve and a fourth main control valve connected in parallel, as well as a third hydraulic frequency conversion adjustment valve connected to the third main control valve and a fourth hydraulic frequency conversion adjustment valve connected to the fourth main control valve.

[0009] In one possible implementation, the middle and rear axle branch includes a left middle and rear locking valve, a right middle and rear locking valve, a left middle pneumatic spring locking valve, a left rear pneumatic spring locking valve, a right middle pneumatic spring locking valve, a right rear pneumatic spring locking valve, a left middle and rear connecting valve, a right middle and rear connecting valve, a left middle suspension, a left rear suspension, a right middle suspension, and a right rear suspension; the left middle and rear locking valves and the right middle and rear locking valves are connected in parallel, and their input ends are connected to the oil outlet of the middle and rear axle control valve; both ends of the left middle suspension are respectively connected to the left middle and rear locking valve and the left middle pneumatic spring locking valve. The left and right rear suspensions are connected to the left and right center-rear locking valves and the right and right center-rear locking valves respectively. The left and right rear suspensions are connected via the left and right center-rear connecting valve.

[0010] The hydraulic frequency conversion adjustment mechanism for the middle and rear wheels includes a left, middle, and rear wheel hydraulic frequency conversion adjustment mechanism and a right, middle, and rear wheel hydraulic frequency conversion adjustment mechanism. The left, middle, and rear wheel hydraulic frequency conversion adjustment mechanism includes a fifth main control valve and a sixth main control valve connected in parallel, as well as a fifth hydraulic frequency conversion adjustment valve connected to the fifth main control valve and a sixth hydraulic frequency conversion adjustment valve connected to the sixth main control valve. The right, middle, and rear wheel hydraulic frequency conversion adjustment mechanism includes a seventh main control valve and an eighth main control valve connected in parallel, as well as a seventh hydraulic frequency conversion adjustment valve connected to the seventh main control valve and an eighth hydraulic frequency conversion adjustment valve connected to the eighth main control valve.

[0011] In one possible implementation, the hydraulic regulating system further includes a proportional flow divider valve and a proportional flow combiner valve. The first outlet of the proportional flow divider valve is connected to the inlet of the front axle control valve, the second outlet of the proportional flow divider valve is connected to the inlet of the middle and rear axle control valve, the return port of the front axle control valve is connected to the first inlet of the proportional flow combiner valve, the return port of the middle and rear axle control valve is connected to the second inlet of the proportional flow combiner valve, and the outlet of the proportional flow combiner valve is connected to the hydraulic oil tank.

[0012] In one possible implementation, the hydraulic pump includes a hydraulic oil pump and a manual hydraulic pump connected in parallel.

[0013] In one possible implementation, the proportional flow divider valve divides the high-pressure oil in the front axle branch and the middle and rear axle branch at a flow ratio of 1:2; the proportional flow combiner valve combines the high-pressure oil in the front axle branch and the middle and rear axle branch at a flow ratio of 1:2.

[0014] In one possible implementation, the hydraulic regulating system further includes a first check valve disposed on the oil outlet branch of the hydraulic pump, a second check valve disposed on the oil inlet branch of the manual hydraulic pump, and a third check valve disposed on the oil outlet branch of the manual hydraulic pump.

[0015] On the other hand, the present invention also provides a variable frequency leveling control method, applied to a hydraulic variable frequency hydraulic-pneumatic suspension system in any of the above possible implementations, the method comprising:

[0016] The vehicle sensors acquire real-time vehicle and road information, and the suspension pre-adjustment state is determined based on pre-built suspension pre-adjustment rules, the real-time vehicle information, and the real-time road information; the suspension pre-adjustment state includes a first-level pre-adjustment state, a second-level pre-adjustment state, and a third-level pre-adjustment state.

[0017] Obtain the leveling mode; the leveling mode includes a coarse leveling mode and a fine leveling mode. The coarse leveling mode is used to level the vehicle's body posture with the road surface, and the fine leveling mode is used to adjust the vehicle's body posture to the target horizontal range.

[0018] The suspension height adjustment working mode is determined based on the suspension pre-adjustment state and the leveling mode, and the hydraulic variable frequency oil-air suspension system is adjusted based on the suspension height adjustment working mode; the suspension height adjustment working mode includes first-level pre-adjustment-fine leveling, first-level pre-adjustment-coarse leveling, second-level pre-adjustment-fine leveling, second-level pre-adjustment-coarse leveling, and third-level pre-adjustment-non-operation.

[0019] In one possible implementation, the front wheel hydraulic frequency converter includes a left front wheel hydraulic frequency converter and a right front wheel hydraulic frequency converter. The left front wheel hydraulic frequency converter includes a first main control valve and a second main control valve connected in parallel, a first hydraulic frequency converter valve connected to the first main control valve, and a second hydraulic frequency converter valve connected to the second main control valve. The right front wheel hydraulic frequency converter includes a third main control valve and a fourth main control valve connected in parallel, a third hydraulic frequency converter valve connected to the third main control valve, and a fourth hydraulic frequency converter valve connected to the fourth main control valve. The hydraulic frequency conversion regulating mechanism for the left and right rear wheels includes a left, middle, and rear wheel hydraulic frequency conversion regulating mechanism and a right, middle, and rear wheel hydraulic frequency conversion regulating mechanism. The left, middle, and rear wheel hydraulic frequency conversion regulating mechanism includes a fifth main control valve and a sixth main control valve connected in parallel, as well as a fifth hydraulic frequency conversion regulating valve connected to the fifth main control valve and a sixth hydraulic frequency conversion regulating valve connected to the sixth main control valve. The right, middle, and rear wheel hydraulic frequency conversion regulating mechanism includes a seventh main control valve and an eighth main control valve connected in parallel, as well as a seventh hydraulic frequency conversion regulating valve connected to the seventh main control valve and an eighth hydraulic frequency conversion regulating valve connected to the eighth main control valve.

