Steering system for a fork lift truck

Abstract

A fork truck (10) has pairs of wheel assemblies (21) each rotatable about a pivot point (24) relative to a chassis (12) of the fork truck through at least 90 degrees between a forward mode and a sideways mode. The wheels (18, 20) of each assembly are laterally offset from the pivot point (24) of the assembly so that the wheels trace an arcuate path on the ground as the wheels are transitioned between the forward and sideways modes. During the transition, an actuator acts on each wheel assembly (21) to cause the assembly to pivot about the pivot point (24) while simultaneously applying a driving force to the wheels to positively drive the wheels along the arcuate path at a speed that matches the pivoting caused by the actuator. During the transition, if the truck is located on a slope, the positive driving force imparted to the wheels (18, 20) by the wheel assemblies (21) as the direction is changed can prevent the truck from rolling.

Description

Technical Field

[0001] This invention relates to a steering system for lift trucks, and more particularly to a lift truck capable of steering in both forward and lateral modes. Background Technology

[0002] WO03 / 059799 describes a forklift with forward and lateral operating modes. The document describes and illustrates a three-wheeled truck with two front wheels and one rear wheel, all of which are driveable and steerable.

[0003] In forward operation mode (or "forward-reverse mode," since the steering setup is the same regardless of whether the carrier is moving forward or backward), the two front wheels are fixed at a straight-line angle parallel to the main longitudinal axis of the forks and chassis, and the steering mechanism is connected to the rear wheels to steer the carrier. In lateral operation mode, all three wheels steer perpendicular to the longitudinal axis, and the steering angle of the rear wheels is fixed at this position. Simultaneously, the steering mechanism is coupled to the front wheels, and the front wheels steer synchronously to guide the carrier.

[0004] In this type of transport vehicle, the wheels are positioned with steering from above; that is, the bogies with the wheels are mounted on pivots on the chassis, the pivots being vertically positioned above the center of the wheels, and steering motors rotate the bogies so that the wheels can rotate 90 degrees from their ground position. During mode transitions, brakes are applied to the wheels so that if the transport vehicle is, for example, located on a slope with its longitudinal axis perpendicular to the incline, the vehicle will not begin to roll laterally when the wheels turn laterally. Once the mode transition is complete, driving force is applied to the wheels and the brakes are released.

[0005] This arrangement is disadvantageous because space is required above the bogie to accommodate the steering mechanism. In some specialized transport vehicles, such as truck-mounted forklifts (forklifts transported by trucks), the height of the chassis and wheel mechanism should be minimized. Summary of the Invention

[0006] In a first independent aspect of the invention, a steering system for a forklift is provided, the forklift having a chassis with a longitudinal axis, the steering system comprising:

[0007] A pair of wheel assemblies, each wheel assembly mounted on the chassis at its respective pivot point, the wheel assemblies being spaced apart from each other in the lateral direction on opposite sides of the longitudinal axis;

[0008] Each wheel assembly has a corresponding ground wheel that can rotate on its respective axle, the ground wheel being laterally offset from the pivot point on which the wheel assembly is mounted to the chassis;

[0009] When the forklift is supported on the ground, each wheel assembly can rotate about its pivot point in a plane parallel to the ground and can rotate freely at least 90 degrees between forward and lateral modes. In forward mode, the axle is laterally pointed to the longitudinal axis, and in lateral mode, the axle is parallel to the longitudinal axis. When the wheel switches between forward and lateral modes, the lateral offset of the wheel from the pivot point causes the wheel to trace an arc path on the ground.

[0010] An actuator that acts on each wheel assembly and operablely controls the angular orientation of the wheel assembly about a pivot point;

[0011] A drive unit, which can operate on each of the wheels to drive the wheels on the ground; and

[0012] The controller can simultaneously actuate the actuators of the wheel assemblies to pivot the wheel assemblies about their pivot points, and actuate the drive devices running on the wheels of the wheel assemblies to provide positive driving force to the wheels and drive the wheels along the arcuate path to assist the pivoting caused by the actuators, thereby operably enabling each wheel assembly to transition between forward and lateral modes.

[0013] By laterally offsetting the wheels from the pivot point where the wheel assembly is mounted, the steering actuator no longer needs to be located above the assembly or bogie. This allows for a reduction in the height of the mechanism. However, the lateral offset of the wheels prevents them from changing their angular orientation while remaining in the same fixed position: they must travel on the ground. By applying a positive driving force to the wheels, driving them along an arc-shaped path determined by the lateral offset of the wheels from the pivot point between the wheel assembly and the chassis, the driving force of the wheels assists the pivoting caused by the actuator. This reduces stress on the pivoting mechanism and lowers the likelihood of the vehicle unintentionally rolling or shifting its position during mode-changing operations.

[0014] If the transport vehicle is located on a slope, the positive driving force of the drive unit on the wheels will help prevent the transport vehicle from rolling down the slope.

[0015] Furthermore, since the steering actuator is assisted by the drive unit of the power wheel, the forces within the system during mode switching are reduced, allowing the actuator to be smaller and more compact, while also reducing wear and the likelihood of actuator failure when encountering resistance during wheel switching.

[0016] Simultaneous complementary control of the actuator and drive unit can reduce tire friction, thereby reducing tire wear.

[0017] Preferably, the drive mechanism is controlled to drive the wheels along the arcuate path at a speed matching the pivoting caused by the actuator.

[0018] Speed ​​matching does not need to be precise: as long as the speed at which the wheels receive positive driving force is sufficient to prevent wheel scuffing and to counteract any rolling tendency when operating on sloping surfaces, it is acceptable, depending on the vehicle's weight and the range of inclines designed for operation. However, precise speed matching is preferred. For example, the controller may preferably be designed to match the wheel's travel speed on the ground with the speed transmitted to the wheel by the pivot mechanism on the ground, with a difference not exceeding 10% or 5%.

[0019] Preferably, the drive device is controlled so that the distance it drives the wheels matches the length of the arc-shaped path.

[0020] The transition between forward mode and side mode can be from forward mode to side mode or from side mode to forward mode.

[0021] The controller is preferably configured or programmed in an operational sequence to actuate the actuators and drive mechanisms of the paired wheel assemblies in a controlled and coordinated manner, thereby enabling the transition.

[0022] It can control the rotation of paired wheel assemblies around their respective pivot points to occur simultaneously, in a controlled sequence, or independently.

[0023] Preferably, the controller is operable to further control the forklift's braking system, thereby enabling independent application or release of the brakes on each of the wheels.

[0024] In a preferred embodiment, during the transition, the controller is configured to apply braking to each wheel such that each wheel does not move due to the pivoting of the associated wheel assembly about its pivot point.

