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Description  |
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FIELD OF THE INVENTION
This invention relates to vehicle suspensions, and more particularly, to a
new and improved suspension of an endless drive track of a snowmobile that
provides improved vehicle control and comfort of humans using the vehicle
over a wide range of terrain from smooth to rough holed and mounded areas
of snow and ice and a wide range of speeds and when cornering.
BACKGROUND OF THE INVENTION
Prior art U.S. Pat. Nos. 4,518,056 and 3,966,188 whose detailed description
and drawings are specifically incorporated by reference into this
specification.
Tracked vehicles such as snowmobiles have rear suspension systems generally
consisting of front and rear suspension arms pivotally mounted on a shaft
rotatably connected to the frame of the snowmobile and a slide frame
comprising a pair of laterally spaced slide rails or longitudinal skids
interconnected transversely on opposite sides of the machine. The slide
rails are in sliding contact with an endless belt which provides ice and
snow surface contact and friction drive for the snowmobile. In many
current arrangements, there are four suspension arms: a front pair of arms
located on opposite sides of the snowmobile and pivotally connected to the
forward end of the slide rails, and a separate rear pair of arms. Each
pair is connected to the slide rails or to a bracket capable of pivoting
movement. A shackle or sliding block mechanism interconnects the rear
suspension arm and the slide rails to permit relative linear movement.
This configuration allows the front and rear suspension arms to operate
independent of one another which is thought advantageous in the prior art
because of favorable weight transfer characteristics which enhance
traction. This independence, however, has been found to result in rough
and unsteady rides for the rider, particularly when the rear suspension of
the track encounters an elevated mound of ice or snow or the upward side
of a depression. This detracts from the enjoyment and the utility of the
vehicle since there are many areas which, when traversed, will unduly
subject the rider(s) to severe jolts and stress.
The independence between the front and rear suspension arms adversely
affects the snowmobile in several ways. First, track tension is not
adequately maintained when there is extreme deflection of either one of
the front or rear suspension arms. Particularly, when there is an excess
of 7 inches of suspension arm travel measured vertically between the
suspension arm connection to the chassis and the suspension arm connection
to the slide rails.
Second, it requires the associated springs and shock absorbers to be sprung
and dampened stiffly because each must individually support the high loads
when impact occurs at either the front or rear extreme of the slide rails.
That is, because each suspension arm acts independently, it must be
engineered to withstand and control the full impact of the bump and weight
of the snowmobile by itself. This results in a normal ride that is less
comfortable due to stiffness.
Third, when the front suspension arm deflects as it contacts a bump, the
independent rear suspension arm remains in its ride position or fully
extended position. This results in an angle of incidence between the slide
rails and the bump. Unless the impact is then large enough to compress the
rear suspension arm spring and shock absorber assembly, thereby flattening
the angle of incidence, the slide rails will act as a ramp forcing the
rear of the snowmobile upward. That is, with the slide rails angled in an
upward incline due to the independent deflection of the front suspension
arm but not the rear suspension arm, the snowmobile will hop over the
pump, imparting a secondary jolt which increases in intensity with the
speed of the snowmobile.
Some prior art suspensions have been made to reduce the independent
movement between the front and rear suspension arms in an attempt to
diminish the adverse effects described above. However, such attempts have
resulted in the creation of additional problems. One of these additional
problems relates to traction of the snowmobile upon acceleration caused by
the improper transfer of weight by the suspension assembly. When a
snowmobile is rapidly accelerated, a drive sprocket driven by the engine
creates an abrupt tension in the upper surface of the track. This tension
reacts through the rear track support wheels resulting in a forwardly
directed force to the slide rails. Therefore, upon rapid acceleration, the
slide rails are urged forwardly.
SUMMARY OF THE INVENTION AND ADVANTAGES
The present invention comprises a suspension assembly for suspending an
endless track beneath the chassis of a tracked vehicle, e.g., a
snowmobile, and maintaining the track traction at a substantially uniform
tension while the snowmobile accelerates and traverses bumpy terrain. The
assembly comprises an elongated slide rail having an upwardly curved
forward end and a rearward end. A front suspension arm has an upper end
adapted for pivotal connection to the snowmobile chassis and a lower end
pivotally connected to the slide rail adjacent its forward end. A rear
suspension arm has an upper end adapted for pivotal connection to the
snowmobile chassis and a lower end connected to the slide rail adjacent
its rearward end. A biasing means urges the slide rail away from the upper
ends of the front and rear suspension arms. The improvement of the
invention comprises a weight transfer coupler means disposed between the
lower end of the rear suspension arm and the slide rail for urging the
rearward end of the slide rail in an elevated inclined condition relative
to the forward end of the slide rail in response to forwardly acting
forces imposed on the slide rail to transmit an increasing percentage of
the snowmobile weight through the front suspension arm and the forward end
of the slide rail during acceleration.