[0020] The first-level pre-adjustment mode is as follows: the first and second hydraulic frequency converter valves are opened simultaneously, the third and fourth hydraulic frequency converter valves are opened simultaneously, the fifth and sixth hydraulic frequency converter valves are opened simultaneously, and the seventh and eighth hydraulic frequency converter valves are opened simultaneously.

[0021] The secondary pre-adjustment mode is as follows: the first hydraulic frequency converter or the second hydraulic frequency converter is open, the third hydraulic frequency converter or the fourth hydraulic frequency converter is open, the fifth hydraulic frequency converter or the sixth hydraulic frequency converter is open, and the seventh hydraulic frequency converter or the eighth hydraulic frequency converter is open.

[0022] The three-level pre-adjustment mode is: the hydraulic adjustment system cannot be hydraulically adjusted.

[0023] In one possible implementation, the leveling principle of the fine-tuning mode is: first adjust the roll angle, then adjust the pitch angle, and the adjustment principle of the roll angle adjustment and the pitch angle adjustment is: first decrease and then increase.

[0024] The beneficial effects of this invention are as follows: The hydraulic variable frequency air suspension system provided by this invention, by setting up a front wheel hydraulic variable frequency adjustment mechanism and a middle and rear wheel hydraulic variable frequency adjustment mechanism, can achieve precise release of different hydraulic frequencies in the front axle branch and the middle and rear axle branch. Fast frequency release can improve the hydraulic variable frequency adjustment speed and hydraulic height adjustment accuracy of the front axle branch and the middle and rear axle branch, while slow frequency release can improve the smoothness of hydraulic adjustment. It provides multiple hydraulic adjustment schemes for different driving needs of the driver, making the hydraulic variable frequency air suspension system suitable for special vehicles, off-road vehicles and other scenarios with relatively large vehicle weight and load, improving the response speed and adjustment smoothness in the adjustment process in the above scenarios, thereby improving ride comfort. Attached Figure Description

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

[0026] Figure 1 A schematic diagram of an embodiment of the hydraulic adjustment system provided by the present invention;

[0027] Figure 2 The schematic diagram of the solenoid valve on / off control principle of the hydraulic regulating system provided by the present invention;

[0028] Figure 3 This is a schematic flowchart of an embodiment of the frequency conversion leveling control method provided by the present invention;

[0029] Figure 4 A schematic flowchart of an embodiment of the front and rear axle leveling steps provided by the present invention;

[0030] Figure 5 A schematic flowchart of an embodiment of the roll angle adjustment steps provided by the present invention;

[0031] Figure 6 A schematic flowchart of an embodiment of the pitch angle adjustment steps provided by the present invention;

[0032] Figure 7 This is a schematic flowchart of an embodiment of the leveling process of the coarse leveling mode provided by the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] It should be understood that the illustrative drawings are not drawn to scale. The flowcharts used in this invention illustrate operations implemented according to some embodiments of the invention. It should be understood that the operations in the flowcharts may be implemented out of order, and steps without logical contextual relationships may be reversed or performed simultaneously. Furthermore, those skilled in the art, guided by the content of this invention, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor systems and / or microcontroller systems.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] This invention provides a hydraulic variable frequency hydraulic-pneumatic suspension system and a variable frequency leveling control method, which will be described below.

[0037] The hydraulic variable frequency air suspension system includes a hydraulic adjustment system, on-board sensors, and a vehicle frame. Figure 1 A schematic diagram of the hydraulic adjustment system provided in an embodiment of the present invention is shown below. Figure 1 As shown, the hydraulic adjustment system 1 includes a hydraulic pump 10, a hydraulic oil tank 20, a front axle control valve 30, a middle and rear axle control valve 40, a front axle branch 50, a middle and rear axle branch 60, a front wheel hydraulic pressure frequency conversion adjustment mechanism 70, and a middle and rear wheel hydraulic pressure frequency conversion adjustment mechanism 80. The input end of the hydraulic pump 10 is connected to the oil outlet of the hydraulic oil tank 20, and the output end of the hydraulic pump 10 is connected to the front axle control valve 30 and the middle and rear axle control valve 40 respectively. The front wheel hydraulic pressure frequency conversion adjustment mechanism 70 is located between the front axle branch 50 and the front axle control valve 30, and the middle and rear wheel hydraulic pressure frequency conversion adjustment mechanism 80 is located between the middle and rear axle branch 60 and the middle and rear axle control valve 40.

[0038] The working principle of the hydraulic variable frequency hydraulic suspension system proposed in this embodiment of the invention is as follows: based on the real-time vehicle information and real-time road information obtained by the vehicle-mounted sensors, the on- and off-board of each solenoid valve of the hydraulic adjustment system 1 is controlled to realize the adjustment of force and torque between the wheel and the frame.

[0039] Compared with the prior art, the hydraulic variable frequency air suspension system provided in this embodiment of the invention, by setting the front wheel hydraulic variable frequency adjustment mechanism 70 and the middle and rear wheel hydraulic variable frequency adjustment mechanism 80, can achieve precise release of different hydraulic frequencies in the front axle branch and the middle and rear axle branch. Fast frequency release can improve the hydraulic variable frequency adjustment speed and hydraulic height adjustment accuracy of the front axle branch and the middle and rear axle branch, while slow frequency release can improve the smoothness of hydraulic adjustment. It provides multiple hydraulic adjustment schemes for different driving needs of the driver, making the hydraulic variable frequency air suspension system suitable for special vehicles, off-road vehicles and other scenarios with relatively large vehicle weight and load, improving the response speed and adjustment smoothness in the adjustment process in the above scenarios, thereby improving ride comfort.

[0040] Among them, the hydraulic adjustment system 1 is a hydraulic adjustment system used to adjust the oil pressure of the variable frequency oil-air suspension.

