Note: Descriptions are shown in the official language in which they were submitted.
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miS invention relates to improvements in snowmobiles, and in
particular to a new or i~,proved ski suspension for snowmobiles and
similar vehicles.
Conventionally, snc~mobile ski suspensions have included a
bowed leaf spring longitudinally arranged akove the ski, the ends of the
spring being connected to the ski, and the upper bowed part of the
spring having a bracket by which is connected to the ski leg. The bowed
leaf spring is capable of deflection by flattening to accommodate to
irregularities in the terrain over which the vehicle is driven, and it
is also known to incorporate a hydraulic damper angularly arranged
between a forward part of the ski and the ski leg bracket, to dampen
such displacements. Such known ski suspensions have proved not altogether
satisfactory in terms of ride comfort on very rough terrains, a primary
limiting factor in this respect being the relatively small range of
deflection which can be accommodated by the leaf spring configuration.
m e present invention provides a snowmobile having a body with
a rear part supported on a track belt, and a front part supported upon a ;
pair of laterally spaced steerable ski assemblies, steering means on
said body for effecting steering control of said ski assemblies, and
suspension means acting between said body and each said ski assembly;
said suspension means comprising a pair of trailing arms each supported
on a ~ounting in the front part of the snowmobile and extending downwardly
and rearwardly therefrom, said trailing arms being pivotable in their
mountings akout a ccm~on transverse axis, torsion bar means extending
transversely in said front part and having opposite ends coupled to
respective ones of said trailing arms so as to resist relative angular
vement of said trailing arms; steering tube means at the lower end of
each treiling arn: each ss d ski a:sembly conprising sn elongate ski
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runner haying an upwardly curved fxont end a mounting bracket on the
upper side of the runner at an intermediate point in its length, an
upstanding ski leg and means forming a pivotal connection between said
mounting bracket and a lower end of the ski leg on an axis transverse to
the length of the ski runner, said ski leg having an upper portion
engaged by a respective one of said steering tubes to be pi wtable
thereon about a generally upright axis, said steering means being coupled
with said ski legs to effect steering control of said ski assemblies
through joint pivotal movement of said ski legs, said suspension means
further comprising spring means associated with each said trailing arm
and operative to urge the associated ski assembly downwardly, and damper
means operative to dampen angular movements of each said trailing arm.
The foregoing arrangement enables the suspension to acconmcdate
a much larger range of deflection than has hitherto been possible, and
accordingly provides a greater degree of comfort to the vehicle occupant,
particularly when travelling over rough terrain.
The torsion bar means acts to urge either ski to follow a
deflection imposed upon the other, and thus greatly enhances the roll
stab~ility of the vehicle. In one preferred arrangement the torsion bar
is positioned within a tu~e mounted transversely within the forward part
of the sncwmDbile, the ends of the tube forming bearings for the pivotal
mounting of the forward upper end of the trailing arms. In this arrangement
the ends of the torsion bar extend through the bearings and are connected
to radially arranged stabilizer arms the ends of which are in turn
attached to the trailing anms.
In another arrangement each steering tube is connected to the `
snowmobile through a pair of trailing arms to provide a parallelogram
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steering linkage, there being a separate torsion bar stabilizer associated
with each of the pair of trailing arms.
me inventi~n will further be described, by way of example
only, with reference to the accompanying drawings, wherein:
Figure 1 is a front perspective view of a snowmobile incorporating
an improved ski suspension means in accordance with the in~ention;
Figure 2 is a fragmentary side view of the front part of the
sno~mobile;
Figure 3 is a fragmentary perspective view of the improved
suspension system;
Figure 4 is an exploded view illustrating ~arious elements of
the suspension system schematically;
Figure 5 is a view corresponding to Figure 3 showing a modified
suspension system;
Fig~re 6 is a view corresponding to Figure 4 of the mcdified
suspension system; and
Figure 7 is a view generally corresponding to Figure 3 but
showing a modified suspension system.
Referring to Figures 1 to 4, a snowmobile 1 is supported in ;
cRnventional fashion at its forward end upon a laterally spaced pair of
ski assemblies 2, and at its rear end upon a ground engaging track belt
3. An engine ~not shcwn) is drivingly connected to the trac~ belt to -
propel the vehicle which is steered by operator-controlled handle bars
4 connected to the ski assemblies through a steering mechanism 5.
