Double-side independent steering system of multi-axle vehicle

Abstract

The invention relates to the technical field of vehicle steering systems, in particular to a multi-axle vehicle double-side independent steering system which comprises single-side independent steering mechanisms which are symmetrically arranged, and each single-side independent steering mechanism comprises a driving assembly. The driving assembly is in transmission connection with a front steering assembly used for controlling the front end of the vehicle to steer, a middle steering assembly used for controlling the middle of the vehicle to steer and a rear steering assembly used for controlling the tail end of the vehicle to steer, and the middle steering assembly is arranged between the front steering assembly and the rear steering assembly; the driving assembly comprises a steering machine, and a transmission gear of the steering machine is meshed with a front axle steering rack used for driving the front steering assembly to act and a rear axle steering rack used for driving the rear steering assembly to act. Through the single-side independent steering mechanisms which are symmetrically arranged, the space occupied by the steering system on the chassis is effectively reduced; and each side of the vehicle can be independently steered, so that the steering flexibility and the cross-country performance are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle steering systems, and in particular to a dual-side independent steering system for a multi-axle vehicle. Background Art

[0002] With the rapid development of transportation demand, multi-axle vehicles are widely used in special vehicle fields such as military and engineering due to their excellent load capacity and off-road performance. Special vehicles have higher requirements in heavy-load transportation, power performance, off-road passability, etc. Therefore, the design of its steering system has extremely high requirements on performance, reliability and space utilization.

[0003] In traditional multi-axle vehicles, the Ackerman steering system has long been the mainstream design due to its trapezoidal linkage-based mechanical structure. However, this design has significant deficiencies in the steering system of multi-axle vehicles. The transverse trapezoidal linkage structure requires a large installation space, while the chassis of multi-axle vehicles is complex and carries a variety of equipment and power units, leaving limited space for the layout of the steering system. In addition, as the number of axles increases, the traditional design requires additional mechanical components for each steering axle, resulting in a significant increase in system complexity, manufacturing costs, and vehicle weight.

[0004] With the development of wire-controlled technology, independent wire-controlled steering systems have become a research hotspot. This system eliminates the mechanical linkage and improves steering flexibility and reduces space occupancy by independently controlling each steering wheel, while optimizing the dynamic performance and maneuverability of multi-axle vehicles. However, the application of wire-controlled independent steering in multi-axle vehicles still faces challenges. First, independent steering requires the configuration of an actuator and a steering motor for each steering wheel, which significantly increases the system complexity and cost for multi-axle vehicles. Secondly, multi-axle steering requires precise coordinated control under different vehicle speeds and road conditions. The wire-controlled system has extremely high requirements for the real-time and accuracy of the steering algorithm. If the coordination is insufficient, it may cause tire slip, inconsistent steering, or excessive power loss, which seriously affects the vehicle's handling performance and stability.

[0005] Therefore, there is an urgent need for a dual-side independent steering system for a multi-axle vehicle that can both reduce space occupancy and improve overall steering performance. Summary of the invention

[0006] The purpose of the present invention is to provide a dual-side independent steering system for a multi-axle vehicle to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above-mentioned purpose, the present invention provides the following scheme: a double-sided independent steering system for a multi-axle vehicle, comprising a symmetrically arranged single-sided independent steering mechanism, the single-sided independent steering mechanism comprising a drive assembly, the drive assembly is transmission-connected with a front steering assembly for controlling the steering of the front end of the vehicle, an intermediate steering assembly for controlling the steering of the middle part of the vehicle, and a rear steering assembly for controlling the steering of the rear end of the vehicle, the intermediate steering assembly is arranged between the front steering assembly and the rear steering assembly; the drive assembly comprises a steering gear, the transmission gear of the steering gear is meshed with a front axle steering rack for driving the front steering assembly to move, and a rear axle steering rack for driving the rear steering assembly to move.

[0008] Preferably, the front axle steering rack and the rear axle steering rack are arranged symmetrically.