Good weight transfer is the result of torque applied to the track and then
imparted to the slide rail through the front suspension arm. This allows
the chassis to rotate around the front suspension arm during acceleration.
The subject weight transfer coupler means is so effective that, upon
initial acceleration, this rotation raises the front of the snowmobile
often times lifting the skies slightly off of the ground. The result is a
greatly increased amount of traction on the snowmobile as the weight force
of the snowmobile and rider is concentrated over the very small surface
area of track beneath the forward end of the slide rail. To accomplish
this, the weight transferring coupler means elevates the rearward end of
the slide rail during acceleration while simultaneously urging the forward
end of the slide rail downwardly into contact with the ground support,
thereby concentrating the weight force of the snowmobile and rider over a
very small area of the track.
In addition, the unique geometric configuration of the subject suspension
assembly provides an increased range of travel of the slide rail with an
undue tilting of the slide rail when rough and bumpy surfaces are
encountered. This is accomplished through a .coupling of the front and
rear suspension arms to limit the amount of angular variations in the
slide rail as it traverses uneven terrain. The limited angular movement of
the slide rail allows the rear suspension to traverse snow bumps with
little or no secondary impact to the rider(s). This limited angular
movement of the slide rail also reduces the stretching and loosening of
the track which is encountered in prior art designs whenever a track and
slide rail assembly are displaced significantly. In other words, the
suspension assembly of the subject invention maintains the track within an
optimum tension range during all phases of operation to prevent derailment
or breakage of the track.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the present invention will be readily appreciated as
the same becomes better understood by reference to the following detailed
description when considered in connection with the accompanying drawings
wherein:
FIG. 1 is a side view of a snowmobile equipped with the prior art
suspension assembly traversing a bump;
FIG. 2 is a view as in FIG. 1 showing the prior art suspension assembly
clearing the bump;
FIG. 3 is a side view of a snowmobile assembly equipped with a suspension
assembly according to the subject invention;
FIG. 4 is a perspective view of the suspension assembly of the subject
invention;
FIG. 5 is a side view of the suspension assembly during normal operation;
FIG. 6 is a view as in FIG. 5 showing the suspension assembly traversing a
bump;
FIG. 7 is a view as in FIG. 6 showing the suspension assembly clearing the
bump;
FIG. 8 is a side view of the suspension assembly during acceleration, and
with the suspension assembly shown in the normal travel (zero
acceleration) position in phantom;
FIG. 9 is a cross-sectional view taken along lines 9--9 of FIG. 6;
FIG. 10 is a view as in FIG. 9 showing an alternative embodiment of the
weight transferring coupler means;
FIG. 11 is a simplified side view of the improved shock absorber assembly
of the subject invention; and
FIG. 12 is a simplified partial cross-sectional view of the shock absorber
assembly of FIG. 11.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 and 2 illustrate a prior art snowmobile and suspension assembly
wherein the front and rear suspension arms act independently of one
another. As illustrated, when the front suspension arm contacts a bump, it
raises while the rear suspension arm remains extended, thus creating an
angle of incidence between the slide rails and the bump. The slide rails
act as a ramp forcing the rear of the snowmobile chassis upward as the
track climbs over the bump. This angled approach to the bump imparts a
secondary jolt to the rider which increases in intensity with an increase
in the speed at which the bump is approached. Additionally, this
independence between the front and rear suspension arms causes
uncontrollable slackening or tightening of the track, which ultimately
results in track derailment or breakage.
Turning now in greater detail to FIG. 3, a snowmobile is generally shown at
10 having a body frame or chassis 12 that mounts a seat 14 on the upper
side thereof. A suspension and endless track assembly is generally
indicated at 16.
When seated on the snowmobile seat 14, a driver manually steers the vehicle
10 by a handlebar assembly 18 that is secured to a steering shaft 20 which
extends through a compartment 22 for the internal combustion engine 24 and
belly pan 26 into operable connection with a pair of steerable skis 28
through suitable steering linkage preferably arranged so that the inside
cornering ski 28 turns at a greater angle than the outside ski 28 of the
turn to provide comfortable steering. Also, a forward angling of the ski
support legs causes the steering skis 28 to bank into turns for improved
maneuverability and handling.