[0041] The vehicle-mounted sensors include, but are not limited to, speed sensors, suspension height sensors, vehicle tilt sensors, and road monitoring sensors. These sensors are used to identify real-time vehicle speed, real-time suspension height of each wheel, real-time vehicle pitch angle, roll angle, road surface unevenness, and road environment information. Speed ​​sensors include, but are not limited to, accelerometers, which are respectively installed at the wheel rims of each vehicle. Suspension height sensors are respectively installed above each wheel, at a preset distance from the wheel's axle. Vehicle tilt sensors include, but are not limited to, gyroscopes, used to acquire the vehicle's real-time pitch angle and roll angle. Road monitoring sensors include, but are not limited to, vision sensors, lidar sensors, and ultrasonic sensors, used to acquire ultrasonic data, image data, and laser point cloud data in the vehicle's direction of travel, and to determine real-time road information in the vehicle's direction of travel based on the ultrasonic data, image data, and laser point cloud data.

[0042] In some embodiments of the present invention, the front axle branch 50 includes a left front locking valve 51, a right front locking valve 52, a left front pneumatic spring locking valve 53, a right front pneumatic spring locking valve 54, a left front suspension 55, and a right front suspension 56; the left front locking valve 51 and the right front locking valve 52 are connected in parallel and their input ends are connected to the oil outlet of the front axle control valve 30; the two ends of the left front suspension 55 are respectively connected to the input ends of the left front locking valve 51 and the left front pneumatic spring locking valve 53; and the two ends of the right front suspension 56 are respectively connected to the input ends of the right front locking valve 52 and the right front pneumatic spring locking valve 54.

[0043] The front wheel hydraulic frequency conversion regulating mechanism 70 includes a left front wheel hydraulic frequency conversion regulating mechanism 71 and a right front wheel hydraulic frequency conversion regulating mechanism 72. The left front wheel hydraulic frequency conversion regulating mechanism 71 includes a first main control valve 711 and a second main control valve 712 connected in parallel, as well as a first hydraulic frequency conversion regulating valve 713 connected to the first main control valve 711 and a second hydraulic frequency conversion regulating valve 714 connected to the second main control valve 712. The right front wheel hydraulic frequency conversion regulating mechanism 72 includes a third main control valve 721 and a fourth main control valve 722 connected in parallel, as well as a third hydraulic frequency conversion regulating valve 723 connected to the third main control valve 721 and a fourth hydraulic frequency conversion regulating valve 724 connected to the fourth main control valve 722.

[0044] This embodiment of the invention includes a front wheel hydraulic pressure variable frequency adjustment mechanism 70 comprising a first hydraulic pressure variable frequency adjustment valve 713 and a second hydraulic pressure variable frequency adjustment valve 714 connected in parallel with the left front wheel. When both valves are opened simultaneously, rapid hydraulic pressure release is achieved, improving the variable frequency adjustment speed and hydraulic height adjustment accuracy of the left front wheel. When only valves 713 or 714 are opened, the smoothness of hydraulic adjustment is improved, balancing the adjustment speed and smoothness of the left front wheel adjustment with driving comfort during the adjustment process. Similarly, the inclusion of a third hydraulic pressure variable frequency adjustment valve 723 and a fourth hydraulic pressure variable frequency adjustment valve 724 connected in parallel with the right front wheel also balances the adjustment speed and smoothness of the right front wheel adjustment with driving comfort during the adjustment process.

[0045] Furthermore, in this embodiment of the invention, the left and right front wheels can be adjusted independently, further improving the adjustability of the hydraulic variable frequency air suspension system.

[0046] In some embodiments of the present invention, such as Figure 1As shown, the middle and rear axle branch 60 includes a left middle and rear locking valve 61, a right middle and rear locking valve 62, a left middle hydraulic spring locking valve 63, a left rear hydraulic spring locking valve 64, a right middle hydraulic spring locking valve 65, a right rear hydraulic spring locking valve 66, a left middle and rear connecting valve 67, a right middle and rear connecting valve 68, a left middle suspension 69-1, a left rear suspension 69-2, a right middle suspension 69-3, and a right rear suspension 69-4; the left middle and rear locking valve 61 and the right middle and rear locking valve 62 are connected in parallel and their input ends are connected to the oil outlet of the middle and rear axle control valve 40; the two ends of the left middle suspension 69-1 are respectively connected to the left middle and rear locking valve 61 and the left middle... The input end of the pneumatic spring locking valve 63 is connected to the left rear suspension 69-2, and the two ends of the left rear suspension 69-2 are connected to the input ends of the left center rear locking valve 61 and the left rear pneumatic spring locking valve 64, respectively. The two ends of the right center suspension 69-3 are connected to the input ends of the right center rear locking valve 62 and the right center pneumatic spring locking valve 65, respectively. The two ends of the right rear suspension 69-4 are connected to the input ends of the right center rear locking valve 62 and the right rear pneumatic spring locking valve 66, respectively. The left center suspension 69-1 and the left rear suspension 69-2 are connected through the left center rear connecting valve 67, and the right center suspension 69-3 and the right rear suspension 69-4 are connected through the right center rear connecting valve 68.

[0047] The hydraulic frequency conversion regulating mechanism 80 for the middle and rear wheels includes a left, middle, and rear wheel hydraulic frequency conversion regulating mechanism 81 and a right, middle, and rear wheel hydraulic frequency conversion regulating mechanism 82. The left, middle, and rear wheel hydraulic frequency conversion regulating mechanism 81 includes a fifth main control valve 811 and a sixth main control valve 812 connected in parallel, as well as a fifth hydraulic frequency conversion regulating valve 813 connected to the fifth main control valve 811 and a sixth hydraulic frequency conversion regulating valve 814 connected to the sixth main control valve 812. The right, middle, and rear wheel hydraulic frequency conversion regulating mechanism 82 includes a seventh main control valve 821 and an eighth main control valve 822 connected in parallel, as well as a seventh hydraulic frequency conversion regulating valve 823 connected to the seventh main control valve 821 and an eighth hydraulic frequency conversion regulating valve 824 connected to the eighth main control valve 822.

