CA 02282787 1999-09-17
1
TITLE OF THE INVENTION
SNOWMOBILE SUSPENSION SYSTEM
FIELD OF THE INVENTION
The present invention relates to suspension systems.
More specifically, the present invention is concerned with a snowmobile
suspension system.
BACKGROUND OF THE INVENTION
It is well known in the art to suspend the drive belt of a
snowmobile below the body thereof for suspension movements.
These suspension systems are usually provided with a
pair of side rails to guide the drive belt, a pair of suspension arms each
having a proximate end pivotally mounted to the snowmobile and a distal
end pivotally mounted to both side rails. The side rails, suspension arms
and the snowmobile are so configured as to form a deformable
parallelogram, thereby allowing suspension movements of the side rails
with respect to the snowmobile between a fully extended and a fully
retracted position. Shock absorbers and compression springs are also
provided between the side rails and the snowmobile to bias the side rails
towards their extended position.
CA 02282787 1999-09-17
2
Such conventional snowmobile suspension systems
suffer from many drawbacks. A first drawback relates to the material
used to make the side rails. Indeed, side rails are usually made of
aluminum which yields relatively heavy and complicated to manufacture
side rails. Furthermore, aluminum side rails have other drawbacks
related to the nature of the material such as, for example, poor resistance
toughness and low fatigue life.
A second drawback of the conventional snowmobile
suspension systems is revealed when a force, overcoming the forces
applied by the shock absorbers and the springs, causes the side rails to
go from their fully extended position to their fully retracted position. When
this is the case, the side rails will hit the underside of the snowmobile,
which may damage the vehicle and/or endanger the driver.
To overcome this drawback, commercially available
snowmobile suspension systems are provided with a piece of resilient
material, for example, rubber, strategically positioned to intercept the side
rails before they contact the underside of the snowmobile. The contact
is therefore much less violent since the resilient material absorbs a
portion of the energy of the impact. However, the contact between the
side rails and the rubber piece still causes undesired sensations to the
driver.
A third drawback is the lack of adjustability of the
suspension characteristics or the complexity of adjustment of these
characteristics. Indeed, conventionally, the pivotal attachments securing
the distal end of the rear suspension arm to the side rails and the shock
CA 02282787 1999-09-17
3
absorbers to the side rails are at predetermined fixed positions which
results, for a given configuration, in predetermined suspension
characteristics. This is a drawback since it removes the possibility for the
driver to select different suspension characteristics for different type of
rides.
To address this problem, many adjustable snowmobile
suspension systems have been proposed. For example, United States
Patent N° 5,692,579 issued on December 2nd 1997, naming Keith W.
Peppel et al. as inventors and entitled “Adjustable Snowmobile Track
Suspension” discloses a system provided with a rear suspension arm
having a distal end which is so mounted to the side rails that limited
longitudinal movements of the distal end may be achieved. The systems
also include adjustable limits allowing the characteristics of the
suspension to be adjusted by the user.
While Peppel’s suspension is an improvement in terms
of adjustability, it involves many mechanical elements to allow the
longitudinal movements and to limit these movements. Furthermore, the
user needs some tools to loose the fasteners, rotate the rectangular limits
and to tighten the fasteners.
OBJECTS OF THE INVENTION
An object of the present invention is therefore to provide
an improved snowmobile suspension system.
CA 02282787 1999-09-17
4
SUMMARY OF THE INVENTION
More specifically, in accordance with the present
invention, there is provided A snowmobile suspension system configured
to suspend a drive track to a snowmobile; the suspension system
comprising:
a front suspension arm having a proximate end pivotally
mounted to the snowmobile; the front suspension arm having a distal end;
a rear suspension arm having a proximate end pivotally
mounted to the snowmobile; the rear suspension arm having a distal end;
a pair of side rails; each side rail being pivotally mounted
to the distal ends of the front and rear suspensions for suspension
movements between a retracted position where the side rails are adjacent
to the snowmobile and an extended position; each side rail being made
of composite material and provided with a concave undersurface; and
a biasing assembly pivotally mounted to the snowmobile
and to both side rails; the biasing assembly biasing both side rails
towards the extended position.
