GB2594691A

GB2594691A - Axle unit

Info

Publication number: GB2594691A
Application number: GB2003271.0A
Authority: GB
Inventors: Karlstad Henrik; Stubberud Atle; Skaarud Anders
Original assignee: Rollersafe AS
Current assignee: Rollersafe AS
Priority date: 2020-03-06
Filing date: 2020-03-06
Publication date: 2021-11-10
Anticipated expiration: 2040-03-06
Also published as: GB2594691B; GB202003271D0

Abstract

The axle unit includes two shafts 16 rotatable about a common axis X, each having a respective shaft retainer, sleeve or axle housing 18 rotatably supporting the shafts 16. There are two braking mechanisms 20 to apply a braking force to increase the friction of the rotation of the shafts 16 with respect to the retainers 18. There is a control unit 22 to supply either hydraulic fluid or electricity to the braking mechanisms 20. The axle unit may be used in a wheelchair, pram or buggy. The control unit 22 may wirelessly communicate with brake actuators or a remote controller. The shafts 16 may have a universal joint for an adjustable camber and the shaft retainers 18 may have two parts adjustable linked at the universal joint. Brackets may hold the braking mechanisms 20 and may have an adjustable width and support drive mechanisms.

Description

AXLE UNIT

TECHNICAL FIELD

The present invention relates generally to an axle unit, particularly suitable for application to a wheelchair.

BACKGROUND

In general, there are two types of wheelchairs: powered wheelchairs, where propulsion is provided by electric motors; and manually propelled wheelchairs, where the propulsive power is provided either by the wheelchair user or by an attendant pushing from the rear.

The manually propelled wheelchair typically comprises a frame, a seat fixed to the frame, and four wheels including two caster wheels at the front and two larger main wheels at the rear. The larger rear wheels usually have hand-rims which are slightly smaller in diameter than tyres of the rear wheels.

Each main wheel may be attached to the frame with a negative camber, that is, with an inclination that increases the distance between the pair of main wheels as they approach the ground. Larger negative cambers are often set for sports wheelchairs.

Some manually propelled wheelchairs also have brakes in the form of a lever or toggle that bear on the tyres of the main wheels. These are used to prevent unintentional movements when the wheelchair is being parked or when the wheelchair user is getting in or out of the wheelchair. These brakes are not appropriate to use for in-motion braking due to unevenly generating braking forces between the right and left brakes, resulting in an extremely unstable posture of the wheelchair. Structurally, the lever or toggle type brake has a small metal piece that exerts a frictional force by pressing against the tread surface of the main wheel. Since the braking force depends on the friction force between the metal piece and the tread surface of the main wheel, the intended braking force may not be obtained due to low tyre pressure of the main wheel, or a worn or wet tyre surface condition.

Further, there is a disadvantage with the conventional lever or toggle brakes in that a relatively large force is required for their operation. This means that it may be difficult for children or people with limited handgrip strength to properly operate the brakes. In view of this, technically speaking, although it might be possible to use existing bicycle brake systems such as rim brakes or disc brakes as a wheelchair brake, this is not practically applicable because of the limited installation space around the main wheel. Nevertheless, if such a disc brake system were arranged on the sides of the main wheels, the width of the wheelchair significantly increases. This results in limiting the activity area of the wheelchair users.

Accordingly, it is an object of the present invention to provide an axle unit, preferably configured as a replacement part for existing wheelchairs, that is able to secure a desired braking force regardless of by whom it is operated, without increasing the width of the wheelchair.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an axle unit includes first and second shafts rotatable about a common axis, and first and second shaft retainers for rotatably supporting the first and second shafts, respectively. The axle unit also includes first and second braking mechanisms configured to apply a braking force to increase the friction of the rotation of the first and second shafts with respect to the retainers, respectively. The axle unit further includes a control unit configured to supply either hydraulic fluid or electricity to the first and second braking mechanisms to generate the braking force.

The axle unit will be placed under the seat of a wheeled vehicle such as a wheelchair, as a replacement part of an existing axle, or as a built-in part. In either case, since the braking mechanisms are arranged in a space under the seat of the wheeled vehicle, the width of the wheeled vehicle does not increase.

In addition, since the control unit controls the braking mechanisms via a user operation to generate the braking force, the desired braking force can be ensured regardless of by whom it is operated.

