Note: Descriptions are shown in the official language in which they were submitted.
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Wheel Mount Assembly
Field of the Invention
This invention relates in general to improvements in wheel mount
assemblies of the type used with wheelchairs and other devices. More
particularly, this invention relates to an improved wheel mount assembly that
provides center of gravity adjustability and wheel camber angle adjustability.
Background of the Invention
Wheel mount assemblies in general are well known in the art for use
with many different types of wheeled devices. Such wheel mount assemblies
are commonly employed for mounting the rear wheels on a typical wheelchair.
Each wheel mount assembly typically incorporates a number of adjustments
that allow the wheelchair occupant to customize the wheelchair to his or her
body proportions, body mechanics, and driving conditions. Frequently, the
rear wheels of the wheelchair are cambered, or angled with respect to a
vertical plane. A wheelchair with a large camber angle has more responsive
turning, which is typically beneficial in sports applications. A wheelchair
with a
little to no camber angle has a smaller overall width and thus greater
manoeuvrability in tight confines. Often the wheels can be adjusted so that
their camber angle can be changed from 0 degrees to 12 degrees, or
sometimes substantially more, where the top of the wheel is closer to the
chair than the bottom of the wheel.
Some wheelchairs provide the ability to adjust the fore/aft position of
the rear wheel with respect to the wheelchair frame. Such adjustment is
known as a "center-of-gravity" adjustment. Shifting the rear wheels rearward
produces a more stable wheelchair that is less likely to tip backwards.
Shifting
the rear wheels forward makes the wheelchair easier to balance on the rear
wheels. This helps with manoeuvrability over obstacles, such as curbs, where
the wheelchair occupant must lift the front casters off the ground in order to
traverse the obstacles.
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When an adjustment is made to the rear wheel camber angle the rear
height of the wheelchair may also change, which may in turn cause the rear
wheels to toe-in or toe-out. That is to say, the rear wheels become misaligned
with respect to the frame. This misalignment is undesirable because it
increases rolling friction. If the act of decreasing the camber angle raises
the
rear wheel height, the rear wheels may toe-in. Conversely, increasing the rear
wheel camber angle typically lowers the rear wheel height, which may cause
the rear wheels to toe-out. To correct toe-in or toe-out, the mounting
hardware
that attaches the rear wheels to the wheelchair frame must allow the axles of
the rear wheel to rotate in order to re-align the camber angle with respect to
a
vertical sagittal plane. Alternatively, the height of either the rear wheels
or the
front caster wheels may be changed to adjust the toe-in or toe-out of the
drive
wheels as well as to keep the main pivot axis of each of the caster wheels
vertical.
With some conventional wheelchairs that offer adjustable camber
(although note that in many wheelchairs the camber angle is fixed), the
camber adjustment takes the user a significant amount of time. Adjusting the
camber often requires removing quite a number of parts and adding or
subtracting washers or other spacers to achieve the proper angle.
Alternatively adjusting the camber may entail needing different camber inserts
each with fixed angles. Even when done by a trained technician, the process
may still take considerable time.
In some wheelchairs that provide easier means of changing camber
angle and center gravity adjustment, often the result is an overly flexible
wheelchair frame. A wheelchair that lacks rigidity or is overly flexible
typically
has reduced performance, may feei cumbersome or un-safe, and may be
more prone to breakage.
While many wheelchairs provide wheel camber angle, toe-in, toe-out,
and center of gravity adjustability, there is a need for a lightweight, user-
friendly adjustment design that minimizes parts, complexity, and adjustment
difficulty while at the same time providing adequate rigidity and performance.
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Summary of the Invention
It is therefore an object of the invention to provide a wheel mount
assembly of the type used with wheelchairs and other devices that satisfies
the foregoing as well as other needs and issues.
