Variable wheelbase distributed four-wheel independent steering chassis platform

Abstract

This invention relates to a variable wheelbase distributed four-wheel independent steering chassis platform, belonging to the field of vehicle chassis technology. It includes a reconfigurable chassis beam, a variable wheelbase mechanism, a distributed four-wheel independent steering device, and control components. The reconfigurable chassis beam adopts a nested guide rod structure of square tubes within square tubes, with the inner and outer square tubes fitted with a clearance and equipped with a guide and limiting mechanism. The variable wheelbase mechanism includes a hydraulic cylinder or servo electric cylinder and a mechanical locking mechanism. The distributed four-wheel independent steering device includes two independent steering motors (front and rear), steering tie rods, and angle sensors. The control components switch steering modes according to vehicle speed and achieve linkage control between wheelbase and steering. This invention adapts to different upper platforms through wheelbase adjustment, reduces turning radius and improves high-speed stability through four-wheel independent steering and mode switching, and is suitable for special vehicles, engineering vehicles, and multi-functional mobile platforms.

Description

Technical Field

[0001] This invention belongs to the field of vehicle chassis technology, specifically relating to an integrated chassis platform with adjustable wheelbase and four-wheel independent steering, suitable for special vehicles, engineering vehicles, multi-functional mobile platforms and modular transportation equipment. Background Technology

[0002] Existing automobile chassis, engineering vehicle chassis, and mobile work platform chassis generally adopt a fixed wheelbase structure, and the steering method is mostly front-wheel steering or simple front-and-rear wheel steering. This traditional structure has the following technical defects: Poor versatility and high development costs: The fixed wheelbase cannot be adapted to upper functional platforms of different sizes and load capacities. For each type of operation (such as aerial work, cargo transportation, and special hoisting), a special chassis must be redesigned and developed, resulting in low component interchangeability, long R&D cycles, and high manufacturing costs.

[0003] Insufficient maneuverability and large turning radius: Vehicles with only front-wheel steering have a turning radius that is strictly limited by the wheelbase in narrow alleys, workshops, or complex off-road environments, resulting in poor maneuverability and making it difficult to meet the high passability requirements of special operations.

[0004] The trade-off between load-bearing capacity and off-road capability: A long wheelbase is beneficial for increasing the load-bearing area and driving stability, but it will reduce the longitudinal approach angle and make it easier to bottom out on rough terrain; a short wheelbase has good off-road capability, but the load-bearing space is limited. A fixed wheelbase cannot dynamically balance this trade-off according to working conditions.

[0005] Challenges in the strength and reliability of telescopic structures: Although some existing technologies have proposed the concept of telescopic frames, they mostly use simple sleeve or slide rail structures, lacking reliable mechanical locking and high-strength guiding mechanisms. Under heavy loads, these structures are prone to swaying, uneven wear, and even structural failure, making it difficult to meet the safety requirements of engineering vehicles.

[0006] Although existing technologies also include rear-wheel steering (such as the rear-wheel active steering mechanism used in some passenger cars) or variable wheelbase platforms (such as some concept logistics vehicles), the following technical problems have not yet been solved: how to combine a high-strength square tube nested telescopic guide rod structure with a mechanical locking mechanism to achieve reliable wheelbase adjustment under heavy load conditions; and how to coordinate the distributed four-wheel independent steering with the wheelbase status to enable the vehicle to obtain optimal maneuverability and stability under different wheelbases.

[0007] The combination of the above-mentioned technical problems is not a simple patchwork, but involves the coordinated optimization of structural strength, control strategies and overall vehicle safety. Summary of the Invention

[0008] To address the problems in the prior art, this invention proposes a variable wheelbase distributed four-wheel independent steering chassis platform. This platform utilizes a high-strength nested guide rod structure with square tubes within square tubes, coupled with mechanical locking, to achieve reliable wheelbase adjustment under heavy load conditions. Furthermore, through the coordinated control of the distributed four-wheel independent steering device and the wheelbase status, optimal maneuverability and stability are achieved under different wheelbases.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: including a reconfigurable chassis beam, wherein the reconfigurable chassis beam serves as the bottom frame of the whole vehicle, runs transversely along the longitudinal centerline of the vehicle, and constitutes the load-bearing base of the entire chassis platform; It also includes a variable wheelbase mechanism, which is embedded in a large number of internal cavities and sidewall areas of the reconfigurable chassis and moves telescopically along the longitudinal centerline of the vehicle. It also includes a distributed four-wheel independent steering device, which is respectively set at both ends of the longitudinal direction of the reconfigurable chassis beam to perform steering.

[0010] It also includes a control component, which is connected to the variable wheelbase mechanism and the distributed four-wheel independent steering device via circuitry and signaling. The control component switches the steering mode according to the vehicle speed signal and steering command, and controls the extension and retraction of the variable wheelbase mechanism.

[0011] Furthermore, the reconfigurable chassis beam adopts a nested guide rod structure of square tubes within square tubes, including an outer square tube and an inner square tube that is fitted inside the outer square tube with a clearance fit. A guide limiting mechanism and a dustproof sealing mechanism are provided between the inner square tube and the outer square tube. The guide limiting mechanism includes a wear-resistant slider and a guide sleeve. The wear-resistant slider is embedded in the outer wall of the inner square tube, and the guide sleeve is located on the inner wall of the outer square tube. The guide limiting mechanism is equipped with a graphite copper sleeve self-lubricating structure. The dustproof sealing mechanism includes a sealing ring and a dust cover. The sealing ring is located inside the outer square tube port, and the dust cover is located outside the outer square tube port to prevent mud and sand from entering the guide rod mating surface. A grease channel is provided on the outer wall of the inner square tube. The outer square tube and the upper surface of the inner square tube are provided with standardized upper-level platform connection interfaces to adapt to upper-level functional platforms of different sizes.

[0012] Furthermore, the variable wheelbase mechanism includes a telescopic drive device and a locking mechanism; the telescopic drive device is a hydraulic cylinder or a servo electric cylinder, with its two ends respectively hinged to the inner square tube and the outer square tube, for driving the inner square tube to extend and retract axially relative to the outer square tube; the locking mechanism is arranged longitudinally at intervals along the side wall of the outer square tube, for mechanically locking the inner square tube and the outer square tube after the wheelbase is adjusted to the correct position.

[0013] Furthermore, the telescopic drive device has a telescopic stroke of 300mm to 800mm; when the telescopic drive device is a hydraulic cylinder, its cylinder diameter is 80mm to 100mm, its working pressure is 12MPa to 16MPa, and it is equipped with a displacement sensor; when the telescopic drive device is a servo electric cylinder, it includes a servo motor and a ball screw transmission pair, and its repeatability is no greater than ±0.05mm.

[0014] Furthermore, the locking mechanism includes a plurality of locking holes evenly distributed along the longitudinal direction of the outer square tube, corresponding mating holes provided on the inner square tube, and a mechanical pin that can be inserted into or withdrawn from the locking holes and the mating holes; the mechanical pin is driven by an electric push rod or an electromagnetic drive device; the spacing between the locking holes is 100mm to 150mm.

[0015] Furthermore, the distributed four-wheel independent steering device includes a front wheel steering mechanism and a rear wheel steering mechanism; the front wheel steering mechanism includes a front wheel steering motor, a front wheel steering tie rod, and a front wheel angle sensor; the rear wheel steering mechanism includes a rear wheel steering motor, a rear wheel steering tie rod, and a rear wheel angle sensor; the front wheel steering mechanism and the rear wheel steering mechanism are distributed and independently or in conjunction with each other.

[0016] Furthermore, the front wheel steering motor is an electric power steering motor, and the rear wheel steering motor is an integrated unit of a servo motor and a worm gear reducer; the steering angle range of the front wheel steering mechanism is ±35°, and the steering angle range of the rear wheel steering mechanism is ±15°; both the front wheel steering tie rod and the rear wheel steering tie rod are ball joint type tie rods.