Referring particularly to Fig~res 2, 3 and 4, it will be seen ;~
that each ski assembly comprises a longitudinally extending sk.i runner
6 having an upwardly curved front end 7. A ski coupler in the form of a
mounting bracket 8 is attached to the upper side of the ski runner 6 at
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a point intermediate its ends. m e mounting bracket is attached to the
ski runner by any suitable means and includes a pair of upstanding
longitudinal walls 9 (Figure 4) having aligned apertures 10.
As best seen in Figure 4, a ski leg assembly 11 in the form of
an upstanding circular rod 12 with a splined upper end 13 has a bracket
14 at its lower end having a pair of downwardly projecting laterally
spaced apertured plates 15 on its underside. m e plates 15 fit between
the walls 9 of the mounting bracket 8 Qn the ski assembly, and a bolt 16
or other suitable fastener can be inserted between the aligned holes in
the walls 9 and plates 15 to secure the ski leg assembly 11 to the ski
assembly 2, and form a pivotal COnneCtiQn therebetween on an axis transverse
to the length of the ski.
m e config~rations of the mounting bracket 8 and the ski leg
bracket 14 are selected such as to acccwmodate the desired range of
pivotal movement between the ski assembly 2 and the ski leg assembly 11
about the pivotal axis provided by the bolt 16, and resilient abutment
means such as elastameric blocks 17a and 17b are provided to act as an
abutment between these members in defining the limits of such pivotal
m~v~ent.
m e ski suspensian system also includes a front tube 18 mounted
in spaced longitudinal frame nembers 19 at the front of the snowmobile
and extending in a transverse horizontal direction. As best seen in
Figure 4, the front tube 18 has outboard ends 20 defined by collars 21, ;
these outboard ends projecting laterally beyond the vertical walls 22 of
the frame members 19 into a recessed well 23 formed at each side of the
front part of the snowmobile i~bove the resFective ski assembly. me
front tube 18 is secured non-rotatably to the frame members 19, and each
outboard end has a screw-threaded terminal section 24.
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The suspension also includes on each side of the snowmobile a
trailing swing arm 25 having at its upper forward end a tubular bearing
sleeve 26 adapted to be received over the outboard end 20 of the front
tube to form a pivotal mounting for the arm 25 on the front of the
snowmobile. m e trailing swing arm extends downwardly and rearwardly
from this pivotal mounting and at its rear end has a steering tube 27
which extends at right angles to the sleeve 26. Bushings 28 are received
in opposite ends of the steering tube 27 and form bearing means for the
ski leg rod 12 which can be inserted therein so that its splined upper
end 13 projects above the steering tube 27 as seen in Figures 2 and 3.
Referring to Figure 4, the top sleeve 26 of the trailing swing
arm can be passed onto the outboæd end 20 of the front tube 18 until
it abuts the coll æ 21, and retained in position by a nut 29 and lockwasher
30 engaged on the threaded terminal section 24, suitable shims 31 being
interposed between the lockwasher and the end of the sleeve 26 to provide
the required amount of clearance without undue play.
Extending coaxially within the front tube 18 is a stabilizer
torsion b æ 32 of a length slightly in excess of that of the tube 18 and
having splined ends 33 which project somewhat beyond the ends of the
tube 18. m e b,æ 32 is freely rotatable with respect to the tube 18 and
is supported therein at each end by a be æing sleeve 34 (Figure 4)
received within the screw threaded terminal sections 24 of the tube 18.
Each splined end 33 is engaged in a split eye 35 at one end of a short
stabilizer æm 36, the stabilizer æm being non-rotatably secured to the
splined end 33 of the torsion bar by a screw-threaded fastener arrangement
indicated at 37. m e stabilizer arm 36 extends generally parallel to
the swing arm 25 on the outbcard side thereof and is secured thereto at
its re æwæd end by a screw-threaded fastener 38. The fastener 38
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extends through aligned apertures in the end of the stabilizer arm 36
and a lug 39 (Figure 4~ on the side of the trailing arm 25, the fastener
incorporating resilient washers 40 to attenuate the transmission of
vibrations from the trailing arm 25 to the stabilizer bar 32 and prevent
premature wear of the connection.
From the above described arrangement it will be seen that the
stabilizer torsion bar 32 remains unstressed when the trailing c~rms 25
are pivoted in unison, but will act to resist relative angukar movement
of the trailing arms, such angular movement producing a torsional stress
in the stabilizer bar 32.