According to a second aspect of the present invention,
there is provided a A snowmobile suspension system configured to
suspend a drive track to a snowmobile; the suspension system
comprising:
a front suspension arm having a proximate end pivotally
mounted to the snowmobile; the front suspension arm having a distal end;
a rear suspension arm having a proximate end pivotally
mounted to the snowmobile; the rear suspension arm having a distal end;
CA 02282787 1999-09-17
a pair of side rails; each side rail being pivotally mounted
to the distal ends of the front and rear suspensions for suspension
movements between a retracted position where the side rails are adjacent
to the snowmobile and an extended position;
5 a biasing assembly pivotally mounted to the snowmobile
and to both side rails; said biasing assembly biasing both side rails
towards the extended position; and
a progressive spring assembly so mounted to the pair
of side rails as to contact at least one of the front and rear suspension
arms when the pair of side rails nears the retracted position thereby
absorbing excess energy from the side rails to prevent forceful contact
between the side rails and the snowmobile.
According to a third aspect of the present invention,
there is provided a A snowmobile suspension system configured to
suspend a drive track to a snowmobile; the suspension system
comprising:
a front suspension arm having a proximate end pivotally
mounted to the snowmobile; the front suspension arm having a distal end;
a rear suspension arm having a proximate end pivotally
mounted to the snowmobile; the rear suspension arm having a distal end;
first and second longitudinal side rails; each longitudinal
side rail being pivotally mounted to the distal end of the front suspension
arm; each longitudinal side rail having a generally transversal rear pivotal
axis and a semi-circular channel coaxial with the rear pivotal axis; the
semi-circular channel having opposite ends;
CA 02282787 1999-09-17
6
a linkage assembly connecting the distal end of the rear
suspension arm to the pair of side rails; the linkage assembly including,
for each side rail:
an adjustable cam assembly so mounted to the side rail
as to pivot about the rear pivotal axis; the cam
assembly having an off-center arm mounting aperture
to which the distal end of the rear suspension arm is
pivotally mounted; and
at least one adjustable abutment element so mounted
to the cam assembly as to extend in the semi-circular
channel; the abutment element limiting the pivoting
movements of the cam assembly by abutting the ends
of the semi-circular channel; and
a biasing assembly pivotally mounted to the snowmobile
and to both side rails; the biasing assembly biasing both side rails
towards an extended position.
Other objects, advantages and features of the present
invention will become more apparent upon reading of the following non
restrictive description of preferred embodiments thereof, given by way of
example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
CA 02282787 1999-09-17
7
Figure 1 is a sectional side elevational view illustrating
a snowmobile suspension system according to an embodiment of the
present invention; the snowmobile suspension system being shown
mounted to a snowmobile;
Figure 2 is a sectional side elevational view of the
snowmobile suspension system of Figure 1;
Figure 3 is a side elevational view of one of the side rails
of the snowmobile suspension system of Figure 1;
Figure 4 is a plan view taken along line 4-4 of Figure 1;
Figure 5 is a side elevational view illustrating the
snowmobile suspension system of Figure 1 in a resting state;
Figure 6 is a side elevational view illustrating the
snowmobile suspension system of Figure 1 when the snowmobile is
under a normal acceleration;
Figure 7 is a side elevational view illustrating the
snowmobile suspension system of Figure 1 when the snowmobile is
under a strong acceleration;
Figure 8 is a side elevational view illustrating the
snowmobile suspension system of Figure 1 when the front portion of the
suspension system hits a bump; and
CA 02282787 1999-09-17
Figure 9 is a side elevational view illustrating the
snowmobile suspension system of Figure 1 in a retracted position.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to Figures 1 to 4 of the appended drawings,
a snowmobile suspension system 10 according to an embodiment of the
present invention will be described.
