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Description of
EP1000846
[0001] The present
invention relates to a steering assembly for a vehicle,
and more particularly, but not exclusively, to an
improved steering assembly for a motorcycle.
[0002] Hitherto, nearly all commercially
available motorcycles have been steered using a
telescopic fork. This arrangement also provides front
wheel suspension. Whilst this design has a simple
structure, it has many disadvantages. Each side of the
fork comprises a pair of tubes, one of which slides
within the other. These tubes suffer from stiction and
binding, especially when subjected to lateral loading,
which reduces the effectiveness of the suspension. Also,
due to the angle that the telescopic fork has to be set
at, this tends to produce dive during front wheel
braking, reducing the amount of suspension travel
available (a particular problem when braking hard over
uneven surfaces). It has also been found that on high
performance motorcycles that the tubes comprising the
telescopic fork must be made of a fairly large diameter
in order to resist flexing. However, this increases the
frictional area between the sliding surfaces of the
tubes, resulting in greater friction, and also increases
the mass of the system. It is undesirable to increase
the mass around the steering axis. Further, during front
wheel braking, because of the length of the telescopic
fork, the fork can apply a large leverage force on the
steering bearings as well as the frame of the
motorcycle. In order to withstand such force, the frame
of the motorcycle must be strong and inevitably heavy.
The force also tends to cause excessive wear to the
steering bearings.
[0003] Many alternatives to
the telescopic fork have been proposed, but none have
been so universally accepted as the telescopic fork.
Many of the designs have failed because they provide
inferior performance to the conventional telescopic
fork. Commonly, prior proposals have tended to be
over-complicated, which not only makes them costly to
manufacture and maintain, but also prevents the rider
from receiving satisfactory handling feedback from the
motorcycle. Previous systems have been criticised for
their vague handling, which causes the rider to have
little faith in the steering systems.
[0004]
Examples of such prior art alternatives to the
conventional telescopic fork are disclosed in British
patent number 1274441 and European patent number 0 432
107.
[0005] According to a first aspect of the
present invention, there is provided a steering assembly
for a vehicle, the assembly comprising a hub
mechanically connected to the steering mechanism of the
vehicle for changing the direction of a wheel rotatably
coupled to the hub; wishbone means coupled to a main
body portion of the vehicle, the two arms of which
extend either side of the wheel; a member which passes
through the hub and which is rigidly coupled to each of
the arms of the wishbone means; a sleeve mounted around
the member for allowing relative rotation therebetween,
the sleeve being pivotally coupled to the hub so as to
provide for changing the direction of the wheel; and a
link extending from the sleeve and connected to a main
body portion of the vehicle.
[0006] By providing
a member which rigidly couples each of the arms of the
wishbone means, the torsional rigidity at the wishbone
means may be increased.
[0007] A further, outer
hub is preferably mounted around the aforesaid hub by,
for example, wheel bearings, in order to allow relative
rotation between the hubs. The further hub may be
attached to or integral with the wheel. An aperture is
advantageously provided in the further hub to allow
adjustment of and/or access to the pivotal coupling
between the inner hub and the sleeve. This may allow the
pivotal coupling to be serviced without dismantling the
steering assembly.
[0008] The pivotal coupling
between the hub and the sleeve may comprise taper roller
bearing means secured between the hub and the sleeve.
[0009] The pivotal coupling between the hub and
the sleeve may be located relative to the hub by a pin,
for example. This arrangement may conveniently
facilitate removal or adjustment of the pivotal coupling
using the aperture in the further, outer hub.
[0010] Removal of the pin through the aperture
may allow the sleeve to be withdrawn from the hub.
[0011] The sleeve may be mounted around the
member coupled to the arms of the wishbone means by
needle roller bearing means.
[0012] The sleeve
preferably includes an extension part extending
therefrom to which the link is connected at one end, the
other end of the link being connected to a main body
portion of the vehicle.
[0013] The orientation
of this extension part of the sleeve conveniently sets
the steering axis angle of the wheel of the vehicle.
[0014] The length of the link may be adjusted so
as to change the orientation of the extension part in
order to set the steering axis angle of the wheel of the
vehicle. This feature may allow the geometry of the
steering to be adjusted so that the desired handling
characteristics can be obtained.
[0015] The
inner hub may be provided with an extension part and a
further, steering link may be connected between this
extension part and the steering mechanism of the
vehicle.
[0016] Preferably, this further,
steering link is substantially the same length as the
aforementioned link. With this arrangement, bump steer
may be minimised.
[0017] Means may be provided
for adjusting the length of the further, steering link.
This allows greater flexibility in changing the geometry
of the steering, and allows the respective links to be
maintained at the same length.