[0009] Preferably, the front steering assembly includes a front wheel, the front wheel is connected to a front axle steering rocker arm, and the front axle steering rocker arm is transmission-connected to the front axle steering rack via a front axle steering tie rod.

[0010] Preferably, the front wheel is hinged to a front wheel kingpin via a front axle steering knuckle, so that the front wheel rotates around the front wheel kingpin.

[0011] Preferably, the rear steering assembly includes a rear wheel, the rear wheel is connected to a rear axle steering rocker arm, and the rear axle steering rocker arm is transmission-connected to the rear axle steering rack via a rear axle steering tie rod.

[0012] Preferably, the rear wheel is hinged to a rear wheel kingpin via a rear axle steering knuckle, so that the rear wheel rotates around the rear wheel kingpin.

[0013] Preferably, the intermediate steering assembly includes a second-axle wheel and a third-axle wheel, the second-axle wheel is arranged close to the front wheel, and the third-axle wheel is arranged close to the rear wheel.

[0014] Preferably, the second axle wheel is connected to a second axle steering rocker arm, and the second axle steering rocker arm is connected to the front axle steering tie rod.

[0015] Preferably, the third-axle wheel is connected to a third-axle steering rocker arm, and the third-axle steering rocker arm is connected to the rear-axle steering tie rod.

[0016] Preferably, the second axle vehicle is hinged to the second axle kingpin through the second axle steering knuckle wheel, so that the second axle wheel rotates around the second axle kingpin; the third axle vehicle is hinged to the third axle kingpin through the third axle steering knuckle wheel, so that the third axle wheel rotates around the third axle kingpin.

[0017] The present invention discloses the following technical effects:

[0018] The present invention uses a symmetrically arranged single-sided independent steering mechanism, which not only effectively reduces the space occupied by the steering system on the chassis and provides greater freedom for the layout of the suspension and power unit; it also enables each side of the vehicle to steer independently, effectively improving the steering flexibility and off-road performance of multi-axle vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a schematic diagram of the double-side independent steering structure of a two-axle vehicle of the present invention;

[0021] Figure 2 This is a schematic diagram of the double-side independent steering structure of a three-axle vehicle of the present invention;

[0022] Figure 3 This is a schematic diagram of the double-sided independent steering structure of a four-axle vehicle of the present invention;

[0023] Figure 4 A schematic diagram of the relationship between the displacement of the steering rack and the wheel angle of the present invention;

[0024] Figure 5 A graph showing the relationship between the displacement of the steering rack and the wheel angle of the present invention;

[0025] Figure 6 It is a schematic diagram of the left turn process of the two-axle vehicle with independent steering on both sides according to the present invention;

[0026] Figure 7 It is a schematic diagram of the instantaneous turning center of the two-axle vehicle with independent steering on both sides according to the present invention;

[0027] Figure 8 It is a schematic diagram of the process of left turning with independent steering on both sides of a three-axle vehicle according to the present invention;

[0028] Fig. 9 It is a schematic diagram of the instantaneous turning center of the three-axle vehicle with independent double-side steering according to the present invention;

[0029] Fig.10 It is a schematic diagram of the process of the four-axle vehicle turning left independently on both sides of the present invention;

[0030] Fig.11 It is a schematic diagram of the instantaneous turning center of the dual-side independent steering of the four-axle vehicle of the present invention;

[0031] Among them, 1. front wheel kingpin; 2. front axle steering knuckle; 3. front wheel; 4. front axle steering rocker arm; 5. front axle steering rod; 6. front axle steering rack; 7. steering gear; 8. rear axle steering rack; 9. rear axle steering rod; 10. rear axle steering rocker arm; 11. rear axle steering knuckle; 12. rear wheel; 13. rear wheel kingpin; 14. second axle kingpin; 15. second axle wheel; 16. second axle steering knuckle; 17. second axle steering rocker arm; 18. third axle wheel; 19. third axle steering rocker arm; 20. third axle steering knuckle; 21. third axle kingpin. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Reference Figure 1-Figure 11 The present invention provides a dual-side independent steering system for a multi-axle vehicle, including a symmetrically arranged single-side independent steering mechanism, the single-side independent steering mechanism including a driving assembly, the driving assembly is transmission-connected with a front steering assembly for controlling the steering of the front end of the vehicle, an intermediate steering assembly for controlling the steering of the middle part of the vehicle, and a rear steering assembly for controlling the steering of the rear end of the vehicle, the intermediate steering assembly being arranged between the front steering assembly and the rear steering assembly; the driving assembly includes a steering gear 7, the transmission gear of the steering gear 7 is meshed with a front axle steering rack 6 for driving the movement of the front steering assembly and a rear axle steering rack 8 for driving the movement of the rear steering assembly. The front axle steering rack 6 and the rear axle steering rack 8 are limitedly translated along the front and rear directions of the vehicle.

