Note: Descriptions are shown in the official language in which they were submitted.
CA 02244520 1998-07-29
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Technical Field: This invention relates to snowmobile skis, and more
particularly to steering skis for snowmobiles and similar vehicles.
Backeround: Steering a snowmobile is typically accomplished by a pair of
steering skis pivotally attached to the front of the snowmobile. The steering
skis
glide over the surface of the snow and may be angularly turned from side-to-
side in
response to movement of a pair of handlebars grasped by a user. The snowmobile
generally follows in the direction the skis are pointed.
Under most snow conditions, especially at high speeds, steering skis, when
turned, have a tendency to slide sideways, i.e., "plow" forward over the
surface of
the snow rather than tracking as intended. The turning radius of the
snowmobile thus
becomes larger than anticipated, and may result in the user hitting something
or
losing control of the vehicle. If the sliding ski happens to suddenly "catch"
in the
snow, the momentum of the snowmobile can cause it to overturn and injure the
rider.
This situation is particularly hazardous under snowmobile-racing circumstances
where
the snowmobiles are driven at high speed. If a racer does not make a turn as
anticipated, or suddenly lases control of his snowmobile, he can cause a high-
speed
accident, resulting in injury to the racers.
Various methods have been employed to lend increased predictability and
control to snowmobile steering skis. One of the more common methods is
inclusion
of a longitudinal keel along the underside or running surtace of the ski. The
keel
bites into the surface of the snow and enhances steering characteristics,
particularly at
high speeds.
U.S. Design Patent Des. 366,014 to Lindquist et al. dated January 9, 1996
illustrates a conventional snowmobile ski having a straight central keel. The
top
surface of the ski has a continuous head along each edge and a plurality of
very
small, (thin in width and short in depth) straight, longitudinal ribs along
the running
(bottom) surface of the ski. .
A keel for a snowmobile steering ski is disclosed in U.S. Patent No.
3,632,126 to Shorrock. The keel disclosed in Shorrock has a straight running
edge,
and is adjustable to compensate for wear. U.S. Patent No. 3,711,109 to
Hofbauer
discloses a snowmobile steering ski having a very short, curved keel
resiliently
CA 02244520 1998-07-29
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attached to the ski runner. U.S. Patent No. 3,643,978 to Westberg discloses a
short
curved flange which may be attached to the edge of a snowmobile ski, and which
is
intended to function similar to a keel.
U.5. Patents 5,040,818 and 5,145,201 to Metheny illustrate snowmobile skies
having a central keel with a planar lower surface as a part of a ski which has
a
laterally arched lower running surface.
Although the above inventions represent alternatives to a snowmobile ski
without a keel, they are subject to several problems. The weight of both the
snowmobile and the user is distributed evenly over the t7at running surface of
the skis
in Shorrock. This places a portion of the weight at the ends of the straight
keel and
makes the skis difficult to turn and lessens its usefulness. The bite of the
keel into
the surface of the snow is also distributed over a large area instead of
concentrated in
the most efficient location directly beneath the steering spindles. The short
keel in
Hofbauer tends to provide a concentration of weight beneath the steering
spindles, but
the amount of bite is reduced in soft snow due its short length. Also, because
it is
hinged, it tends to retract on hard snow pack or on ice, when a keel is very
important. The short flange in Westberg also tends to concentrate weight
beneath the
steering spindles, but since it mounts on the edge of the ski, it actually
exacerbates
the problem of the ski "catching" in the snow during a turn, causing a loss of
control
even at moderate speeds. (The phenomenon is similar to the effect of a
downhill
skier catching a downhill edge during a turn.) Also, such short keels do not
provide
steering stability during straight runs and show a reduced steering ability in
soft
snow.
The inventions disclosed in Shorrock, Hofbauer and Westberg bring to light
what has heretofore been a dilemma with respect to the design of snowmobile
steering skis. Increased positive steering brought about by a long keel comes
at the
expense of ease of steering. Accordingly, a short keel makes the skis easier
to steer,
but reduces the amount of positive control. There is a need for a snowmobile
steering ski that provides improved controllability and positive turning
without a
concomitant increase in steering difficulty.