[0017] Furthermore, the control components adopt a hierarchical distributed architecture, including a vehicle controller, a wheelbase adjustment controller, and a steering controller; The vehicle controller, as the top-level decision-making unit, is located on the longitudinal beam in the middle of the chassis, near the driver's seat. It is used to switch steering modes and generate control commands based on vehicle speed signals and steering instructions. The wheelbase adjustment controller is located near the frame mounting position of the wheelbase variable mechanism and communicates with the vehicle controller via the CAN bus to receive wheelbase target commands and control the operation of the telescopic drive device. The steering controller is located near the chassis mounting position of the distributed four-wheel independent steering system. It communicates with the vehicle controller via the CAN bus to receive steering mode and target steering angle commands and control the front wheel steering motor and the rear wheel steering motor respectively. The vehicle controller, wheelbase adjustment controller, and steering controller form a distributed control architecture with one master and two slaves.

[0018] Furthermore, the control component switches the following steering modes based on the vehicle speed signal: a. Four-wheel reverse steering mode: When the vehicle speed is below the first threshold, the front and rear wheels are controlled to steer in opposite directions to reduce the turning radius; b. Normal front wheel steering mode: When the vehicle speed is between the first threshold and the second threshold, only the front wheels are controlled to steer, while the rear wheels keep going straight; c. Four-wheel steering mode: When the vehicle speed is higher than the second threshold, the front and rear wheels are controlled to steer in the same direction to improve driving stability.

[0019] Furthermore, the control component is also configured with a wheelbase-steering linkage control strategy: a. When the wheelbase is in the short wheelbase L < 2500mm state, the maximum allowable rear wheel steering angle is ±15°; b. When the wheelbase is in the long wheelbase L>3000mm state, limit the maximum steering angle of the rear wheels to no more than ±5°, or switch to front wheel steering mode only.

[0020] Furthermore, the control component is also configured with a vehicle speed-wheelbase adjustment interlock strategy: a. When the vehicle speed exceeds the second threshold, the telescopic drive device is prohibited from operating, and the current wheelbase is kept locked. b. When the vehicle speed is between the first threshold and the second threshold, wheelbase adjustment is allowed, but the steering angle of the front and rear wheels must be brought to zero and the steering motor drive must be turned off first. Wheelbase adjustment can only be performed after the steering has been brought to zero. c. When the vehicle speed is below the first threshold and the vehicle is stationary, wheelbase adjustment is allowed to be performed directly; when the vehicle speed is below the first threshold but the vehicle is in a crawling state, wheelbase adjustment is allowed but the rate of change of the rear wheel steering angle is limited, and wheelbase adjustment is prohibited when the crab mode is activated. d. When the vehicle is stationary or the speed is below 5km / h, the driver can actively select to activate the crab mode, which controls the front and rear wheel steering motors to deflect in the same direction at equal angles, so that the whole vehicle moves laterally; the crab mode is interlocked with the wheelbase adjustment function, and wheelbase adjustment is prohibited when activated.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0022] 1. This invention adopts a four-in-one collaborative architecture consisting of a reconfigurable chassis beam, a variable wheelbase mechanism, a distributed four-wheel independent steering device, and control components. This enables the entire machine to simultaneously possess dynamic wheelbase reconfiguration capability and four-wheel independent steering capability, thereby achieving a balance between load-bearing space, driving stability, and maneuverability across all working conditions. Through the overall design of reconfigurable structure, distributed steering, and collaborative control, it achieves a comprehensive leap in the versatility, mobility, load-bearing capacity, and safety of special vehicle chassis. It is suitable for various complex application scenarios such as engineering work vehicles, special transport vehicles, multi-functional mobile platforms, and modular unmanned chassis.

[0023] 2. This invention utilizes a high-strength nested guide rod structure with square tubes within square tubes, combined with a mechanical locking mechanism, to ensure that the chassis beam maintains sufficient bending and torsional rigidity during extension and retraction. After locking, it forms a rigid whole, meeting the requirements for heavy-duty driving. Simultaneously, the wheelbase can be steplessly adjusted within the range of 300mm to 800mm via hydraulic cylinders or servo electric cylinders, and quickly locked by mechanical pins after adjustment. This allows a single chassis to adapt to upper functional platforms of different sizes without replacing the frame, achieving "one vehicle for multiple uses." This significantly reduces the number of chassis models and mold investments, lowering R&D and manufacturing costs by more than 30%.

[0024] 3. This invention utilizes a distributed, independent steering mechanism for both front and rear wheels, enabling flexible switching between front-wheel steering, rear-wheel steering, or four-wheel coordinated steering under unified control. In low-speed, narrow scenarios, the counter-steering of the front and rear wheels reduces the minimum turning diameter of the vehicle by more than 40% compared to traditional fixed-wheelbase front-wheel steering vehicles. The short wheelbase configuration, combined with four-wheel steering, allows the vehicle to navigate narrow passages. In high-speed scenarios, the unidirectional steering of the front and rear wheels effectively suppresses yaw and improves lane-changing stability. Under normal operating conditions, only front-wheel steering reduces overall vehicle energy consumption and tire wear. Therefore, the vehicle achieves optimal steering characteristics at different speeds and wheelbases, resolving the inherent trade-off between maneuverability and stability inherent in traditional chassis designs.

[0025] 4. This invention employs a wheelbase-steering linkage control strategy to match wheelbase status with rear wheel steering angle permissions in real time: when the machine is in a short wheelbase state, the rear wheels are allowed to exert a full-stroke steering angle of ±15° to minimize the turning radius; when the machine is in a long wheelbase state, the rear wheel steering angle is automatically limited or the steering is switched to front-wheel steering only to prevent high-speed steering instability caused by increased wheelbase and rearward shift of the center of gravity. This linkage mechanism ensures that the machine maintains a driving safety margin throughout the entire process of dynamic wheelbase changes, avoiding the overall risks caused by independent structural adjustments and steering control.

[0026] 5. This invention adopts a standardized upper platform connection interface, combined with adjustable wheelbase, allowing for quick replacement of different functional modules such as cargo boxes, crane booms, and aerial work platforms on the same chassis. The upper platform size is no longer constrained by a fixed wheelbase, significantly improving the overall versatility of the machine. At the same time, the square tube nested guide rod structure, combined with multiple sealing and self-lubricating designs, ensures that the machine can maintain smooth extension and retraction and positioning accuracy even under harsh working conditions such as mud, sand, and dust, resulting in a long maintenance cycle and high reliability. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1This is a structural schematic diagram of the variable wheelbase distributed four-wheel independent steering chassis platform described in this invention; Figure 2 This is a schematic diagram of the reconfigurable chassis beam of the present invention; Figure 3 This is a schematic diagram of the variable wheelbase mechanism of the present invention; Figure 4 This is a schematic diagram of the distributed four-wheel independent steering device of the present invention; Figure 5 This is a logic block diagram of the control component of the present invention; Figure 6 This is a flowchart illustrating the steering mode switching logic of the present invention.

[0028] Explanation of reference numerals in the attached figures: 1. Reconfigurable chassis beam; 11. Outer square tube; 12. Inner square tube; 111. Locking hole; 121. Mating hole; 131. Guide sleeve; 132. Wear-resistant slider; 141. Sealing ring; 142. Dust cover; 2. Variable wheelbase mechanism; 21. Hydraulic cylinder; 23. Displacement sensor; 221. Mechanical pin; 222. Electric push rod; 223. Locking position detection sensor; 3. Distributed four-wheel independent steering device; 31. Front wheel steering mechanism; 311. Front wheel steering motor; 312. Front wheel steering tie rod; 313. Front wheel angle sensor; 32. Rear wheel steering mechanism; 321. Rear wheel steering motor; 322. Rear wheel steering tie rod; 323. Rear wheel angle sensor; 4. Control components; 41. Vehicle controller; 42. Wheelbase adjustment controller; 43. Steering controller; 44. Steering wheel angle sensor; 45. Wheel speed sensor. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0030] In the description of this invention, it should be understood that the technical terms "transverse," "inner," "bottom layer," "side wall," "longitudinal," "inner," "outer," "long," "short," "outer wall," "upper surface," "inner wall," "inner side," "front," "rear," and "middle," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. The terms "first," "second," and similar words used in the embodiments of this invention do not indicate any order, quantity, or importance, but are only used to distinguish different components.

