HUB MOTOR DESIGN

A powered unicycle device has a hub motor and a tyre around the motor. A motor casing around the motor defines side walls (300,305) and an outer annular rim (301,306), and the tyre is mounted around the outer annular rim (301,306). The motor casing is formed of only two side walls (300,305) each having a rim portion (301,305), and the rim portions (301,305) connect to each other, together defining the outer annular rim (301,305).

FIELD OF INVENTION

The present invention relates to hub motors designs, for example for powered single-wheeled devices and more particularly to powered unicycles with self-balancing functionality.

BACKGROUND TO THE INVENTION

Powered self-balancing vehicles for use while standing are known. Such vehicles include two-wheeled vehicles and single-wheeled vehicles (i.e. unicycles).

In a powered self-balancing unicycle, an electronic or mechanical system that controls the wheel in the appropriate direction is typically used to achieve fore-and-aft balance. This type of automatic fore-and-aft balance technology is well known and described, for example, in U.S. Pat. No. 6,302,230. A sensor and electronic equipment are typically provided. Information detected by the sensor and the electronics is relayed to a motor. The motor drives the wheel in the appropriate direction and at sufficient speed to maintain fore-and-aft balance.

The market for self-balancing unicycles of this type is strongly dependent on the weight of the product, which also influences the cost of manufacture of the device. There is therefore always a need to reduce production costs where possible.

One aspect is the number of different components that need to be manufactured to make the overall design.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a hub motor for driving a wheel, wherein the hub motor comprises:a motor casing around an inner part of the motor, wherein the casing defines side walls and an outer annular rim,wherein the motor casing comprises a first side wall and a second side wall, each side wall comprising a rim portion, wherein the side walls are coupled together with the rim portions in contact with each other thereby together defining the outer annular rim.

There is thus provided a motor casing for a hub motor which is formed from only two casing parts or sub-assemblies, and these casing parts define both the side walls, which form the wheel hub, and a rim for example on which a tyre can be mounted. This provides a low component count and therefore reduces weight and thus manufacturing and assembly cost.

The hub motor for example has an inner stator and an outer rotor, and the outer rotor is mounted within the outer annular rim.

The first and second side walls are preferably identical in shape. In this way, there is a single component design for the two casing halves.

In one set of examples, each side wall comprises an integral side wall plate and rim portion. Thus, there are two identical individual components, which together define the side plates of the hub as well as the wheel rim.

In another set of examples, each side wall comprises a side wall plate and the rim portion, and the rim portion or a section of the rim portion is removable from the remainder of the side wall. In this design, the rim portion or a second if it can be separated. This enables easier tyre replacement, but without exposing the sealed motor cavity, which would result from fully dismantling the casing.

Different designs may be chosen either to optimise the ease of use, or else to reduce the weight, or number of components, or ease and cost of manufacture.

Preferably, two foot platforms are provided for supporting a user of the unicycle device. This is mounted on a non-rotating part of the device, for example coupled to the central stator.

In some embodiments, each side wall comprises a set of tabs around the inner periphery of the rim portion, the tabs being over an outer periphery of the outer rotor. These tabs provide fixing points. The side walls may be connected together at the tabs. The tabs provide strong connection points for fixing the casing parts together.

The outer rotor for example comprises a cylindrical carrier on which an array of permanent magnets is mounted. This carrier is sandwiched between the side walls. The carrier is made from a ferromagnetic material. The side walls then may be made of a lighter or lower cost material, for example aluminium. Alternatively, if the side walls are ferromagnetic, the magnets may be coupled directly to one or both side walls, avoiding the need for the carrier.

The hub motor for example has an inner stator which comprises an electromagnet coil arrangement. It is for example mounted around a fixed central axis about which the motor casing rotates.

The invention also provides a powered unicycle device, comprising:a hub motor as defined above; anda balance control system adapted to maintain fore-aft balance of the unicycle device.

A tyre is typically mounted around the annular outer rim. The hub motor forms a single wheel hub. There may however be two or more tyres mounted on the same hub.