[0018] According
to a second aspect of the present invention, there is
provided a steering assembly for a vehicle, the assembly
comprising handlebars attached to a steering column; a
first lever extending from the steering column; a hub
for changing the direction of a wheel rotatably coupled
to the hub; a second lever extending from the hub; and a
link mechanically connecting the first and second
levers; the arrangement being such that steering inputs
from the handlebars are translated into direction
changes of the wheel.
[0019] This steering
assembly is relatively simple, and has fairly few moving
parts. This may give good feedback to the rider.
[0020] The steering axis rotation of the wheel
and the steering axis of rotation of the handlebars may
be different. These axes may not be parallel.
[0021] According to a third aspect of the
present invention, there is provided a steering assembly
for a vehicle, the assembly comprising a hub
mechanically connected by means of a first linkage to
the steering mechanism of the vehicle for changing the
direction of a wheel rotatably coupled to the hub; and a
member pivotally coupled to the hub so as to provide for
changing the direction of the wheel, the member being
connected by means of a second linkage to a main body
portion of the vehicle; wherein an imaginary line
connecting at least one attachment point of the first
linkage and at least one attachment point of said second
linkage lies substantially parallel to the axis of
rotation of the wheel when in the straight ahead
position.
[0022] This arrangement may minimise
or reduce bump steer.
[0023] According to a
fourth aspect of the present invention, there is
provided a steering assembly for a vehicle, the assembly
comprising a hub mechanically connected by means of a
first linkage to the steering mechanism of the vehicle
for changing the direction of a wheel rotatably coupled
to the hub; and a member pivotally coupled to the hub so
as to provide for changing the direction of the wheel,
the member being connected by means of a second linkage
to a main body portion of the vehicle; wherein the
length of at least one of the first and second linkages
is/are adjustable.
[0024] According to a fifth
aspect of the present invention, there is provided a
steering assembly for a vehicle, the assembly comprising
an inner hub mechanically connected to the steering
mechanism of the vehicle; a member pivotally coupled to
the inner hub so as to provide for changing the
direction of the wheel, the member being connected to a
main body portion of the vehicle; and an outer hub
mounted around said inner hub for rotation relative
thereto, the outer hub being attached to or integral
with a wheel of the vehicle, and having an aperture
therein to allow adjustment of and/or access to the
pivotal coupling between the inner hub and the member.
[0025] The present invention also provides a
motorcycle including a steering assembly including any
of the features discussed above.
[0026] For a
better understanding of the present invention, an
embodiment will now be described by way of example, with
reference to the accompanying drawings, in which:
Figure 1 shows a motorcycle having a steering
assembly in accordance with the present invention;
Figure 2 is a perspective view showing the
connection between the front wheel of the motorcycle and
the handlebars;
Figure 3 is a side plan view of the
front wheel of the motorcycle and the connection between
the front wheel and the handlebars;
Figure 4 is a
perspective view showing the connection between the
front wheel of the motorcycle and the main body part of
the motorcycle;
Figure 5 is a side plan view showing
the connection between the front wheel of the motorcycle
and the main body portion of the motorcycle;
Figure
6 is a cross-sectional view taking along line A-A shown
in Figure 1;
Figure 7 shows a perspective detailed
view of the hub assembly;
Figure 8 shows an exploded
view of the hub assembly of Figure 7;
Figure 9 shows
a cross-sectional view of a spherical rod end used in
the steering assembly; and
Figure 10 is a schematic
overhead plan view of a motorcycle with the front wheel
and handlebars in the straight ahead position.
[0027] Throughout the drawings, like
referencing rules are used to designate similar elements
appearing in different drawings.
[0028] Figure 1
shows a motorcycle including a front wheel 1 and rear
wheel 3, both of which are attached to a main body part
or frame 5. The front wheel 1 is steered by turning the
handlebars 7. With the exception of the front wheel
steering wheel mechanism described below, the motorcycle
may otherwise be conventional. However, it should be
noted that the frame 5 may be made less substantial (and
hence lighter) than would be possible conventionally due
to the advantages of the new steering mechanism.
[0029] Referring now to Figures 1 to 5, it can
be seen that the front wheel 1 is attached to the frame
5 of the motorcycle by means of a swinging arm or
wishbone 9. The wishbone 9 is pivotally attached to the
frame 9, and moves around axis x1. Damping means (not
shown) may be provided between the frame 5 and the
wishbone 9 to control relative movement therebetween.
The wishbone comprises first and second arms 11 and 13.
At the end of the arms 11 and 13 furthest from the frame
5 of the motorcycle, these arms are attached to the hub
assembly 15 of the front wheel 1. The hub assembly 15
will be described in greater detail below.