[0031] Words such as "include" or "contain" mean that the element preceding the word covers the elements listed after the word and their equivalents, without excluding other elements. Words such as "connect" or "fix" are not limited to a single connection or fixing method, but can include multiple connection or fixing methods, such as screw fastening, threaded connection, welding, etc. "Multiple" means two or more.

[0032] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0033] The variable wheelbase distributed four-wheel independent steering chassis platform includes: a reconfigurable chassis beam 1, an outer square tube 11, an inner square tube 12, a locking hole 111, a mating hole 121, a guide sleeve 131, a wear-resistant slider 132, a sealing ring 141, a dust cover 142, a wheelbase variable mechanism 2, a hydraulic cylinder 21, a displacement sensor 23, a mechanical pin 221, an electric push rod 222, a locking position detection sensor 223, a distributed four-wheel independent steering device 3, a front wheel steering mechanism 31, a front wheel steering motor 311, a front wheel steering tie rod 312, a front wheel angle sensor 313, a rear wheel steering mechanism 32, a rear wheel steering motor 321, a rear wheel steering tie rod 322, a rear wheel angle sensor 323, a control assembly 4, a vehicle controller 41, a wheelbase adjustment controller 42, a steering controller 43, a steering wheel angle sensor 44, and a wheel speed sensor 45.

[0034] The reconfigurable chassis beam 1 adopts a nested guide rod structure of square tubes within square tubes, with the inner square tube 12 and the outer square tube 11 in clearance fit and equipped with a guide and limit mechanism; the wheelbase variable mechanism 2 includes a hydraulic cylinder 21 and a mechanical locking mechanism; the distributed four-wheel independent steering device 3 includes two independent steering motors, steering tie rods and angle sensors at the front and rear; the control component 4 switches the steering mode according to the vehicle speed and realizes the linkage control of wheelbase and steering.

[0035] Preferably, the reconfigurable chassis beam 1 adopts a nested guide rod structure of square tubes within square tubes, including an outer square tube 11 and an inner square tube 12 with a clearance fit inside the outer square tube 11. A guide limiting mechanism and a dustproof sealing mechanism are provided between the inner square tube 12 and the outer square tube 11. The nested guide rod structure of square tubes within square tubes utilizes the geometric characteristics of the closed section of the square tubes to form a double load-bearing skeleton between the outer square tube 11 and the inner square tube 12. The bending section modulus is increased by about 30% compared with the same specification of round tube. At the same time, the nested square tube method maintains a continuous force transmission path in the expansion and contraction direction, which meets the requirements of heavy-duty chassis for beam stiffness. The inner and outer square tubes adopt a clearance fit, which not only ensures the nested expansion and contraction function, but also controls the fit gap within the range of 0.1mm to 0.3mm through the guide limiting mechanism, avoiding structural loosening caused by uneven wear under heavy load.

[0036] The guiding and limiting mechanism includes a PTFE wear-resistant slider 132 embedded in the outer wall of the inner square tube 12 and a copper-based alloy guide sleeve 131 disposed on the inner wall of the outer square tube 11. The guiding and limiting mechanism is equipped with a graphite copper sleeve self-lubricating structure. The guiding and limiting mechanism adopts a combination of PTFE wear-resistant slider 132 and copper-based alloy guide sleeve 131: the PTFE wear-resistant slider 132 has a low coefficient of friction (μ≤0.08), which makes the expansion and contraction resistance of the inner and outer square tubes small and the response fast; the copper-based alloy guide sleeve 131 has moderate hardness, which not only supports the wear-resistant slider 132, but also prevents the outer wall of the inner square tube from directly contacting the metal of the inner wall of the outer square tube 11, avoiding seizure or damage; the graphite copper sleeve self-lubricating structure can still provide solid lubrication when the grease is insufficient, reducing the frequency of maintenance and extending the service life of the guiding mechanism.

[0037] The dustproof sealing mechanism includes a double-lip rubber sealing ring 141 and a folding dust cover 142. The double-lip rubber sealing ring is located inside the port of the outer square tube 11, and the folding dust cover 142 is located outside the port of the outer square tube 11 to prevent mud and sand from entering the guide rod mating surface. A grease channel is provided on the outer wall of the inner square tube 12. The dustproof sealing mechanism adopts double protection from the inside and outside with the double-lip rubber sealing ring 141 and the folding dust cover 142: the inner double-lip sealing ring 141 fits against the outer wall of the inner square tube 12 to form a radial dynamic seal, preventing hydraulic oil or grease from leaking out and liquid from entering; the outer folding dust cover 142 unfolds / folds with the telescopic movement to intercept large particulate pollutants such as mud and dust. The two work together to keep the guide rod mating surface clean in the dusty and muddy environment commonly encountered in engineering operations, ensuring smooth telescopic movement and positioning accuracy. The grease channel on the outer wall of the inner square tube 12 is used to periodically inject grease through the grease nipple. The grease is distributed along the longitudinal channel to the friction surfaces of each guide and limit mechanism to achieve fixed-point and quantitative lubrication. Combined with the self-lubricating properties of the graphite copper sleeve, the chassis can still work reliably for a long time in remote construction sites or under maintenance-free conditions, reducing the maintenance cost throughout the entire life cycle.

[0038] The upper surfaces of the outer square tube 11 and the inner square tube 12 are equipped with standardized upper platform connection interfaces to adapt to upper functional platforms of different sizes. The standardized upper platform connection interfaces (T-slots or ISO threaded hole arrays) on the upper surfaces of the outer square tube 11 and the inner square tube 12 allow different functional modules such as cargo boxes, crane booms, and aerial work platforms to be quickly installed directly using standard fasteners, without the need to customize connection structures for each type of upper structure. Combined with the adjustable wheelbase, the same chassis can be adapted to upper platforms of various sizes and specifications, achieving "one vehicle for multiple uses" and significantly reducing the number of chassis models and R&D and manufacturing costs.

[0039] Preferably, the variable wheelbase mechanism 2 includes a telescopic drive device and a locking mechanism; the telescopic drive device is a hydraulic cylinder 21 or a servo electric cylinder, with its two ends respectively hinged to the inner square tube 12 and the outer square tube 11, for driving the inner square tube 12 to extend and retract axially relative to the outer square tube 11; the locking mechanism is arranged longitudinally at intervals along the side wall of the outer square tube 11, for mechanically locking the inner square tube 12 and the outer square tube 11 after the wheelbase is adjusted to the correct position. The telescopic drive unit (hydraulic cylinder or servo electric cylinder) is only responsible for driving the telescopic movement. Its two ends are hinged to the inner and outer square tubes, allowing for slight vertical sway to adapt to frame deformation and avoid additional bending moments caused by rigid connections. The locking mechanism is independently arranged on the side wall of the outer square tube 11. After the wheelbase is adjusted, it forms a shear lock perpendicular to the telescopic direction through mechanical pin 221, bearing the longitudinal and lateral loads during driving. The two functions are decoupled—it does not bear load when driving and does not drive when locked, protecting the telescopic drive unit from heavy-load impacts and extending its service life. At the same time, the mechanical locking ensures that the chassis beam forms a rigid whole after locking, meeting the strength requirements for heavy-load driving. Locking holes 111 are evenly distributed along the longitudinal direction of the outer square tube 11, with a spacing of 100mm to 150mm, so that the wheelbase adjustment can be quickly positioned in multiple discrete positions without relying on the absolute accuracy of the displacement sensor 23 to achieve mechanical limit; the electric push rod 222 or electromagnetic drive device realizes the automation of locking, and forms a closed loop with the locking position detection sensor 223 to ensure reliable locking.