[0048] This invention, through the parallel connection of a fifth hydraulic frequency converter valve 813 and a sixth hydraulic frequency converter valve 814, and a seventh hydraulic frequency converter valve 823 and an eighth hydraulic frequency converter valve 824, enables high-frequency and low-frequency hydraulic pressure release for the left, middle, and rear wheels and the right, middle, and rear wheels, thus balancing the adjustment speed and smoothness of the left front wheel adjustment, as well as driving comfort during the adjustment process.

[0049] Furthermore, in this embodiment of the invention, the left center suspension 69-1 and the left rear suspension 69-2 are connected by a left center-rear connecting valve 67, and the right center suspension 69-3 and the right rear suspension 69-4 are connected by a right center-rear connecting valve 68, forming a structure similar to a balanced suspension. The center and rear wheels bear the load evenly, improving off-road mobility. Under specific working conditions, the left center-rear connecting valve 67 and the right center-rear connecting valve 68 are closed, and the center and rear wheels bear the load independently, improving obstacle crossing ability.

[0050] In some embodiments of the present invention, such as Figure 1 As shown, the hydraulic adjustment system 1 also includes a proportional flow divider valve 90 and a proportional flow combiner valve 100. The first oil outlet of the proportional flow divider valve 90 is connected to the oil inlet of the front axle control valve 30, the second oil outlet of the proportional flow divider valve 90 is connected to the oil inlet of the middle and rear axle control valve 40, the return oil port of the front axle control valve 30 is connected to the first oil inlet of the proportional flow combiner valve 100, the return oil port of the middle and rear axle control valve 40 is connected to the second oil inlet of the proportional flow combiner valve 100, and the oil outlet of the proportional flow combiner valve 100 is connected to the hydraulic oil tank 20.

[0051] In a specific embodiment of the present invention, the proportional flow divider 90 divides the high-pressure oil of the front axle branch 50 and the middle and rear axle branch 60 at a flow ratio of 1:2; the proportional flow combiner 100 combines the high-pressure oil of the front axle branch 50 and the middle and rear axle branch 60 at a flow ratio of 1:2.

[0052] Since the main oil inlet line is divided into two branches, namely the front axle branch 50 and the middle and rear axle branch 60, the front axle branch 50 supplies oil to the two hydraulic springs of the front axle, and the middle and rear axle branch 60 supplies oil to the four hydraulic springs of the middle and rear axles. The cylinder diameters of the six hydraulic springs are the same. In this embodiment of the invention, by setting a proportional flow divider valve 90 to divide the high-pressure oil of the front axle branch 50 and the middle and rear axle branch 60 into a flow ratio of 1:2, and a proportional flow combiner valve 100 to combine the high-pressure oil of the front axle branch 50 and the middle and rear axle branch 60 into a flow ratio of 1:2, the synchronous lifting and synchronous lowering of the front axle branch and the middle and rear axle branch can be achieved, thereby improving the smoothness of the adjustment.

[0053] To improve the operational reliability and redundancy of the hydraulic variable frequency hydraulic-pneumatic suspension system, in some embodiments of the present invention, such as... Figure 1 As shown, the hydraulic pump 10 includes a hydraulic oil pump 11 and a manual hydraulic pump 12 connected in parallel.

[0054] By setting up a hydraulic oil pump 11 and a manual hydraulic pump 12 in parallel, the hydraulic oil pump 12 can supply oil when the vehicle motor or engine fails and the hydraulic oil pump 11 cannot work, thereby improving the working reliability and redundancy of the hydraulic variable frequency air suspension system.

[0055] To prevent high-pressure oil from returning to the hydraulic oil tank 20 from another branch when the hydraulic pump 11 or manual hydraulic pump 12 is working, in some embodiments of the present invention, such as Figure 1 As shown, the hydraulic regulating system 10 also includes a first check valve 110 disposed on the oil outlet branch of the hydraulic oil pump 11, a second check valve 120 disposed on the oil inlet branch of the manual hydraulic pump 12, and a third check valve 130 disposed on the oil outlet branch of the manual hydraulic pump 12.

[0056] In some embodiments of the present invention, such as Figure 1As shown, the hydraulic regulating system 1 also includes a level gauge 140, an oil temperature sensor 150, and an oil inlet 160 with an oil filter, all installed in the hydraulic oil tank 20.

[0057] In some embodiments of the present invention, such as Figure 1 As shown, the hydraulic regulating system 1 also includes a first oil filter 170 and a manual shut-off valve 180 installed on the oil inlet branch of the hydraulic pump 10. When the hydraulic regulating system 1 is under maintenance, the manual shut-off valve 180 can be closed to cut off the connection between the hydraulic oil tank 20 and the hydraulic regulating system 1, which facilitates maintenance.

[0058] Furthermore, such as Figure 1 As shown, the hydraulic regulating system 1 also includes a second oil filter 190 disposed on the oil outlet branch of the hydraulic pump 10, for filtering out impurities from the oil pumped out by the hydraulic pump 10.