In Figure 1, the snowmobile suspension system 10 is
illustrated suspended from the underside of a snowmobile 12. As will be
described hereinbelow, the snowmobile suspension system 10 may move
from a fully extended position to a fully retracted position.
As can be better seen from Figure 2, the snowmobile
suspension system 10 is provided with a pair of side rails 14 and 16 (only
one shown) to guide a drive belt (not shown), front and rear identical
suspension arms 18 and 20, a biasing assembly 22 and a progressive
spring assembly 24.
The side rails 14 and 16 are identical. They are
advantageously made of a Ultra-High Molecular Weight (UHMW) material
such as, for example, Ultra-High Molecular Weight Polyethylene (UHMW
PE) manufactured under the tradename Tivarc~ 1000 by Poly Hi Solidur,
a division of Menasha Corporation.
CA 02282787 1999-09-17
9
Since the side rails 14 and 16 are made of a polymeric
material, they are advantageously provided with a concave undersurface
(see undersurface 26 in Figure 3). Therefore, when pressure is applied
in the direction of arrow 28, the side rails 14 and 16 will have the
tendency to flatten to therefore present a generally flat undersurface and
increase the stiffness of the side rails. It has been found that when
Tivart~ 1000 is used, a side rail 14 of about 46 inches (about 1.17 meters)
operates in a satisfactory manner when the undersurface 26 is generally
semicircular and has a radius of about 400 inches (about 10.16 meters).
Of course, the above measurements are given as an example only and
depend, amongst others, on the shape of the rails, the type of material
used and the type of snowmobile used.
Another way of looking at the undersurface 26 of the rail
14 is that it presents an inward central deflection of about’/4 of an inch
(about 0.006 meters). Of course, the undersurface 26 could present
another profile, as long as the undersurface is not straight. For example,
2 straight surfaces (not shown) could be joined to present a central
deflection of about’/4 inch.
As will be apparent to one skilled in the art, the term
“concave”, as used in the present description and in the appended claims,
is to be construed as meaning any surface that presents an inward
deflection, not necessarily semi-circular in shape.
The rail 14 includes a plurality of thinner portions 29 so
configured, sized and positioned as to decrease the overall weight of the
rail 14 without significantly decreasing its stiffness.
CA 02282787 1999-09-17
It has been found that rails following the shape
illustrated in the appended figures, when made of Tivar~ 1000, offer
similar performances as conventional aluminum rails while being lighter
and free of the above-noted drawbacks of conventional aluminum side
5 rails. The weight required to flatten the undersurface 26 of the rails
described hereinabove is about 500 pounds (about 227 kg).
The front and rear suspension arms 18 and 20 define,
with the side rails 14 and 16 and with the underside of the snowmobile
10 12, a parallelogram, allowing suspension movements of the side rails 14
and 16 with respect to the snowmobile between fully extended and fully
retracted positions.
The front suspension arm 18 is generally Y-shaped (see
Figure 4) and includes a proximate portion 30 provided with a cylindrical
mounting rod 32 having opposite projections 34 and 36 configured and
sized to be pivotally mounted to corresponding cylindrical apertures (not
shown) of the snowmobile. The front suspension arm 18 also includes a
distal portion 38 provided with a cylindrical mounting rod 40 having
opposite projections 42 and 44 configured and sized to be pivotally
mounted to corresponding cylindrical apertures of respective side rails 14
and 16.
Similarly, the rear suspension arm 20 is generally Y-
shaped (see Figure 4) and includes a proximate portion 46 provided with
a cylindrical mounting rod 48 having opposite projections 50 and 52
configured and sized to be pivotally mounted to corresponding cylindrical
apertures (not shown) of the snowmobile. The rear suspension arm 20
CA 02282787 1999-09-17
11
also includes a distal portion 54 provided with a cylindrical mounting rod
56. The mounting rod 56 is pivotally mounted to both side rails 14 and 16
via identical adjustable cam assemblies 58, 60. For concision purposes,
only the adjustable cam assembly 58 will be described hereinbelow.