[0040] Preferably, the telescopic drive device has a telescopic stroke of 300mm to 800mm; when the telescopic drive device is a hydraulic cylinder 21, its cylinder diameter is 80mm to 100mm, its working pressure is 12MPa to 16MPa, and it is equipped with a displacement sensor 23; when the telescopic drive device is a servo electric cylinder, it includes a servo motor and a ball screw transmission pair, and its repeatability is no more than ±0.05mm. The telescopic travel is limited to 300mm to 800mm, allowing a single chassis to cover wheelbase requirements ranging from light-duty work platforms to medium-duty cargo boxes without replacing the frame. When equipped with a 2.5m × 1.5m superstructure, the wheelbase is shortened to 2400mm to improve aisle accessibility; when equipped with a 3.2m × 2.0m cargo box, the wheelbase is extended to 3000mm to increase the load-bearing area. This travel range has been engineering-proven, balancing structural compactness (too short a travel would limit the effectiveness of adjustment) with maintaining beam rigidity (too long a travel would lead to bending attenuation due to the cantilever of the nested guide rods). The system employs a double-acting hydraulic cylinder 21 with a diameter of 80mm to 100mm and a working pressure of 12MPa to 16MPa. Its theoretical thrust can reach 60kN to 125kN, sufficient to drive the relative sliding of the inner and outer square tubes under a full load of 5 tons. With the addition of a displacement sensor 23, closed-loop detection of the telescopic position is achieved, ensuring the wheelbase adjustment accuracy is controlled within ±2mm, meeting the alignment requirements of the upper platform installation interface. The hydraulic drive has overload protection (pressure limited by an overflow valve), preventing motor burnout under jamming conditions, making it suitable for the harsh operating environments of engineering vehicles. Employing a servo motor paired with a ball screw drive, the repeatability is ≤±0.05mm, two orders of magnitude higher than hydraulic solutions. This makes it suitable for high-precision electric work platforms (such as automated logistics vehicles and chassis for precision testing equipment). The servo electric cylinder eliminates the need for a hydraulic pump station, oil tank, and piping, reducing the overall weight by approximately 15% and eliminating the risk of hydraulic oil leakage, thus meeting the environmental requirements for indoor cleaning operations or the food and pharmaceutical industries.

[0041] Preferably, the locking mechanism includes a plurality of locking holes 111 evenly distributed along the longitudinal direction of the outer square tube 11, corresponding mating holes 121 provided on the inner square tube 12, and a mechanical pin 221 that can be inserted into or withdrawn from the locking holes 111 and the mating holes 121; the mechanical pin 221 is driven by an electric push rod 222 or an electromagnetic drive device; the spacing between the locking holes 111 is 100mm to 150mm. Multiple locking holes 111 are evenly distributed along the longitudinal direction of the outer square tube 11, which, in conjunction with corresponding mating holes 121 on the inner square tube 12, allow for multi-position mechanical locking of the wheelbase within a spacing of 100mm to 150mm. A mechanical pin 221 simultaneously penetrates both the locking holes 111 of the outer square tube 11 and the mating holes 121 of the inner square tube 12, forming a shear bearing surface perpendicular to the direction of extension and retraction. This converts the relative movement of the inner and outer square tubes into shear resistance of the pin, rather than relying on friction or hydraulic tightening. This purely mechanical locking method exhibits no creep or loosening under full load, ensuring that the chassis beam forms a rigid whole during heavy-load driving, meeting the stringent structural strength requirements of engineering vehicles. The mechanical latch 221 is driven by an electric push rod 222 or an electromagnetic drive device, replacing the traditional manual insertion and removal method, and incorporating the locking and unlocking actions into the closed-loop control of the control component 4. After the driver issues a wheelbase adjustment command through the control panel, the control component 4 can automatically drive the latch to retract and unlock, and then automatically push the latch out to lock after it has extended to the correct position, without any manual intervention. The response time of the electric push rod 222 is typically within 0.5s to 1s. In conjunction with the locking position detection sensor 223, it can provide real-time feedback on the locking status, realizing automated operation of "one-button adjustment" and improving work efficiency. The spacing of the locking holes 111 is limited to 100mm to 150mm. This range has been optimized: if the spacing is too small (less than 100mm), the locking holes 111 will be too dense, weakening the section modulus of the outer square tube 11 sidewall and reducing the bending strength of the main beam; if the spacing is too large (greater than 150mm), the wheelbase adjustment range will be too sparse, making it impossible to precisely adapt to upper platforms of different sizes. The 100mm to 150mm spacing allows the chassis to have 3 to 6 adjustable levels within a total travel of 300mm to 800mm, ensuring both structural integrity and meeting the versatility requirement of "one vehicle for multiple uses".

[0042] Preferably, the distributed four-wheel independent steering device 3 includes a front wheel steering mechanism 31 and a rear wheel steering mechanism 32; the front wheel steering mechanism 31 includes a front wheel steering motor 311, a front wheel steering tie rod 312 and a front wheel angle sensor 313; the rear wheel steering mechanism 32 includes a rear wheel steering motor 321, a rear wheel steering tie rod 322 and a rear wheel angle sensor 323; the front wheel steering mechanism 31 and the rear wheel steering mechanism 32 are distributed and controlled independently or in conjunction. The front-wheel steering mechanism 31 and the rear-wheel steering mechanism 32 can independently respond to control commands, enabling the vehicle to have four basic operating conditions: front-wheel steering alone, rear-wheel steering alone, front and rear wheel steering in opposite directions, and front and rear wheel steering in the same direction, covering all scenarios from extremely narrow roads to high-speed cruising. The two mechanisms are uniformly scheduled through the control component 4 to achieve real-time decoupling and dynamic matching of the front and rear wheel steering angles. At low speeds, the front and rear wheels deflect in opposite directions to compress the turning radius, and at high speeds, the front and rear wheels deflect in the same direction to suppress yaw. Under normal operating conditions, only the front wheels work to reduce energy consumption, thereby solving the contradiction between maneuverability and stability in traditional fixed-wheelbase front-wheel steering chassis. In addition, the rear-wheel steering mechanism 32, as an independent addition unit, can be modularly expanded based on the existing front-wheel steering architecture without modifying the front axle structure, improving the versatility and modification convenience of the chassis platform.

[0043] Preferably, the front wheel steering motor 311 is an electric power steering motor, and the rear wheel steering motor 321 is an integrated unit of a servo motor and a worm gear reducer, realizing differentiated configuration of steering power for the front and rear wheels. The front wheel electric power steering motor directly utilizes mature automotive steering technology, forming a standardized transmission chain with the steering column and rack and pinion steering gear, reducing development costs; the rear wheel servo motor, in conjunction with the worm gear reducer, utilizes the self-locking characteristic of the worm gear (self-locking angle less than 5°), so that when the steering motor is powered off or malfunctions, the rear wheel steering mechanism 32 can automatically maintain the current steering angle position and will not rebound due to road reaction force, ensuring driving safety; The front wheel steering mechanism 31 has a steering angle range of ±35°, and the rear wheel steering mechanism 32 has a steering angle range of ±15°, enabling the front wheels to undertake the main steering function and the rear wheels to undertake the auxiliary steering function. The large steering angle range of the front wheels ensures steering sensitivity and minimum turning ability during normal driving; the small steering angle range of the rear wheels can provide sufficient angle compensation to significantly reduce the turning radius when turning in the opposite direction at low speeds, and can limit the steering angle amplitude when turning in the same direction at high speeds to prevent the vehicle from yawing and becoming unstable due to excessive rear wheel steering angle. Both the front wheel steering tie rod 312 and the rear wheel steering tie rod 322 are ball joint type tie rods, which eliminates backlash and degree-of-freedom constraints in the steering transmission process, allowing the tie rod to swing slightly in three-dimensional space. This adapts to changes in the relative position of the steering knuckle and the frame during wheelbase extension and retraction, avoiding interference or jamming of the steering mechanism during wheelbase adjustment. At the same time, the ball joint structure has high transmission efficiency and low wear, ensuring steering accuracy and fatigue life under heavy load conditions.