[0059] In a specific embodiment of the present invention, for the sake of simplicity, the proportional flow divider valve 90 is 1DT, the front axle control valve 30 is 2DT, the middle and rear axle control valve 40 is 3DT, the first main control valve 711 is 4DT, the second main control valve 712 is 5DT, the third main control valve 721 is 6DT, the fourth main control valve 722 is 7DT, the fifth main control valve is 8DT, the sixth main control valve is 9DT, the seventh main control valve is 10DT, the eighth main control valve is 11DT, the left front locking valve 51 is 12DT, and the right front locking valve is 12DT. Locking valve 52 is 13DT, left-middle-rear locking valve 61 is 14DT, right-middle-rear locking valve 62 is 15DT, left front pneumatic spring locking valve 53 is 16DT, right front pneumatic spring locking valve 54 is 17DT, left middle pneumatic spring locking valve 63 is 18DT, left rear pneumatic spring locking valve 64 is 19DT, right middle pneumatic spring locking valve 65 is 20DT, right rear pneumatic spring locking valve 66 is 21DT, left-middle-rear connecting valve 67 is 22DT, and right middle-rear connecting valve 68 is 23DT. Therefore, if... Figure 2 As shown, the on / off control principle of the solenoid valves corresponding to each execution state of the hydraulic regulating system 1 is as follows:

[0060] State 1: When the execution state is that the overall vehicle height is raised, 1DT, 2DT, 3DT, 4DT, 5DT, 6DT, 7DT, 8DT, 9DT, 10DT, 11DT, 12DT, 13DT, 14DT, and 15DT are turned on, and 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off.

[0061] State 2: When the execution state is that the overall vehicle height is reduced: 1DT, 4DT, 5DT, 6DT, 7DT, 8DT, 9DT, 10DT, 11DT, 12DT, 13DT, 14DT, and 15DT are turned on, and 2DT, 3DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off;

[0062] State 3: When the execution state is left front elevation: 1DT, 2DT, 4DT, 5DT, and 12DT are turned on, and 3DT, 6DT, 7DT, 8DT, 9DT, 10DT, 11DT, 13DT, 14DT, 15DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off;

[0063] State 4: When the execution state is left front decrease: 1DT, 4DT, 5DT, and 12DT are turned on, and 2DT, 3DT, 6DT, 7DT, 8DT, 9DT, 10DT, 11DT, 13DT, 14DT, 15DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off;

[0064] State 5: When the execution state is right front rise: 1DT, 2DT, 6DT, 7DT, and 12DT are turned on, and 3DT, 4DT, 5DT, 8DT, 9DT, 10DT, 11DT, 13DT, 14DT, 15DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off;

[0065] State 6: When the execution state is right front decrease: 1DT, 6DT, 7DT, and 12DT are turned on, and 2DT, 3DT, 4DT, 5DT, 8DT, 9DT, 10DT, 11DT, 13DT, 14DT, 15DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off;

[0066] State 7: When the execution state is left-middle-upward: 1DT, 3DT, 8DT, 9DT, and 14DT are turned on, and 2DT, 4DT, 5DT, 6DT, 7DT, 10DT, 11DT, 12DT, 13DT, 15DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off;

[0067] State 8: When the execution state is left-middle-rear decrease: 1DT, 8DT, 9DT, and 14DT are turned on, and 2DT, 3DT, 4DT, 5DT, 6DT, 7DT, 10DT, 11DT, 12DT, 13DT, 15DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, and 23DT are turned off;

[0068] State 9: When the execution state is right-middle-upward: 1DT, 3DT, 10DT, 11DT, 15DT1 are turned on, 2DT, 4DT, 5DT, 6DT, 7DT, 8DT, 9DT, 12DT, 13DT, 4DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, 23DT are turned off;

[0069] State 10: When the execution state is reduced from right to middle: 1DT, 10DT, 11DT, 15DT1 are turned on, 2DT, 3DT, 4DT, 5DT, 6DT, 7DT, 8DT, 9DT, 12DT, 13DT, 4DT, 16DT, 17DT, 18DT, 19DT, 20DT, 21DT, 22DT, 23DT are turned off;

[0070] State 11: When the execution state is obstacle crossing assist: 22DT and 23DT are turned on, and 1DT, 2DT, 3DT, 4DT, 5DT, 6DT, 7DT, 8DT, 9DT, 10DT, 11DT, 12DT, 13DT, 14DT, 15DT, 16DT, 17DT, 18DT, 19DT, 20DT, and 21DT are turned off;

[0071] State 12: When the execution state is rigid locking: 16DT, 17DT, 18DT, 19DT, 20DT, and 21DT are turned on, and 1DT, 2DT, 3DT, 4DT, 5DT, 6DT, 7DT, 8DT, 9DT, 10DT, 11DT, 12DT, 13DT, 14DT, 15DT, 22DT, and 23DT are turned off.

[0072] This invention also provides a variable frequency leveling control method, applied to the aforementioned hydraulic variable frequency hydropneumatic suspension system, such as... Figure 3 As shown, the variable frequency leveling control method includes:

[0073] S301. Real-time vehicle information and real-time road information are acquired based on onboard sensors, and the suspension pre-adjustment state is determined based on pre-built suspension pre-adjustment rules, real-time vehicle information, and real-time road information; the suspension pre-adjustment state includes first-level pre-adjustment state, second-level pre-adjustment state, and third-level pre-adjustment state;

[0074] S302. Obtain the leveling mode; the leveling mode includes coarse leveling mode and fine leveling mode. The coarse leveling mode is used to level the vehicle body posture with the road surface, and the fine leveling mode is used to adjust the vehicle body posture to the target level range.

[0075] S303. Determine the suspension height adjustment working mode based on the suspension pre-adjustment state and leveling mode, and adjust the hydraulic variable frequency oil-air suspension system based on the suspension height adjustment working mode; the suspension height adjustment working modes include first-level pre-adjustment-fine leveling, first-level pre-adjustment-coarse leveling, second-level pre-adjustment-fine leveling, second-level pre-adjustment-coarse leveling, and third-level pre-adjustment-no operation.

[0076] The embodiments of the present invention determine the suspension pre-adjustment state based on real-time vehicle information and real-time road information, and combine it with the leveling mode selected by the driver to balance system responsiveness and driving comfort, thereby achieving multi-level adjustment under various road surface and road conditions.