[0035] The present invention uses a symmetrically arranged single-sided independent steering mechanism, which not only effectively reduces the space occupied by the steering system on the chassis and provides greater freedom for the layout of the suspension and power unit; it also enables each side of the vehicle to steer independently, effectively improving the steering flexibility and off-road performance of multi-axle vehicles.

[0036] The steering gear 7 is a key component in the automobile steering system, which is mainly used to control the direction of the vehicle's steering and help the driver to accurately control the vehicle. Its function is to appropriately transform the steering torque and steering angle from the steering wheel, and then output them to the steering rod mechanism to achieve the steering of the vehicle. The steering gear 7 is a reduction transmission device that can increase the force transmitted from the steering wheel to the steering transmission mechanism and change the transmission direction of the force.

[0037] The transmission gear of the steering gear 7 synchronously drives the front axle steering rack 6 and the rear axle steering rack 8 to move, so that the front axle steering rack 6 can effectively drive the front steering assembly to move and the rear axle steering rack 8 can effectively drive the rear steering assembly to move, so that each side of the vehicle can be steered independently.

[0038] Rack and pinion steering gear: simple and compact structure, high rigidity, low cost, sensitive steering, high positive and reverse rates, easy layout, suitable for cars and micro and light trucks.

[0039] Recirculating ball steering gear: flexible steering, large steering torque, suitable for situations where high-speed steering is required, such as highways.

[0040] Worm crank pin steering gear: complex structure, but large steering torque, suitable for large vehicles.

[0041] Further optimizing scheme, front axle steering rack 6 and rear axle steering rack 8 are symmetrically arranged. Make front axle steering rack 6 and rear axle steering rack 8 can move synchronously.

[0042] According to a further optimized solution, the front steering assembly includes a front wheel 3, the front wheel 3 is connected to a front axle steering rocker arm 4, and the front axle steering rocker arm 4 is transmission-connected to a front axle steering rack 6 via a front axle steering tie rod 5.

[0043] According to a further optimized solution, the front wheel 3 is hinged to the front wheel kingpin 1 through the front axle steering knuckle 2, so that the front wheel 3 rotates around the front wheel kingpin 1.

[0044] The front axle steering rack 6 drives the front axle steering rod 5 to move, the front axle steering rod 5 drives the front axle steering rocker arm 4 to move, and the front axle steering rocker arm 4 can drive the front wheel 3 to move, so that the front wheel 3 can stably rotate around the front wheel kingpin 1 through the front axle steering knuckle 2, thereby completing the steering action of the front wheel 3.

[0045] According to a further optimized solution, the rear steering assembly includes a rear wheel 12 , the rear wheel 12 is connected to a rear axle steering rocker arm 10 , and the rear axle steering rocker arm 10 is transmission-connected to the rear axle steering rack 8 via a rear axle steering tie rod 9 .

[0046] According to a further optimized solution, the rear wheel 12 is hinged to the rear wheel kingpin 13 through the rear axle steering knuckle 11 , so that the rear wheel 12 rotates around the rear wheel kingpin 13 .

[0047] The rear axle steering rack 8 drives the rear axle steering rod 9 to move, the rear axle steering rod 9 drives the rear axle steering rocker arm 10 to move, and the rear axle steering rocker arm 10 can drive the rear wheel 12 to move, so that the rear wheel 12 can stably rotate around the rear wheel kingpin 13 through the rear axle steering knuckle 11, completing the steering action of the rear wheel 12.