The braking mechanisms may be operated by a user actuator and/or a remote controller via the control unit. The user actuator may be with a user of a wheeled vehicle and operated by the user. The remote controller may be with an attendant of the user and operated by the attendant. The user actuator includes at least a function of activating and deactivating the brake mechanisms. The brake mechanisms may be configured to be activated whenever the user is not operating the user actuator and/or the user is not sitting on the seat based on signal from a seat sensor. Preferably, the user actuator has a function of varying the braking force available according to its operation amount.

In a preferred arrangement, the first and second shaft retainers have cylindrical shapes so as to accommodate the first and second shafts therein. This arrangement provides a compact axle unit whilst supporting the first and second shafts in a stable manner within the first and second shaft retainers.

In a preferred arrangement, each of the first and second shafts includes a universal joint. This allows the wheel of the wheeled vehicle to have a variable camber.

In a preferred arrangement, each of the first and second shaft retainer is divided into two parts which are linked together at a position of the universal joint. This allows the shaft retainer to support the inner shaft with a variable bending angle, at the position of the universal joint.

In a preferred arrangement, the angle between the two divided parts of each shaft retainer is configured to be adjustable. According to this arrangement, the angle of the universal joint of the shaft, and thus the camber angle of the wheel can be easily adjusted.

In a preferred arrangement, the control unit is arranged between the first and second braking mechanisms. A further compact axle unit can be provided.

In a preferred arrangement, the axle unit further includes first and second brackets for holding the first and second braking mechanisms, respectively. Each bracket may be attached to a holding shaft which is provided between the first and second shaft and connects them. The holding shaft may also hold the control unit.

Preferably, at least one of the first and second brackets is configured such that its width position is adjustable. To this end, at least one of the first and second brackets may be attached on the holding shaft in a displaceable manner in the width direction. The position of the bracket can be changed according to the distance between the pair of wheels of the wheeled vehicle to which the axle unit is applied.

In a preferred arrangement, the first and second braking mechanisms are driven by hydraulic fluid supplied from a hydraulic supply system. The hydraulic supply system may be built in a casing of the control unit. A further compact axle unit can be obtained.

In a preferred arrangement, the axle unit further comprises first and second driving mechanisms which are configured to rotationally drive the first and second shafts, respectively. The driving mechanisms may be configured to provide full propulsion force for the wheeled vehicle, or may be configured to provide only a portion thereof to assist the user's pushing.

In a preferred arrangement, the first and second driving mechanisms are held by the first and second brackets, respectively. A further compact axle unit can be provided.

In a preferred arrangement, the first and second driving mechanisms are disposed at an axially inward position of the first and second braking mechanisms. A further compact axle unit can be provided.

In a preferred arrangement, the first and second driving mechanisms include electric motors. However, another driving mechanism such as an internal combustion engine is applicable.

In a preferred arrangement, the axle unit further includes one or more anti-tipping bars. In a wheelchair application, the anti-tipping bars can prevent the wheelchair from accidentally flipping over backwards. The one or more anti-tipping bars maybe configured to be movable between a functional position and a rest position. The anti-tipping bars may be operated by the user actuator and/or the remote controller via the control unit. The one or more anti-tip bars may be attached to the first and second brackets.

According to another aspect of the invention, an axle system is provided. The axle system includes the axle unit described above, and a user actuator configured to transmit signal to the control unit to activate the first and second braking mechanisms.

In a preferred arrangement, the axle system further includes a remote controller which is configured to transmit signal to the control unit and activate the first and second braking mechanisms via the control unit when the axle unit is away from the remote controller by a predetermined distance. If an attendant holds the remote controller and the vehicle is too away from the attendant, for example, the vehicle will be automatically stopped through the activation of the first and second braking mechanisms. This enhances the safeness of the wheeled vehicle.

In a preferred arrangement, the control unit is configured to activate the first and second braking mechanisms, upon instruction from the user actuator, such that the first and second braking mechanisms generate stepwise constant brake force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a wheelchair as one example of a wheeled vehicle, with an axle unit according to the present invention.

FIG. 2 is a perspective view of the axle unit of FIG. 1.

FIG. 3 is a perspective view of a control unit of the axle unit of FIG. 1, with an upper cover being omitted.

FIG. 4 is a perspective view of a braking mechanism and a driving mechanism that are attached to a holding shaft via a bracket.

FIG. 5 is a rear view of a part of the axle unit of FIG. 1.

FIG. 6 is a transparent view of the part of the wheelchair and the axle unit shown in FIG. 1.