Swinging movements of the trailing arms 25 caused by vertical
movements of the ski assemblies 2, are controlled by respective coil
spring-hydraulic damper units 41 arranged in a generally upright orientation.
Each unit 41 is pivotally mounted at its lower end on a pin 42 (s e
Figure 4) projecting laterally inwardly from the lower end of the steering
tube 27, and at its upper end on a pin 43 carried on a bracket 44 on
the snowmobile frame. The upper end of the unit 41 is enclosed within
a resilient boot 45 which forms a seal with the opening in the upper
wall of the frame member 19 through which the unit 41 extends, and thus
prevents snow or the like entering the cab of the snowmobile through
this opening. The pins 42 and 43 are parallel to the top sleeve 26 of
the respective swing arm 25, and that the damper units 41 can piv~t
slightly in a vertical plane to accommodate to the arcuate path of
movement of the pin 41 as the arm 25 swings about its pivotal mounting
20.
The steering means of the snow~obile is best illustrated in
Figures 3 and 4 and comprises a steerIng shaft 46 connected to the
handlebars 4 and rotatably mounted in the snowmobile cab in suitable
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bearing means (not shown). At its lower end the shaft has a radial
arm 47. A crank lever 48 is pivDtally mounted at 49 on the frame of the
snowmobile, and has two arms extending at right angles therefrom. A
link 50 having ball joints 51 at opposite ends forms a connection between
the radial arm 47 and one of the crank lever 48, the latter being arranged
to pivot in a substantially horizontal plane.
On the left hand side of the snowmobile (Figures 2 and 3), the
splined end 13 of the ski leg projecting above the steering tube 27 has
attached thereto a steering arm 52 projecting forwardly substantially at
right angles to the ski leg. A tie rod 53 having ball joints at its
opposite ends forms a pivoted link swivel connection between the second
arm of the lever 48 and the steering arlm 52. On the opposite side of
the snowmobile, the corresponding ski leg has a similar steering arm 52a
attached to its splined end, and a transverse track rod 54 having ball
joints at its opposite ends forms an interconnection between the steering
arms on opposite sides of the snowmobile. On the left hand side of the
snowmDbile, the tie rod 53 and track rod 54 extend through a large
aperture 55 in the vertical wall of the frame 19, this aperture being
closed by a substantially rectangular elastic gasket 56 which forms a
s~l around the rods 53 and 54 while accommodating large displacements
of these rods in the plane of the aperture 55. A similar gasket 57 is
provided in the wall of the frame member 19 on the opposite side of the
machine to provide a seal which will accomm~date displacements of the
track rod 54 at that end.
From the above it will be appreciated that steering movements
of the handlebars 4 are transmitted through the shaft 46 link 50, crank
lever 48 and tie rod 53 to the steering arm 52 of the left hand ski
assembly 2, and thence through the track rod 54 to the steering arm 52a
of the right hand ski assembly.
It will be seen that the suspension configuration is such that
the elements of the steering means are constrained to follow the deflections
of the skis, and the design must be able to accommodate such movements.
Referring to Figure 2, it will be seen that if the ski assembly 2 is
moved vertically upwards with respect to the sncwmobile body 1, then
the trailing arm 25 will be sw~ng counterclockwise with res~ect to its
front mounting causing the associated ends of the tie rod 53 and track
rod 54 to move upwardly in an arc about the pivot mounting 20. However
since the steering arm 52 extends forwardly, i.e. towards the pivot
mounting 20 the actual distance moved by the rod ends is very much less
than the upwards deflection of the ski assembly 2, and in fact by suitable
design of the geometry of the system, a very large range of deflection
of the ski assembly 2 can be accQmmodated. m e effects of deflection of
the ski assemblies upon the geometry of the steering system are minimized
in two ways. Firstly, the crank lever 48 is displaced close to the
right hand side of frame member 19 to miaximize the length of the tie rod
53, and thus minimize lateral movement of this tie rod consequent to the
arcuate path described by the tie rod attached to the steering arm 52
upon deflection of the left hand ski assembly 2. Similarly, the length
of the track rod 54 minimizes lateral movement of the steering arm 52a
caused by deflection of the right hand ski assembly 2. Secondly, the
arrangement of the stabilizer torsion bar 32 helps to minimize adverse
effects upon the steering geometry of the snowmobile caused by differential
deflections of the respective ski asse~blies, by generating a torsiona] ~-
stress which resists such differential deflection. mus, if the left
hand ski assembly 2 is deflected`upwardly, swinging move~ent of the arm
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25 is transmitted through the stabilizer arm 36 to the torsion bar 32
producing a torsional stress therein which in turn acts to induce a
corresponding deflection in the ski assembly on the opposite side of
the vehicle. me arrangement of the torsion bar stabilizer therefore besides
improving the roll stability of the vehicle, also enhances its steering
characteristics.