According to a first aspect of the invention, there is provided a wheel
mount assembly for mounting a drive wheel to a frame of a wheelchair, the
assembly comprising a camber body attachable to an axle of one of the drive
wheels and operable to pivotably couple about the frame through a range of
camber angles; a spacer operable to set a desired camber angle, the spacer
contacting the camber body at the desired camber angle; and a clamp
operable to secure the camber body and the spacer to the frame at the
camber angle. The wheel mount assembly may comprise a clamping
member coupled to the frame so as to fix the camber body from pivoting
through the camber angles; and a fastener operable to secure the clamping
member to the camber body and to the frame. The fastener may be a
clamping screw extending through the clamping member and screwed into the
camber body. Optionally, the clamping member may be welded to the frame.
Additionally, the spacer may be a set screw screwed into the camber body.
Furthermore, the wheel mount assembly may comprise left and right
camber bodies, each attachable to one of the drive wheels and each operable
to pivotably couple one of the drive wheels about the frame through the range
of camber angles; and left and right spacers, each operable to set the desired
camber angle, each spacer contacting one of the camber bodies at the
desired camber angle; wherein the clamp may comprise a transverse member
extendable between the drive wheels and having two ends, each end
operable to engage a portion of the frame such that the clamp is prevented
from pivoting through the camber angles of each respective camber body; and
a pair of fasteners, each fastener operable to secure one of the camber
bodies to one of the ends of the transverse member. Each spacer may be a
set screw screwed into the camber body. The set screw may abut against the
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transverse member at the camber angle. The two ends of the transverse
member can slidably engage respective longitudinally extending portions of
the frame in a longitudinal direction. Furthermore, there may be two metal
plugs, each inserted into one of the ends of the transverse member, each
metal plug having a radially extending bore therethrough for accepting one of
the fasteners. For each drive wheel, an axle receiver insert can be interposed
between the axle and the camber body, the axle receiver insertable to
different depths in the camber body. The axle receiver insert may comprise
an eccentrically located hole for receiving the axle, the hole rotatable
within
the camber body for adjusting a height of the drive wheel.
According to another aspect of the invention, there is provided a
wheelchair comprising a frame; a pair of drive wheels, each having an axle;
and a wheel mount assembly for mounting one of drive wheels to the frame,
the assembly comprising a camber body attachable to an axle of one of the
drive wheels and operable to pivotably couple about the frame through a
range of camber angles; a spacer for setting a desired camber angle, the
spacer contacting the camber body at the desired camber angle; and a clamp
operable to secure the camber body and the spacer to the frame at the
camber angle. The clamp may comprise a clamping member coupled to the
frame so as to fix the camber body from pivoting through the camber angles;
and a fastener operable to secure the clamping member to the camber body
and to the frame. The fastener can be a clamping screw extending through
the clamping member and screwed into the camber body. Furthermore, the
clamping member may be welded to the frame, and the spacer can be a set
screw screwed into the camber body.
Furthermore, the wheelchair may comprise left and right camber
bodies, each attachable to one of the drive wheels and each operable to
pivotably couple one of the drive wheels about the frame through the range of
camber angles; and left and right spacers, each operable to set the desired
camber angle, each spacer contacting one of the camber bodies at the
desired camber angle; wherein the clamp may comprise a transverse member
extendable between the drive wheels and having two ends, each end
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operable to engage a portion of the frame such that the clamp is prevented
from pivoting through the camber angles of each respective camber body; and
a pair of fasteners, each fastener operable to secure one of the camber
bodies to one of the ends of the transverse member. The spacer may be a a
set screw screwed into the camber body. The set screw can abut against the
transverse member at the camber angle. The two ends of the transverse
member can slidably engage respective longitudinally extending portions of
the frame in a longitudinal direction. Furthermore, there may be two metal
plugs, each inserted into one of the ends of the transverse member, each
metal plug having a radially extending bore therethrough for accepting one of
the fasteners. For each drive wheel, an axle receiver insert can be interposed
between the axle and the camber body, the axle receiver insertable to
different depths in the camber body. The axle receiver insert may comprise
an eccentrically located hole for receiving the axle, the hole rotatable
within
the camber body for adjusting a height of the drive wheel.