FIG. 7 is a schematic view illustrating an inner shaft of the axle unit of FIG. 1, and a push axle for assembling the axle unit to a wheel hub.

FIG. 8a is a perspective view illustrating the inner shaft of the axle unit of FIG. 1 being connected to the main wheel via the push axle.

FIG. 8b is a perspective view of the push axle. FIG. Sc is a transparent view of the push axle. FIG. 8d is perspective view of a part of the main wheel, showing the wheel hub. FIG. 9a is a perspective view of a part of a shaft retainer of the axle unit of FIG. 1. FIG. 9b is a perspective view of the shaft retainer of FIG. 9a in a bent state.

FIG. 9c shows that the inner shaft is disposed in the shaft retainer and the angle of the shaft retainer is fixed by a fastener.

FIG. 10 is a perspective view of an axle unit of another embodiment according to the present invention, which further comprises anti-tipping bars in a functional position.

FIG. 11 is a perspective view of the axle unit of FIG. 10 with the anti-tipping bars in a rest position.

DETAILED DESCTIPTION OF THE INVENTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. For instance, although the following description discusses an example where the inventive axle unit is applied to a wheelchair, particularly to a manually propelled wheelchair, the axle unit can be applied to other wheeled vehicles such as a pram, carrycot, pushchair, or baby buggy.

FIG. 1 is a schematic view of a wheelchair 100 as an example of wheeled vehicle, with an axle unit 10 according to the present invention. A typical manually propelled wheelchair such as shown in FIG. 1 mainly comprises a frame 102, a seat 104 mounted on the frame 102, two caster wheels (not shown) at the front, and two larger main wheels 106, 106 at the rear. In an application for a pram, carrycot, or the like, these four wheels can be identical in size and/or form. The frame 102 and the seat 104 thereon are supported on the axle unit 10 of the present invention via two supporting rods 108. Each main wheel 106 includes a push rim or hand rim 106a of slightly smaller diameter than a tyre 106b of the main wheel 106.

As is apparent from FIG. 1, the axle unit 10 can be applied to existing wheelchairs as a replacement part of the axle, and in particular is not necessarily built in at manufacture. Needless to say, the axle unit 10 can be built in a wheelchair at manufacture.

It is further apparent from FIG. 1 that the axle unit 10 of the present invention can be placed in a relatively wide, unused space under the seat 104, and thus does not increase the width of the wheelchair 100.

The axle unit 10 is adapted to be operated by an electric signal from a user actuator 12 and/or the remote controller 14. The user actuator 12 is operated by a user of the wheelchair 100 and transmits the signal to a control unit 22 of the axle unit 10. The remote controller 14 may be operated by an attendant of the user. The user actuator 12 and/or the remote controller 14 may preferably be in wireless communication with the control unit 22, such as via an RE (Radio Frequency) communication. Additionally or alternatively, the user actuator 12 and the control unit 22 may communicate via physical wires.

Referring to FIG. 2, details of the axle unit 10 is illustrated. In this example, since the axle unit 10 is symmetric laterally, the terms "first" and "second" used for distinction in the claims are not used hereinafter.

The axle unit 10 includes two shafts 16 on the right and left sides rotatable about a common axis X. The axis X is oriented so as to be orthogonal, in a plane parallel to the ground, to the forward or reverse direction of the wheelchair.

The axle unit 10 further includes two shaft retainers 18 on the right and left sides for rotatably supporting the inner shafts 16, respectively. In FIG. 2, the shaft retainer 18 on the right side is not shown so as to reveal the inner shaft 16. Each shaft retainer 18 defines a cylindrical room for the inner shaft 16 therein. The shaft retainers 18 can be considered as supporting the inner shafts 16, but conversely, the shaft retainers 18 can also be considered as being supported by the inner shafts 16.

The axle unit 10 may further comprise two braking mechanisms 20 on the right and left sides configured to apply a braking force to increase the friction against rotation of the inner shafts 16 with respect to the shaft retainers 18. Since the braking mechanisms 20 can generate equal braking force with each other, they may be used not only as parking brakes but also as in-motion brakes. The braking mechanisms 20 may be activated when the user or the attendant operates the actuator 12 or the remote controller 14, or when the remote controller 14 is more than a predetermined distance away from the wheeled vehicle. Stepwise constant brake force, such as 25%, 50%, 75% of the full brake is also possible, adjusted to the user's wish. Such a gradual and reduced braking force is highly beneficial, in that it can prevent the wheels from locking, particularly when used as the in-motion brake. Additionally or alternatively, the maximum braking force may be limited based on a signal from a speed sensor (not shown). The speed sensor may be arranged in association with the inner shaft 16.