It is to be noted that since the front and rear suspension
arms 18 and 20 are advantageously made of Tivar~ 1000, which is a self-
lubricating material having a low coefficient of friction, other friction
reducing material is not required between the mounting rods 32, 40 and
the front suspension arm 18 and between the mounting rods 48, 56 and
the rear suspension arm 20.
The adjustable cam assembly 58 includes first and
second semi-circular disks 62, 64 so mounted to an aperture 66 (Figure
3) of the side rail 14 as to pivot about a central first pivotal axis 67. The
semi-circular disks are interconnected via a fastener 68 and may include
cylindrical projecting portions (not shown) configured and sized to enter
the aperture 66. Again, since Tivar~ 1000 is a self lubricating material
having a low coefficient of friction, other friction reducing material is not
required between the projection and the aperture 66.
Each semi-circular disk 62 and 64 includes a series of
circular apertures 70a-70h equidistant from the first pivotal axis 67. The
apertures 70a-70h are therefore positioned on an hypothetical semi
circular line.
Each disk 62 and 64 also includes an offset mounting
aperture 72 to which the distal end 54 of the rear suspension arm 20 may
CA 02282787 1999-09-17
12
be pivotally mounted. As can be better seen from Figure 4, the mounting
rod 56 is mounted to the adjustable cam assemblies 58 and 60 via
fasteners 74, 76 so as to pivot about a second pivotal axis 78.
Returning to Figure 3, the side rail 14 is provided with a
semi-circular slot 80 aligned with the hypothetical semi-circular line
defined by the apertures 70a-70h. The slot 80 has a front end 82 and a
rear end 84 (see Figure 3) and allows a front adjusting pin 86 and a rear
adjusting pin 88 to be inserted in respective apertures 70a-70h of both
disks 62 and 64 while extending through the slot 80. As will be further
described hereinbelow, the adjusting pins 86 and 88 respectively limit the
pivotal movement of the adjustable cam assembly 58 in clockwise and
counterclockwise directions, since the adjustable cam assembly 58 may
not pivot further when one of the adjusting pin contacts one of the ends
of the slot. Advantageously, the front adjusting pin 86 is inserted in one
of the first five apertures 70a-70e, while the rear adjusting pin 88 is
inserted in one of the last three apertures 70f-70h.
The biasing assembly 22 includes a pair of shock
absorbers 90, 92 each having a proximate end mounted to the mounting
rod 48 of the rear suspension arm 20 and a distal end mounted to an
adjustable spacer rod 94. The spacer rod 94 is slidably mounted in a
rectangular aperture 96 of the rails (see Figure 3) thereby allowing limited
longitudinal adjustment of the mounting position of the distal end of the
shock absorbers 90, 92. The biasing assembly 22 also includes
compression springs 98, 100 conventionally provided around the shock
absorbers 90, 92, respectively.
CA 02282787 1999-09-17
13
Of course, the biasing assembly 22 is provided between
the side rails and the snowmobile to bias the side rails towards their
extended position.
As will be apparent to one skilled in the art, the
longitudinal adjustment of the spacer rod 94 enables the user to modify
the stiffness of the biasing assembly 22.
The snowmobile suspension system 10 also includes a
slide bar 102 having a proximate end 104 pivotally mounted to the
mounting rod 32 of the front suspension arm 18 and a distal end 106
provided with an elongated slot 108 mounted to a spacer rod 110
interconnecting the side rails 14 and 16. Of course, as will be apparent
to one skilled in the art, the purpose of the slide bar 102 is to limit the
opening of the front suspension arm 18.