m e above described arrangement provides a suspension system
which can accommodate a much greater degree of vertical deflection of
the ski assemblies than was possible with prior art structures employing
bowed leaf springs. m e actual deflection is determined by the dimensions
of the various components and the length and characteristics of the
coil spring-hydraulic damper units 41.
me stabilizer torsion bar 32 can have various characteristics
selected to match the envisaged conditions of use. me bar 32 can be
round, hexagonal, square, or many other desired shapes in cross section,
ana within the limits of the inside diameter of the front tube 18, can
be of various cross sectional areas to provide the required degree of
stiffness. Different cross sectional areas can be acccmmcdated merely
by replacing the bearing sleeves 34 with sleeves adapted to accommodate --
the desired cross section of the bar 32.
An alternative arrangement is illustrated in Figures 5 and 6
in which like parts are designated by similar reference numerals as in
Figures 1 to 4. In Figures 5 and 6, the structure of the ski assemblies,
2a ski leg assemblies lla, coil spring-hydraulic damper units 41a and
steering mechanism 5a are substantially identical to the e~bodiment of
Figures 1 to 4. ~owever in place of the trailing swing arm 25, there
is provided a parallelogram linkage mechanism 58 which includes spaced
parallel upper and lower links 59 the lower trailing ends of which are
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pivoted to respective ones of a pair of clevises 60 attached to the
steering tube 27a. The upper end of each link 59 cæries a top sleeve
26a carried on a pivotal beæing formed by the outboard end 20a of one
of a pair of front tubes 18a mounted on a transverse horizontal axis in
the front part of the sncwmobile la. Each front tube 18a houses a
stabilizer torsian bar 32a, the splined ends of which are attached
through stabilizer arms 36a to respective ones of the links 59 in a
manner similar to the mounting of the stabilizer arms 36 in Figures 1 to
4. ;
It will be evident that with the arrangement of Figures 5 and
6 the attitude of the ski leg 11 is not altered during vertical dis-
placement of the ski assembly, but on the contrary always remains parallel
to the plane joining the axis of the tubes 18a. Furthermore, the provision
of tWD stabilizer torsion bars 32a enables the design to incorporate
much greater side-to-side roll stability than is possible with a single
torsion bar.
In the m~dified suspension system as shown in Fig~re 7, the
torsion bar 32b is not provided within the front tube 18 as is the case
in Fig~re 3, but is mDunted separately. The torsion bar 32b is of
generally wide U-shaped configuration having a straight transverse central
section 32c and rearwardly bent limbs or end sectians 32d. The central
section 32c is pivotally supported in a pair of transversely spaced
mounting brackets 65 near the ends thereof. The limbs 32d extend rear-
wardly from the outer ends of the central section of the torsion bar, and
each is pivotally attached to the u~per end of a short connecting link
66 the lower end of which is pivotally connected to the trailing swing
arm 25. The link 66 may be of any suitable construction, for example
it may oomprise a short central pin the ends of which are in screw ;
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threaded engagement with respective clevises, the lower clevis being
pivoted on a pin carried by the trailing swing arm 25, and the upper
clevis being pivoted to a pin carried on the torsion bar limb 32d.
For this purpose, the limb 32d is provided with a series of longitudinally
spaced holes 67, and by suitable selection of the hole which fo~ms a
connection from the link 66 to the torsion bar limb 32d, the character-
istics of the suspension can be altered. It will ke appreciated that
such adjustment varies the angle of the link 66 relative to both the
limb 32d and the trailing arm 25, and accordingly varies the angle of
displacement of the limb 32d per unit angular displacement of the
trailing swing arm. Thus, the roll stiffeners of the suspension can
be selectively varied.
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