CA 02244520 1998-07-29
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The snowmobile steering ski of the present application includes an elongated
ski having at least a pair of protruding keels that emerge from the bottom
running
surface of the ski runner proximal the front end of the ski. At least one keel
gradually increases in its depth of protrusion with respect to the bottom
running
surface of the ski to a maximum protrusion at a point on the ski bottom which
is
preferably close to the ski connector for connection to the steering spindles
of the
snowmobile. The keel may then gradually decrease in its protrusion depth to
merge
substantially back into the bottom running surface proximal the rear end of
the ski.
Several significant advantages result from the design of the improved
snowmobile steering ski. Positive steering is improved because the keel may be
made to extend along substantially the entire length of the bottom running
surface of
the ski. Further, the maximum bite of the keel into the snow is in the most
efficient
position substantially directly beneath the steering spindles. The ski is easy
to turn,
however, because the keel design results in a lesser percentage of snowmobile
and
user weight being distributed at the ends of the keel.
In a preferred embodiment, both the ski and its protruding keels are curved
through their mid-sections, with curves being slightly upward away from the
snow
surface and with the curvature of the keel having a similar or slightly
smaller radius
of curvature than that of the ski. A smaller radius of curvature of one or
more of the
keels causes the ends of the keel to merge substantially into the curved
bottom
running surface of the ski. However, a ski and keel curved to substantially
the same
radius of curvature also works well for the purposes of the invention.
In another embodiment, the ski is curved slightly upward through its mid-
section and the keel tapers in either direction from a point of maximum
protrusion
below the steering spindles attachment region of the ski into the bottom
surface of the
ski. In still another embodiment, the running surface of the ski is flat, i.e.
a straight,
substantially planar surface, and the keel is curved in a convex shape. In yet
another
embodiment, the ski runner is flat, i.e. substantially straight in a
longitudinal
direction, and the keel tapers substantially linearly in either direction from
a point of
maximum depth below the steering spindles to merge substantially with the
bottom
surface of the ski near the front and rear of the running surface of the ski.
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4a
Accordingly, in one aspect of the present invention, there is provided a
snowmobile steering ski assembly comprising:
attachment of said frame to the steering mechanism of a snowmobile;
and an elongated ski fixedly attached to said frame and having a curved
bottom running surface having a first radius of curvature and structured for
gliding over a surface of snow, an upturned front end having a relatively
short
radius of curvature, a rear end distal from said front end, and three curved
protruding keels having a second effective radii of curvature smaller than
said
first radius of curvature of said bottom running surface, said protruding
keels
gradually emerging from said bottom running surface proximal said front end
and extending along a portion of said length of said ski runner and gradually
merging into said bottom running surface proximal said rear end and wherein
said keels are molded as a part of said bottom running surface.
According to another aspect of the present invention, there is provided
a curved plastic snowmobile ski having a front-tip end and an aft with a
bottom running surface therebetween, said bottom running surface being an
elongated, rocker-shaped surface between said front tip end and said aft end
and at least a pair of protruding keels molded into said rocker-shaped bottom
surface, said keels having an elongated, rocker-shaped bottom surface curved
to a radius of curvature significantly less than the radius of curvature for
said
bottom running surface.
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Several additional advantages result from a steering ski having a slightly
curved bottom running surface. The curved ski runner carries the largest
percentage
of snowmobile and user weight substantially directly under the steering
spindles of
the snowmobile rather than evenly distributed over the bottom surface of the
ski.
This produces more positive turning and permits the snowmobile to maneuver
faster
through a turn without losing steering stability during straight-away runs.
The ends
of the keel also carry a lesser percentage of weight which makes the ski
easier to
steer. Keel length, however, may remain long to provide increased positive
steering
and good tracking during straight runs. Keel penetration into the snow is thus
concentrated where it is most effective, and reduced near the ends of the ski
to
provide easier steering. These advantages exist for a curved ski even if the
ski has no
keel, although typically a keelless curved ski would be fitted with a wear bar
which
substantially conformed to the curved running surface of the ski.
A further understanding of the improved snowmobile steering ski may be had
from the following detailed description together with reference to the
drawings.
DESCRIPTION OF THE DRAWING
FIG. 1 is a side, elevational view of a longitudinally curved snowmobile ski
and a trio of rocker-like keels.