The belly pan 26 curves rearwardly to the forward end of the endless track
assembly 16 of the vehicle 10. The full weight of the driver and a major
percentage of the vehicle weight rides directly over the track assembly 16
for improved traction.
The track assembly 16 has a cushioning track suspension system which is of
the slide rail type, as illustrated in FIGS. 4-8, which can be adjusted
for weight distribution and ride. A pair of slide rails 30 mount track
support wheels 32, 34, 36 which contact an inner surface of the track 38
so that the snowmobile 10 can traverse uneven surfaces of the snow and ice
with a smoother ride and firmer control as compared to various alternative
prior art systems.
The engine 24 has a drive chain or other system that transmits engine
torque to a pair of main drive wheels or sprockets 40 which drivingly
engage the inner drive surface of the track 38. Trailing rear track
support wheels 42 are supported on the slide rails 30 by an axle shaft 44.
Front and rear suspension arms 46 and 48, respectively, interconnect the
slide rails 30 with the body frame 12. The front suspension arm 46 has a
lower end pivoted at 50 to an ear 54 or other support structure extending
upward from the respective slide rails 30. The upper end 52 of the front
suspension arm 46 is pivotally supported by the upper pivot 56 connected
to the chassis or frame 12. The rear suspension arm 48 is similar to the
front suspension arm 46 in construction and length. The rear suspension
arm 48 includes a lower end 58 and an upper pivoted end 60 connected to
the snowmobile chassis 12, as shown in FIGS. 4 and 9.
A biasing means is provided for urging the slide rails 30 away from the
upper ends 52, 60 of the front 46 and rear 48 suspension arms. The biasing
means preferably includes helical compression springs 62, 64 however other
spring forms such as torsion springs or composite leaf springs may also be
used. An extension limiter, such as straps 65 shown in FIG. 4, may be used
to prevent over extension of the slide rails 30 by the springs 62, 64. A
dampener means is provided for dampening the displacement and return rate
of the biasing means. The dampener means includes front and rear
suspension struts 66, 68, shown in FIGS. 4-8, each comprising a double
acting hydraulic shock absorber with an outer support tube 70 pivotally
connected at its lower end by a mounting member 75 to the slide rails 30
by a cross shaft 76. Alternatively, one or both of the shock absorbers 66,
68 may be of the gas-filled type. If of the gas-filled type, the rear
shock absorber 68 may include a reservoir 71, as shown in FIG. 4.
The shock absorbers 66, 68 of the struts have a piston assembly 72
operatively mounted therein. Each piston assembly 72 has a piston rod 74
which has a mounting member 73 at their distal upper end that pivotally
connects by the upper ends 52, 60 of the suspension arms 46, 48 to the
body frame 12. Suspension springs 62, 64 seated on the lower shock
absorber mounts 75 extend upward therefrom around the shock absorber
piston rods 74 to an upper seat 78 within the mounting member 73 that is
connected to a shock mount extension 79 from the upper ends 52, 60 of the
suspension arms 46, 48. The upper end 60 of the rear suspension arm 48 is
connected with the rear spring 64 suspension and shock absorber 68 unit.
The springs 62, 64 provide spring suspension for the slide rails 30 as the
shock absorbers 66, 68 reciprocate in their cylinder tubes 70 to
hydraulically (or gas-hydraulically) check the action of the suspension
springs 62, 64.
A weight transferring coupler means, generally indicated at 80 in FIGS.
4-9, is disposed between the lower end 58 of the rear suspension arm 48
and each of the slide rails 30 for urging the rearward end of the slide
rails 30 in an elevated inclined condition relative to the forward end of
the slide rails 30 in response to forwardly acting forces imposed on the
slide rails 30 to transmit an increasing percentage of the snowmobile 10
weight through the front suspension arm 46 and the forward end of the
slide rails 30 during acceleration. Thus, the weight transferring coupler
means 80 results in good weight transfer when accelerating torque is
applied to the track 38 through the slide rails 30. This allows the
snowmobile chassis 12 to rotate around the front suspension arm 46,
initially raising the front of the snowmobile 10 and often times lifting
the skis 28 off the ground.