[0025] More preferably, the controller is configured to release the brakes on each wheel as the associated wheel assembly pivots.

[0026] Thus, if the front wheel assembly pivots at different times, additional stability can be achieved by braking the non-pivoting front wheel during the transition of the pivoting front wheel, with the brakes being released or applied sequentially depending on whether the wheel is currently pivoting.

[0027] Preferably, the controller applies braking to each wheel at the beginning of the transition and at the end of the transition.

[0028] Preferably, when a third wheel is spaced apart from the paired wheel assembly, the third wheel is also braked when the wheel assembly pivots.

[0029] The transport vehicle is usually a three- or four-wheeled vehicle (although it is easy for those skilled in the art to understand that there may be more wheels).

[0030] Preferably, each pair of wheels is driven by an independent electric drive motor.

[0031] Compared to hydraulic drives or differentials powered by drive levers in traditional vehicles, using an electric motor for drive provides better control during transitions. This is because in hydraulic drives, the hydraulic fluid takes the path of least resistance and tends to balance the forces on each driven wheel. If the two wheels encounter different external resistances when cornering, such as when the vehicle is on a slope during maneuvering, the cornering power applied to each wheel will also be different. Similar considerations apply to the case where a differential distributes power to the two wheels.

[0032] Preferably, the actuator for each wheel assembly is a hydraulic actuator.

[0033] Furthermore, preferably, the hydraulic actuators of the paired wheel assemblies are linked, with one actuator being the master actuator and the other the slave actuator, such that the displacements of the two hydraulic actuators are the same and the steering angles of each wheel are equal.

[0034] Preferably, during the transition, the angular positions of the wheels change in equal and opposite directions.

[0035] In the case of a three-wheeled vehicle, the third wheel is typically mounted on a chassis that is spaced apart from the wheel assembly in the longitudinal direction.

[0036] Preferably, the third wheel is mounted on the longitudinal axis of the chassis.

[0037] Preferably, the third wheel can turn at least 90 degrees between a forward mode and a lateral mode. In the forward mode, the axle of the third wheel points laterally toward the longitudinal axis, and in the lateral mode, the axle of the third wheel is parallel to the longitudinal axis.

[0038] Furthermore, preferably, the third wheel is controlled to coordinate with the paired wheel assembly to switch between forward and lateral modes.

[0039] Furthermore, preferably, as part of the programmed operation sequence, the controller is operable to coordinate the transition of the third wheel between forward and lateral modes with the paired wheel assemblies.

[0040] In some embodiments, the third wheel is pivotally mounted on the chassis so that it can rotate in place without translation when transitioning between forward and lateral modes. For example, the pivot may be mounted directly above the point of contact between the third wheel and the ground (when the vehicle is in its normal orientation on a level surface).

[0041] Preferably, in this case, the controller is also adapted to brake the third wheel throughout the transition.

[0042] Wheel braking can be mechanical braking, or it can be achieved through, for example, electric braking by an electric motor or hydraulic braking by a hydraulic motor.

[0043] In other embodiments, the third wheel is mounted on the third wheel assembly in the same manner as the paired wheel assemblies, the third wheel assembly is pivotally mounted on the chassis, and the third wheel is offset from the pivot mounting point of the third wheel assembly.

[0044] In such an embodiment, the brake on the third wheel is preferably released during the pivoting of the third wheel assembly and applied at other times during the transition.

[0045] Preferably, the steering system further includes a third actuator that acts on a third wheel assembly to control the angular orientation of the third wheel assembly about a pivot point; a drive unit disposed on the third wheel to drive the third wheel on the ground; and a controller that can simultaneously actuate the third actuator to pivot the third wheel assembly about its pivot point and actuate the third wheel drive unit to provide a positive driving force to the third wheel and drive the third wheel along an arcuate path at a speed matching the pivot caused by the third actuator.

[0046] In the case where the carrier is a four-wheeled carrier, the fourth wheel is preferably located on the opposite side of the longitudinal axis, spaced apart from the third wheel, and the third and fourth wheels are spaced apart from the paired wheel assemblies in the longitudinal direction.

[0047] With a fourth wheel, all the steering and control features described above for the third wheel can be applied equally and additionally to the fourth wheel. Therefore:

[0048] - Preferably, the fourth wheel can turn at least 90 degrees between a forward mode and a lateral mode. In the forward mode, the axle of the fourth wheel points laterally toward the longitudinal axis, and in the lateral mode, the axle of the fourth wheel is parallel to the longitudinal axis.

[0049] -In addition, preferably, the fourth wheel is controlled to cooperate with the paired wheel assembly in switching between forward and lateral modes.

[0050] - Furthermore, preferably, as part of the programmed operation sequence, the controller is operable to make the transition of the fourth wheel between forward and lateral modes coordinated with the paired wheel assemblies.

[0051] - In some embodiments, the fourth wheel is pivotally mounted on the chassis so that it rotates in place without translation when transitioning between forward and lateral modes.

[0052] - Preferably, in this case, the controller is also adapted to brake the fourth wheel until the transition of each wheel is complete.

[0053] - In other embodiments, the fourth wheel is mounted on the fourth wheel assembly in the same manner as the paired wheel assemblies, the fourth wheel assembly is pivotally mounted on the chassis, and the fourth wheel is offset from the pivot mounting point of the fourth wheel assembly.

[0054] - Preferably, the steering system further includes a fourth actuator that acts on a fourth wheel assembly to control the angular orientation of the fourth wheel assembly about a pivot point; a drive unit disposed on the fourth wheel to drive the fourth wheel on the ground; and a controller that can simultaneously actuate the fourth actuator to pivot the fourth wheel assembly about its pivot point and actuate the fourth wheel drive unit to provide a positive driving force to the fourth wheel and drive the fourth wheel along an arcuate path at a speed matching the pivot caused by the fourth actuator.

[0055] It should be understood that in all cases where functionality is assigned to a controller, this includes distributed architectures where the aforementioned functionality is provided jointly by multiple controllers.

[0056] A second independent aspect of the invention is also provided, namely a steering system for a forklift having a chassis with a longitudinal axis, the steering system comprising:

[0057] A first wheel assembly and a second wheel assembly, each wheel assembly being mounted on the chassis at its respective pivot point, the first wheel assembly and the second wheel assembly being spaced apart from each other in the lateral direction on opposite sides of the longitudinal axis.

[0058] Each wheel assembly has a corresponding ground wheel that can rotate on its respective axle, the ground wheel being laterally offset from the pivot point on which the wheel assembly is mounted to the chassis;

[0059] Each wheel assembly has its own brake, which is capable of selectively applying brakes to its respective ground wheel in response to a control input;

[0060] When the forklift is supported on the ground, each wheel assembly can rotate about its pivot point in a plane parallel to the ground and can rotate freely at least 90 degrees between forward and lateral modes. In forward mode, the axle is laterally pointed to the longitudinal axis, and in lateral mode, the axle is parallel to the longitudinal axis. When the wheel switches between forward and lateral modes, the lateral offset of the wheel from the pivot point causes the wheel to trace an arc path on the ground.

