Note: Descriptions are shown in the official language in which they were submitted.
2~7~
SNOWMOBILE TORSION JAR SUSPENSION
TECHNICAL F I E Lo
The invention relates to a torsion bar suspend
soon system for snowmobiles.
BACKGROUND ART
The front suspension of snowmobiles, i.e., the
suspension for the two front skis, characteristically
has been comprised of leaf springs attached from a
steering column to the upper surface of each ski.
Commonly the skis are allowed to pitch about a trays-
lo verse axis according to the terrain encountered, and
the pitch of each ski is commonly dampened by a device
such as a shock absorber.
Attempts have been made to stabilize snowmo-
bites with such suspensions utilizing a torsion bar,
but such attempts have been frustrated by the fact
that the skis are the steering mechanism of a snowmo-
bile and must therefore be allowed to turn freely from
side to side. US. Patent 3,674,103, Kiekhaefer, de-
plats one such snowmobile utilizing a torsion bar to
stabilize a suspension as described above. The bar
engages a slot, formed adjacent the top surface of
each ski by a strap of iron, at the point where the
steering axis intersects the ski, thereby preventing
the bar from being withdrawn from the slot when the
ski is turned.
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This system has serious drawbacks, however, in
that the fit between tune torsion bar and the slot must
necessarily be loose enough to allow the ski to be
turned through substantial angles. The loose fit pro-
motes deformation and misalignment of the parts under
rough terrain conditions, particularly since the parts
are close to the ground and unprotected from debris
which may be encountered on the trail. Also, the slot
area may easily become clogged with ice or snow, in-
lo habiting proper steering.
More recently, alternate torsion bar system shave been developed which avoid the above-mentioned
problems but involve considerable complexity of menu-
lecture, assembly, and/or maintenance.
DISCLOSURE OF INVENTION
The present invention provides a torsion bar
suspension for the two front skis of a snowmobile.
The suspension includes means for independently mount-
in each ski to the snowmobile chassis so that each
ski independently and resiliently recoils vertically
in response to uneven terrain, the mounting means be-
in fixed against rotation but permitting rotation of
the skis to facilitate steering. Torsion bar means is
provided for elastically biasing the mounting means of
each ski vertically in response to vertical movement
of the mounting means of the other ski, and a sliding
insert is carried by the mounting means for engaging
the torsion bar means, permitting limited relative
longitudinal movement of the torsion bar means with
respect to the mounting means.
In a preferred embodiment, the mounting means
includes, for each ski, a mounting column extending
generally vertically from the ski, a pair of trays-
verse parallel pivot bars, each pivotal attached at
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one end to the chassis and at the other end to the
mounting column, the pivot bars allowing generally
vertical movement of the column, and a trailing arm
extending rearwardly from the mounting column and pi-
ovally attached a its rearward end to the chassis,
the trailing arm allowing generally vertical movement
of the column and having a longitudinal channel for
closely receiving the sliding insert.
Preferably the torsion bar means is a contain-
o use rod of circular cross-section having a plurality
of bends so that it includes a central portion extend-
in laterally across the chassis, a lever portion ox-
tending laterally and forwardly from each end of the
central portion, and a sliding insert engaging portion
extending laterally to be received by a lateral hole
in the sliding insert. The suspension system prefer-
ably includes one or more bushings carried by the
chassis for closely engaging the torsion bar, each
bushing having a rounded bar engaging surface to allow
the bushing to so de past the bends in the bar during
assembly. Preferably the radius of the rounded bar
engaging surface is equal to or less than the radius
of the bends in the torsion bar.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a broken-away partial perspective
view of a snowmobile chassis fitted with a torsion bar
suspension of the invention,
Figure is a broken side elevation Al view
of Figure l;
Figure 3 is a cross-sectional view of Figure 2
taken along line 3-3 thereof;
Figure 4 is a perspective view of a sliding
insert;
Figure 5 is a broken-away view of a torsion bar
passing through a bushing of the invention;
Figure 6 is a grog -sectional broken-away view
of Figure 5;
Figure 7 is a partial cross-sectional broken-
away View of a bushing sliding past a bend in a
torsion bar;
Figure 8 is a cross-sectional view of a bushing
of the invention;
- Figure 9 is a cross-sectional view of another
bushing of the invention; and
lo Figure ill is a cross-sectional broken-away vie
of another bushing of the invention.