[0077] The real-time vehicle information includes real-time vehicle speed information and real-time vehicle attitude information. Real-time vehicle speed information includes, but is not limited to, vehicle speed and acceleration. Real-time vehicle attitude information includes, but is not limited to, pitch angle, roll angle, and the adjustable range of the above angles. Real-time road information includes real-time road surface information (road surface unevenness) and real-time road environment information (adhesion coefficient). Real-time road surface features of real-time road surface information include, but are not limited to, craters, continuous steps, etc. Real-time road environment features of real-time road environment information include, but are not limited to, snow, mud, and gravel, etc.

[0078] In a specific embodiment of the present invention, the first-level pre-adjustment mode is as follows: the first hydraulic frequency converter valve 713 and the second hydraulic frequency converter valve 714 are opened simultaneously, the third hydraulic frequency converter valve 723 and the fourth hydraulic frequency converter valve 724 are opened simultaneously, the fifth hydraulic frequency converter valve 813 and the sixth hydraulic frequency converter valve 814 are opened simultaneously, and the seventh hydraulic frequency converter valve 823 and the eighth hydraulic frequency converter valve 824 are opened simultaneously.

[0079] The two-stage pre-adjustment mode is as follows: the first hydraulic frequency converter valve 713 or the second hydraulic frequency converter valve 714 is open, the third hydraulic frequency converter valve 723 or the fourth hydraulic frequency converter valve 724 is open, the fifth hydraulic frequency converter valve 813 or the sixth hydraulic frequency converter valve 814 is open, and the seventh hydraulic frequency converter valve 823 or the eighth hydraulic frequency converter valve 824 is open.

[0080] The third-level pre-adjustment mode is: hydraulic adjustment system 1 cannot be hydraulically adjusted.

[0081] Specifically, the first-level pre-adjustment mode corresponds to the vehicle state as follows: the vehicle is at a low to medium speed, with a good body posture, good road conditions, and suitable road environment, allowing for adjustable suspension. The hydraulic variable frequency air suspension system can then achieve rapid hydraulic adjustment. Specifically, the two hydraulic variable frequency adjustment valves in each wheel's hydraulic variable frequency adjustment mechanism open simultaneously. Under favorable suspension adjustment conditions, this achieves rapid hydraulic pressure release, improving the speed of hydraulic variable frequency adjustment and the accuracy of hydraulic height adjustment in each wheel, thus greatly enhancing the responsiveness of the hydraulic variable frequency air suspension system.

[0082] The secondary pre-adjustment mode corresponds to the vehicle state as follows: the vehicle is at a low to medium speed, with normal body posture, normal road conditions, and normal road environment, allowing for adjustable suspension. In this mode, the hydraulic variable frequency suspension system can achieve relatively gentle hydraulic adjustment. Specifically, only one hydraulic variable frequency adjustment valve in each wheel's hydraulic variable frequency adjustment mechanism is open. Under normal suspension adjustment conditions, this achieves slow-frequency release of hydraulic pressure, improving the smoothness and safety of the system's hydraulic adjustment, and greatly enhancing driving comfort.

[0083] The vehicle state corresponding to the three-level pre-adjustment mode is: the vehicle is in a state where the suspension cannot be adjusted due to high speed, poor body posture, poor road surface conditions, or poor road environment. The hydraulic variable frequency oil-air suspension system cannot be hydraulically adjusted.

[0084] It should be noted that the leveling principle of the fine-tuning mode is: first adjust the roll angle, then adjust the pitch angle, and the adjustment principle for both the roll angle and pitch angle is: first decrease, then increase.

[0085] Specifically, the fine-tuning mode is suitable for any road surface environment and can achieve horizontal leveling of the vehicle body within the allowable travel range of the suspension; the coarse-tuning mode is better suited for driving on relatively level roads and can quickly achieve parallelism between the vehicle body and the road surface.

[0086] In a specific embodiment of the present invention, the leveling process of the fine leveling mode includes front and rear axle leveling steps, roll angle adjustment steps, and pitch angle adjustment steps.

[0087] like Figure 4As shown, the specific steps for front and rear axle leveling are as follows: First, determine if the height difference between the left and right front axles is greater than a height threshold. If it is, determine if the absolute value of the roll angle |Y| is greater than the maximum roll angle threshold (Angel_Y_max-α) or the absolute value of the pitch angle |X| is greater than the maximum pitch angle threshold (Angel_X_max-α). If yes, lower the right front axle, set the flag F_up = 0, and return to the step determining if the height difference between the left and right front axles is greater than the height threshold. If no, raise the left front axle, set the flag F_up = 0, and return to the step determining if the height difference between the left and right front axles is greater than the height threshold. If not, determine if the height difference is less than the height threshold and greater than the negative height threshold. If yes, the front axle leveling is complete, set the flag F_up = 1, and then... If the rear axle flag R_up is 1, and R_up = 0, return to the step of determining whether the height difference between the left and right front axles is greater than the height threshold. If the height difference is less than the negative height threshold, then determine whether the height difference between the right and left front axles is greater than the height threshold. If not, then determine whether the absolute value of the roll angle is greater than the maximum roll angle threshold or the absolute value of the pitch angle is greater than the maximum pitch angle threshold. If yes, then execute the left front axle lowering, with the flag F_up = 0, and return to the step of determining whether the height difference between the right and left front axles is greater than the height threshold. If not, then execute the right front axle raising, with the flag F_up = 0, and return to the step of determining whether the height difference between the right and left front axles is greater than the height threshold. If F_up = 1 and R_up = 1, then the front and rear axles have been leveled, and proceed to the roll angle adjustment step.