[0061] An actuator that acts on each wheel assembly and operablely controls the angular orientation of the wheel assembly about a pivot point;

[0062] A drive unit, which can operate on each of the wheels to drive the wheels on the ground; and

[0063] A controller operable to transition each wheel assembly between a forward mode and a lateral mode by: (i) simultaneously actuating the actuator of the first wheel assembly to pivot the first wheel assembly about its pivot point without braking the wheel of the first wheel assembly, and applying braking to the wheel of the second wheel assembly during the pivoting of the first wheel assembly; and then (ii) simultaneously actuating the actuator of the second wheel assembly to pivot the second wheel assembly about its pivot point without braking the wheel of the second wheel assembly, and applying braking to the wheel of the first wheel assembly during the pivoting of the second wheel assembly.

[0064] By pivoting the wheel assemblies sequentially, and braking the non-pivoting wheel assemblies while another wheel assembly is pivoting, additional traction and drag are obtained to prevent the vehicle from moving unexpectedly.

[0065] In the embodiments described below, the unbraked and pivoted wheels are in a freewheel state, which simplifies the mode switching operation because no positive driving force needs to be applied to the wheels during the switching.

[0066] However, in this aspect of the invention, as an alternative, as previously described, the pivoting of the wheel assembly can also be optionally assisted by driving the wheels of the pivoting wheel assembly on the ground.

[0067] Furthermore, the preferred features listed above relating to the first independent aspect of the invention, as well as the dependent claims relating to that aspect, also apply to the second independent aspect of the invention. Those skilled in the art will understand that the same embodiments can support both aspects as long as the wheel assemblies are controlled to rotate sequentially relative to each other.

[0068] Therefore, advantageously, the second independent aspect may also have the following characteristics:

[0069] Preferably, the controller simultaneously actuates the actuator of the wheel assembly to pivot the wheel assembly about its pivot point, and actuates a drive device running on the wheel of the wheel assembly to provide a positive driving force to the wheel and drive the wheel along the arcuate path to assist the pivoting caused by the actuator.

[0070] Preferably, the drive mechanism is controlled to drive the wheels along the arcuate path at a speed matching the pivoting caused by the actuator.

[0071] Preferably, the drive device is controlled so that the distance it drives the wheels matches the length of the arc-shaped path.

[0072] The controller is preferably configured or programmed in an operational sequence to actuate the actuators and drive mechanisms of the paired wheel assemblies in a controlled and coordinated manner, thereby enabling the transition.

[0073] The transition between forward mode and side mode can be from forward mode to side mode or from side mode to forward mode.

[0074] The transport vehicle is usually a three- or four-wheeled vehicle (although it is easy for those skilled in the art to understand that there may be more wheels).

[0075] Preferably, each pair of wheels is driven by an independent electric drive motor.

[0076] The actuator for each wheel assembly could be a hydraulic actuator. However, since the wheel assemblies are not actuated simultaneously in this embodiment, the pivoting can instead be driven independently by an electric motor.

[0077] Preferably, during the transition, the angular positions of the wheels change in equal and opposite directions.

[0078] In the case of a three-wheeled vehicle, the third wheel is typically mounted on a chassis that is spaced apart from the wheel assembly in the longitudinal direction.

[0079] Preferably, the third wheel is mounted on the longitudinal axis of the chassis.

[0080] Preferably, the third wheel can turn at least 90 degrees between a forward mode and a lateral mode. In the forward mode, the axle of the third wheel points laterally toward the longitudinal axis, and in the lateral mode, the axle of the third wheel is parallel to the longitudinal axis.

[0081] Furthermore, preferably, the third wheel is controlled to coordinate with the paired wheel assembly to switch between forward and lateral modes.

[0082] Furthermore, preferably, as part of the programmed operation sequence, the controller is operable to coordinate the transition of the third wheel between forward and lateral modes with the paired wheel assemblies.

[0083] In some embodiments, the third wheel is pivotally mounted on the chassis so that it rotates in place without translation when transitioning between forward and lateral modes.

[0084] Preferably, in this case, the controller is also adapted to brake the third wheel until the transition of each wheel is complete.

[0085] When the third wheel is mounted to pivot about an axis passing through the point of contact between the wheel and the ground, the third wheel can remain braked during pivoting.

[0086] Wheel braking can be mechanical braking, or it can be achieved through, for example, electric braking by an electric motor or hydraulic braking by a hydraulic motor.

[0087] In other embodiments, the third wheel is mounted on the third wheel assembly in the same manner as the paired wheel assemblies, the third wheel assembly is pivotally mounted on the chassis, and the third wheel is offset from the pivot mounting point of the third wheel assembly.

[0088] Preferably, in these embodiments, the steering system further includes a third actuator that acts on a third wheel assembly to control the angular orientation of the third wheel assembly about a pivot point;

[0089] A drive mechanism disposed on a third wheel to drive the third wheel on the ground; and a controller that can simultaneously actuate a third actuator to pivot the third wheel assembly about its pivot point, and actuate the third wheel drive mechanism to provide a positive driving force to the third wheel and drive the third wheel along an arcuate path at a speed matching the pivot caused by the third actuator.

[0090] Alternatively, the third wheel may be in a state of inertial gliding when it pivots, in which case the other two wheels are preferably stationary and braked during the transition of the third wheel.

[0091] In the case where the carrier is a four-wheeled carrier, the fourth wheel is preferably located on the opposite side of the longitudinal axis, spaced apart from the third wheel, and the third and fourth wheels are spaced apart from the paired wheel assemblies in the longitudinal direction.

[0092] With a fourth wheel, all the steering and control features described above for the third wheel can be applied equally and additionally to the fourth wheel. Therefore:

[0093] - Preferably, the fourth wheel can turn at least 90 degrees between a forward mode and a lateral mode. In the forward mode, the axle of the fourth wheel points laterally toward the longitudinal axis, and in the lateral mode, the axle of the fourth wheel is parallel to the longitudinal axis.

[0094] -In addition, preferably, the fourth wheel is controlled to cooperate with the paired wheel assembly in switching between forward and lateral modes.

[0095] - Furthermore, preferably, as part of the programmed operation sequence, the controller is operable to make the transition of the fourth wheel between forward and lateral modes coordinated with the paired wheel assemblies.

[0096] - In some embodiments, the fourth wheel is pivotally mounted on the chassis so that it rotates in place without translation when transitioning between forward and lateral modes.