BEST MODE FOR CARRYING OVA THE INVENTION
_
Referring to Figure 1, a snowmobile chassis
(10) is provided with two front skis (11), each ski
being independently mounted to the chassis (10). The
mounting means allows each ski to independently and
resiliently recoil generally vertically in response to
uneven terrain. Although the mounting means may be of
any of a variety of types, the skis must be rotatable
with respect to the mounting means to allow the snow-
mobile to be steered properly. Figure 1 depicts a
preferred mounting means in which a steering post (12)
is attached to the ski (11) and passes upwardly within
a mounting post l21 ) . The steering post 112) is
rotatable with respect to the column (21) and is at-
lacked above the column (21) to a steering mechanism
by well-known mechanical linkages which are not shown
in Figure 1 for purposes of clarity.
A pair of transverse parallel pivot bars (23)
are attached from the mounting column (21) to the
chassis (10). The pivot bars (23) pivot at each end,
allowing the mounting column (21) to freely move gent
orally vertically. A trailing arm (22) is rigidly
attached to the mounting column (21) and is pivotal
attached at its rearward end to the chassis (10) by a
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pivot bolt ~25). the trailing arm ~22~ therefore also
permits generally vertical movement of the mounting
column (21). A suspension spring is also provided,
the preferred embodiment of Figure 1 depicting a coil
spring (13) attached between the mounting column (21)
and the chassis (10). The spring desirably also is
provided with a dampening means, which may be a shock
absorber (14) or similar device mounted coccal with
the coil spring (13).
lo A suspension SEIKO as has been described is
stabilized by providing a torsion bar (20) to transmit
vertical forces acting upon either ski (11) and its
respective mounting means to the other ski (11) by way
of its mounting means. Such a torsion bar (20) goner-
ally includes a central portion (17) extending later-
ally across the snowmobile chassis (10), a lever port
lion (18) extending generally forwardly, and a
mounting means engaging portion (19) extending later-
ally.
The function of a torsion bar such as (20) is
to elastically transmit vertical forces acting upon
one ski (11) to the other ski (11) to stabilize the
snowmobile against rolling by jell known principles.
According to the described function of the ion-
soon bar (20), it is inherent in its structure that
the engaging portion (19) move along an arc coaxial
with the axis of the central portion (17) of the ion-
soon bar (20). us the engaging portion (19) moves
along this arc, the vertical component of this motion
0 corresponds to the vertical movement of the ski (11)
and the mounting means. The horizontal component of
this movement, however, must be mechanically absorbed
because the ski (11) and its mounting means is not
permitted such horizontal movement.
The invention provides a sliding insert (24)
closely received within a channel in the trailing arm
it ;2;2~7~;~3
- 6 -
~22). The insert is proviaecl with a lateral hole ~27)
for closely receiving the engaging portion (19) of the
torsion bar (20). The engaging portion (19) is per-
milted both rotational and transverse movement with
respect to the insert (24), but the insert (24) and
the enraging portion (19) fit snugly to prevent any
significant longitudinal movement there between. Aver-
lures (26) are provided in the trailing arm (22) to
reveal the hole (27) of the insert (24) when the in-
sort (24) is in the channel of the trailing arm (22),
allowing the engaging portion (19) of the torsion bar
(20) to pass through the insert (24). See Figure 2.
As a ski (11) encounters a bump in the trail,
the ski (11) will deflect upwardly thereby causing the
mounting means to likewise move upwardly. The torsion
bar (20) will twist, its engaging portion (19) moving
along an arc, the vertical component of which core-
spends to the vertical movement of the mounting means,
and the horizontal component of which is taken up by
the sliding insert (24). The upward reflection is
thereby transmitted to the other ski (11) to stabilize
the snowmobile.