[0048] According to a further optimized solution, the intermediate steering assembly includes a second axle wheel 15 and a third axle wheel 18 , wherein the second axle wheel 15 is disposed close to the front wheel 3 , and the third axle wheel 18 is disposed close to the rear wheel 12 .

[0049] According to a further optimized solution, the second axle wheel 15 is connected to a second axle steering rocker arm 17 , and the second axle steering rocker arm 17 is connected to the front axle steering tie rod 5 .

[0050] According to a further optimization scheme, the third-axle wheel 18 is connected to a third-axle steering rocker arm 19 , and the third-axle steering rocker arm 19 is connected to the rear-axle steering tie rod 9 .

[0051] According to a further optimization scheme, the second axle wheel 15 is hinged to the second axle kingpin 14 through the second axle steering knuckle 16, so that the second axle wheel 15 rotates around the second axle kingpin 14; the third axle wheel 18 is hinged to the third axle kingpin 21 through the third axle steering knuckle 20, so that the third axle wheel 18 rotates around the third axle kingpin 21.

[0052] The front axle steering rack 6 drives the front axle steering rod 5 to move, and the front axle steering rod 5 drives the second axle steering rocker arm 17 to move. The second axle steering rocker arm 17 can drive the second axle wheel 15 to move, so that the second axle wheel 15 can stably rotate around the second axle kingpin 14 through the second axle steering knuckle 16, completing the steering action of the second axle wheel 15.

[0053] The rear axle steering rack 8 drives the rear axle steering rod 9 to move, and the rear axle steering rod 9 drives the third axle steering rocker arm 19 to move. The third axle steering rocker arm 19 can drive the third axle wheel 18 to move, so that the third axle wheel 18 can stably rotate around the third axle kingpin 21 through the third axle steering knuckle 20, thereby completing the steering action of the third axle wheel 18.

[0054] The present invention eliminates the traditional trapezoidal transverse link structure, optimizes the vehicle space utilization, and can adjust the wheel angles on the left and right sides of the vehicle through the unilateral independent steering mechanisms on both sides of the vehicle. It also supports multi-wheel coordinated control and reverse steering functions, effectively improving the steering flexibility of the vehicle.

[0055] The intermediate steering assembly can be flexibly adjusted according to different vehicle configurations.

[0056] Working process:

[0057] The steering wheel angle input signal is transmitted to the steering gears 7 on both sides through the vehicle control unit (VCU). The transmission gear of the steering gear 7 synchronously drives the front axle steering rack 6 and the rear axle steering rack 8 to move, generating linear displacement, and driving the front axle steering rocker arm 4 and the rear axle steering rocker arm 10 to rotate respectively through the front axle steering rod 5 and the rear axle steering rod 9, thereby generating a steering angle for the front wheels 3 and the rear wheels 12.

[0058] Reference Figure 4-Figure 5 , the relationship between rack displacement Δx and wheel angle δ, using the planar mechanism motion analysis vector equation graphical method, the relationship can be obtained as follows

[0059]

[0060] Where: x0 is the initial position of the steering rack relative to the steering kingpin; Δx is the displacement of the steering rack; l AB is the distance from the kingpin to the intersection of the steering rocker and the steering tie rod; θ is the initial angle of the steering rocker; δ is the wheel angle; l BC is the straight-line distance between the steering rod point BC; e is the offset between the rack and the steering kingpin.

[0061] Based on the relationship between the steering rack displacement and the wheel angle of the bilateral independent steering system, the numerical solution is solved by the numerical iteration method given the design parameters, and the relationship curve between the steering rack displacement Δx and the wheel angle δ is obtained, which can be used as a calibration curve to optimize the steering ratio or steering control.