[0097] - Preferably, in this case, the controller is also adapted to brake the fourth wheel until the transition of each wheel is complete.

[0098] - In other embodiments, the fourth wheel is mounted on the fourth wheel assembly in the same manner as the paired wheel assemblies, the fourth wheel assembly is pivotally mounted on the chassis, and the fourth wheel is offset from the pivot mounting point of the fourth wheel assembly.

[0099] - Preferably, the steering system further includes a fourth actuator that acts on a fourth wheel assembly to control the angular orientation of the fourth wheel assembly about a pivot point; a drive unit disposed on the fourth wheel to drive the fourth wheel on the ground; and a controller that can simultaneously actuate the fourth actuator to pivot the fourth wheel assembly about its pivot point and actuate the fourth wheel drive unit to provide a positive driving force to the fourth wheel and drive the fourth wheel along an arcuate path at a speed matching the pivot caused by the fourth actuator.

[0100] - Optionally, the fourth wheel may be allowed to change its angular direction while in a state of inertial coasting, while the other wheel assemblies are preferably in a braking and stationary state to prevent the carrier from rolling during further wheel changes. Attached Figure Description

[0101] The invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0102] Figure 1 This is a plan view of a forklift, which is traveling in a straight line in forward operation mode;

[0103] Figure 2 and Figure 3 They are shown respectively Figure 1 The forklift's left and right turns;

[0104] Figure 4 It shows Figure 1 The forklift turns in a turntable pattern around the center point between the front wheels;

[0105] Figure 5 It shows Figure 1 The forklift travels in a straight line in lateral operation mode;

[0106] Figure 6 and Figure 7 The diagrams show the actions when turning left and right, respectively. Figure 5 forklifts;

[0107] Figure 8 It shows Figure 5 The forklift turns in a turntable pattern around the center point between the three wheels;

[0108] Figures 9 to 11 It shows the continuous stages of transition from forward mode to lateral mode;

[0109] Figures 12 to 14 This is a front view of the transport vehicle positioned on a slope, indicating that the transport vehicle is in operation. Figures 9 to 11 The transition shown;

[0110] Figure 15 This shows a perspective view of the left front wheel assembly of a transport vehicle traveling in a straight direction when the transport vehicle is in forward mode;

[0111] Figure 16 It shows Figure 15 The wheel assembly in the middle turns to the right during the transition to lateral mode, or during normal operation;

[0112] Figure 17 Shown as viewed from the outside Figure 15 The wheel assembly, in which the wheels are not installed;

[0113] Figure 18 It is a flowchart of the overall steering operation of the transport vehicle in forward and lateral modes;

[0114] Figure 19 This is a flowchart illustrating the operational sequence for transitioning from forward mode to side mode;

[0115] Figure 20 This is a flowchart illustrating the operational sequence for transitioning from lateral mode to forward mode;

[0116] Figure 21 This is a schematic block diagram of the control circuit of a forklift;

[0117] Figure 22 This is the hydraulic circuit diagram for the steering and braking circuits of a forklift;

[0118] Figures 23 to 25 Each includes Figure 22 Enlarged details of different parts of the circuit diagram;

[0119] Figures 26 to 31 A second embodiment is shown, illustrating the continuous stages of transition from forward mode to lateral mode; and

[0120] Figures 32 to 36 A second embodiment is shown, illustrating the continuous stages of the transition from lateral mode to forward mode. Detailed Implementation

[0121] exist Figure 1 In the forklift, generally represented by 10, the forklift has a chassis 12 with a longitudinal axis 14 and a pair of forks 16 mounted on a lifting mechanism (not shown).

[0122] A pair of front wheels, namely the left front wheel 18 and the right front wheel 20, are mounted on the chassis via their respective wheel assemblies, schematically indicated by 21, which will be described in more detail below. The wheels (and wheel assemblies) are spaced apart from each other laterally on opposite sides of the longitudinal axis 14, and forks 16 are positioned between the front wheels to maintain stability when carrying heavy loads. Each front wheel is driven by its own electric motor (not shown), and each wheel assembly can be steered by its own actuator (not shown).

[0123] The rear wheel (or third wheel) 22 is mounted on the chassis along the longitudinal axis 14 and is spaced apart from the front wheels 18, 20 in the longitudinal direction. The rear wheel is mounted on the chassis by a wheel assembly or bogie schematically shown as 23, driven by its own electric motor (not shown) and operated by a third actuator (not shown).

[0124] It can be seen that the wheel assemblies 21 are mounted on the chassis 12 at their respective pivot points 24, and the front wheels 18 and 20 are laterally offset from the pivot points 24 (i.e., offset in a plane parallel to the ground, such as...). Figure 1 (As seen from above). The rear wheel assembly 23 is mounted on the chassis at pivot point 26, which is located directly above the center of the rear wheel 22.

[0125] In forward operation mode (the term is used regardless of whether the three wheels are driven forward or backward), the steering angle of the front wheels is fixed to be parallel to the longitudinal axis 14, i.e., the wheel axle is transverse to or perpendicular to the longitudinal axis 14. Steering is achieved by changing the angle of the rear wheels 22.

[0126] Figure 2 The image shows the carrier moving forward (forks in front) and turning left. Rear wheels 22 define the turning direction, and the carrier travels along an arc-shaped path around center point 28. The rear wheels remain positioned directly below pivot point 26. Similarly, Figure 3 The image shows the transport vehicle turning right.

[0127] exist Figure 4 In the middle, the rear wheels have already turned 90 degrees to the right, thus determining that the center point of the steering arc is located between the front wheels 18 and 20. This will cause the carrier to rotate around the forks.

[0128] Figures 5 to 8 The same vehicle is shown in lateral mode. Figure 5As shown, all three wheels 18, 20, and 22 have rotated so that they are transverse to the longitudinal axis. The rear wheel 22 has rotated 90 degrees to the right, and the two front wheels have moved on their respective wheel assemblies 21, which move rearward and inward along arcs centered on their respective pivot points 24.

[0129] exist Figure 5 In the image, the transport vehicle is traveling in a straight line in the direction indicated by the arrows next to the three wheels (from left to right as seen on the page). When in lateral mode, the rear wheel 22 is fixed at this angle, and steering is achieved by the front wheels 18 and 20.

[0130] Figure 6 This shows the vehicle turning left in lateral mode, causing it to travel along an arc-shaped path centered at point 28, in conjunction with... Figure 5 In comparison, the left front wheel (18) has a larger clockwise angle, while the right front wheel (20) has a larger counter-clockwise angle. Figure 7 In the middle, the transport vehicle turns in the opposite direction, and the center of the arc path coincides with the pivot point 26 of the rear wheel assembly 23.