The axle unit 10 may further include a control unit 22 configured to supply either hydraulic fluid or electricity to the braking mechanisms 20, 20.

The axle unit 10 may further include two driving mechanisms 24 on the right and left sides which are configured to rotationally drive the inner shafts 16, respectively. In another embodiment, no driving mechanism may be provided. The driving mechanism 24 should be considered as one of the options a user may adopt for the disclosed axle unit.

Referring to FIG. 3, details of the control unit 22 are shown. The control unit 22 is adapted to receive the signal from the user actuator 12 and/or the remote controller 14. The control unit 22 may include a casing 26, two hydraulic cylinders/reservoirs 28, two pistons 30 for pressurizing the hydraulic cylinders 28, two motors 32, preferably servo motors 32 for driving the pistons 30, and conversion mechanisms 34, preferably screw mechanisms 34 that convert the rotational motions of the motors 32 into linear motions of the pistons 30. Each cylinder/reservoir 28 is fluidly connected to the braking mechanism 20 via a hose 36 (see FIG. 2), preferably a flexible hose 36.

The casing 26 is mounted on a holding shaft 38 which is disposed between the two inner shafts 16, 16 and connects them. In the illustrated example, the holding shaft 38 is embodied by a cylindrical pipe having a predetermined strength. Both end portions 38a, 38a of the holding shaft 38 extend along the axis X and support the inner shafts 16, 16 therein, in a rotatable manner around the axis X. It can also be considered that the holding shaft 38 is supported by the inner shafts 16, 16. A bearing mechanism 40 (see FIG. 6) for rotatably supporting one end of the inner shaft 16 may be provided inside each end portion 38a.

The outer surface of each end portion 38a also functions as a holding surface that holds a bracket 42 (see FIG. 4) described later. In order for the bracket 42 to be held at different axial positions on the end portion 38a, the axial length of the end portion 38a is preferably greater than an adjustment distance for the bracket 42. The desired position adjustment distance of each bracket 42 may be at least 30mm, preferably at least 40mm. The outer shape of the end portion 38a of the holding shaft 38 may be a non-circular shape so that rotational displacement of the bracket 42 with respect to the holding shaft 38 is prevented.

Although not shown, the control unit 22 includes various devices necessary for activating and controlling at least the braking mechanisms 20 and the driving mechanism 24, such as one or more memories, one or more processing units (CPU), buses, one or more batteries, one or more antennas, one or more sensors, and one or more input-output interfaces.

Referring to FIG. 4, one of the brackets 42, one of the braking mechanisms 20, and one of the driving mechanisms 24 are shown. The same components are also provided on the opposite side of the control unit 22.

One example of the braking mechanism 20 is a disc brake system having a disc 20a that is non-rotatably connected to the inner shaft 16, and a brake calliper 20b. The brake calliper 20b incorporates one or more brake pads 20c that are hydraulically or electrically driven and pressed against the disc 20a to generate a frictional force.

An alternative braking mechanism 20 may be configured to press one or more brake pads (not shown) directly against the surface of the inner shaft 16.

Further alternative braking mechanism 20 may be an eddy-current braking means. In this sense, an electric motor may be employed as the eddy-current braking means. One or more electric motors of the driving mechanism 24 may be switched to the regeneration mode and used as the braking mechanism.

One example of the driving mechanism 24 includes one or more electric motors 24a. In the illustrated example, each driving mechanism 24 has one electric motor 24a. The electric motor 24a may be electrically disconnected when using the brakes. The electric motor 24a is preferably arranged such that its rotational axis is parallel to the axis X. The electric motor 24a is preferably held by the bracket 42. The torque of the rotating shaft of the electric motor 24a is transmitted to the inner shaft 16 via toothed pulleys 24b, 24c and a toothed transmission belt 24d. A predetermined reduction ratio may be set between the pulleys. A chain may be used instead of the transmission belt 24d, but the transmission belt 24d is preferable in terms of quietness. The rotational torque may be transmitted via gears (not shown) without using the transmission belt 24d or chain.

Each bracket 42 may include an attachment portion 42a which is put on the end portion 38a of the holding shaft 38 and is then fixed thereto by a fastener or clamp 44. The bracket 42 may also include a calliper holding portion 42b which holds the brake calliper 20b, and a motor holding portion 42c which holds the electric motor 24. The attachment portion 42a defines an inner surface corresponding to the outer shape of the end portion 38a of the holding shaft 38.