[0062] Reference Figure 1 and Figure 6 When a two-axle vehicle is used, the middle steering assembly is not installed, only the front steering assembly and the rear steering assembly need to be installed. The left turn process of the two-axle vehicle is as follows: the steering wheel angle input signal is transmitted to the steering machines 7 on both sides through the vehicle control unit (VCU). The steering gear 7 rotates clockwise to drive the front axle steering rack 6 to move forward, and then the front axle steering rocker arm 4 rotates counterclockwise by pushing the front axle steering tie rod 5, so that the left front wheel 3 rotates around the front wheel kingpin 1 to generate a left turning angle; at the same time, it drives the rear axle steering rack 8 to move backward, and then the rear axle steering rocker arm 10 rotates clockwise by pushing the rear axle steering tie rod 9, so that the left rear wheel 12 generates a right turning angle around the rear wheel kingpin 13; similarly, the steering gear 7 on the right side drives the front axle steering rack 6 and the rear axle steering rack 8 to move, generating linear displacement, and drives the front axle steering rocker arm 4 and the rear axle steering rocker arm 10 to rotate respectively through the front axle steering tie rod 5 and the rear axle steering tie rod 9, so that the front wheel 3 and the rear wheel 12 generate left and right turning angles respectively; the right turning process of a two-axle vehicle is the same as the left turning process, that is, when turning right, the steering gear 7 rotates counterclockwise.

[0063] Reference Figure 7 The vehicle control unit (VCU) calculates the control signals of the left and right steering motors according to the steering wheel input signal and the real-time status of the vehicle to accurately determine the steering angle relationship between the left and right wheels; this relationship is calculated based on the instantaneous turning center (ICR) principle to ensure that the wheels meet the pure rolling conditions during the steering process, thereby effectively avoiding tire slippage, extending tire service life, and improving the vehicle's steering performance and handling stability.

[0064] Reference Figure 2 and Figure 8-Figure 9 When a three-axle vehicle is used, the intermediate steering assembly is installed at the second-axle wheel 15. Since the second-axle wheel 15 of the three-axle vehicle is located at the longitudinal center of the vehicle and its tire track is always consistent with the vertical direction of the instantaneous steering center, there is no need to steer the intermediate steering assembly of the three-axle vehicle; the second-axle wheel 15 maintains a fixed direction to meet the geometric constraints of vehicle steering, thereby simplifying the steering system structure and reducing system complexity and manufacturing costs.

[0065] Reference Figure 3 and Figure 10-11 When a four-axle vehicle is used, the front steering assembly for controlling the steering of the front end of the vehicle, the middle steering assembly for controlling the steering of the middle part of the vehicle, and the rear steering assembly for controlling the steering of the rear end of the vehicle are all installed; when turning left, the steering gear 7 rotates clockwise to drive the front axle steering rack 6 to move forward, and then the second axle steering rocker arm 17 rotates counterclockwise by pushing the front axle steering tie rod 5, so that the left second axle wheel 15 rotates counterclockwise around the second axle kingpin 14 to generate a leftward turning angle. At the same time, the rear axle steering rack 8 is driven to move backward, and the third axle steering rocker arm 19 rotates clockwise by pushing the rear axle steering tie rod 9, so that the left third axle wheel 18 rotates clockwise around the third axle kingpin 21 to generate a rightward turning angle; at the same time, the right steering gear 7 pulls the right front axle steering tie rod 5 and the rear axle steering tie rod 9 to make the right front wheel 3 and the rear wheel 12 generate leftward and rightward turning angles respectively; the right turning process of the four-axle vehicle is the same as the left turning process, that is, when turning right, the steering gear 7 rotates counterclockwise.

[0066] The turning angle of the second-axle wheel 15 is smaller than that of the front wheel 3, and the turning angle of the third-axle wheel 18 is smaller than that of the rear wheel 12, which can meet the pure rolling condition of each wheel during the steering process, thereby effectively avoiding tire slip.

[0067] Through the steering machines 7 on both sides of the vehicle, various multi-axle vehicles can achieve multi-wheel reverse steering, reduce the turning radius, and improve the flexibility of the vehicle.