FIG. 2 is a cross-sectional view of the ski of FIG. 1 along section lines 2-2.
FIG. 3 is a perspective view of the ski bottom of the ski of FIGS. 1 and 2.
FIGS. 4, 5 and 6 show alternative cross-sectional configurations of a ski
having three curved keels.
FIGS. 7, 8, 9, 10 and 11 show various cross-sectional configurations of skis
having a pair of outrigger, rocker-shaped keels.
FIG. 12 illustrates a cross-sectional view similar to FIG. 2 wherein the
penetration of the keels of the ski into various types of snow conditions is
illustrated.
FIGS. 13, 14, 15, 16, 17 and 18 illustrate in cross-sectional view a variety
of
multiple-keeled skis having at least one primary longitudinally curved keel.
CA 02244520 1998-07-29
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MODES FOR CARRYING OUT THE INVENTION
A particular embodiment of the invention is illustrated in FIGS. 1, 2 and 3
wherein a snowmobile ski 10, preferably of a one-piece plastic construction,
has three
depending keels; a central keel 11 located along the central longitudinal axis
of the
bottom running surface and a pair of outrigger keels 12 and 13 located along
each
outward edge of the bottom running surface. One, two or all three keels may be
independent structures which are attached to the ski by screws, bolts, rivets,
glue or
the like.
FIG. 1, an elevational, side view, illustrates a curved ski 14 having a
generally rocker-shaped appearance. The ski has a tip segment 15 and an aft
segment
16 and a central segment 17. The turned up tip segment 14 and the sharply bent
aft
segment 16 are curved to much shorter radii of curvature than the central
segment 17.
On the top surface of the ski a pair of longitudinally oriented reinforcing
ribs
18 and 19 strengthen at least the mid-portion and forward portion of the ski,
which in
FIG. 1 is most of the central segment 17 and tip segment 15 of the ski. A
metal
bracket 20 is affixed between the ribs (see FIG. 2) for attachment to a
steering
mechanism (steering spindles) of a snowmobile. The ribs 18 and 19 have a
plurality
of spaced fillets 21 laterally bracing the ribs to provide additional
structural support.
The particular ski shown in FIG. 1, in a preferred embodiment provides a
one-piece structure, preferably of molded plastic, which is both strong and
flexible
while providing the unique advantages of a curved ski running surface and a
curved,
deep central keel with its excellent turning capabilities. A pair of outrigger
keels
provide stability and tracking capabilities.
The central keel 11 is generally curved to about the same or a shorter radius
of curvature than the central segment 17 of the ski running surface. The
central keel
11 runs substantially the whole length of the ski, merging into the running
surface
near the forward extremity of the tip 15 of the ski and into the aft bottom
surface
near its terminus. The keel as desired may also protrude from the entire
undersurface
of the ski tip 15 and aft segment 16.
The left outrigger keel 12 is shown in FIG. 1. The outrigger keels are
generally more shallow in depth than the central keel and are curved,
preferably, to a
radius of curvature intermediate those of the running surface and the central
keel.
CA 02244520 1998-07-29
_7-
Thus, the radius of curvature for an outrigger keel preferably will be shorter
than the
radius of curvature for the ski running surface and longer than the radius of
curvature
of the central keel in this preferred construction. The outrigger keels may,
without
loss of functionality, be approximately the same curvature as the ski running
surface
and/or the central keel. The outrigger keels, particularly if they are of a
shallow
depth and especially if they are short in length, may have a substantially
lower edge
with only a slight loss of effectiveness when used in conj unction with a
curved
centeral keel.
The outrigger keels preferably form the outer, longitudinal edges of the ski,
adding strength and twisting (torsional) resistance to the ski as well as
functionally
improving the tracking and turning capabilities of the ski, especially when
such
outrigger keels have curved lower edges.
The outrigger keels 12 and 13 also preferably run substantially the entire
length of the ski, gradually merging with the ski's bottom surface at the tip
and aft
end of the ski. However, the outrigger keels may be slightly shorter or longer
than
the central, primary keel.
FIG. 2 illustrates the cross-sectional structure of this unique triple-keeled
ski.