[0030] On the same side of the front wheel 1 as
the first arm 11 of the wishbone 9, a first lever 17
extends from the hub assembly 15. At the end of the
first lever 17 furthest from the hub assembly, a
steering linkage 19 connects the first lever 17 to a
lever 21 attached to the steering column 23 of the
motorcycle. The steering column 23 is rotated about axis
y1 by using the handlebars 7. The steering column 23
rotates about articulated joints to the frame 5 and to
column bracket 24. The steering linkage 19 is connected
to the end of the lever 21 furthest from the axis y1.
The connection between the steering column 23 and the
front wheel 1 is such that the wheel 1 can be steered.
[0031] On the same side of the front wheel 1 as
the second arm 13 of the wishbone 9 a second lever 25
forms part of the hub assembly 15. At the end of the
second lever 25 furthest from the hub assembly 15, the
lever 25 is coupled to a second linkage 27. The linkage
27 connects the second lever 25 to the frame 5 of the
motorcycle. The orientation of the second lever 25
determines the steering axis y2. The linkage 27 controls
rotation of the lever 25 (and hence the angle of
steering axis y2). The linkage maintains the desired
steering axis y2 during the suspension movements of the
wishbone 9 about axis x1.
[0032] The orientation
of the second lever 25 can be adjusted by altering the
length of the second linkage 27. A method of providing
alteration to the length of the linkage 27 would be well
known to those skilled in the art. For example, the
connection between the second linkage 27 and the second
lever 25 may be by means of a spherical rod end 70
(Figure 9). A pin (not shown) extending from the second
lever 25 passes through the aperture 72 in the rod end
70. The rod end includes an internally threaded part 74
which receives a threaded part 76 of the second linkage
27. The effective length of the second linkage 27 can be
adjusted by setting the amount of the treaded part 76 of
the second linkage 27 that is received in the threaded
part 74 of the rod end 70. A locknut 78 locks the
linkage 27 to the rod end 70.
[0033] Similarly,
the orientation of the first lever 17 for a given
steering input is set by the length of the steering
linkage 19. Obviously, the orientation of the first
lever 17 will change when the wheel 1 is steered. The
effective length of the steering linkage 19 may be set
also using a spherical rod end.
[0034] It has
been found that bump steer is minimised when the
steering linkage 19 and the second linkage 27 are of
substantially equal effective length and the points of
connection of the linkages to the levers 17 and 25, and
to the frame 5 and steering lever 21 (when the front
wheel 1 and handlebars 7 are pointing straight ahead)
are mirrored about any plane which lies parallel to both
axes y1 and y2. This arrangement is shown in Figures 1
and 10 (Figure 10 is a schematic overhead plan view of a
motorcycle with the front wheel 1 and handlebars in the
straight ahead position). The point of connection of
linkage 19 to the steering lever 21 is aligned with the
point of connection of linkage 27 to the frame 5 (see
line I). The point of connection of the linkage 19 to
the lever 17 is aligned with the point of connection of
linkage 27 to lever 25 (see line II). The central axis
of the point of connection of the lever 17 to the inner
hub 31 is aligned with the central axis of the point of
connection of the lever 25 to the sleeve 35 (both these
axes corresponding to axis x2 when the wheel 1 is
pointing straight ahead).
[0035] In other words,
bump steer can be minimised by the positioning of the
linkage connection points. When the front wheel 1 and
the handlebars 7 are pointing straight ahead, the
position of these connecting points can be described in
the following way:
An imaginary line I passing
through points of connection of the linkage 27 with the
frame 5 and the linkage 19 with the lever 21 is parallel
to an imaginary line II passing through points of
connection of the linkage 27 with the lever 25 and the
linkage 19 with the lever 17. These lines I and II are
also parallel to axes x1 and x2. Also the linkages are
parallel to the plane of the front wheel 1 when it is
pointing straight ahead.
[0036] Such an
arrangement dictates that the linkages have the same
length.
[0037] For this reason, steering linkage
19 is also made adjusable in length so that the steering
linkage 19 can be made the same length as the second
linkage 27 when the length of the second linkage 27 is
adjusted. The length of the second linkage determines,
as explained above, the angle of the steering axis y2 of
the motorcycle, and this effects the stability of the
motorcycle. Therefore, providing for variation of the
lengths of linkages 19 and 27 allows the handling
characteristics of the motorcycle to be optimised whilst
minimising a bump steer.
[0038] It should be
noted that bump steer does not occur with conventional
motorcycles having telescopic forks.