[0131] exist Figure 8 In the middle, the transport vehicle is in the turntable turning position, and the angle of the front wheels 18 and 20 is sufficient to make the center of rotation 28 within the coverage area of ​​the transport vehicle, and the distance between the center of rotation 28 and all three wheels is approximately equal, so that when the transport vehicle is driven, the transport vehicle will rotate in place around the center point 28.

[0132] It should be understood that three wheels driven by an electric motor can... Figures 1 to 8 In any of the steering configurations shown, it is driven in either forward or reverse mode.

[0133] Figures 9 to 11 This shows when the transport vehicle is in forward mode ( Figure 9 Transition to lateral mode ( Figure 11 The process of ).

[0134] exist Figure 9 In the diagram, dimension 30 represents the lateral offset distance between the pivot point 24 of the left front wheel assembly 21 and the center of the left front wheel 18. It can be seen that the right front wheel 20 also exhibits a similar offset distance.

[0135] When the controller receives a signal to transition from forward mode to lateral mode, the brakes are applied to all three wheels, and the third actuator rotates the rear wheel 22 90 degrees while maintaining the application of brakes. Figure 10In this embodiment, wheel 22 remains stationary and rotates into position about pivot point 26 located directly above the wheel's center. As previously described, braking can be provided by mechanical brakes, electric braking from a motor on the wheel, or hydraulic braking. Combinations of braking mechanisms can act on different wheels or on the same wheel.

[0136] Then, the front wheel assemblies are driven by their respective actuators, simultaneously applying forward drive to both front wheels to cause the assemblies to pivot about their respective pivot points 24, passing through... Figure 10 The position shown, until reached Figure 11 The location.

[0137] refer to Figure 10 and Figure 11 , Figure 9 The original wheel positions are shown as dashed outlines at 18' and 20'. Figure 11 As shown in bold at “A”, the center of the left front wheel 18 is depicted as a quarter circle arc when the left front wheel 18 moves from position 18' to its lateral position.

[0138] During the transition, the brakes on the front wheels are released, and the rotational force of the actuators is assisted by electric motors. Under the control of the controller, the electric motors drive the left and right front wheels to rotate in the forward direction, with the rotation amount being the path length of arc A. The drive speed of each wheel is controlled to match the drive speed with the movement of the actuators on the wheel assembly, thus preventing tire chafing. The electric drive motors on the wheels assist the hydraulic actuators in acting on the wheel assembly 21.

[0139] After the transition is completed, such as Figure 10 As shown, the rear wheel brakes can be released. Then, the steering control device switches to transfer steering control to the front wheels, causing the actuators to operate in series, as shown... Figures 5 to 8 Operate the transport vehicle as shown.

[0140] The transition from lateral to rearward mode is the same sequence reversed. When the actuator moves the wheel assembly from... Figure 11 Pull the position back to the middle Figure 9 When the position is in the middle, the distance for reverse driving of the front wheels is equal to the path length A. In both cases, the driving of the wheels and the operation of the actuator are controlled by the controller.

[0141] Figures 12 to 14 A transport vehicle 10 is shown positioned on ramp 32, with the vehicle laterally positioned on the ramp such that the left front wheel 18 is located on the downhill section of the right front wheel. Figures 12 to 14 As shown, although the rear wheel 22 is partially obscured, it is still clearly visible under the vehicle and is positioned on the central longitudinal axis extending from front to back.

[0142] exist Figures 12 to 14 In the process, the sequence of operations performed by the transport vehicle is similar to... Figures 9 to 11 The diagram is the same as the one shown. Therefore, the rear wheel 22 is braked and rotates perpendicular to the axis (in...). Figure 13 and Figure 14 In the middle, when the rear wheels are aligned with the downhill direction, the brakes prevent the wheels from going downhill. The front wheels rotate around a pivot point, which is positioned at... Figure 12 The position in the middle (the position where the front wheels are aligned on the slope) and Figure 14 The position in the middle (the position where the front wheels are aligned in the downhill direction).

[0143] During this operation, positive drive is applied to the wheels, thus not only assisting the actuators that move the front wheel assemblies around their respective pivot points, but also enabling the wheels, under drive control, to counteract and prevent the tendency of the front of the vehicle to roll downhill during maneuvering (a tendency that would occur if the wheels were not driven). Furthermore, by controlling the drive distance and speed of the front wheels to match the path followed by the wheels when the actuators move the assemblies 90 degrees around their pivot points, the vehicle remains under control throughout the maneuvering process.

[0144] Figure 15 The left front wheel assembly of the forklift 10 is shown, and the right front wheel is a mirror image relevant to this specification. Figure 15 This shows the vehicle's movement in a straight direction when it is in forward mode.

[0145] Figure 16 It shows the relationship with Figure 15 The same vehicle section, in which the wheel assembly is in the middle position of transitioning to the lateral mode, or in the case where the wheel assembly turns to the right during normal operation.

[0146] A portion of the chassis 12 is visible as an upper arm 12A and a lower arm 12B, which extend forward parallel to one of the forks 16. Figure 16 and Figure 15 As shown in the comparison, each arm supports its own pivot point 24, on which the wheel assembly 21 is mounted for pivoting about a vertical axis passing through the pivot point.

[0147] Back Figure 15 An electric motor 34 mounted on the wheel hub provides power or driving force to the wheel when power is supplied according to an appropriate throttle valve signal. Each of the three wheels is independently powered by a corresponding motor of this type. A directional cylinder 36 can be seen at the front of the wheel assembly; this cylinder can extend downwards to lift the wheel off the ground.

[0148] The steering of the wheel assembly is controlled by a steering cylinder 38, which is fixed to the chassis arm 12B at the pivot 40 (e.g., Figure 16 (as shown) and wheel assembly 21 at pivot 42 (as shown) Figure 15 As shown in the image, the cylinder is already between [the two points]. It can be seen that when the steering wheel is turned to the right, the cylinder is already [relative to the [point]... Figure 15 The cylinder retracts partially. Further retraction of the cylinder will complete the transition to the middle steering position in lateral mode (from...). Figure 15 The position is rotated 90 degrees to the right. It should be understood that the cylinder can be further retracted beyond the position required to rotate it 90 degrees in lateral mode to achieve the intermediate steering position, thus allowing simultaneous left and right steering when driving in lateral mode, for example... Figure 2 and 3 As shown. In this embodiment, the cylinder in its fully extended state places the wheel in... Figure 15 The straight-ahead position is because when in forward mode, the front wheels are fixed and the rear wheels are steered, but those skilled in the art will understand that this implementation detail can vary and that steering mechanisms can be provided to allow the wheels to move through a greater rotation angle.