This view along section lines 2-2 of FIG. 1 show a cross-section of keels near
the
mid-point of the length of the ski at their maximum depth. The center keel is
shown
with sloping sides 22 and 23 so that it is wider at its junction 24 with the
ski running
surface than it is its bottom surface 25. The cross-sectional shape of the
central keel
11, or the outrigger keels 12, may, however, be any convenient shape. The
central
keel has a depth of about 2.54 centimeters (one inch) to about 5.08
centimeters (two
inches), preferably from about 2.54 centimeters (one inch) to about 3.81
centimeters
(1'/z inches) below the ski running surface. The central keel preferably had a
width
of about 1.27 centimeters (one-half inch) to about 4.445 centimeters (1 ~/
inches) at
its junction with the ski running surface and a width of about 0.635
centimeters
('/ inch) to about 2.54 centimeters (one inch) at its lower surface (snow
penetrating
surface) 25.
A typical ski has a width of about 10.16 centimeters (four inches) to 17.78
centimeters (seven inches). Each outrigger keel has a width of about 1.27
centimeters (one-half inches) to about 2.54 centimeters (one inch), preferably
from
CA 02244520 1998-07-29
_g_
about 1.9 centimeters (~/ inch) to 2.54 centimeters (one inch), at its
junction with the
ski running surface and a width of about 0.635 centimeters (one-fourth inch)
to about
2.22 centimeters ('/8 inch) at the lower surface 26 or 27. The depth of an
outrigger
keel is from about 1.27 centimeters (one-half inch) to about 2.54 centimeters
(one
inch), preferably from about 1.27 centimeters (one-half inch) to 1.9
centimeters
{~/ inch), below the ski running surface.
The width of the lower surface of each keel should be sufficient to
accommodate and support a wear bar, which is usually a round rod. The lower
surface of each keel may contain a slight longitudinal groove into which a
wear bar
may nest.
The spacing on either side of the central keel to the closest surface of an
outrigger keel is preferably from about one to about 5.08 centimeters (5.08
centimeters (two inches)). This may be expressed as a ratio of available
running
surface width to ski width as follows:
Least ratio: Approximately 30%
Maximum ratio: Approximately 70%
The maximum ratio contemplates a maximum area of running surface, which
would be generally preferred for loose, powder snow, provided that an
appropriate
width of ski is used. The minimum ratio provides the least running surface,
which
contemplates that the lower surface widths of the keels are greater with
respect to the
ski width, which may be a. preferred construction for hard-pack, icy
conditions.
Since skis are not changed for changing conditions, an all-purpose ski is
usually
preferred, although in some regions of snowmobile country one extreme or the
other
may be most useful. For example, in the western United States and Canada, more
powdery snow may be encountered while in the midwest and east, more icy
conditions may have to be dealt with.
FIG. 3 is a perspective view of the ski bottom of the ski illustrated in FIGS.
1
and 2.
FIGS. 4, 5 and 6 illustrate various cross-sectional configurations for a tri-
keeled ski.
FIG. 4 is a lateral cross-sectional view of a tri-keeled ski wherein the
central
keel 28 has a generally longitudinal rocker-like shape similar to that
illustrated in
CA 02244520 1998-07-29
-9-
FIG. 1. The bottom running surface of the ski may be longitudinally flat or
curved,
as in FIG. 1. The running surface, in a lateral cross-section, has a very wide
angled
V-shape, similar to the wings of a plane, i.e. higher at its tips (outboard
edge) than
near the central keel. At each outboard edge of the ski is an outrigger keel
which
projects a short distance down from the running surface of the ski. Each
outrigger
ski is curved (convex) along its longitudinal length.
The ski illustrated by FIG. 4 is especially useful for steering systems which
tilt the ski during turns (camber). The ski of FIG. 4, assuming that one is
looking
head on at the ski, tends to have the right running surface (surface to the
right of the
central keel) substantially flat upon the snow during a left turn of the ski.
This may,
in many instances, be advantageous. Also, the outrigger keel is affixed at
approximate right angles to the adjacent running surface of the ski so that
during a
turn, the outrigger keel on the inside of the turn will be in substantially
true vertical
orientation with the snow and will present its maximum vertical surface area
to the
snow to provide maximum "bite."