[0044] Preferably, the control component 4 adopts a hierarchical distributed architecture, including a vehicle controller 41, a wheelbase adjustment controller 42, and a steering controller 43; The vehicle controller 41, as the top-level decision-making unit, is located on the longitudinal beam in the middle of the chassis near the driver's seat. It is used to switch the steering mode and generate control commands based on the vehicle speed signal and steering command. The wheelbase adjustment controller 42 is located near the frame mounting position of the wheelbase variable mechanism and communicates with the vehicle controller 41 via the CAN bus. It is used to receive wheelbase target commands and control the operation of the telescopic drive device. The steering controller 43 is located near the frame mounting position of the distributed four-wheel independent steering device 3 and communicates with the vehicle controller 41 via the CAN bus. It is used to receive steering mode and target steering angle commands and control the front wheel steering motor 311 and the rear wheel steering motor 321 respectively. Among them, the vehicle controller 41, the wheelbase adjustment controller 42 and the steering controller 43 constitute a distributed control architecture with one master and two slaves. The vehicle controller 41, as the sole decision-making unit, focuses on top-level logic such as vehicle speed threshold judgment, steering mode switching, and wheelbase-steering linkage strategy, avoiding conflicts between multiple controllers. The wheelbase adjustment controller 42 and steering controller 43, as dedicated execution units, are responsible for the closed-loop position of the hydraulic cylinder 21 and the closed-loop steering angle of the front and rear wheels, respectively. They are arranged close to the frame mounting position of their respective execution mechanisms, shortening the length of the hard wiring harness, reducing signal transmission delay and electromagnetic interference risks, and ensuring real-time response of the underlying control. The "one master and two slaves" distributed architecture ensures that each controller operates independently with clear responsibilities: when the steering controller 43 fails, the vehicle controller 41 can instruct it to shut down the rear wheel steering motor 321, degrading to a front-wheel steering-only mode; when the wheelbase adjustment controller 42 fails, the vehicle controller 41 disables the telescopic drive mechanism, maintaining the current wheelbase locked. The failure of any slave node will not cause the entire vehicle to lose control, significantly improving system safety and availability. The vehicle controller 41 is interconnected with the two actuators via a CAN bus, requiring only two twisted-pair cables to achieve multi-node data exchange, greatly simplifying the chassis wiring harness layout; at the same time, the CAN bus supports multi-master communication and node expansion, making it easy to add other functional controllers (such as suspension controllers and brake controllers) in the future, and has good platform expansion capabilities. The wheelbase adjustment controller 42 is located near the telescopic drive device, and the steering controller 43 is located near the front and rear wheel steering motors, which minimizes the power drive wiring harness and reduces line voltage drop and energy consumption. The vehicle controller 41 is located on the longitudinal beam on the driver's side, which facilitates the access of the human-machine interface (steering wheel angle sensor 44, control panel) nearby, and is centrally encapsulated in a waterproof electrical control box, which is suitable for the harsh environment of vibration, mud and water splash of engineering vehicles.

[0045] Preferably, the control component 4 switches the following steering modes based on the vehicle speed signal: a. Four-wheel reverse steering mode: When the vehicle speed is below the first threshold, the front and rear wheels are controlled to steer in opposite directions to reduce the turning radius; b. Normal front wheel steering mode: When the vehicle speed is between the first threshold and the second threshold, only the front wheels are controlled to steer, while the rear wheels keep going straight; c. Four-wheel steering mode: When the vehicle speed is higher than the second threshold, the front and rear wheels are controlled to steer in the same direction to improve driving stability; By dividing the vehicle speed into three ranges and matching them with different steering modes, the vehicle achieves optimal steering dynamics characteristics under any driving conditions. At low speeds, the "differential effect" of front and rear wheel steering in opposite directions is used to compress the turning radius; at medium speeds, traditional front-wheel steering is used to reduce energy consumption; and at high speeds, the "yaw damping effect" of front and rear wheel steering in the same direction is used to suppress crosswinds and lane change disturbances, achieving full-condition coverage of "low-speed agility and high-speed stability." Through speed threshold switching, rear-wheel steering is "intervened on demand"—activated only when needed and deactivated when not needed, retaining the maneuverability advantages of four-wheel steering while avoiding the stability risks of its application across the entire speed range. Compared to a full-time four-wheel steering solution, this reduces steering system energy consumption by approximately 30% and extends tire life.

[0046] Preferably, the control component 4 is further configured with a wheelbase-steering linkage control strategy: a. When the wheelbase is in the short wheelbase L < 2500mm state, the maximum allowable rear wheel steering angle is ±15°; b. When the wheelbase is in the long wheelbase L>3000mm state, limit the maximum steering angle of the rear wheels to no more than ±5°, or switch to front wheel steering mode only.

[0047] The control unit is also equipped with a speed-wheelbase adjustment interlock strategy: a. When the vehicle speed exceeds the second threshold, the telescopic drive device is prohibited from operating, and the current wheelbase is kept locked. b. When the vehicle speed is between the first and second thresholds, wheelbase adjustment is allowed, but the steering angles of the front and rear wheels must first be brought to zero and the steering motor drive must be turned off. Wheelbase adjustment can only be performed after the steering has been brought to zero. c. When the vehicle speed is below the first threshold and the vehicle is stationary, wheelbase adjustment is allowed to be performed directly; when the vehicle speed is below the first threshold but the vehicle is in a crawling state, wheelbase adjustment is allowed but the rate of change of the rear wheel steering angle is limited, and wheelbase adjustment is prohibited when the crab mode is activated. d. When the vehicle is stationary or the speed is below 5km / h, the driver can actively select to activate the crab mode, which controls the front and rear wheel steering motors to deflect in the same direction at equal angles, so that the whole vehicle moves laterally; the crab mode is interlocked with the wheelbase adjustment function, and wheelbase adjustment is prohibited when activated. Wheelbase-steering linkage control fundamentally eliminates the instability risk of "long wheelbase + large steering angle". When the chassis is in a long wheelbase state, the center of gravity shifts rearward and the turning radius increases. If the rear wheels still maintain a large steering angle of ±15°, excessive yaw moment will be generated during high-speed steering, leading to rollover. By limiting the rear wheel steering angle to within ±5° or directly switching to front-wheel steering only, the steering response of the entire vehicle at high speed is consistent with that of traditional vehicles, and the driver does not need to adapt to special steering characteristics. The speed-wheelbase adjustment interlock prevents the structural risk of "accidental wheelbase adjustment while driving." When the vehicle speed exceeds 55 km / h, if the chassis beam expands or contracts, the relative slippage between the inner and outer square tubes can cause a sudden change in tire slip angle and longitudinal shift of the center of gravity, leading to loss of steering control. By prohibiting adjustment at high speeds and forcibly maintaining the current wheelbase lock, it is equivalent to setting a "structural safety lock" for high-speed driving. The low-speed crawl speed limit and crab-like interlock further address safety vulnerabilities in low-speed scenarios. Even at speeds below 20 km / h, if the vehicle is still adjusting its wheelbase while moving, rapid changes in the rear wheel angle can cause sudden changes in tire lateral force, resulting in sideslip. By limiting the rate of angle change to ≤5° / s, steering actions become smooth and controllable; while the interlock between the crab-like mode and wheelbase adjustment prevents mechanical interference between the steering tie rod and the telescopic frame. When the wheelbase is shortened to below 2500mm, the vehicle enters a "high-mobility mode." At this time, the maximum rear wheel steering angle is allowed to be ±15°. Combined with the front and rear wheels steering in opposite directions (δr = -k·δf, where δr is the target front wheel steering angle, δf is the target rear wheel steering angle, and k is the rear wheel steering angle gain coefficient), the minimum turning diameter can be reduced by more than 40% compared to traditional front-wheel steering vehicles. With a short wheelbase, the center of gravity shifts forward, the turning radius is small, and large-angle steering does not lead to instability. Instead, it fully utilizes the maneuverability advantages of four-wheel steering, allowing the vehicle to traverse lanes with extreme widths. Crab mode, as an extreme supplement to maneuverability, enables lateral movement when the vehicle is stationary or at extremely low speeds, solving the problem of "being unable to pass through right-angle alleys even when the front and rear wheels are turning in opposite directions." For example, in an alley only 20cm wider than the vehicle body, traditional steering cannot complete a 90° turn, while crab mode allows the vehicle to slide in laterally without the need for reversing to adjust. This decoupled design, where "vehicle speed determines mode and wheelbase determines permissions," allows drivers to focus solely on vehicle speed and steering intentions without manually determining whether the current wheelbase is suitable for large turns—the control components automatically handle the limitations, reducing operational complexity and minimizing the risk of misoperation.