DETAILED DESCRIPTION

The invention provides a hub motor, for example for use in a powered unicycle device in which there is a tyre around the hub motor. A motor casing around the motor defines side walls and an outer annular rim. The motor rotor is mounted within the outer annular rim. The motor casing is formed of only two side walls each having a rim portion, and the rim portions connect to each other, together defining the complete outer annular rim. When used in a powered unicycle device, the hub motor itself defines the wheel rim over which the tyre is mounted.

Before describing the motor casing arrangement of the invention, the operation of the general type of powered unicycle device is described with reference toFIGS. 1-4. These figures show a hubless design.

This invention is of particular interest for a hub motor design. However, a hubless design is first described in order to explain some of the possible features of the device, which may be employed in both hub and hubless designs.

FIG. 1shows the powered unicycle device100with a casing110in a closed configuration so that it encases a single wheel120. In this particular example, the casing110is formed from a first, upper portion110A that covers the top (uppermost) half of the wheel120, and a second, lower portion110B that covers the bottom (lowermost) half of the wheel120.FIG. 2illustrates an exploded view of components internal to the casing110, namely a wheel120and drive arrangement135.

Referring back toFIG. 1, the wheel120spins about a central axis125. The first, upper portion110A of the casing is retained in a fixed position relative to the central axis125, whereas the second, lower portion110B of the casing is adapted to rotate about the central axis125. Rotation of the second lower portion110B about the central axis125moves the casing between closed and open configurations (as illustrated byFIGS. 3-4). In the closed configuration (shown inFIG. 1), the casing110encloses the wheel120so that the outer rim130of the wheel120is not exposed. In the open configuration (shown inFIG. 5), the outer rim130of the wheel120is exposed so that it can contact a ground surface.

Referring now toFIG. 2, rotation of the single wheel120is driven by a drive arrangement135. The drive arrangement135includes guide wheels140attached to an outwardly facing side of respective batteries145. In this example, there are two pairs of guide wheels140, wherein the two guide wheels in each pair share the same axis of rotation (e.g. by sharing the same axle) and are positioned spaced apart to provide a gap between the two guide wheels.

A rib150is provided around the inner rim of the wheel120and fits into the gap between the two guide wheels140in each pair. The guide wheels140are therefore adapted to contact with the inner rim of wheel120where they spin along with wheel120and hold wheel120in place by way of the rib150. Of course, it will be appreciated that other arrangements, including those with only one guide wheel per battery145, are possible.

The batteries145are mounted on a motor155which drives a drive wheel160(shown inFIG. 4) positioned at the lowermost point along the inner rim of the wheel120. The batteries145supply power to motor155and, this example, there are two batteries in order to create a balanced distribution of volume and weight. However, it is not necessary to employ two batteries145. Also, alternative energy storage arrangements may be used, such as a flywheel, capacitors, and other known power storage devices for example.

The drive wheel160is adapted to contact the inner rim of the wheel120. The drive wheel160for example comprises a wide roller with a groove in the center into which the rib150fits. By way of contact with the inner rim of the wheel120, the drive wheel160transmits torque from the motor155to the wheel120. It will be understood that this drive system operates by friction and it may be preferable to avoid slippage between the drive wheel160and the inner rim of wheel120. Positioning the drive wheel160at the lowermost point enables the weight of a user to provide a force which presses the drive wheel160against the inner rim of the wheel120, thereby helping to reduce or avoid slippage.

Referring toFIGS. 3 and 4, two foot platforms165are coupled to the second, lower portion1106of the casing110, with one on each side of wheel120. In the open configuration, the foot platforms165are movable between a stowed configuration, wherein the foot platforms are substantially parallel with the plane of the wheel (as shown inFIG. 4), and an active configuration, wherein the foot platforms are substantially perpendicular to the plane of the wheel so as to support a user's weight. Thus, in this example, the foot platforms165are movable between: (i) a stowed configuration wherein they are flat against the side of the wheel and can be rotated (with the second, lower portion1106of the casing) about the central axis125so as to be positioned inside (and covered by) the first, upper portion110A of the casing; and (ii) an active configuration, wherein they project outwardly from the side of the wheel to provide a support surface for the feet of a user (not shown).

