Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to a new or improved snowmobile
track designed to provide improved traction, particularly in
light or powder snow.
b) Description of the Prior Art
Snowmobile tracks conventionally include on the
exterior surface thereof a pattern of projecting ribs or lugs
that are designed to engage the snow or other ground surface and
apply traction forces thereto to propel the snowmobile.
Numerous prior art patents are concerned with different means of
improving the traction characteristics of snowmobile tracks, see
for example U.S. 3,704,918 Perreault, U.S. 3,762,779 Russ, and
Canadian Patent 1,117,570 Skega Aktiebolag, and Canadian Patent
Application 2,014,852 published October 18th, 1990 Yokohama
Rubber Co., Ltd.
Nevertheless, there remains a need for a snowmobile
track configuration that will provide satisfactory traction in
soft or powder snow. With existing track configurations, modern
day high powered snowmobiles when operating in soft or powder
snow have a tendency when power is applied to the track simply
to dig a hole in the snow rather than generate effective
t ract ion forces between the t rack and the snow.
SUMMARY OF THE INVENTION
The present invention aims to overcome these
difficulties and provide a snowmobile track that is effective
particularly in soft or powder snow conditions.
According to the invention there is provided a
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snowmobile track comprising: an endless belt of reinforced
rubber composition having embedded therein at intervals along
its length a series of transverse reinforcing rods so that the
belt is relatively stiff in the transverse direction while being
flexible in the length direction thereof; said belt having
opposed major surfaces that comprise an interior side and an
exterior side respectively, said interior side being configured
with driving formations for engagement by drive means of the
snowmobile, said exterior side having integral ground-engaging
traction elements formed thereon; said traction elements
comprising projecting ribs each having a height of at least
about 1 1/4 inches, the ribs being spaced along the length of
the track in a repeating pattern and together extending over
most of the width of the track, each said rib extending somewhat
in the transverse direction of the track, and the major part of
the ribs being angled with respect to said transverse direction
at an angle in the range 0° to 45° towards the closest
longitudinal edge of said belt.
The ribs have a height of between 1 1/4 and 2 inches,
and their angle to the transverse direction is preferably in the
range 15° to 30°, and most preferably about 20°.
The ribs taper in thickness towards an elongate crest,
and in the region of their crests the ribs, while still being
stiff, have a degree of resilient flexibility, preferably having
a hardness in the range of 50 to 90, and most preferably about
70 durometer.
The rib crest is preferably flat and to improve
traction may include a groove extending longitudinally thereof.
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The ribs are preferably in register with the
reinforcing rods embedded in the snowmobile track and are
discontinuous, having gaps between adjacent ribs, the ribs in
one row being aligned with the gaps in the adjacent rows so that
the ribs have a repeating pattern corresponding to twice the
spacing between the reinforcing rods.
Preferably in alternate rows of ribs there is a
central rib that is of wide angled V-shape configuration, the
ribs to each side of this central rib being similarly angled in
opposite directions, although in one embodiment it is preferred
to arrange for ribs located to the outboard side of each row of
sprocket holes to be generally parallel to the longitudinal
direction.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will further be described, by way of
example only, with reference to the accompanying drawings
wherein:
Figure 1 is a side perspective view of a snowmobile;
Figure 2 is an enlarged perspective view of a section
of the snowmobile track showing the configuration of the
exterior side thereof;
Figure 3 is a sectional view taken on the line 3-3 in
Figure 2;
Figure 4 is a plan view corresponding to Figure 3;
Figure 5 is a sectional view taken on the line 5-5 in
Figure 4;
Figure 6 is a view taken on the line 6-6 in Figure 4;
Figure 7 is a view corresponding to Figure 4 showing
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an alternate configuration; and
Figure 8 is a view taken on the line 8-8 in Figure 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As seen in Figure 1, a snowmobile 10 is supported at
its forward end on a pair of steerable skies 12 and at its
rearward end on a track 14 in the form of an endless belt which
passes in a ground-engaging round beneath a slide suspension 25,
and at the rear end passes around idler wheels 13.
The track 14 as is known is fabricated as a moulding
of fabric reinforced natural or synthetic rubber, and comprises
an endless loop having an exterior side formed with an array 16
of projecting ground-engaging traction elements, and on its
interior side has rows of integral projecting drive lugs for
engagement by elements of the snowmobile drive train (not
shown). Typically the lugs 18 are arranged at regular spacing
in longitudinally extending rows, and between the outermost rows
the belt is formed with a series of rectangular holes 14. By
virtue of its const ruct ion the belt is f lexible in a
longitudinal direction, and it is stiffened in the transverse
direction by a series of regularly spaced reinforcing rods 22
(Figure 5) which extend throughout substantially the entire
width of the belt, the thickness of the belt being locally
increased in the region of the rods 22 as is evident in Figures
2, 5 and 6. The rods 22 pass through the portions of the belt
that lie between the successive holes 20, and these portions are
reinforced by metal clips 24 of generally C-shaped profile, the
ends 24a of which are clinched into the outer side of the track
whereas the central portion 24b lie flat against the interior
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side 15 of the track and form bearing means for engagement with
the slide rails of the slide suspension 25, as is well
understood in the art.