The bracket 42 can be configured to be displaceable along the end portion 38a of the holding shaft 38 in a state where the fastener or clamp 44 is loosened. When the bracket 42 is displaced in the axial direction X, the attached braking mechanism 20 and drive mechanism 24 also move relative to the holding shaft 38, along the axis X. The inner shaft 16 is displaced together with the displacement of the braking mechanism 24, resulting in a change in the distance between the pair of inner shafts 16, 16. Therefore, the width of the shaft unit 10 can be changed according to the distance between the main wheels 106 of the wheelchair 100, for example.

Referring to FIG. 5, the axle unit 10 assembled to the main wheel 106 of the wheelchair 100 is shown. The lower end of the supporting rod 108 of the wheelchair 100 is fixed to the shaft retainer 18. It is observed that the brake calliper 20b is mounted on the calliper holding part 42b of the bracket 42, and the attachment portion 42a is fixed to the end portion 38a of the holding shaft 38 with the fastener 44.

Referring to FIG. 6, the inner shaft 16 and the braking mechanism 20 are seen. It can be observed that the first end 16a of the inner shaft 16 is attached to the hub 106c of the main wheel 106 via a push axle 46 described later, and the second end 16b of the inner shaft 16 is rotatably held by the end portion 38a of the holding shaft 38 via the bearing 40. The inner shaft 16 may be displaceable in the axis X with respect to the holding shaft 38 by a first adjustable distance dl. The second end 16b may include a stopper 16c in the form of an enlarged diameter which can abut against the bearing 40 to prevent the inner shaft 16 from being detached.

Referring to FIG. 7, it can be seen that the push axle 46 of the main wheel 106 and the first end 16a of the inner shaft 16 are connected. To this end, the first end 16a of the inner shaft 16 include a recess 16d with a non-circular cross section. The non-circular cross section may be a polygon, a spline, or a key or keyway. Correspondingly, the push axle 46 may include a protrusion 46a that will be inserted into the recess 16d. The protrusion 46a has a shape that matches the shape of the recess 16d. Thereby, the push axle 46 and the inner shaft 16 are connected so as to transmit the rotational torque.

The recess 16d has a length d2 in the axial direction X. The length d2 provides the axle unit 10 with a second adjustable distance that is less than the length d2. Accordingly, the width of the axle unit 10 can be varied by the amount of the first adjustable distance dl and the second adjustable distance.

FIG. 7 further shows that the inner shaft 16 may include a universal joint 16e. The universal joint 16e may be disposed between the first end 16a and the braking mechanism 20. In the illustrated example, the universal joint 16e is implemented as a Cardan joint which include a pair of hinges 16e1, 16e2 oriented at 900 in angle to each other, but may be implemented as a constant-velocity joint such as a Rzeppa joint.

Referring to FIGS. 8a-8c, the push axle 46 is shown. FIG. 8d shows the wheel hub 106c to which the push axle 46 is attached. The push axle 46 is a component for interconnecting the main wheel 106 and the axle unit 10 and transmitting rotational torque therebetween.

Referring to FIGS. 9a-9c, a portion of the shaft retainer 18 is shown. Each shaft retainer 18 is divided into two parts 18a, 18b in the axial direction X. These two parts 18a, 18b are linked together at the position of the universal joint 16e of the inner shaft 16. The second part 18b disposed at an axially outward position, is configured to be bendable with respect to the first part 18a, around an axis Y perpendicular to both the axis X and the vertical direction. The second part 18b may include two projecting pieces 18b1 extending toward the first part 18a and rounded at the tip. Correspondingly, the first part 18a may include recesses 18a1 that receive the projecting pieces 18b1. These two parts 18a, 18b can be fixed at any angle by a fastener 18c. A plurality of teeth 18d, 18e that engage each other may be formed on the mutual contacting surfaces of the rounded projecting piece 18b1 and the recess 18al. Such teeth engagements also tend to prevent the two parts 18a, 18b from bending with respect to each other around the axis Y when fastened with the fastener 18c.

In this way, the angle adjustable shaft retainer 18 can keep the angle of the universal joint 16e of the inner shaft 16 at an arbitrary angle. Thereby, an arbitrary inclination, that is, a camber is set to the main wheel 106. The camber of the main wheel 106 can be adjusted at any time by varying the angle between the two parts 18a, 18b of the shaft retainer 18.