It should be noted that, for the mounting means
depicted in Figure 1, the sliding insert must also
allow for lateral movement of the insert ~24) with
respect to the torsion bar (20). Referring to Figure
1, as the mounting column (21~ moves vertically in
response to terrain variations it will also move
slightly laterally as it travels along an arc having a
radius defined by the parallel pivot bars (23).
Similarly, the insert also compensates for the
longitudinal movement of the trailing arm (22) with
respect to the torsion bar (20) due to the fact that
the trailing arm is also moving along an arc having
its axis as the pivot bolt (25).
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It will now be understood that the insert (24)
compensates for and absorb movement of the parts in
three directions: the longitudinal movement of the
torsion bar (20) due to its movement along an art the
longitudinal movement of the trailing arm (22) due to
its movement along an arc, and the lateral movement of
the trailing arm (22) due to its movement along the
arc defined by the pivot bars (23).
The insert (24) thus provides a very simple
o solution to what has heretofore been a relatively come
placated mechanical problem. The insert (24) sub Stan-
tidally eliminates all play between the respective
parts, significantly reducing wear, and reducing or
eliminating the danger of permanent deformation of the
parts under even severe and sudden stresses, as may be
encountered on rough trails.
The mechanical linkage is also economically
manufactured. The insert (24) is preferably molded
from any of a variety of low friction, high density
plastics. Figure 4 depicts a preferred configuration
for the insert (24), although it will be understood
that any of a variety of configurations which effect
lively engage the torsion bar (20) and ride longitude-
natty along the trailing arm ~22) would suffice.
Referring to figures I the invention also
provides a unique bushing (30) for mounting the ion-
soon bar l20) to the chassis (10). As the torsion bar
is preferably a single, continuous, generally Solon-
Dracula rod, it is particularly suited to be mounted to
the chassis (10) by a collar-shaped bushing. In order
to assemble the parts, however, it is necessary to
slide the bushing vast bends in the torsion bar (20).
If the interior bushing surface (31) which engages the
torsion bar (20) is generally cylindrical, it will
pass these bends only with difficulty, if at all. The
invention therefore provides a bushing (30) having a
generally towardly collar (32), the interior surface
(31) of which is curved convexly. If the radius of
the curve is equal to or less than the radius of the
bends in the torsion bar (20), the bushing (30) will
slide past these bends without difficulty, and yet
snugly engage the torsion bar (20) when assembled.
Figures 5-10 show a variety of configurations
for such a bushing (30). In Figure 6 the bushing (30)
is comprised of two pieces, a collar (32) and a no-
lo twining shell (34). Figure 7 depicts a bushing (MU)
molded integrally from any of a variety of durable
plastics. Figures 8 and show alternate curvatures
for the interior engaging surface (31). In figure 8
the surface (31) is generally funnel-shaped rather
than semi-circular; in Figure 9 the curvature is pros-
en only for a portion of the circumference of the
bushing (30).
Figure 10 shows a particularly preferred con-
figuration in which the bushing (30) is partially no-
cussed into the chassis (10) for added strength. The
interior surface (31) is comprised of a plurality of
generally flat surfaces which approximate the required
curvature. Such a configuration is easier to manufac-
lure than a perfectly curved surface.
As depicted in Figures 5, 6, and 10, preferably
the bushing includes a disc-shaped flange (33) for
mounting the bushing to the chassis (10). This may be
accomplished by using any of a variety of well-known
fasteners; preferably, rivets are employed.
It will now be understood that by practicing
the invention a torsion bar suspension for a snowmo-
bile may be cheaply and easily manufactured and as-
symboled. The system requires comparatively few parts,
and the parts provide a simple assembly which company
sates for divergent movement of the parts while elm-
inating unnecessary play to avoid the danger of
I
deformation of the parts under severe and sudden
stresses.
While a preferred embodiment of the present
invention has been described, it should be understood
that various changes, adaptations and modifications
may be made therein without departing from the spirit
of the invention and the scope of the appended claims.