The design of the ski of FIG. 6 is similar to that of FIG. 4 except that the
running surface is curved laterally and the outboard keels are oriented with
their
vertical axes substantially parallel to the vertical axis of the central keel.
The running
surface of the ski may be linear or curved in a longitudinal direction. All
three
illustrated keels are preferably curved. Each keel of the ski of FIG. 6 is
shown
equipped with a wear bar.
The ski of FIG. 5 has a cross-sectional shape in which outer edges of the ski
running surface are lower than at the juncture of the running surface with the
base of
the central keel. This structure may be advantageous, especially with a ski
having a
longitudinally curved running surface, since the running surface, laterally
drooping to
outboard, also tends to dig into the snow during a turn to give a more
aggressive bite
during a turn. The outboard keels in FIG. 5 are convex as is the central keel.
Thus,
in a side view, the ski of FIG. 5 would resemble the ski of FIG. 1 with the
running
surface, central keel and outrigger keels each convexly curved along its
length.
As with any tri-keel structure of the instant invention, the outrigger keels
are
preferably of approximately equal lengths which may be shorter or longer than
the
central keel. The outrigger keels preferably have identically curved lower
surfaces
CA 02244520 1998-07-29
-10-
which may be similar or different than the central keel or the running surface
of the
ski. If skis are made to be a pair, i.e. a right and left ski, then the
outrigger keels of
each ski may be different in length, depth and curvature. Typically, for a
"right" or
"left" ski that outrigger keel which would be along the inside edge of a ski
would
have a greater depth, greater degree of curvature, etc. to provide more "bite"
during
turns if the keels were to be different.
The central keel of a tri-keeled ski preferably has a curved lower surface
(which may be approximated by a series of straight, i.e., linear or planar
surfaces).
The tri-keel contiguration is useful for skis having a flat running surface,
i.e., planar,
or a curved running surface. A curved keel fitted to a curved running surface
will
have a curvature approximately the same as the running surface or a greater
degree of
curvature, i.e., a shorter radius of curvature.
The curved surface of a ski or keel may be a regular arc of a circle (or
cylinder) or it may be a compound curve or even a "curve" approximated by a
series
of joined planar or straight (linear) surfaces, e.g., three or more straight
line surfaces
although two long straight surfaces which meet to form an obtuse (e.g.
150° - 170°)
included angle may work satisfactorily. However, since keel lower surfaces are
generally fitted with wear bars it is generally preferred to avoid "bend" of
even
"wide" angles since wear will tend to occur there to a greater extent than on
other
portions of the wear bar. Thus, a relatively smoothly "curved" lower surface
for a
keel is preferred.
The structure of a curved keel in this invention is such that its greatest
depth is
preferably near to the point where the ski connects to the steering mechanism
of a
snowmobile.
The keels described herein generally have a length which is from about 75 %
to 100% of the running surface of a ski, and, in many structures, the keel may
protrude from beneath the tip and turned up aft end of a ski, so that it runs
essentially
the whole length of the ski.
The outrigger keels generally have a curvature which ranges from linear, i.e.,
a flat, straight, lower surface useful with flat skis to a curved lower
surface,
especially at a curvature essentially equivalent to the ski or the central
keel.
CA 02244520 1998-07-29
Generally, the depth of an outrigger keel is less than that of the central
keel except
when an outrigger keel is the primary keel.
As illustrated in FIGS. 7, 8, 9, 10 and 11 a ski having only a pair of keels
(outrigger or in-rigger) which may be especially useful in loose, powdery
snow.
Although the skis illustrated and described hereinabove have a central
longitudinal keel, a double-keel arrangement without a central keel may also
be
constructed to employ the structure of the instant invention.
A double-keel ski having a substantially flat running surface and a straight
lower-edged keel and having the cross-sectional shape similar to that shown in
lateral
cross-section in FIGS. 7 and 8 have been developed by inventor, although
without
being put into commercial use. Skis with dual rocker-like keels of the type
described
herein as outrigger keels existing on both the inner and outer sides of the
steering ski,
as shown in FIGS. 7 and 8, do not experience control problems associated with
a ski
having only a single short, deep outboard keel; a structure suggested in some
prior
patents.