[0088] like Figure 5As shown, the specific steps for adjusting the lateral roll angle are as follows: First, determine if the lateral roll angle is less than the negative lateral roll angle adjustment threshold Angle_Allow_min. If so, determine if the left front height or left rear height is less than the minimum limit height. If so, determine if the right front height or right rear height is greater than or equal to the maximum limit height and the lateral roll angle is less than the negative preset value -α. If so, the current state cannot be leveled. If the right front height or right rear height is less than the maximum limit height and the lateral roll angle is greater than or equal to the negative preset value -α, then the right side is raised, and the flag is set to auto_y = 0. If the left front height or left rear height is greater than or equal to the minimum limit height, then the left side is lowered, and the flag is set to auto_y = 0. If the lateral roll angle is not less than the negative lateral roll angle adjustment threshold, then determine if the lateral roll angle is greater than the negative lateral roll angle adjustment threshold and less than... If the roll angle adjustment threshold is not met, then check if the roll angle is greater than the roll angle adjustment threshold. If it is, then check if the left front height or left rear height is less than the minimum limit height. If it is, then check if the right front height or right rear height is greater than or equal to the maximum limit height and the roll angle is greater than the preset value α. If both are met, the current state cannot be leveled. If the right front height and right rear height are less than the maximum limit height or the roll angle is greater than or equal to the preset value α, then the right side is raised, and the flag is: auto_y = 0. If the left front height or left rear height is greater than or equal to the minimum limit height, then the left side is lowered, and the flag is: auto_y = 0. If the roll angle is greater than the negative roll angle adjustment threshold and less than the roll angle adjustment threshold, then the roll angle leveling is completed, the flag is: auto_y = 1, and the pitch angle adjustment step is entered.

[0089] like Figure 6The pitch angle adjustment steps are as follows: First, determine if the pitch angle is less than the negative pitch angle adjustment threshold. If so, determine if the left rear height or right rear height is less than the minimum height limit. If so, determine if the left front height or right front height is greater than or equal to the maximum height limit and the pitch angle is less than the negative preset value -α. If so, the current state cannot be leveled. If the left front height or right front height is less than the maximum height limit and the pitch angle is greater than or equal to the negative preset value -α, then the front axle is raised, and the flag is set to auto_x = 0. If the left rear height or right rear height is greater than or equal to the minimum height limit, then the rear axle is lowered, and the flag is set to auto_x = 0. If the pitch angle is not less than the negative pitch angle adjustment threshold, then determine if the pitch angle is greater than the negative pitch angle adjustment threshold and less than the pitch angle adjustment threshold. If the value is not specified, check if the pitch angle is greater than the pitch angle adjustment threshold. If it is, check if the left front height or right front height is less than the minimum limit height. If it is, check if the left rear height or right rear height is greater than or equal to the maximum limit height and the pitch angle is greater than the preset value α. If both are specified, the current state cannot be leveled. If the left rear height and right rear height are less than the maximum limit height or the pitch angle is greater than or equal to the preset value α, then the rear axle is raised, and the flag is set to: auto_x = 0. If the left front height or right front height is greater than or equal to the minimum limit height, then the front axle is lowered, and the flag is set to: auto_x = 0. If the pitch angle is greater than the negative pitch angle adjustment threshold and less than the pitch angle adjustment threshold, then the pitch angle leveling is completed, the flag is set to: auto_x = 1, and the leveling process ends.

[0090] In specific embodiments of the present invention, such as Figure 7 As shown, the leveling process in coarse leveling mode is as follows:

[0091] Based on the current suspension height of each wheel, determine the current suspension height and the desired suspension height. The desired suspension height for the front axle is the average of the left front height and the right front height, and the desired suspension height for the rear axle is the average of the left rear height and the right rear height. Determine if the height difference between the current suspension height and the desired suspension height is greater than a height threshold. If yes, lower the suspension of that single wheel. If no, determine if the absolute value of the height difference between the current suspension height and the desired suspension height is less than a height threshold. If yes, do not operate on the single wheel suspension. If no, determine if the height difference between the desired height and the current height is greater than a height threshold and the suspension of the wheel on the same axle is in a non-operational state. If yes, perform a single wheel suspension raising operation and return to the step of determining if the height difference between the desired height and the current height is greater than a height threshold and the suspension of the wheel on the same axle is in a non-operational state. If no, do not operate on the single wheel suspension. Determine if all four suspensions are in a non-operational state. If yes, end the process. If no, return to the step of determining if the height difference between the current suspension height and the desired suspension height is greater than a height threshold.

[0092] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware (such as a processor, controller, etc.), and the computer program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0093] The hydraulic variable frequency hydraulic suspension system and variable frequency leveling control method provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A variable frequency leveling control method, characterized by, An application is made to a hydraulic variable frequency air suspension system, the hydraulic variable frequency air suspension system including on-board sensors, a hydraulic adjustment system, and a vehicle frame. The hydraulic adjustment system includes a hydraulic pump, a hydraulic oil tank, a front axle control valve, a center and rear axle control valve, a front axle branch, a center and rear axle branch, a front wheel hydraulic variable frequency adjustment mechanism, and a center and rear wheel hydraulic variable frequency adjustment mechanism. The input end of the hydraulic pump is connected to the outlet of the hydraulic oil tank, and the output end of the hydraulic pump is connected to the front axle control valve and the center and rear axle control valve respectively. The front wheel hydraulic variable frequency adjustment mechanism is located between the front axle branch and the front axle control valve, and the center and rear wheel hydraulic variable frequency adjustment mechanism is located between the center and rear axle branch and the center and rear axle control valve. The method includes: The vehicle sensors acquire real-time vehicle and road information, and the suspension pre-adjustment state is determined based on pre-built suspension pre-adjustment rules, the real-time vehicle information, and the real-time road information; the suspension pre-adjustment state includes a first-level pre-adjustment state, a second-level pre-adjustment state, and a third-level pre-adjustment state. Obtain the leveling mode; the leveling mode includes a coarse leveling mode and a fine leveling mode. The coarse leveling mode is used to level the vehicle's body posture with the road surface, and the fine leveling mode is used to adjust the vehicle's body posture to the target horizontal range. The suspension height adjustment working mode is determined based on the suspension pre-adjustment state and the leveling mode, and the hydraulic variable frequency oil-pneumatic suspension system is adjusted based on the suspension height adjustment working mode; the suspension height adjustment working mode includes first-level pre-adjustment-fine leveling, first-level pre-adjustment-coarse leveling, second-level pre-adjustment-fine leveling, second-level pre-adjustment-coarse leveling, and third-level pre-adjustment-non-operation; The leveling principle of the fine-tuning mode is: first adjust the roll angle, then adjust the pitch angle, and the adjustment principle of the roll angle adjustment and the pitch angle adjustment is: first decrease and then increase.