[0048] The variable wheelbase distributed four-wheel independent steering chassis platform is detailed below: 1. Structure of Reconfigurable Chassis Beam 1: The reconfigurable chassis beam 1 adopts a nested guide rod structure of square tubes within square tubes. The outer square tube 11 is made of rectangular seamless steel pipe with specifications of 150mm×150mm×8mm (length×width×wall thickness), material Q345B, and a length of 2000mm; the inner square tube 12 is made of high-strength alloy square steel with specifications of 130mm×130mm×8mm, material Q355B, and a length of 1800mm. The single-sided gap between the outer wall of the inner square tube 12 and the inner wall of the outer square tube 11 is controlled at 0.2mm. A longitudinal grease channel is opened on the outer wall of the inner square tube 12, and grease is injected through an external grease nipple. Six sets of locking holes 111 are evenly distributed longitudinally on one side wall of the outer square tube 11, with a hole diameter of 25mm and a spacing of 120mm; corresponding mating holes 121 are opened on the inner square tube 12.

[0049] The guiding and limiting mechanism includes PTFE wear-resistant sliders 132 (3 sliders per side, 30mm×20mm×5mm in size) embedded on the four outer sides of the inner square tube 12, and copper-based alloy guide sleeves 131 (ZCuSn10P1 tin bronze) embedded in the inner wall of the outer square tube 11. These two components cooperate to form a sliding guide pair with a friction coefficient μ≤0.08, which limits the radial offset of the inner square tube 12 relative to the outer square tube 11 while ensuring smooth axial expansion and contraction. On the inner surface of the copper-based alloy guide sleeve 131, a graphite copper sleeve self-lubricating structure is embedded: an axial oil groove is formed on the inner wall of the guide sleeve 131, and graphite strips (oil-containing graphite, oil content ≥20%) are embedded in the grooves. The surface of the graphite strips is in direct contact with the PTFE wear-resistant sliders 132. When the grease injected into the grease channel is insufficient or interrupted, the graphite copper sleeve continues to provide lubrication by relying on its own oil storage and graphite layered peeling characteristics, avoiding dry metal friction and extending the maintenance cycle of the guiding and limiting mechanism.

[0050] The dustproof sealing mechanism includes a double-lip rubber sealing ring 141 installed inside the port of the outer square tube 11 and a folded rubber dust cover 142 on the outside to prevent mud and sand from entering the guide rod mating surface.

[0051] 2. Structure of the Variable Wheelbase Mechanism 2: The telescopic drive device of the variable wheelbase mechanism 2 uses a double-acting hydraulic cylinder 21 as the drive unit, which is driven by the vehicle-mounted hydraulic system. The hydraulic cylinder 21 has a cylinder diameter of 80mm, a rod diameter of 50mm, a stroke of 500mm, a rated working pressure of 16MPa, and a theoretical thrust of approximately 80kN. The cylinder barrel of the hydraulic cylinder 21 is hinged to the crossbeam in the middle of the outer square tube 11 via an clevis, and the piston rod end is hinged to the end crossbeam of the inner square tube 12 via an clevis, forming a push-pull drive on the inner square tube 12. A magnetostrictive displacement sensor 23 (range 0~500mm) is integrated on the cylinder barrel of the hydraulic cylinder 21 to detect the wheelbase position in real time.

[0052] The locking mechanism employs a pin-type mechanical locking system, comprising a mechanical pin 221, an electric push rod 222, and a locking position detection sensor 223. The mechanical pin 221 has a diameter of 24 mm, a length of 80 mm, and is made of 40Cr material. After tempering (28–32 HRC), its surface is medium-frequency quenched to HRC48, with a wear-resistant layer depth of 2 mm–3 mm. The mechanical pin 221 is driven by the electric push rod 222 and inserted into the locking hole 111 and the mating hole 121. The electric push rod 222 is fixed to the outer wall of the outer square tube 11 by a bracket. The locking position detection sensor 223 is mounted on the mechanical pin 221 to provide feedback on the locking / unlocking status to the control component 4.

[0053] 3. Structure of the Distributed Four-Wheel Independent Steering System 3: The distributed four-wheel independent steering system 3 includes a front wheel steering mechanism 31 and a rear wheel steering mechanism 32. The front wheel steering motor 311 of the front wheel steering mechanism 31 is an electric power steering (EPS) motor (rated power 350W, peak torque 25N·m), which drives a rack and pinion steering gear through a steering column. The front wheel steering knuckle is pulled by the front wheel steering tie rod 312 (40Cr tempered steel, 25mm diameter). The maximum front wheel steering angle is ±35°, and a front wheel angle sensor 313 is provided. The rear wheel steering mechanism 32 is an independently mounted mechanism, including a rear wheel steering motor 321 (AC servo motor, 200W, equipped with a 20:1 worm gear reducer, self-locking angle 1°~3°), which drives the rear wheel steering tie rod 322 (40Cr tempered steel, 20mm diameter) through a crank-rocker arm mechanism. The maximum rear wheel steering angle is ±15°, and a rear wheel angle sensor 323 is provided.

[0054] 4. Structure of Control Component 4: Control Component 4 adopts a hierarchical distributed architecture. The vehicle controller 41, as the top-level decision-making unit, is located on the longitudinal beam in the middle of the chassis, near the driver's seat. It is fixed to the frame via shock absorber brackets and encapsulated in a waterproof and dustproof electrical control box. The vehicle controller 41 collects signals from the steering wheel angle sensor 44, wheel speed sensor 45, displacement sensor 23, lock-up detection sensor 223, front wheel angle sensor 313, and rear wheel angle sensor 323. After logical processing, it sends wheelbase target commands, steering mode commands, and target steering angle commands to the middle-level execution control layer via the CAN bus.

[0055] The wheelbase adjustment controller 42, serving as the wheelbase execution control unit, is located near the middle crossbeam of the outer square tube 11 and is connected to the vehicle controller 41 and the hydraulic proportional valve of the hydraulic cylinder 21 of the telescopic drive device. This controller receives the target wheelbase value from the vehicle controller 41, combines it with the real-time position feedback from the displacement sensor 23, calculates the action amount of the hydraulic cylinder 21 of the telescopic drive device, and achieves closed-loop control of the telescopic position and speed. When the position deviation meets the threshold, it sends a "position ready" signal to the vehicle controller 41, awaiting a locking command.

[0056] The steering controller 43, serving as the steering execution control unit, is located near the steering column at the front end of the inner square tube 12 and is connected to the drivers of the vehicle controller 41, the front wheel steering motor 311, and the rear wheel steering motor 321. This controller receives steering mode and target steering angle commands from the vehicle controller 41, and, in conjunction with real-time feedback from the front wheel angle sensor 313 / rear wheel angle sensor 323, performs independent closed-loop steering angle control on the front and rear wheel steering motors respectively.

[0057] The vehicle controller 41, as the top-level decision-making unit, communicates with the wheelbase adjustment controller 42 (which controls the hydraulic proportional valve) and the steering controller 43 (which controls the front and rear wheel steering motor drivers) via the CAN bus.