It is well known that the friction associated with traction is dependent
upon the contact pressure, i.e., the weight forces distributed over the
contacting surface area. Thus, the weight transferring coupler means 80
greatly increases the amount of traction of the snowmobile 10 by lifting
the rearward end of the slide rails 30 up, away from the ground, and
forcing the forward end of the slide rails 30 and track 38 forwardly and
downwardly into biting engagement with the ground, thereby concentrating
the weight force of the snowmobile 10 and rider over a very small surface
area.
The weight transferring coupler means 80 includes a pintle 82 extending
from each side of the lower end 58 of the rear suspension arm 48 such that
one pintle 82 is provided for each of the slide rails 30. A slot 84 is
formed in each of the slide rails 30 with the pintles 82 disposed in the
slots 84. A slide block 86 pivotally surrounds each pintle 82 and is
slideably disposed in each of the slots 84, as shown in FIGS. 5-9.
Alternatively, as shown in FIG. 10, instead of the slide block 86' the
pintles 82' may be held in the slots 84' with an elastomer 88' which
allows resilient pintle 82' displacement only in the direction of the slot
84'.
As well known in the art, the slide rails 30 have a generally linear bottom
track engaging portion 90 which extends rearwardly from their upwardly
curved forward ends. The slots 84 formed in the slide rails 30 preferably
extend at an acute angle relative to the linear bottom track engaging
portion 90 of the slide rails 30. In practice, angles of 45.degree. have
been found to provide satisfactory results, however it will be readily
appreciated by those skilled in the art that other acute angles or
curvilinear configurations are also possible.
The angle of the slot 84 provides two important functions. First, the angle
of the slot 84 is generally aligned with the angle of the rear suspension
arm 48 when a driver is mounted on the snowmobile 10. Thus, because the
slot 84 is generally aligned with the angle of the rear suspension arm 48,
any forces transmitted along the rear suspension arm 48 are eliminated.
This is because, due to the rear suspension arm 48 pivotable upper
connection 60 the rear suspension arm 48 is not capable of transmitting a
moment, or torque, thus allowing only linear force transmission only along
its length. Said another way, the shock absorber 68 and spring 64
combination adjacent the rear suspension arm 48 necessarily transmits all
weight force at that rearward end of the slide rails 30 because the rear
suspension arm 48 is generally aligned with the angle of slot which
provides no back-up, or restraint, to the forces otherwise transferred
down the length of the rear suspension arm 48 because the slide block 86
will not bottom in the slot 86 simply under the static weight of a rider.
Therefore, very little friction (i.e., only that friction caused by the
vector component of the weight force resulting from any misalignment
between the angle of the slot 84 and the rear suspension arm 48) is
imparted between the slide block 86 and the side walls of the slot 84. The
reduction in friction allows the couple mechanism 80 to operate with very
little resistance.
Secondly, the angled orientation of the slot 84 provides a ramping effect,
or camming effect, urging the rearward end of the slide rails 30 upwardly
upon application of a forwardly directed force to the slide rails 30
during acceleration. Or, thought of in the reverse relative sense, the
camming action forces the snowmobile chassis 12 to rotate in nose-up
condition thus shifting weight from the front skies 28 to the rear
suspension assembly 16. This, coupled with the fact that very little
friction is generated by way of the generally aligned angle of the rear
suspension arm 48 and the slots 84 means that during acceleration of the
snowmobile 10 there is very little resistance to this transfer of weight
which results in an increase belt 38 traction. Said another way, the
angled slots 84 allow the front of the chassis 12 to rotate upwardly,
i.e., clockwise as viewed from FIGS. 5-8, about the front suspension arm
46 upon acceleration thus concentrating the weight forces upon the forward
ends of the slide rails 30.
A small debris escape port 92 is formed in the lowermost corner of each
slot 84 for expelling snow, dirt and other debris which may locate in the
slot 84 during operation. Also, preferably, the slide blocks 86 are
fabricated from a synthetic material, such as nylon or other high density,
high lubricity polymer.
There is normally a slight clearance (e.g., 0.25 inch) between the upper
contact face of the slide block 86 and the upper end of the slot 84, as
shown in FIG. 5. When the forward end of the slide rails 30 first
encounter a mound of snow or other bump, the slide rails 30 will move
rearwardly and the front suspension arm 46 will begin to turn at its upper
end pivot 52. When this occurs, as shown in FIG. 6, the inclined walls of
the slide block 86 and the slot 84 will take up the clearance (e.g., 0.25
inch) so that the rear suspension arm 48 then automatically couples with
the front suspension arm 46 so that they move in concert. On this
automatic coupling, a parallelogram linkage is established so that as the
slide rails 30 move, their linear bottom track engaging portions 90 remain
substantially parallel to the ground.