2. The variable frequency leveling control method according to claim 1, characterized in that, The front wheel hydraulic frequency conversion adjustment mechanism includes a left front wheel hydraulic frequency conversion adjustment mechanism and a right front wheel hydraulic frequency conversion adjustment mechanism. The left front wheel hydraulic frequency conversion adjustment mechanism includes a first main control valve and a second main control valve connected in parallel, a first hydraulic frequency conversion adjustment valve connected to the first main control valve, and a second hydraulic frequency conversion adjustment valve connected to the second main control valve. The right front wheel hydraulic frequency conversion adjustment mechanism includes a third main control valve and a fourth main control valve connected in parallel, a third hydraulic frequency conversion adjustment valve connected to the third main control valve, and a fourth hydraulic frequency conversion adjustment valve connected to the fourth main control valve. The rear wheel hydraulic frequency conversion adjustment mechanism includes a left, middle, and rear wheel hydraulic frequency conversion adjustment mechanism and a right, middle, and rear wheel hydraulic frequency conversion adjustment mechanism. The left, middle, and rear wheel hydraulic frequency conversion adjustment mechanism includes a fifth main control valve and a sixth main control valve connected in parallel, as well as a fifth hydraulic frequency conversion adjustment valve connected to the fifth main control valve and a sixth hydraulic frequency conversion adjustment valve connected to the sixth main control valve. The right, middle, and rear wheel hydraulic frequency conversion adjustment mechanism includes a seventh main control valve and an eighth main control valve connected in parallel, as well as a seventh hydraulic frequency conversion adjustment valve connected to the seventh main control valve and an eighth hydraulic frequency conversion adjustment valve connected to the eighth main control valve. The first-level pre-adjustment state is as follows: the first and second hydraulic frequency converter valves are opened simultaneously, the third and fourth hydraulic frequency converter valves are opened simultaneously, the fifth and sixth hydraulic frequency converter valves are opened simultaneously, and the seventh and eighth hydraulic frequency converter valves are opened simultaneously. The secondary pre-adjustment state is as follows: the first hydraulic frequency converter or the second hydraulic frequency converter is open, the third hydraulic frequency converter or the fourth hydraulic frequency converter is open, the fifth hydraulic frequency converter or the sixth hydraulic frequency converter is open, and the seventh hydraulic frequency converter or the eighth hydraulic frequency converter is open. The third-level pre-adjustment state is: the hydraulic adjustment system cannot be hydraulically adjusted.

3. The variable frequency leveling control method according to claim 1, characterized in that, The front axle branch includes a left front locking valve, a right front locking valve, a left front pneumatic spring locking valve, a right front pneumatic spring locking valve, a left front suspension, and a right front suspension. The left front locking valve and the right front locking valve are connected in parallel, and their input ends are connected to the oil outlet of the front axle control valve. The two ends of the left front suspension are respectively connected to the input ends of the left front locking valve and the left front pneumatic spring locking valve. The two ends of the right front suspension are respectively connected to the input ends of the right front locking valve and the right front pneumatic spring locking valve.

4. The variable frequency leveling control method according to claim 1, characterized in that, The middle and rear axle branch includes a left middle and rear locking valve, a right middle and rear locking valve, a left middle pneumatic spring locking valve, a left rear pneumatic spring locking valve, a right middle pneumatic spring locking valve, a right rear pneumatic spring locking valve, a left middle and rear connecting valve, a right middle and rear connecting valve, a left middle suspension, a left rear suspension, a right middle suspension, and a right rear suspension; the left middle and rear locking valves and the right middle and rear locking valves are connected in parallel, and their input ends are connected to the oil outlet of the middle and rear axle control valve; both ends of the left middle suspension are respectively connected to the inputs of the left middle and rear locking valves and the left middle pneumatic spring locking valves. The left and right rear suspensions are connected at both ends, with the left and right rear suspensions connected to the input ends of the left center-rear locking valve and the left rear pneumatic spring locking valve, respectively. The left and right rear suspensions are connected via the left center-rear connecting valve and the right center-rear connecting valve, respectively.

5. The variable frequency leveling control method according to claim 1, characterized in that, The hydraulic regulating system also includes a proportional flow divider valve and a proportional flow combiner valve. The first oil outlet of the proportional flow divider valve is connected to the oil inlet of the front axle control valve, the second oil outlet of the proportional flow divider valve is connected to the oil inlet of the middle and rear axle control valve, the return oil port of the front axle control valve is connected to the first oil inlet of the proportional flow combiner valve, the return oil port of the middle and rear axle control valve is connected to the second oil inlet of the proportional flow combiner valve, and the oil outlet of the proportional flow combiner valve is connected to the hydraulic oil tank.

6. The variable frequency leveling control method according to claim 1, characterized in that, The hydraulic pump includes a hydraulic oil pump and a manual hydraulic pump connected in parallel.

7. The variable frequency leveling control method according to claim 5, characterized in that, The proportional flow divider valve divides the high-pressure oil in the front axle branch and the middle and rear axle branch at a flow ratio of 1:2; the proportional flow combiner valve combines the high-pressure oil in the front axle branch and the middle and rear axle branch at a flow ratio of 1:

2.

8. The variable frequency leveling control method according to claim 6, characterized in that, The hydraulic regulating system also includes a first check valve installed on the oil outlet branch of the hydraulic oil pump, a second check valve installed on the oil inlet branch of the manual hydraulic pump, and a third check valve installed on the oil outlet branch of the manual hydraulic pump.

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