The progressive spring assembly 24 includes two
separate springs 112 and 114 having a rising strength rate. Each spring
is mounted in a semicircular opening 116 of the rails (see Figure 3) and
includes a generally L-shaped leg 118 inserted in an aperture 120 of the
rails to prevent rotation of the spring in the semi-circular opening 116.
Each spring also includes a generally straight contact portion 122 so
positioned, configured and sized as to contact the rear suspension arm
20 when the snowmobile suspension system 10 is near its fully retracted
position. The purpose of the progressive spring assembly 24 is to
prevent forceful contact between the elements of the snowmobile
suspension system 10 and the underside of the snowmobile 12 by
progressively absorbing energy as the snowmobile suspension system 10
CA 02282787 1999-09-17
14
nears its fully retracted position. This energy absorption will slow the
movement of the snowmobile suspension system 10, therefore minimizing
the chances of contact.
It is to be noted that the snowmobile suspension system
includes other elements that are not relevant to the present invention,
such as, for example, spacer rods 124 and endless track contacting
wheels 126. These elements will not be further discussed herein since
they are believed well known to one skilled in the art.
Turning now more specifically to Figures 5-9 of the
appended drawings, the operation of the snowmobile suspension system
10 according to an embodiment of the present invention will be described.
Figure 5 illustrates the snowmobile suspension system
10 mounted to the snowmobile 12 when the snowmobile suspension
system is in a resting state. Therefore, only the weight of the snowmobile
12 and of the user (not shown) applied downward pressure onto the
snowmobile suspension system 10 which is thus in its fully extended
operating position.
It is to be noted that when the snowmobile suspension
system 10 is in this position, the rear adjusting pin 88, which is inserted
in the aperture 70f, abuts the rear end 84 of the slot 80. The cam
assembly 58 has therefore pivoted about axis 67 (see arrow 128) with
respect to the position of the snowmobile suspension system 10 shown
in Figure 2. However, even if more weight is applied to the snowmobile
suspension system 10, there will be no further counterclockwise rotation
CA 02282787 1999-09-17
of the cam assembly 58 since there is contact between the rear adjusting
pin 88 and the rear end 84 of the slot 80. Therefore, if more weight is
applied to the snowmobile suspension system 10, the parallelogram
defined by the underside of the snowmobile 12, the suspension arms 18
5 and 20, and the rail 14 will flatten.
It is to be noted that if the rear adjustment pin 88 had
been inserted in one of the aperture 70g or 70h, the position of the
snowmobile 12 at its resting state would have been different from the one
10 illustrated in Figure 5. Indeed, since the weight of the snowmobile is
sufficient to ensure that the rear adjustment pin 88 contacts the rear end
84 of the slot 80, the insertion of the adjustment pin 88 in another
aperture change the dynamic of the snowmobile suspension system 10.
More specifically, when the adjustment pin 88 is inserted in the aperture
15 70h the ride is smoother than if the adjustment pin 88 is inserted in the
aperture 70f since the insertion in aperture 70h causes a pre-pivoting
action of the cam assembly 58, therefore shortening the effective length
of the rear suspension arm 20 which, as will be described hereinafter,
increases the pulling action (see arrow 160 in Figure 8) when the
snowmobile hits a bump.
Turning now to Figure 6 of the appended drawings, the
operation of snowmobile suspension system 10 when the snowmobile 12
is under normal forward acceleration (see arrow 130) will be described.
When this is the case, the front portion of the snowmobile 12 is lifted from
the ground while the rear portion of the snowmobile 12 drops towards the
ground (see arrow 132). The acceleration forces cause a downward
force on the rear suspension arm 20 (se arrows 134 and 138) that cause
CA 02282787 1999-09-17
16
the clockwise rotation (see arrow 140) of the cam assembly 58 about
pivot axis 67. This clockwise rotation causes the rearward displacement
of the pivotal axis 78 therefore modifying the shape of the parallelogram
defined by the front and rear suspension arms 18 and 20, the side rails
14 and 16 and the underside of the snowmobile 12. Hence, the
downward movement of the rear portion of the snowmobile 12 has been
absorbed by the pivotal movement of the cam assembly 58 without
requiring any movement of the front suspension arm.