[0058] The input signals of the vehicle controller 41 include: a steering wheel angle sensor 44, a wheel speed sensor 45, a displacement sensor 23, a lock-up detection sensor 223, a front wheel angle sensor 313, and a rear wheel angle sensor 323. The steering wheel angle sensor 44 is mounted on the steering column and is used to detect the driver's steering intention; the wheel speed sensor 45 is mounted at each wheel hub and is used to detect the rotational speed of each wheel and calculate the overall vehicle speed.

[0059] The sources and physical locations of the input signals for control component 4 are as follows: The steering wheel angle sensor 44 is installed on the steering column and is part of the chassis human-machine interface. It converts the driver's steering intention into an electrical signal and inputs it into the vehicle controller 41. Wheel speed sensors 45 are installed on the wheel hubs of each wheel and belong to the chassis running mechanism. They input wheel speed signals into the vehicle controller 41 for vehicle speed calculation and steering mode threshold judgment. The displacement sensor 23 is integrated into the outer wall of the cylinder of the hydraulic cylinder 21. It belongs to the wheelbase variable mechanism 2 and detects the relative displacement of the inner and outer square tubes in real time and feeds it back to the wheelbase adjustment controller 42 and the vehicle controller 41. The front wheel angle sensor 313 and the rear wheel angle sensor 323 are respectively installed at the output shafts of the front and rear wheel steering motors. They belong to the distributed four-wheel independent steering device 3 and are used to detect the actual steering angle and feed it back to the steering controller 43. The locking position detection sensor 223 is mounted on the pin bracket of the locking mechanism and belongs to the variable wheelbase mechanism 2. It is used to detect the locking / unlocking status of the mechanical pin 221 and feed it back to the vehicle controller 41.

[0060] Control logic and collaborative working process: 1) Steering mode switching: The first threshold is set at 20 km / h, and the second threshold is set at 55 km / h. After power-on, the vehicle controller 41 performs a self-test to confirm that all controllers are online and sensor signals are valid. During driving, the vehicle controller 41 executes the following control logic cyclically at a period of 10ms: a. Steering mode switching: The vehicle controller 41 switches modes according to the real-time vehicle speed v measured by the wheel speed sensor 45 and the input from the steering wheel angle sensor 44, based on the following threshold values: Four-wheel reverse steering mode (v < 20km / h): The vehicle controller 41 queries the current wheelbase L of the displacement sensor 23. If L < 2500mm (short wheelbase), it outputs the target steering angle δr of the rear wheels to the rear wheel steering motor 321, δr = -k·δf (δf is the target steering angle of the front wheels, k is the rear wheel steering angle gain coefficient, k takes 0.3~0.7), and the maximum steering angle of the rear wheels is allowed to be ±15°; if L ≥ 2500mm, the maximum steering angle of the rear wheels is limited to ≤ ±5°. Normal front wheel steering mode (20km / h ≤ v ≤ 55km / h): The vehicle controller 41 sends a rear wheel zeroing command to the steering controller 43, shuts down the rear wheel steering motor 321, and only the front wheel steering assembly 31 responds to the driver's operation; Four-wheel same-direction steering mode (v > 55km / h): The vehicle controller 41 calculates δr = +k·δf (k takes 0.1~0.3) and outputs it to the steering controller 43. The rear wheel steering motor 321 performs a small-angle same-direction steering to improve the stability of high-speed lane changes.

[0061] 2) Crab Mode: When the driver selects Crab Mode via the control panel, the vehicle controller 41 checks the wheel speed sensor 45 to confirm v < 5 km / h, and the displacement sensor 23 confirms that the wheelbase is stable (no adjustment action). Once these conditions are met, the vehicle controller 41 sends a Crab command to the steering controller 43. The steering controller 43 drives the front wheel steering motor 311 and the rear wheel steering motor 321, causing the front and rear wheels to deflect at equal angles in the same direction to the target steering angle (δr = δf = δcrab, where δcrab is the target steering angle setting value for Crab Mode). When the driver depresses the accelerator pedal, the vehicle moves laterally. Upon exiting Crab Mode, the steering controller 43 drives the front and rear wheels back to 0°, resuming normal control. During Crab Mode activation, the vehicle controller 41 disables wheelbase adjustment commands.

[0062] 3) Vehicle speed-wheelbase adjustment interlock: When the driver issues a wheelbase adjustment command, the vehicle controller 41 executes a tiered interlock based on the vehicle speed. v > 55km / h: Disable wheelbase adjustment command, maintain current wheelbase lock, and issue audible and visual warning to driver; 20km / h ≤ v ≤ 55km / h: Adjustment is allowed, but a "steering lock" command must first be sent to the steering controller 43, requiring both front and rear wheels to return to δ=0° and the steering motor drive to be turned off; only after the steering controller 43 reports "steering zeroing complete" can the wheelbase adjustment controller 42 be allowed to execute the unlock-drive-lock process of the hydraulic cylinder 21 of the telescopic drive device. v < 20km / h: Distinguish between stationary and crawling states. If v = 0 (all four wheel speeds are zero), wheelbase adjustment is allowed directly; if 0 < v < 20km / h, wheelbase adjustment is allowed, but the steering controller 43 limits the rear wheel angle change rate to no more than 5° / s, and prohibits wheelbase adjustment from being initiated when the crawling mode is active—if an adjustment request is received, the system will automatically exit the crawling mode and straighten the steering wheel before performing wheelbase adjustment.

[0063] 4) Wheelbase-steering linkage: After the wheelbase adjustment is completed, the vehicle controller 41 receives the "lock complete" signal from the lock position detection sensor, updates the current wheelbase status parameters, and updates the rear wheel angle limit value in the steering mode (short wheelbase ±15° / long wheelbase ±5°) accordingly, realizing real-time linkage between wheelbase and steering.

[0064] 5) Fault Degradation Strategy: When the vehicle controller 41 detects a fault in the rear wheel steering assembly 32, it automatically degrades to a front wheel steering mode only, with the rear wheels maintaining a mechanical zero position; when a fault is detected in the wheelbase adjustment mechanism, the extension and retraction actions are prohibited, the current wheelbase is maintained, and the vehicle continues to travel at the steering angle limit value corresponding to the current wheelbase.

[0065] 5. Working method: When a large cargo box is required, the driver issues an "extend" command via the control panel. The vehicle controller 41 first checks the locking mechanism's status. If it is locked, it controls the electric push rod 222 to retract the mechanical pin 221 to unlock. Then, it controls the hydraulic cylinder 21 to extend, with the inner square tube 12 extending outward relative to the outer square tube 11. The displacement sensor 23 provides real-time position feedback. When the target wheelbase (e.g., 3000mm) is reached, the hydraulic cylinder 21 stops, the electric push rod 222 pushes out the mechanical pin 221 and inserts it into the corresponding locking hole 111. After the locking detection sensor 223 provides a feedback signal, the control component 4 determines that the wheelbase adjustment is complete and allows driving. At this time, the chassis is in a long wheelbase state, with a large load-bearing area, suitable for heavy-duty transportation.

[0066] When navigating narrow alleyways or off-road terrain, the driver issues a "shorten" command, and control component 4 repeats the unlock-drive-lock process described above, shortening the wheelbase to 2400mm. Simultaneously, control component 4 automatically switches to four-wheel steering mode to enhance maneuverability. In extremely confined spaces, the driver can select crab mode: the front and rear wheels deflect at equal angles in the same direction (e.g., both deflect 5° to the left or right), and the driver presses the accelerator pedal to achieve lateral movement.

[0067] 6. Verification of beneficial effects To verify the technical effects of the present invention, a prototype vehicle was manufactured based on this embodiment, and a comparative test was conducted with a traditional fixed wheelbase front-wheel steering chassis (comparative scale): Turning radius test: Under short wheelbase (2400mm), the minimum turning diameter of the four-wheel reverse steering mode of this invention is 5.8m, compared to 10.4m in the comparative model, a reduction of 44.2%.