It will thus be seen that the rows of holes 20 divide
the track 14 in the transverse direction into a wide central
part 14a and narrower outboard parts 14b, although it will be
appreciated that the parts 14a and 14b are integrally connected
by the reinforcing rods 22 and the surraunding rubber material.
Intermediate the location of the successive reinforcing rods 22,
the exterior side 17 of the track 14 is recessed and formed with
a series of shallow transversely extending corrugations 19.
The array 16 of ground-engaging ribs on the exterior
side of the track is shown as comprising a longitudinally
extending row of center ribs 26a on each side of which is a row
of angled flank ribs 26b whereas the outboard portions of the
track each carries a further row of angled ribs 26c.
From Figures 2 and 4 it will be seen that the center
ribs 26a are of wide angled V-shaped configuration having
opposed limbs that are rearwardly angled from the transverse
direction by about 20° so that the rear included angle between
them is about 140°. The flank ribs 26b and the outboard ribs
26c are likewise angled outwardly to the rear at about 200, and
as shown in Figure 5, all ribs are substantially in register
with one or other of the reinforcing rods 22.
Considered in total, the ribs 26a, 26b, 26c extend
over substantially the entire width of the track except for the
region of the holes 24, and this is shown in Figure 3. However
the individual ribs are spaced apart by substantial distances so
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that no rib occupies more than about 1/5 of the width of the
belt. The outboard ribs 26c are aligned with a center rib 26a,
leaving substantial gaps therebetween as seen in Figure 4, the
flank ribs 26b (registering with the adjacent reinforcing) rod
being substantially aligned with these gaps. Thus the
individual ribs, although spaced over substantially the entire
outer side 17, are spaced from one another and provide a repeat
pattern that corresponds to about twice the distance between
adjacent reinforcing rods 22.
The above described arrangement of traction ribs is
beneficial in terms of tractive effort since successive
registering ribs are spaced a sufficient distance apart in the
longitudinal direction that there is an adequate amount of snow
between them to resist the shearing and compaction action of the
ribs. Furthermore, because of the angulation of the ribs, their
interaction with the snow ground surface is such as to retain
the snow within the area of the track rather than pushing it
laterally outwards. This provides good tractive effect and
floatation of the track, which is particularly important in
light powdered snow. Although the ribs are relatively deep, 1
1/4 inches as shown, but in some cases depending on the
application perhaps as much as 2 inches in height, they do not
add excessively to the weight of the track because of the
configuration and spacing of the ribs as shown in the drawings
and discussed above, 1.e. the ribs are relatively small in
length and widely spaced.
As well as providing good tractive effect, the angled
arrangement of the ribs provides effective directional control
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during steering action, and furthermore enhance the stability of
the vehicle against side slip when traversing hillsides.
Additionally, in braking, the configuration of the ribs is
highly effective in providing a large surface for engagement
between the track and the snow.
A modification is shown in Figures 7 and 8. The track
shown herein is essentially the same as the one described in
relation to Figures 2 to 6 except that it has rows of outboard
ribs 26d that extend transversely, rather than at an angle.
In both embodiments, the flat crest of the ribs has a
longitudinally extending groove 30 that effects improved
traction when running on icy surfaces. The ribs are preferably
relatively stiff, but embody a degree of resiliency,
particularly in the region of the crests thereof. Thus the
hardness of the rubber adjacent the crests is preferably about
60 to 70 durometer, although it may vary substantially, e.g.
from 60 to 80 durometer. The hardness of the rubber in the base
portion of the ribs and in the remainder of the track is
preferably about 80 durometer.
In both of the embodiments described in relation to
Figures 4 and 7 the total width of a center rib 26a and an
adjacent pair of flank ribs 26b in the transverse direction is
equal to the spacing between the two rows of sprocket holes 20
so that when viewed in the longitudinal direction the inboard
ends of the flank ribs 23 are in register with the outboard ends
of the center rib 26a, this relationship can be varied as
desired. For example the flank ribs 26b could be extended at
their inboard ends (or the center rib 26a could be extended at
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its outboard ends) to create an overlap as viewed in the
longitudinal direction. Alternatively these ends of the ribs
26b or 26a could be shortened to create gaps as viewed in the
longitudinal direction.
As shown the center rib 26a occupies approximately 44~
of the distance between the rows of sprocket holes 20, each
flank rib 26b occupying approximately 28$ of this distance.
As shown in Figures 3 and 7, the limbs of the center
rib 26a are ankled rearwardly from the transverse direction by
about 20°. This angle can be varied widely, and could be as
much as 45°.
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