[0149] Figure 17 Details of the wheel assembly 21 with wheel 18 removed, viewed from the outside, are shown. Thus, the wheel assembly 21 has a hub 34 mounted thereon, on which the vehicle 18 can be mounted. The steering cylinder 36 and pivot 24 are also visible.

[0150] Wheel hub 34 includes an integrated gearbox and a spring-applied hydraulic release (SAHR) parking brake. Although the SAHR parking brake is mechanical, as mentioned earlier, technicians can also brake the wheels electrically or hydraulically.

[0151] Figure 18 This is a flowchart of the steering control process. The vehicle employs a combination of electronic and hydraulic control to achieve steering. The driver operates the electronic control unit to select either a forward or lateral mode, and the electronic controller outputs appropriate control signals to control the hydraulic valves to achieve the selected mode. Steering is mechanically achieved by a hydraulic circuit that receives steering input from the steering wheel under normal operation and receives steering input from the electronic controller when switching from forward to lateral mode, and vice versa.

[0152] exist Figure 18In the process, starting at 50, the transport vehicle is in either forward or lateral mode (depending on the current wheel direction). First, the case where the transport vehicle is in forward mode 52 is described: the front wheel steering control locks the wheels in the straight position 54, and all steering signals are directed to the rear wheel steering cylinder 56. The controller checks the mode transition signal input by the operator (i.e., decision 58). If no mode transition signal is detected, the process returns to the "No" branch, and the transport vehicle remains in forward mode.

[0153] However, if a mode switching instruction is received (e.g., by the operator pressing the "lateral mode" button on the steering control), the process proceeds to step 60 to perform the switch from forward mode to lateral mode, which will refer to... Figure 19 Describe it.

[0154] After the mode conversion operation is completed Figure 18 The process proceeds to step 62, at which point the vehicle is in lateral mode. The rear wheels are locked in the lateral position 64, and all steering signals are now directed to the front steering wheels, causing the vehicle to turn 66. The controller again checks the mode transition signal input by the operator (i.e., decision 68). If no mode transition signal is detected, the process returns to the "No" branch, and the vehicle remains in lateral mode.

[0155] However, if a mode switching instruction is received (e.g., by the operator pressing the "Forward Mode" button on the steering control), the process proceeds to step 70 to perform a switch from forward mode to lateral mode, as will be referred to Figure 20 The process will then return to step 52, and the transport vehicle will once again be in forward mode.

[0156] In this way, the turn signal can be based on Figure 18 Control is performed via the forward mode branch or the lateral mode branch. The following will combine... Figure 19 and Figure 20 Describe the transition.

[0157] exist Figure 19Upon receiving a signal to switch modes, the transition from forward mode to lateral mode begins (i.e., step 72). Braking is applied to all wheels 74, and then the rear steering cylinder is actuated to turn the rear wheels to a lateral position 76. Subsequently, the front steering cylinder is actuated to turn the front wheels to a lateral position 78 as well. Simultaneously with the steering cylinder actuation, the front brake 80 is released, and the front wheels receive forward driving force to drive them along a 90-degree arc to the desired distance, thereby translating the front wheels from a straight position to a lateral position 82. The front brake 84 is then applied, and steering control is switched to front-wheel steering 86, such that movement of the steering wheel causes actuation of the front steering cylinder, rather than actuation of the rear cylinder as occurred before the mode transition. When the mode transition process ends 88, the vehicle is operating in lateral mode.

[0158] Figure 20 The corresponding process for switching from lateral mode to rearward mode is illustrated. Upon receiving a signal to switch modes, the transition from lateral mode to forward mode begins (i.e., step 90). All wheels are braked 92, and then the rear steering cylinder is actuated to steer the rear wheels to a straight position 94. Subsequently, the front steering cylinder is actuated to steer the front wheels to a straight position 96. Simultaneously with the steering cylinder actuation, the front brake 98 is released, and the front wheels receive forward driving force to drive them along a 90-degree arc to the desired distance, thereby translating the front wheels from the lateral position to the straight position 100. The front brake 102 is then applied, and steering control is switched to rear-wheel steering 104, such that movement of the steering wheel causes actuation of the rear steering cylinder, rather than actuation of the front cylinder as occurred before the mode change. When the mode change process ends 106, the vehicle is operating in forward mode.

[0159] Figure 21 This is a block diagram of the control system, where according to Figures 18 to 20 A set of programmable controllers 110 (appropriately programmed using stored program instructions in a known manner) operates to transmit drive signals to drive motors at the left front wheel 112, right front wheel 114, and rear wheel 116. The programmable controllers 110 also transmit braking signals to the front brake 118 and rear brake 120. A hydraulic steering control unit 122 receives steering signals from the steering wheel and is hydraulically connected to the right front steering cylinder 124 (which in turn is hydraulically connected to the left front steering cylinder 126) and to the rear steering cylinder 128. The hydraulic steering control unit 122 is provided in the form of valves and hydraulic circuits that can be electromechanically switched using signals from the programmable controllers 110 to operate steering in either lateral or forward mode. When the steering wheel is turned, hydraulic fluid may be directed to the front cylinders 124, 126, or the rear cylinder 128, depending on the state of the valves.

[0160] Figure 22It is a detailed schematic diagram of the steering and braking hydraulic circuits, and Figures 23 to 25 It shows Figure 22 Enlarged details of the parts to better show the components shown.

[0161] exist Figure 22 There are four types of hydraulic line connection components. These lines are designated by “SL” for steering lines, “BL” for brake lines, “PF” for pump supply lines, and “RET” for tank return lines (using dashed lines).

[0162] Some components of the already described embodiments are in Figure 22 As can be seen, specifically, there are three electric drive motors, driving the left front wheel (motor 34L), the right front wheel (motor 34R), and the rear wheel (motor 34X), respectively. The front wheels are steered by corresponding steering cylinders 38L and 38R, and the rear wheels are steered by a rear steering cylinder 56. Each motor drives its own axle, which is operated by its own SAHR brake (as shown in the right front brake 164, left front brake 166, and rear brake 168). As previously mentioned, the brakes are advantageously mounted on the wheel hubs and integrated with the corresponding motor and gearbox for each wheel.

[0163] Hydraulic fluid is supplied from tank 152 by pump 150. A filter (unmarked, but shown as a diamond bisected by a line) can be seen at the pump's tank outlet. Fluid for the steering circuit passes through check valve 153 and is then supplied to steering motor 154, which has a lever 156 connected to the steering wheel. A six-port diverter valve 158 receives the steering line SL from steering motor 154 and is operable, as previously described, to direct steering control to rear steering cylinder 56 or front steering cylinders 38L, 38R. It can be seen that the front steering cylinders 38L, 38R are connected in series in a push-pull arrangement, thus allowing them to operate synchronously. Figure 23 The steering motor 154, steering rod 156, and flow divider valve 158 are shown in more detail.