Accordingly, the foot platforms165are upwardly foldable into a stowed configuration that narrows the profile of the unicycle100to aid in storage and carrying. In use, the foot platforms are moved to the active configuration, and the user stands with one foot on each platform165.

The drive arrangement135includes a gyroscope or accelerometer system170which it senses forward and backward tilt of the device in relation to the ground surface and regulates the motor155accordingly to keep the device upright. In this way, the user is provided a way of controlling the acceleration and deceleration of the unicycle by varying the pressure applied to various areas of the foot platforms165. It also enables the unicycle to self-regulate its balance in the fore-and-aft plane.

When not in use, the foot platforms165are moved to the stowed configuration and then rotated (with the second, lower portion1106of the casing) about the central axis125so as to move the casing to the closed configuration. Thus, in the closed configuration, the foot platforms165are stored inside the casing (covered by the first, upper portion110A of the casing).

The example shown also comprises a lifting handle180coupled to the drive arrangement135via a plurality of rods185. The lifting handle180is positioned at the top of the casing110, above the wheel120, and may be used to hold the unicycle100above the ground, for example to enable a user to lift, carry, convey or place the unicycle100.

A retractable carrying strap190is also provided and attached to the top of the casing100. The carrying strap190may be used to carry the unicycle100, for example over the shoulder of user. A hook may be provided on the bottom of the case to create rucksack-like belts from the carrying strap190.

In one example, the handle180is also adapted to trigger an activating system which moves the casing between the closed and open configurations. The lifting handle180may thus be used to initiate the activating system and move the casing from the closed configuration to the open configuration. Thus, when a user holds the unicycle100by the handle above the ground, the force of the unicycle pulling downwards under the influence of gravity causes upward movement of the lifting handle180relative to the casing110which triggers the activating system. In response to this trigger, the activating system moves the casing to the open configuration (depicted inFIG. 4) so that the lowermost portion of the wheel is exposed and can be brought into contact with a ground surface. In other words, when lifted by the lifting handle180, the unicycle may be arranged in an open configuration ready for deployment (e.g. placement on a ground surface).

Further, when placed on the ground, the depression of the handle in a downward/inward direction (towards the centre of the wheel120) moves the rods185and causes the foot platforms to move from the stowed configuration (shown inFIG. 4) to the active configuration. Downward movement of the rods causes the foot platforms165to rotate about an axis and the rods then hold the foot platforms165in place to support the feet of user.

When the user no longer desires to use the unicycle, the user pulls on the lifting handle to lift the unicycle from the ground. This results in upward movement of the lifting handle180and the associated rods185relative to the casing110which then causes the foot platforms to move from the active configuration to the stowed configuration.

The design described above has a static wheel hub. The motor arrangement drives the drive wheel at the bottom of the device and this drives the wheel around the static hub. This design has a relatively large number of components. For example, there are different components for centering the wheel around the outside of the central hub and for driving the wheel, and there are multiple rotating parts between the motor and the wheel.

A design which may employ fewer components forms the wheel directly as the rotor of the motor. This is a so-called hub motor. Thus, the hub contains the motor stator and the wheel rim itself comprises permanent magnets which define the motor rotor. In such a design, there are fewer rotating parts and the alignment of the rotor automatically provides alignment with the wheel hub.

This invention is of particular interest for this type of design and relates specifically to the design of the outer casing around the central motor.

FIG. 5shows a basic design. The motor is enclosed in a cylindrical inner volume as in the example above. This volume is closed by first and second side walls210,215and a central annular rim220. The central rim has a larger diameter and it defines the wheel rim base and side flanges. The rotor of the motor comprises a cylindrical carrier225on which an array of permanent magnets230is carried.

The two side walls210,215are clamped together with the carrier225sandwiched between. Coupling bolts or screws pass through the carrier225so that the rotor225,230and the two side walls define a rotating wheel hub. The wheel rim220sits around the outside of the rotor225,230. It is fixed to the rotor225,230.