Brief Description of the Drawings
Figure 1 is a perspective view of a wheelchair.
Figures 2(a) and (c) are perspective views of a wheel mount assembly
according to one embodiment of the invention; Figure 2(b) is a front elevation
view of the embodiment illustrated in Figures 2(a) and (c).
Figure 3 is a front elevation view a wheel mount assembly according to
a second embodiment of the invention.
Figure 4 is a perspective view of a wheel mount assembly depicting an
eccentric axle receiver insert according to a third embodiment of the
invention.
Figures 5(a) and (c) are perspective views of a wheel mount assembly
according to a fourth embodiment of the invention; Figure 5(b) is a front
elevation view of the embodiment illustrated in Figures 5(a) and (c).
Figures 6(a) and (c) are perspective views of a wheel mount assembly
according to a fifth embodiment of the invention; Figure 6(b) is a front
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elevation view of the embodiment illustrated in Figures 6(a) and (c).
Detailed Description of Embodiments of the Invention
Directional terms such as "left", "right", "horizontal", "vertical",
"transverse" and "longitudinal" are used in this description merely to assist
the
reader to understand the described embodiments and are not to be construed
to limit the orientation of any described method, product, apparatus or parts
thereof, in operation with or in connection to another object.
Referring to Figure 1, an example wheelchair 1 is depicted having a
wheelchair frame 2 with attached rear wheels 3. The rear wheels 3 are
attached to the wheelchair frame 2 by axles inserted into camber bodies 6.
The camber bodies 6 are coupled to horizontal tubes 4 which are members of
the frame 2 and which extend longitudinally; that is, the tubes 4 extend from
the front to the rear of the frame 2. The camber bodies 6 and horizontal tubes
4 are also coupled to a transverse tube 5 that transversely spans across the
frame 2. The front of the wheelchair 1 also has caster wheel assemblies 14
attached to the frame 2. The geometry of this example wheelchair 1 is such
that the horizontal tubes 4 lie in a horizontal plane, parallel to the ground,
and
the housing tubes 18 of the caster wheel assemblies 14 lie in a verticai
plane,
perpendicular to the horizontal plane. In this configuration, a wheel mount
assembly can provide an adjustable camber angle of the rear wheels 3, while
also maintaining negligible toe-in and toe-out effects of the rear wheels.
Such
a configuration would provide low rolling resistance and an efficient wheeling
mechanism.
Referring now to Figures 2(a) - (c), which depict three views of the
exemplary embodiment of the wheel mount assembly in detail, the transverse
tube 5 consists of a tubular structure with alloy plugs 17 inserted into
either
end to a depth of approximately 2.5 inches. The ends of the transverse tube 5
are shaped to concentrically couple to the horizontal tubes 4 of the
wheelchair
frame 2. Oval or elongated through-holes 12 are formed in the transverse
tube 5 through the tube 5 and alloy plugs 17 such that a bolt 8 may pass
through the tube 5 at various angles to the vertical. The end of the elongated
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holes 12 are further shaped to be an elliptical counterbore 11, such as may be
obtained through the use of a ball nose end mill. This counterbore 11 is
shaped to receive a spherical washer 9 through which the bolt 8 passes such
that regardless of the angle of the bolt 8 to the vertical, the bolt may
fasten
firmly to the transverse tube 5. The counterbore 11 is shaped with a
sufficient
depth to enable the spherical washers 9 to snugly couple to the transverse
tube 5. The bolt 8 can be a socket button head cap screw, for instance, with a
head with a flat surface to coincidently mate with the flat side of the
spherical
washer 9. In an alternative embodiment (not shown), instead of using the
counterbore 11 to receive the spherical washer 9, a female spherical washer
can be used to receive the spherical washer 9, with the female spherical
washer sitting flat on a machined flat shoulder.