[0164] The steering circuit also includes an electronically controlled valve assembly 160, which performs the operation of switching the wheel orientation from a forward mode to a lateral mode and vice versa, such as... Figure 24 As shown in more detail above, and in the text above regarding Figure 19 and Figure 20 The description.

[0165] The braking circuit is also supplied with hydraulic fluid by pump 150 via a branch leading to pressure reducing valve 162 to reduce the pump pressure to the lower pressure required by the brakes. Front brake valve 170 and rear brake valve 172 can be operated independently to release paired front brakes 164, 166 or rear brake 168 (note that in this embodiment, the braking is applied by a spring but released hydraulically). Valves 170 and 172 are electrically controlled to apply and release the brakes under operator control and programmable controller control to perform… Figure 19 and Figure 20 The sequence of applying and releasing the brakes as described in [the document / section]. Figure 25 The pressure reducing valve 162, rear brake valve 172, rear motor 34, and rear brake 168 can be seen in more detail.

[0166] Figures 26 to 36 This shows the operation during mode switching. Figure 1 The mode switching operation of the transport vehicle has a different operation sequence than that described above. Figures 26 to 31 In the middle, the transport vehicle switches from forward mode ( Figure 26 Switch to lateral mode ( Figure 31 ), and then Figures 32 to 35 In the middle, the transport vehicle is in lateral mode ( Figure 32 Switch to forward mode ( Figure 36 ).

[0167] exist Figures 26 to 36 In each diagram, the "ON" or "OFF" marking next to each wheel 18, 20, 22 indicates whether the respective brake is applied ("ON") or released ("OFF"). These brakes can independently apply or release the brakes to the wheels under the control of a controller that sequences mode-switching operations. In this series of operations, a thick, curved arrow is seen next to each wheel, indicating a steering operation involving pivoting the wheel assembly shown.

[0168] exist Figure 26 Before the mode transition operation, the transport vehicle can be seen in its forward mode. When the mode transition begins, all brakes will be applied, which can be seen from the "ON" indicator. Figure 27 In the middle, the rear wheel 22 begins to rotate about its vertical axis. Since the axis of pivot rotation passes through the point of contact with the ground, the rear wheel 22 can maintain braking, and as... Figure 28 When the rotation shown ends, the rear wheels are transverse to the symmetrical main axis of the transport vehicle.

[0169] Next, Figure 29 In the middle, the brake on the left front wheel 18 is released, activating the electric motor that drives the pivoting rotation of the left front wheel assembly, causing it to... Figure 28 Forward positioning Figure 30The transition to lateral positioning is achieved in the middle.

[0170] Those skilled in the art will understand that in this embodiment, the other two wheels are in a fixed position and both are braked, thus preventing the vehicle from rolling. Therefore, in this embodiment, the left front wheel 18 can be in a state of inertial gliding as it travels along an arcuate path around the pivot point of the wheel assembly with the chassis. In this embodiment, the means of applying driving force to the wheels to match the rotational speed and the length of the arcuate path is not important.

[0171] However, the embodiment can be modified according to the designer's choice to apply a positive driving force to the wheel as the wheel assembly rotates. It should be understood that if the controller does not include the function of positively driving the wheel along an arc path when the wheel assembly pivots, then the controller can be simpler; however, on the other hand, the highest level of control can also be achieved by adding positive drive to this embodiment.

[0172] The same considerations apply to each of the other transitions of the front wheels 18 and 20, which are described in sequence below.

[0173] Figure 30 The transition of the right front wheel 20 is illustrated, wherein braking is applied to the left front wheel 18, which has already completed its transition, and the braking of the right front wheel 20 is released, causing the right front wheel 20 to pivot via an electric motor acting on the right front wheel assembly and rotate along an arc-shaped path in an inertial gliding state to complete the transition to a lateral mode. As described above, in this embodiment, it is also possible to optionally drive the right front wheel forward along the arc-shaped path during this transition.

[0174] Figure 31 The mode transition operation is shown to be at its end, with all three wheels in the lateral direction and braking applied to all three wheels in preparation for resuming lateral driving control.

[0175] Figure 32 This illustrates the initial stage of the reverse operation of the transport vehicle (converting from lateral mode to forward mode). Because all three wheels are braked and lateral to the main axis of the transport vehicle during the preparation for this operation, therefore... Figure 32 and Figure 31 There is no difference.

[0176] Figure 33 , Figure 34 and Figure 35 They respectively showed the same as Figure 30 , Figure 29 and Figure 27The reverse operation occurs. Therefore, each front wheel releases its brakes sequentially, while the other two wheels remain braked. The unbraken wheel assemblies pivot about their respective pivot points and, upon reapplying braking, pivot back to the forward position. Then, the rear wheel assembly 22 pivots while braking is applied. Figure 35 ), to reach Figure 36 The final position in the [the text].

[0177] Figures 26 to 31 (Back -> Left -> Right) and Figures 32 to 36 The order of the individual pivoting operations in (right -> left -> rear) is not important and can be changed as needed. Furthermore, although the conversion sequence from lateral to forward is the reverse of the conversion sequence from forward to lateral, these are independent mode-changing operations, and reversing them makes no difference. Additionally, while the rear wheels are not currently preferred, they can rotate at any time before, during, or after the front wheel assembly's sequential pivoting, in any one or both mode-changing operations.

[0178] While this teaching has been described with reference to an exemplary arrangement, it should be understood that this is not intended to limit the teaching to this arrangement, as modifications can be made without departing from the scope of the invention. Therefore, it is understood that this teaching is limited only to the extent deemed necessary by the appended claims. The terms "comprises" or "comprising" as used in the specification are used to specify the presence of a said feature, integer, step, or component, but do not exclude the presence or addition of one or more additional features, integers, steps, components, or combinations thereof.

Claims

1. A steering system for a forklift, the forklift having a chassis with a longitudinal axis, the steering system comprising: A pair of wheel assemblies, each wheel assembly mounted on the chassis at its respective pivot point, the wheel assemblies being spaced apart from each other in the lateral direction on opposite sides of the longitudinal axis; Each wheel assembly has a corresponding ground wheel that can rotate on its respective axle, the ground wheel being laterally offset from the pivot point on which the wheel assembly is mounted to the chassis; When the forklift is supported on the ground, each wheel assembly is able to rotate about its pivot point in a plane parallel to the ground and rotate freely at least 90 degrees between forward and lateral modes. In forward mode, the axle is laterally pointed to the longitudinal axis, and in lateral mode, the axle is parallel to the longitudinal axis. When the wheel switches between forward and lateral modes, the lateral offset of the wheel from the pivot point causes the wheel to trace an arc path on the ground. An actuator that acts on each wheel assembly and operablely controls the angular orientation of the wheel assembly about a pivot point; A drive unit that operates on each of the wheels to drive the wheels on the ground; and The controller is capable of pivoting the wheel assembly about its pivot point by simultaneously actuating the actuators of the wheel assembly and actuating the drive mechanism running on the wheels of the wheel assembly to provide positive driving force to the wheels and drive the wheels along the arcuate path to assist the pivoting caused by the actuators, thereby operable to transition each wheel assembly between forward and lateral modes.