FIG. 6shows the assembled wheel hub in side view and end view. This design has three components to form the outer casing. Furthermore, if a user wishes to make removal of the tyre easier to achieve, the only option is to dismantle the whole assembly. This exposes the rotor and the internal motor components to the outside.

FIG. 7shows a design in accordance with an example of the invention, in exploded form. The motor outer casing comprises first and second side walls300,305. Each of these may be a single integrated piece (as shown) or it may be a sub-assembly of components.

These two components together define the two side plates and also the outer annular rim. The wheel is again mounted around the outer annular rim, and the motor rotor, which again comprises a carrier310and an array of magnets315, is mounted within the outer annular rim. The first side wall300has a rim portion301and the second side wall305has a rim portion306. The side walls300,305are coupled together with the rim portions301,306in contact with each other thereby together defining the outer annular rim.

The rim portions may be considered to comprise the annular part which spans between the side walls but also the radially outermost part of the side wall. This radially outermost part of the side wall forms the lateral retaining parts of the wheel rim.

The first and second side walls can be identical in shape. In this way, there is a single component design for the two casing halves.

Each side wall300,305comprises a set of tabs302,307around the inner periphery of the rim portion. These tabs are positioned over the outer periphery of the rotor310. The rotor and the rim are coupled together by any suitable means, with no permitted relative movement. Thus, the rotor of the hub motor directly forms the wheel hub.

The side walls300,305are connected together at the tabs302,307.

FIG. 8shows the central stator320and the tyre325.FIG. 9shows the tabs307of the side wall portions more clearly, and shows a perspective view of the side wall portions as well as a cross section through the side wall portions and the tyre with the side wall portions slightly separated.

FIG. 10shows the closed casing in side view and end view, and shows how each side wall portion forms half of the wheel rim.

FIG. 11shows more clearly how the outer surface of the rotor, in particular the outer surface of the carrier310, is against the tabs307to provide alignment.

The examples above show the side walls as individual components. However, the rim portion of the side wall may be separable from the side plate part. In a particularly advantageous example, a portion of the rim portion can be removed from the side wall (leaving the side plate in place). This idea is shown inFIG. 12.

A portion320of the rim portion is removable from the remainder of the side wall, while maintaining the side wall plates connected together. This creates a gap in the outer edge of the side wall of the rim to assist lateral initial removal of the tyre at that location. However, the side wall plates remain in place so that the motor enclosure is still closed. The magnet ring of the rotor does not need to be interfered with.

InFIG. 12, only a portion of the rim (and by rim is meant a radial outer portion of the circular plate as well as an associated portion of the cylindrical base (301or306) of the wheel rim) is detachable. However, the compete annulus defining the rim portion may be removed so that the tyre can be slid laterally off the hub. Again, the side plates maintain a closed enclosure for the motor.

Many of the features described above with reference toFIGS. 1-4are optional. The retractable housing around the wheel is entirely optional as is the particular handle arrangement shown and the automated operation of the food pedals.

In the example above, the rotor is a continuous ring. However, it may be formed as two ring portions, one of which is mounted to one side casing component and the other of which is mounted to the other side casing component. There may then be two identical sub-assemblies, each sub-assembly being one side wall and half of the rotor.

Similarly, the side walls may be in multiple parts, including with removable rim portions as shown inFIG. 12.

In the example shown, the magnets are attached to a carrier. The magnets are arranged with alternating polarity, and the carrier is ferromagnetic. They may instead be attached directly to the side walls if a suitable material is used for the side walls, for example in recesses formed in the rim portions. Thus, the carrier may not be needed, because the casing side walls may act as the carrier and the conduit for the magnetic flux of the magnets.

The device has a single hub motor. Typically, a single tyre is attached to the hub to form the wheel, but there may be two or more tyres side by side, but essentially still forming a single wheel, i.e. still defining a unicycle.

The hub motor design has been shown used in a powered unicycle device. However, the hub motor may be used in any other application where exising hub motors are used. Some examples assist in tyre changing and others enable weight reductions to be achieved. These advantages are not limited to powered unicycle devices.

While specific embodiments have been described herein for purposes of illustration, various modifications will be apparent to a person skilled in the art and may be made without departing from the scope of the invention.