[0068] The present invention effectively reduces the chassis space occupied by the steering system by eliminating the traditional trapezoidal connecting rod design, provides greater freedom for the layout of the suspension and power unit, and solves the problems of complex chassis and limited layout space of multi-axle vehicles; the present invention can achieve precise control of the left and right wheel angles of the vehicle through the unilateral independent steering mechanism on both sides of the vehicle, supports multi-wheel coordinated control and reverse steering functions, reduces the turning radius, and effectively improves the flexibility and handling performance of the vehicle; at the same time, for vehicles with different numbers of axles, the present invention can also meet the steering requirements of multi-axle vehicles with two, three, four or even more axles, and adapt to the application of various special vehicles in heavy-load transportation and off-road scenarios.

[0069] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0070] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A dual-side independent steering system for a multi-axle vehicle, characterized in that: The invention comprises a symmetrically arranged single-side independent steering mechanism, wherein the single-side independent steering mechanism comprises a driving assembly, wherein the driving assembly is transmission-connected with a front steering assembly for controlling the steering of the front end of the vehicle, an intermediate steering assembly for controlling the steering of the middle part of the vehicle, and a rear steering assembly for controlling the steering of the rear end of the vehicle, wherein the intermediate steering assembly is arranged between the front steering assembly and the rear steering assembly; The driving assembly comprises a steering gear (7), the transmission gear of which is meshed with a front axle steering rack (6) for driving the front steering assembly to move, and a rear axle steering rack (8) for driving the rear steering assembly to move.

2. The multi-axle vehicle double-side independent steering system according to claim 1, characterized in that: The front axle steering rack (6) and the rear axle steering rack (8) are arranged symmetrically.

3. The multi-axle vehicle double-side independent steering system according to claim 1, characterized in that: The front steering assembly comprises a front wheel (3), the front wheel (3) is connected to a front axle steering rocker arm (4), and the front axle steering rocker arm (4) is transmission-connected to the front axle steering rack (6) via a front axle steering tie rod (5).

4. The multi-axle vehicle double-side independent steering system according to claim 3, characterized in that: The front wheel (3) is hinged to the front wheel kingpin (1) via the front axle steering knuckle (2), so that the front wheel (3) rotates around the front wheel kingpin (1).

5. The multi-axle vehicle double-side independent steering system according to claim 3, characterized in that: The rear steering assembly comprises a rear wheel (12), the rear wheel (12) is connected to a rear axle steering rocker arm (10), and the rear axle steering rocker arm (10) is transmission-connected to the rear axle steering rack (8) via a rear axle steering tie rod (9).

6. The multi-axle vehicle double-side independent steering system according to claim 5, characterized in that: The rear wheel (12) is hinged to a rear wheel kingpin (13) via a rear axle steering knuckle (11), so that the rear wheel (12) rotates around the rear wheel kingpin (13).

7. The multi-axle vehicle double-side independent steering system according to claim 5, characterized in that: The intermediate steering assembly comprises a second axle wheel (15) and a third axle wheel (18), wherein the second axle wheel (15) is arranged close to the front wheel (3), and the third axle wheel (18) is arranged close to the rear wheel (12).

8. The multi-axle vehicle double-side independent steering system according to claim 7, characterized in that: The second axle wheel (15) is connected to a second axle steering rocker arm (17), and the second axle steering rocker arm (17) is connected to the front axle steering tie rod (5).

9. The multi-axle vehicle double-side independent steering system according to claim 8, characterized in that: The third-axle wheel (18) is connected to a third-axle steering rocker arm (19), and the third-axle steering rocker arm (19) is connected to the rear-axle steering tie rod (9).

10. The dual-side independent steering system for a multi-axle vehicle according to claim 9, characterized in that: The second axle wheel (15) is hingedly connected to the second axle kingpin (14) via a second axle steering knuckle (16), so that the second axle wheel (15) rotates around the second axle kingpin (14); the third axle wheel (18) is hingedly connected to the third axle kingpin (21) via a third axle steering knuckle (20), so that the third axle wheel (18) rotates around the third axle kingpin (21).

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