The bolt 8 is screwed into the bottom of a camber body 6. The camber
bodies 6 are shaped to concentrically couple to the horizontal tubes 4 of the
wheelchair frame 2. Another bolt 10 is screwed into the camber body medial
to the bolt 8. This bolt 10 is a socket button head cap screw, for instance,
which has a head with a radius. The distal surface of the head of the bolt 10
is
coincidently and approximately concentrically coupled to an elliptical
counterbore hole 13 shaped in top of the transverse tube 5 and alloy plugs 17.
This elliptical hole 13 is sufficiently deep to provide a surface with a
radius
closely matched to the head of the button head screw 10, again optionally by
using a ball nose end mill.
When the bolt 8 is firmly screwed into the camber body 6, the camber
body 6 and the transverse tube 5 mate to the horizontal tube 4 on opposing
sides of the tube 4, the spherical washer 9 mates to the elongated
counterbore 11, and the bolt 10 mates to the elongated counterbore hole 13.
Thus the force of the bolt 8 provides sufficient clamping force to rigidly
secure
the wheel mount assembly to the wheelchair 1.
An axle receiver insert 7 is inserted into the camber body 6. One
example of an axle receiver insert 7 is a threaded rod approximately 2 inches
long with a bored hole through it to accept a wheel axle. The axle receiver
insert 7 can be screwed to various depths into the camber body 6, thus
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effectively spacing the wheels 3 laterally with respect to the wheelchair
frame
2.
The distance that the bolt 10 is screwed into the camber body 6
determines the angle a of the camber body 6 to the horizontal. The more the
bolt 10 is screwed into the camber body 6 (the shorter the bolt 10 has an
exposed length), the greater the angle a becomes. The angle a determines
the angle of the wheels in the following relationship. The angle a between the
camber body 6 and a horizontal plane is equal to the camber angle of the
wheelchair 1 rear wheels 3 with respect to a verticai sagittal plane. The
embodiment depicted in Figures 2(a) -(c) provide for the angle a to be
adjusted from 0 degrees to approximately 12 degrees. It is appreciated that
the angle a can be made even greater by changing the coupling shapes of the
camber bodies 6 and transverse tube 5, as well as the diameters and sizes of
the camber bodies 6, the transverse tube 5, and the horizontal tubes 4, and
the length of the bolt 10.
An alternative embodiment is shown in Figure 3. Essentially, the wheel
mount assembly described above and shown in Figures 2(a) - (c) is flipped
upside down. To similarly achieve adjustable wheel camber angles, the bolt
10 is screwed into the camber body 6 to various depths. In contrast to the
embodiment depicted in Figures 2(a) - (c), a longer exposed length of the bolt
10 equates to a greater wheel camber angle. One benefit of the embodiment
illlustrated in Figure 3 is that the head of the bolts 8, 10 face upwards,
which
can make their adjustment easier than that of the bolts 8, 10 of the
embodiment illustrated in Figures 2(a) - (c).
In both embodiments described above, and referring to the example
wheelchair 1 in Figure 1, it is appreciated that changing the camber angle a
of
the rear wheels 3 would also change the relative height of the rear of the
wheelchair frame 2. Such a change may tilt the plane in which the horizontal
tubes 4 lie such that it is no longer parallel with the horizontal plane, and
may
also tilt the plane in which the housing tubes 18 of the caster wheel
assemblies 14 lie such that it is no longer parallel with the vertical plane.
Such
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changes may increase the toe-in or toe-out of the rear wheels 3 and impact
rolling resistance and pushing efficiency. This could be mitigated in the
example wheelchair 1 by changing the relative height of the housing tubes 18
of the caster wheel assemblies 14 for a given wheel camber angle in order to
adjust the tilt of the planes in which the horizontal tubes 4 and vertical
housing
tubes 18 of the caster wheel assemblies 14 lie. The relative height of the
housing tubes 18 may be changed with washers or spacers. Given the
embodiments of the wheel mount assemblies described above, the toe-in and
toe-out would then be negligible.