The cross-sectional view of FIGS. 9, 10 and 11 are of various dual keeled skis
wherein the running surface may have a slot-like recess (FIG. 9), a
longitudinal ridge
(FIG. 10) or outrigger keels placed inward of the outboard edge of a ski (FIG.
l l).
The structure of the running surface of the ski of FIG. 9 is similar to that
of
an alpine ski with a longitudinal groove which may help in tracking during
straight
running. The function of the longitudinal ridge on the lower running surface
(FIG.
10) is similar to the groove of FIG. 9.
The structure of the ski of FIG. 11 is such that the keels are placed inboard
of
the ski's outer edges.
Although skis having substantially flat (straight) running surfaces and dual
straight keel edges along their length may be useful, a double-keel or triple-
keel
configuration wherein the keels are curved in a convex manner, as explained
above
with regard to skis having a central keel, are preferred and provide excellent
turning
characteristics, especially when used with a ski which is curved along its
central
longitudinal axis.
Skis employing curved double keels, as illustrated in FIGS. 7, 8, 9, 10 and
11, may have flat or curved bottom running surfaces and may be made of metal,
CA 02244520 1998-07-29
-12-
plastic or other strong, smooth material. Als<~, the keels may be an integral
part of
the ski or they may be attachable or replaceable. The composition (material of
construction) of the keels, especially shallow, outrigger keels may be
different than
that of the ski. For example, one shallow metal keels may be attached in a
replaceable manner to plastic skis.
A ski of the instant invention is preferably laterally symmetrical about a
vertical plane passing through the ski perpendicularly to its longitudinal
axis. It
preferably has a keel which is a continuous uninterrupted structure from near
its front
to near its rear end.
Snowmobile steering skis having keels with a lower curved surface along their
length are particularly useful for providing excellent steering control in
virtually all
snow conditions from deep powder to ice. The curved keel works especially well
on
skis which have a curved bottom running surface.
The new triple-keeled ski is designed with a central keel that is the dominant
steering influence in all ice and snow conditions, and is the only steering
control on
icy surfaces, since neither of the outer keels make contact on very hard
surfaces.
But, as surface conditions turn from ice to hard-packed snow, the center keel
penetrates the surface deeper and the two outer keels begin to touch the snow
and
share some of the weight thereby limiting the depth of center keel penetration
to
prevent an overly aggressive bite. An extremely radical keel depth would
normally
be dangerously aggressive in firm, hard-packed snow, commonly experienced on
frequently used and groomed snowmobiles trails, without the penetration
limiting
effect of the two outer keels. When the ski is pointed straight ahead, both
outer keels
are, on the average, level with the snow surface, so both will share the
weight of the
snowmobile equally. As the ski is steered left or right, the ski surface
begins to tilt,
due to the camber effect of the snowmobile steering geometry. This action will
cause
the outer keel nearest the outside radius of the turn to rise transferring
more weight to
the center keel and the opposite outer keel closest to the inside radius of
the turn,
thereby utilizing this keel to steer the snowmobile more positively. This
situation
improves the turning ability of the snowmobile without being dangerously over
aggressive. So, in spite of the radical appearance of the center keel, a
triple keel ski,
CA 02244520 2006-05-19
-13-
even one with a relatively deep center keel is designed to govern its own
turning
aggressiveness by bringing the outer koels into play as the snow conditions
dictate.
Deep snow steering of a tri-keel ski has proven superior to any other ski
tested, because of the three keel structure. This advantage is noticed
whenever the
snow exceeds about three inches in depth, and progressively more apparent as
snow
depth or penetratability increases. In deep snow conditions, all three keels
are
functional steering aid at all times. The tri-keel structure improves straight
line
tracking as well as turning capabilities in deep snow.
It is important to note that, the superior turning and tracking abilities of
this
ski and its aggressive design could only be used comfortably and safely when
combined with the patented curved or rocker-shape of the keels as described in
U. S.
Patent No. 5,700,020.
Tri-keeled skis of an aggressive design are most effective and tractable upon
incorporation of the curved or rocker-shape of the keels. Any other keel
structure
compromises, to some extent, the steering ease and safety of the snowmobile
during
turns.