2. The steering system of claim 1, wherein, The drive mechanism is controlled to drive the wheels along the arcuate path at a speed matching the pivoting caused by the actuator.

3. The steering system of claim 1 or 2, wherein, The drive unit is controlled so that the distance it drives the wheels matches the length of the arc-shaped path.

4. The steering system of claim 1 or 2, wherein, The controller is configured or programmed in an operational sequence to actuate the actuators and drive mechanisms of the paired wheel assemblies in a controlled and coordinated manner, thereby enabling the transition.

5. The steering system according to claim 1 or 2, wherein, The controller is operable to further control the forklift's braking system, thereby enabling the independent application or release of braking on each of the wheels.

6. The steering system according to claim 5, wherein, The controller is configured to release the brakes on each wheel as the associated wheel assembly pivots.

7. The steering system according to claim 5, wherein, The controller is configured to apply braking to each of the wheels before the transition begins and upon completion of the transition.

8. The steering system according to claim 1 or 2, wherein, Each pair of wheels is driven by an independent electric motor.

9. The steering system according to claim 1 or 2, wherein, The actuator for each wheel assembly is a hydraulic actuator.

10. The steering system according to claim 9, wherein, The hydraulic actuators of the paired wheel assemblies are linked, with one actuator being the master actuator and the other the slave actuator, so that the displacements of the two hydraulic actuators are the same and the steering angles of each wheel are equal.

11. The steering system according to claim 1 or 2, wherein, During the transition, the angular position of the wheels changes in equal and opposite directions.

12. The steering system according to claim 1 or 2, wherein, The forklift is a three-wheeled transport vehicle with a third wheel mounted on the chassis, the third wheel being spaced apart from the wheel assembly in the longitudinal direction.

13. The steering system according to claim 12, wherein, The third wheel is mounted on the longitudinal axis of the chassis.

14. The steering system according to claim 12, wherein, The third wheel is capable of turning at least 90 degrees between a forward mode and a lateral mode. In the forward mode, the axle of the third wheel points laterally toward the longitudinal axis, while in the lateral mode, the axle of the third wheel is parallel to the longitudinal axis.

15. The steering system according to claim 12, wherein, The third wheel is controlled to work in conjunction with the paired wheel assembly to switch between forward and lateral modes.

16. The steering system according to claim 15, wherein, As part of the programmed sequence of operations, the controller is operable to coordinate the transition of the third wheel between forward and lateral modes with the paired wheel assemblies.

17. The steering system according to claim 12, wherein, The third wheel is pivotally mounted on the chassis so that it can rotate in place without translation when transitioning between forward and lateral modes.

18. The steering system according to claim 11, wherein, The controller is also adapted to brake the third wheel throughout the transition.

19. The steering system according to claim 6 or 7, wherein, The third wheel is mounted on the third wheel assembly in the same manner as the paired wheel assemblies, the third wheel assembly being pivotally mounted on the chassis, and the third wheel being offset from the pivot mounting point of the third wheel assembly.

20. The steering system according to claim 6 or 7, wherein, The steering system also includes a third actuator that acts on the third wheel assembly to control the angular orientation of the third wheel assembly about the pivot point; A drive unit, which is mounted on a third wheel and operates to drive the third wheel on the ground; and a controller capable of operating to simultaneously actuate a third actuator to pivot the third wheel assembly about its pivot point, and actuate the third wheel drive unit to provide a positive driving force to the third wheel and drive the third wheel along an arcuate path at a speed matching the pivot caused by the third actuator.

21. The steering system according to claim 1 or 2, wherein, The forklift is a four-wheeled vehicle, with the fourth wheel positioned on the opposite side of the longitudinal axis and spaced apart from the third wheel. The third and fourth wheels are spaced apart from the paired wheel assemblies in the longitudinal direction.

22. The steering system according to any one of claims 16 to 18, wherein, Each wheel assembly is driven by an electric motor.

23. A steering system for a forklift, the forklift having a chassis with a longitudinal axis, the steering system comprising: A first wheel assembly and a second wheel assembly, each wheel assembly being mounted on the chassis at its respective pivot point, the first wheel assembly and the second wheel assembly being spaced apart from each other in the lateral direction on opposite sides of the longitudinal axis. Each wheel assembly has a corresponding ground wheel that can rotate on its respective axle, the ground wheel being laterally offset from the pivot point on which the wheel assembly is mounted to the chassis; Each wheel assembly has its own brake, which is capable of selectively applying brakes to its respective ground wheel in response to a control input; When the forklift is supported on the ground, each wheel assembly is able to rotate about its pivot point in a plane parallel to the ground and rotate freely at least 90 degrees between forward and lateral modes. In forward mode, the axle is laterally pointed to the longitudinal axis, and in lateral mode, the axle is parallel to the longitudinal axis. When the wheel switches between forward and lateral modes, the lateral offset of the wheel from the pivot point causes the wheel to trace an arc path on the ground. An actuator that acts on each wheel assembly and operablely controls the angular orientation of the wheel assembly about a pivot point; A drive unit capable of operating on each of the wheels to drive the wheels on the ground; and A controller operable to transition each wheel assembly between a forward mode and a lateral mode by: (i) simultaneously actuating the actuator of the first wheel assembly to pivot the first wheel assembly about its pivot point without braking the wheel of the first wheel assembly, and applying braking to the wheel of the second wheel assembly during the pivoting of the first wheel assembly; and then (ii) simultaneously actuating the actuator of the second wheel assembly to pivot the second wheel assembly about its pivot point without braking the wheel of the second wheel assembly, and applying braking to the wheel of the first wheel assembly during the pivoting of the second wheel assembly.

24. The steering system according to claim 23, wherein, A wheel that is not braked and is pivoting is in a state of inertial sliding.

25. The steering system according to claim 24, wherein, The controller simultaneously actuates the actuator of the wheel assembly to pivot the wheel assembly about its pivot point, and actuates a drive device running on the wheel of the wheel assembly to provide a positive driving force to the wheel and drive the wheel along the arc path to assist the pivoting caused by the actuator.

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