Referring to Figure 4, an axle receiver insert 7 with an eccentrically
placed hole 15 is shown. This alternative embodiment may be needed if by
changing the camber angle of the wheels 3, the rear height of the wheelchair
1 is raised or lowered, and that this changed height could not be
compensated for by changing the height of the caster wheel housings 18.
Such a change in rear height may alter the toe-in toe-out of the rear wheels
3,
thus impacting rolling resistance and pushing efficiency. To alter the toe-in
and toe-out to a negligible amount, the axle receiver insert 7 with an
eccentric
hole 15 can be rotated in the camber body 6. The eccentric hole 15 would
then provide a means to subtly alter the toe-in and toe-out of the rear wheels
3. Once the optimum rotational placement of the axle receiver insert 7 with an
eccentric hole 15 is achieved, the position can be fixed in place by
tightening
the jam nut 16 firmly against the camber body 6.
Referring now to Figures 5(a) - (c) and 6(a) - (c), embodiments of the
present invention wherein the transverse tube 5 is absent are depicted. In
Figures 5(a) -(c) and 6(a) -(c), in lieu of the transverse tube 5, a lower
camber body 19 is present. The bolt 10 abuts against the lower camber body
19 instead of the transverse tube 5 when the camber body 6 is at the desired
camber angle a. Referring specifically to Figures 5(a) - (c), the lower camber
body 19 is welded to the horizontal tube 4, as evidenced by the presence of a
weld bead 20. Referring specifically to Figures 6(a) - (c), the lower camber
body 19 is secured to the horizontal tube 4 with a pin 19, which extends
through the lower camber body 19, the horizontal tube 4, and the camber
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body 6. The combination of the pin 19 and the clamping force resulting from
the bolt 8 result to prevent movement of the camber bodies 6, 19 about the
tube 4. While the camber bodies 6, 19 depicted in Figures 5(a) - (c) are
necessarily fixed to the horizontal tube 4 at the location of the weld bead
20,
the camber bodies 6, 19 depicted in Figures 6(a) -(c) are movable to different
positions along the horizontal tube 4 so long as at each position to which the
camber bodies 6, 19 are to be moved, a channel for receiving the pin 19
exists within the tube 4.
All embodiments described above, and others not shown here, also
provide another feature: the wheel mount assembly can be slid rearwards and
forwards along the horizontal tubes 4 and clamped in position. By changing
the clamping position along the horizontal tubes 4, the center of gravity of
the
wheelchair 1 can be changed.
The components of the wheel mount assembly can be manufactured
from a light alloy material to reduce the weight of the wheelchair 1. Suitable
such materials include steel alloys, aluminum alloys, titanium alloys,
magnesium alloys, plastics such as polycarbonate, carbon fibre composites,
and other materials suitable for such an application. By selecting such
materials and by utilizing the design of the wheel mount assembly described
here, it is expected that the weight of the wheelchair 1 can minimized.
The present invention offers several advantages. For instance, the
lateral distance between the rear wheels 3 may be adjusted by varying the
insertion depth of the axle receiver insert 7 within the camber body 6. In the
embodiments of the invention wherein the camber bodies may be coupled at
different positions along the horizontal tubes 4, the center of gravity of the
wheelchair may be adjusted. The camber angle of the wheels 3 may be
adjusted by removing bolts 8 and un-clamping the wheel mount assemblies.
The depths of the bolts 10 can then be adjusted and the wheel mount
assemblies re-clamped. The toe-in and toe-out of the wheels 3 may be
adjusted by changing the heights of the caster wheel housings 18 or by
rotating the axle receiver inserts 7 with eccentrically placed holes 15.
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While the present invention has been described herein by the preferred
embodiments, it will be understood to those skilled in the art that various
changes may be made and added to the invention. The changes and
alternatives are considered within the spirit and scope of the present
invention.
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