FIG. 12 illustrates the manner in which a preferred tri-keel ski of the
instant
invention interacts with varying snow conditions. On very hard packed snow or
ice,
generally on the central (or dominant keel if the central keel is not the
dominant keel)
will contact the surface. Generally, under such snow conditions only the wear
bar
and a portion of the dominant keel will penetrate the surface. This is shown
in
FIG. 12 as condition "A."
On average hard packed or groomed trails, the central keel and the outrigger
keels will be in contact with the surface. The deepest keel, shown here as the
central
keel, will penetrate the surface to a depth that the outrigger keels have made
some
penetration,which typically includes complete penetration by their wear bars
and
some penetration by the outrigger keel structures (shown as Condition "B").
In soft snow having a depth of three inches or more, all three keels will be
substantially totally immersed in the snow and the running surface of the ski
between
the keels will be in contact with the snow and supporting a substantial
portion of the
forward weight of the snowmobile. In deep, soft snow, the whole ski may sink
into
CA 02244520 1998-07-29
-14--
the snow until the compaction provided by the ski has "densitied" the snow to
the
point where the condition illustrated as condition "C" exists.
Because most snowmobiles occasionally encounter icy surfaces, it is generally
preferred that the dominant keel be the central keel so that uneven stresses
on the ski
and steering mechanism are not encountered. However, if a keel that is not on
the
longitudinal centerline of the ski is the dominant keel, then the ski and
steering
mechanism can be strengthened and reinforced to compensate for such uneven
stresses that may occasionally be encountered.
The dominant or primary keel in a dual keel or triple keel structure is deeper
than the other keels and is a curved keel. While it is preferred that a
multiple keel
ski have all keels curved, a ski with a dominant curved keel, which is
typically the
central keel, may employ subsidiary keels which are very marginally curved or
even
straight over their entire length when the purpose of such subsidiary keels is
to assist
primarily the straight line tracking ability of the ski.
Virtually all snowmobiles are designed so that the steering shafts connecting
to the front skis are at a forward angle rather than in a vertical
orientation. Thus,
when the snowmobile steering handle bars are turned, the angle of the steering
shafts
cause the skis to tilt laterally so that in a left turn, for example, the
inside edge of the
right ski and the outboard edge of the left ski will be lower than the
opposite edge of
each ski. The sharper the turn made by the snowmobile. the greater is the
degree of
tilt of the skis.
The multiple keeled skis of this invention may be structured to maximize the
"biting effect" of one or more of the multiple keels.
FIGS. 13-18 illustrate in cross section various alternative structures which
employ features of the instant invention, namely, at least one primary
(dominant),
rocker-shaped keel in conjunction with secondary keels to provide a ski with
good,
straight tracking ability and excellent turning characteristics in all types
of snow
depths and conditions. The ski running surface of such skis may be flat or
rocker-
shaped, with the latter being preferred.
In each embodiment illustrated here secondary keels, which are sufficiently
large dimensionally (depth, width and length), function for tracking and
turning
purposes. All keels illustrated, except the secondary keels in FIG. 17, have
sufficient
CA 02244520 1998-07-29
-15-
lower (snow-contacting) surface area to accommodate a wear bar. The secondary
keel of FIG. 17 are used in conjunction with a dominant central keel, which
carnes a
wear bar, and wherein this ski may be particularly useful in powdery or soft
packed
snow conditions.
The skis illustrated in FIGS. 13, 14 and 16 are ones in which the lower
running surface of the skis are made up of the sloping sidewalk of the skis.
FIG. 15
is a ski similar to the ski of FIG. 1 except that the ski of FIG. 15 has five
keels, each
accommodating a wear bar on its lower snow-contacting surface. The ski of FIG.
18
is one in which the outrigger keels are the dominant keels which the central
keel may
be straight or curved and function principally to enhance the straight
tracking of the
ski. Each outrigger keel in FIG. 13 is curved and identical, preferably, to
the other
outrigger keel.
Although the invention has been described and illustrated herein with a
certain
degree of particularity of structure, this has been for purposes of
illustration of the
principles of the invention, and is not intended to limit the invention in any
way. It
should be understood that various changes and modifications may be made
without
departing from the spirit and scope of the following claims.