Referring to FIGS. 10 and 11, another embodiment of an axle unit according to the present invention is shown. The axle unit described here is the same as the axle unit described with reference to FIGS. 1-9, except that it includes some additional elements. Therefore, detailed description of the same elements or components as those described in FIGS. 1-9 is omitted by denoting the same reference signs thereto.

In this arrangement, the axle unit 10 further includes one or more anti-tipping bars 48. The anti-tipping bars 48 are provided to prevent the wheelchair from flipping over backwards under certain circumstances. Each anti-tipping bar 48 may include a roller 48a at the tip.

Preferably, each bar 48 is movable between a functional position (FIG. 10) and a rest position (FIG. 11). To this end, each anti-tipping bar 48 may be attached to the bracket 42 so as to rotate with respect to the bracket 42. Additionally or alternatively, each anti-tipping bar 48 may be configured to be extendible in length, such that it is in the functional position when extended and in the rest position when retracted.

More preferably, the axle unit 10 has one or more driving devices 50, 50 in a form of a motor and/or a cylinder for driving the anti-tipping bars 48 between the functional position and the rest position. The driving device 50 may be driven by hydraulic fluid and/or electric power from the control unit 22. In this connection, the control unit 22 may include a plurality of electric outlets and/or a plurality of fluid outlets.

Claims

Claims 1. An axle unit, in particular for a wheelchair, comprising: - first and second shafts rotatable about a common axis; - first and second shaft retainers for rotatably supporting the first and second shafts, respectively; - first and second braking mechanisms configured to apply a braking force to increase the friction of the rotation of the first and second shafts with respect to the retainers, respectively; and - a control unit configured to supply either hydraulic fluid or electricity to the first and second braking mechanisms to generate the braking force.
2. The axle unit according to claim 1, wherein the first and second shaft retainers have cylindrical shapes so as to accommodate the first and second shafts therein.
3. The axle unit according to claim 1 or 2, wherein each of the first and second shafts includes a universal joint.
4. The axle unit according to claim 3, wherein each of the first and second shaft retainer is divided into two parts which are linked together at a position of the universal joint.
5. The axle unit according to claim 3, wherein the angle between the two divided parts of each shaft retainer is configured to be adjustable.
6. The axle unit according to any one of claims 1 to 5, wherein the control unit is arranged between the first and second braking mechanisms.
7. The axle unit according to any one of claims 1 to 6, further comprising first and second brackets for holding the first and second braking mechanisms, respectively.
8. The axle unit according to claim 7, at least one of the first and second brackets is configured such that its width position is adjustable.
9. The axle unit according to any one of claims 1 to 8, wherein the first and second braking mechanisms are driven by hydraulic fluid supplied from a hydraulic supply system.
10. The axle unit according to claim 9, the hydraulic supply system is built in a casing of the control unit.
11. The axle unit according to any one of claims 1 to 10, further comprising first and second driving mechanisms which are configured to rotationally drive the first and second shafts, respectively.
12. The axle unit according to claim 11, when dependent on claim 7 or 8, wherein the first and second brackets further hold the first and second driving mechanisms, respectively.
13. The axle unit according to claim 11 or 12, the first and second driving mechanisms are disposed at an axially inward position of the first and second braking mechanisms.
14. The axle unit according to any one of claims 11 to 13, each of the first and second driving mechanisms includes an electric motor.
15. The axle unit according to any one of claims 1 to 14, further comprising one or more anti-tipping bars.
16. The axle unit according to claim 15, the one or more anti-tipping bars are configured to be movable between a functional position and a rest position.
17. The axle unit according to claim 14 or 15, when dependent on claim 7, 8 or 12, wherein the one or more anti-tipping bars are attached to the first and second brackets.
18. The axle unit according to any one of claims 1 to 17, wherein the axle unit is a replacement part for an existing axle of a wheelchair.
19. A axle system comprising: an axle unit according to any one of claims 1 to 18; and a user actuator configured to transmit signal to the control unit to activate the first and second braking mechanisms.
20. The axle system according to claim 20, further comprising a remote controller which is configured to transmit signal to the control unit and activate the first and second braking mechanisms via the control unit when the axle unit is away from the remote controller by a predetermined distance.
21. The axle system according to claim 19 or 20, wherein the control unit is configured to activate the first and second braking mechanisms, upon instruction from the user actuator, such that the first and second braking mechanisms generate stepwise constant brake force.