[0039] The
hub assembly 15 will now be described in more detail
with reference to Figures 6, 7 and 8. The hub assembly
15 comprises an outer hub 29 which can be either
attached to the spokes of the front wheel 1 or can be
formed integrally therewith. The outer hub 29 surrounds
inner, non-rotating hub 31. Wheel bearings 33 provide
for rotation of the outer hub 29 relative to the inner
hub 31. Both the inner and outer hubs 29 and 31 pivot
about steering axis y2 in response to steering input
from the steering column 23. The pivoting movement about
the steering axis y2 is provided by first lever 17 which
is rigidly connected to the inner hub 31. The second
lever 25 is, as described above, attached to the frame 5
of the motorcycle by second linkage 27. Second lever 25
does not move in response to steering input from the
steering column 23. A sleeve 35 extends from the second
lever 25 to the central region of the inner hub 31.
Sleeve 35 is hollow and includes two opposed spaced
apart circular outwardly disposed flanges 37 and 39. The
spaced apart flanges 37 and 39 accommodate two opposing
taper roller bearings 41 and 43. These taper roller
bearings 41 and 43 are coupled to the inner hub 31 by
two adjuster pins 45 and 47. The two adjuster pins 45
and 47 have a screw thread which cooperates with a screw
thread of the inner hub 31, which allows the adjuster
pins 45 and 47 to be fixed in position with respect to
the inner hub 31. The adjuster pins 45 and 47, as well
as locating the taper roller bearings 41 and 43, and
hence the second lever 25 (by means of the sleeve 35 and
flanges 37 and 39), allow for the correct pre-loading of
the taper roller bearings 41 and 43. The adjuster pins
45 and 47 are locked into position after adjustment by
locknuts 49 and 51.
[0040] This arrangement
allows for steering torque to be transmitted from the
handlebars 7 about the axis y1 through linkage 19 to the
inner hub 31, outer hub 29 and wheel 1, which will
simultaneously rotate about steering axis y2. To allow
this rotation about the axis y2 an enlarged opening 52
is provided in the sides of the inner hub 31.
[0041] A spacer 53 is provided between the end
of the sleeve 35 furthest from the second lever 25 and
the inner side of the first arm 11 of the wishbone 9.
The second arm 13 of the wishbone 9 abuts the side of
the second lever 25 furthest from the taper roller
bearings 41 and 43. A bolt 55 passes through the lever
25, sleeve 35, inner hub 31, outer hub 29, first lever
17, spacer 53, and the first 11 and second 13 arms of
the wishbone 9. A nut 56 has a thread which cooperates
with a thread of the bolt 55 for rigidly connecting the
first arm 11 to the second arm 13 of the wishbone 9.
[0042] Although the second lever and the
wishbone 9 are both coupled to the frame 5 of the
motorcycle there will be some rotation of the lever 25
around the central axis x2 of the bolt 55 due to
suspension movement. This rotation is provided for by
needle roller bearings 57 and 59 mounted between the
sleeve 35 and the bolt 55. A spacer 61 separates the
respective needle roller bearings 57 and 59.
[0043] The bolt provides the wishbone 9 with
greater torsional rigidity.
[0044] For ease of
servicing, the outer hub 29 is provided with apertures
63. Through the apertures 63 access can be gained to the
locknuts 49 and 51 and the adjuster pins 45 and 47. This
is highly advantageous because the steering bearings of
motorcycles require relatively frequent attention.
[0045] To adjust the bearings 41 and 43, the
locknuts 49 and 51 are loosened or removed through the
apertures 63. The adjuster pins 45 and 47 are then
screwed in or out by the required amount, and the
locknuts 49 and 51 are then tightened/replaced. As the
bearings 41 and 43 undergo normal wear, the adjuster
pins should be tightened. The apertures 63 allow the
correct loading of the bearings 41 and 43 without
requiring any disassembly of the steering assembly. In
prior art systems, bearings have been overtightened when
new with hope that, when the bearings wear, they will
have the correct loading.
[0046] To replace the
bearings 41 and 43, the locknuts 49 and 51, and the pins
45 and 47 are removed through the apertures 63. This
allows the sleeve 35 to be withdrawn from the inner and
outer hubs 31 and 29. The bearings 41 and 43 can then be
replaced. No disassembling of the inner hub 31 from the
outer hub 29 is required.
[0047] In the
embodiment described, the point of attachment x1 of the
wishbone 9 to the frame 5 of the motorcycle is
approximately the same distance from the ground as the
central axis x2 of the hub assembly 15 in normal use.
This arrangement allows braking forces to be absorbed
far more effectively than in a conventional telescopic
fork arrangement. Therefore, the frame 5 of the
motorcycle having a steering assembly as hereinbefore
described can be made less strong, and therefore
lighter, thereby reducing fuel consumption and improving
handling. In the embodiment described the linkage
between the handlebars 7 and the wheel 1 is relatively
simple for this type of device, and this gives good
feedback to the rider.
Data supplied from the esp@cenet database
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