It is to be noted that the front adjustment pin 86 does not
contact the front end 82 of the slot 80. Once this contact is made, further
increase in acceleration is translated in a general movement of the
snowmobile suspension system 10 towards its retracted position. Indeed,
if the pin 86 contacts the end 82, further pivotal movement of the rear
suspension arm 20 about axis 67 is prevented, thus forcing the pivotal
movement of the rear suspension arm 20 about pivotal axis 78.
It is also to be noted that when the adjustment pin 86
contacts the front end 82 of the slot 80, further increase in acceleration
does not cause further upward movement of the front portion of the
snowmobile 12 but cause only further downward movement of the rear
portion of the snowmobile 12.
In Figure 7, the front adjustment pin is shown inserted
in aperture 70e while the snowmobile is shown under strong acceleration
(see arrow 142). Again, the front portion of the snowmobile 12 is lifted
from the ground while the rear portion of the snowmobile 12 drops
towards the ground (see arrow 144).
CA 02282787 1999-09-17
17
Under a strong acceleration, the force on the
snowmobile suspension system 10 (see arrow 146) will cause the pivoting
action of the distal ends of the suspension arms (see arrows 148 and
150, respectively) to thereby move the snowmobile suspension system
10 towards its retracted position.
It is to be noted that the undersurface 26 of the rail 14
has lost its deflection since the load transferred to the rail 14 by the
biasing assembly is great.
It is also to be noted that when the adjustment pin 86 is
inserted in the aperture 70e the weight shift effect is greater than if the
adjustment pin 86 is inserted in the aperture 70a since the insertion in
aperture 70e allows a greater upward movement of the front portion of the
snowmobile 12 than would the insertion in aperture 70a.
Figure 8 of the appended drawings illustrates the front
portion of the rail 14 moved upwardly (see arrow 152) by a bump 154
during forward movement of the snowmobile 12 (see arrow 156). When
this is the case, the rail 14 is moved rearwardly (see arrow 158), thereby
causing the rear arm 20 to be pulled (see arrow 160), that, in turn causes
the rear portion of the snowmobile 12 to be moved downward (see arrow
162). Of course, since the adjustment pin 88 abuts the rear end 84 of the
slot 80, the pulling action (arrow 160) will cause the counterclockwise
pivotal movement of the distal end of the rear arm 20 about pivotal axis
78.
CA 02282787 1999-09-17
18
Finally, turning to Figure 9 of the appended drawings,
the operation of the progressive spring assembly 24 will be briefly
described. As can be seen from this figure, the proximate portion 46 of
the rear suspension arm 20 contacts and compresses the contact portion
122 of the spring 112 to absorb energy from the movement of the
snowmobile suspension system 10 towards its retracted position to
eventually stop this movement before the snowmobile suspension system
reaches its fully retracted position.
10 As will be apparent to one skilled in the art, (a) since the
distance 166 between the point of contact of the arm 20 and the spring
112 and the center of the spring 112 decreases as the snowmobile
suspension system 10 moves towards its fully retracted position, and (b)
since the torsion of the spring 112 increases as the above-noted distance
decreases, the strength of the spring 112 increases progressively as the
snowmobile suspension system 10 nears its fully retracted position.
It is to be noted that, in Figure 9, the undersurface 26 of
the side rail 14 does not present a concave profile since the downward
force applied by the snowmobile is sufficient to temporarily deform the
side rails.
Although the present invention has been described
hereinabove by way of preferred embodiments thereof, it can be modified,
without departing from the spirit and nature of the subject invention as
defined in the appended claims.
Français