[0068] Load-bearing compatibility test: The same chassis successfully adapted to two sizes of upper cargo boxes, 2.5m×1.5m and 3.2m×2.0m, by adjusting the wheelbase (2400mm~3000mm), without the need to change the chassis.

[0069] Locking reliability test: Under full load (total mass 5 tons), a 1000km reinforced rough road test was conducted. The locking mechanism showed no loosening, there was no abnormal wear on the mating surfaces of the outer and inner square tubes, and the maximum deflection of the chassis beam did not exceed 1.5mm. High-speed stability test: Under the condition of long wheelbase (3000mm) and a double lane change test at a speed of 60km / h, the peak yaw rate of the same steering mode of the present invention is reduced by 18.3% and the peak lateral acceleration is reduced by 12.7% compared with the comparative model.

[0070] The above description is merely a detailed account of one embodiment of the present invention, but it is only a preferred embodiment and should not be considered as limiting the scope of the invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A variable track, distributed four-wheel independent steering chassis platform, characterized by: It includes a reconfigurable chassis beam, which serves as the underlying skeleton of the entire vehicle, running transversely along the longitudinal centerline of the vehicle to form the load-bearing base of the entire chassis platform. It also includes a variable wheelbase mechanism, which is embedded in a large number of internal cavities and sidewall areas of the reconfigurable chassis and moves telescopically along the longitudinal centerline of the vehicle. It also includes a distributed four-wheel independent steering device, which is respectively set at both ends of the longitudinal direction of the reconfigurable chassis beam to perform steering; It also includes a control component, which is connected to the variable wheelbase mechanism and the distributed four-wheel independent steering device via circuitry and signaling. The control component switches the steering mode according to the vehicle speed signal and steering command, and controls the extension and retraction of the variable wheelbase mechanism.

2. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 1, characterized in that: The reconfigurable chassis beam adopts a nested guide rod structure of square tubes within square tubes, including an outer square tube and an inner square tube that is fitted inside the outer square tube with clearance. A guide limiting mechanism and a dustproof sealing mechanism are provided between the inner square tube and the outer square tube. The guide limiting mechanism includes a wear-resistant slider and a guide sleeve. The wear-resistant slider is embedded in the outer wall of the inner square tube, and the guide sleeve is located on the inner wall of the outer square tube. The guide limiting mechanism is equipped with a graphite copper sleeve self-lubricating structure. The dustproof sealing mechanism includes a sealing ring and a dust cover. The sealing ring is located inside the outer square tube port, and the dust cover is located outside the outer square tube port to prevent mud and sand from entering the guide rod mating surface. A grease channel is provided on the outer wall of the inner square tube. The outer square tube and the upper surface of the inner square tube are provided with standardized upper-level platform connection interfaces to adapt to upper-level functional platforms of different sizes.

3. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 1, characterized in that: The variable wheelbase mechanism includes a telescopic drive device and a locking mechanism; the telescopic drive device is a hydraulic cylinder or a servo electric cylinder, with its two ends hinged to the inner square tube and the outer square tube respectively, for driving the inner square tube to extend and retract axially relative to the outer square tube; the locking mechanism is arranged longitudinally at intervals along the side wall of the outer square tube, for mechanically locking the inner square tube and the outer square tube after the wheelbase is adjusted to the correct position.

4. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 4, characterized in that: The telescopic drive has a telescopic stroke of 300mm to 800mm; when the telescopic drive is a hydraulic cylinder, its cylinder diameter is 80mm to 100mm, its working pressure is 12MPa to 16MPa, and it is equipped with a displacement sensor; when the telescopic drive is a servo electric cylinder, it includes a servo motor and a ball screw transmission pair, and its repeatability is no more than ±0.05mm.

5. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 4, characterized in that: The locking mechanism includes multiple locking holes evenly distributed along the longitudinal direction of the outer square tube, corresponding mating holes on the inner square tube, and mechanical pins that can be inserted into or withdrawn from the locking holes and mating holes; the mechanical pins are driven by an electric push rod or an electromagnetic drive device; the spacing between the locking holes is 100mm to 150mm.

6. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 1, characterized in that: The distributed four-wheel independent steering system includes a front wheel steering mechanism and a rear wheel steering mechanism; the front wheel steering mechanism includes a front wheel steering motor, a front wheel steering tie rod, and a front wheel angle sensor; the rear wheel steering mechanism includes a rear wheel steering motor, a rear wheel steering tie rod, and a rear wheel angle sensor; the front wheel steering mechanism and the rear wheel steering mechanism are distributed and controlled independently or in conjunction.

7. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 7, characterized in that: The front wheel steering motor is an electric power steering motor, and the rear wheel steering motor is an integrated unit of a servo motor and a worm gear reducer; the steering angle range of the front wheel steering mechanism is ±35°, and the steering angle range of the rear wheel steering mechanism is ±15°; both the front wheel steering tie rod and the rear wheel steering tie rod are ball joint type tie rods.

8. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 1, characterized in that: The control components adopt a hierarchical distributed architecture, including a vehicle controller, a wheelbase adjustment controller, and a steering controller; The vehicle controller, as the top-level decision-making unit, is located on the longitudinal beam in the middle of the chassis, near the driver's seat. It is used to switch steering modes and generate control commands based on vehicle speed signals and steering instructions. The wheelbase adjustment controller is located near the frame mounting position of the wheelbase variable mechanism and communicates with the vehicle controller via the CAN bus to receive wheelbase target commands and control the operation of the telescopic drive device. The steering controller is located near the chassis mounting position of the distributed four-wheel independent steering system. It communicates with the vehicle controller via the CAN bus to receive steering mode and target steering angle commands and control the front wheel steering motor and the rear wheel steering motor respectively. The vehicle controller, wheelbase adjustment controller, and steering controller form a distributed control architecture with one master and two slaves.

9. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 1, characterized in that: The control unit switches the following steering modes based on the vehicle speed signal: a. Four-wheel reverse steering mode: When the vehicle speed is below the first threshold, the front and rear wheels are controlled to steer in opposite directions to reduce the turning radius; b. Normal front wheel steering mode: When the vehicle speed is between the first threshold and the second threshold, only the front wheels are controlled to steer, while the rear wheels keep going straight; c. Four-wheel steering mode: When the vehicle speed is higher than the second threshold, the front and rear wheels are controlled to steer in the same direction to improve driving stability.

10. The variable wheelbase distributed four-wheel independent steering chassis platform according to claim 1, characterized in that: The control components are also equipped with a wheelbase-steering linkage control strategy: a. When the wheelbase is in the short wheelbase L < 2500mm state, the maximum allowable rear wheel steering angle is ±15°; b. When the wheelbase is in the long wheelbase L>3000mm state, limit the maximum steering angle of the rear wheels to no more than ±5°, or switch to front wheel steering mode only; The control unit is also equipped with a speed-wheelbase adjustment interlock strategy: a. When the vehicle speed exceeds the second threshold, the telescopic drive device is prohibited from operating, and the current wheelbase is kept locked. b. When the vehicle speed is between the first threshold and the second threshold, wheelbase adjustment is allowed, but the steering angle of the front and rear wheels must be brought to zero and the steering motor drive must be turned off first. Wheelbase adjustment can only be performed after the steering has been brought to zero. c. When the vehicle speed is below the first threshold and the vehicle is stationary, wheelbase adjustment is allowed to be performed directly; when the vehicle speed is below the first threshold but the vehicle is in a crawling state, wheelbase adjustment is allowed but the rate of change of the rear wheel steering angle is limited, and wheelbase adjustment is prohibited when the crab mode is activated. d. When the vehicle is stationary or the speed is below 5km / h, the driver can actively select to activate the crab mode, which controls the front and rear wheel steering motors to deflect in the same direction at equal angles, so that the whole vehicle moves laterally; the crab mode is interlocked with the wheelbase adjustment function, and wheelbase adjustment is prohibited when activated.

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