Then, as shown in FIG. 7, as the slide rails 30 begin to clear the mound of
snow, the biasing action of the front spring 62 suspension and shock
absorber 66 unit and its extended lever arm position force the forward end
of the slide rails 30 downwardly to meet the ground, thereby resulting in
the slide blocks 86 being displaced to the bottom lower ends of the slots
84. Once the slide blocks 86 bottom in their slots 84, the front and rear
suspension arms 46, 48 are once again coupled. This results in a smooth
transition over the bump back to flat ground. Once on flat ground again,
the suspension 16 returns to the normal ride position of FIG. 5 with the
slide blocks 86 located adjacent the upper end of the respective slots 84,
with only a slight clearance, e.g., in the order of 0.25 inch, between the
two members.
Accordingly, when the slide rails 30 encounter a bump, a signal is sent
through the sliding coupling 80 to actively connect the front 46 and rear
48 suspension arms so that both arms swing together for maintaining slide
rail 30 orientation throughout the bump. This, among other advantages,
reduces or eliminates the secondary kick normally experienced when bumps
are encountered.
The improved weight transfer phenomena accomplished by the subject
suspension 16 is illustrated in FIG. 8. In FIG. 8, the suspension assembly
16 is illustrated in phantom in the normal travel position, similar to
that shown in FIG. 5. However, upon application of a torque to the drive
sprocket 40, a forwardly acting force is imparted to the slide rails 30
via increased track tension pulling against the rear track support wheels
42. This creates a camming effect with the slot 84 of the. Weight
transferring coupler means 80 riding up (in a relative sense) the slide
block 86 to upwardly displace the rearward ends of the slide rails 30 and,
at the same time, forwardly and downwardly displace the forward end of the
slide rails 30 about the arc of the front suspension arm 46. This action
causes an increasing percentage of the snowmobile 10 weight and rider
weight to be transferred substantially through the front suspension arm 46
and forward ends of the slide rails 30. This, in turn, concentrates this
weight force over a very small surface area of the track 38 to increase
traction.
The use of coupling between the front 46 and rear 48 suspension arms also
allows for softer spring 62, 64 rates and shock absorber 66, 68
calibrations. This configuration thus permits use of a less expensive
suspension system that would normally be used to isolate the rider from
severe bottoming. The weight transferring coupler means 80 of the subject
invention allows a controlled amount of independence between the front 46
and rear 48 arms, i.e., when accelerating and clearing bumps, but stops
the at front 46 and rear 48 suspension arms from acting totally
independent of one another.
When an impact occurs at either end of the slide rails 30, either at their
forward or rearward ends, the weight transferring couple mechanism 80
forces the other non-impacted suspension arm to engage at a predetermined
displacement when the slide block 86 bottoms or tops out against the slot
84 forming a parallelogram (four-bar linkage) lending spring and dampening
force to the other impacted suspension arm. This lending of spring and
dampening force between the two suspension arms 46, 48 ultimately requires
less work from the individual components. In other words, there is a
sharing of work between the spring 62, 64 and shock absorber 66, 68
combinations at the front 46 and rear 48 suspension arms. This makes is
possible to use softer shock and spring calibrations than normal thus
permitting use of less expensive shock and spring assemblies and also
eliminates the sophisticated linkages normally used on performance
snowmobiles thus further reducing cost as well as weight. Such prior art
linkages used to manipulate the shock absorber travel into progressively
faster shock speed during suspension travel is known as "rising rate" in
the industry.
In the present invention, the shock absorbers 66, 68 are attached in simple
fashion without extra linkages, as was common practice in the prior art.
This geometry, as illustrated in FIGS. 4-8, is known in the industry as
"falling rate", referring to the fact that the speed of the shock
absorbers 66, 68 decreases, i.e., decelerates, during compression travel.
With this decrease in speed comes an increase in rider comfort, resulting
from reducing resistance as the suspension 16 travels. Falling rate
geometry has been looked upon somewhat disfavorably in the prior art
because, in a typical prior art suspension having a maximum of 7 inches of
travel or less (between the suspension arms and the slide rails) there is
a tendency for the suspension to bottom more easily. Even though the
bottoming problem is largely avoided with this invention because of the
increased travel (in excess of 7 inches), an improved dampening means is
employed to provide progressively increased spring dampening as the
suspension 16 approaches its maximum travel limits. Thus, the extra travel
of this invention's suspension assembly 16 is further enhanced by the
prevention of bottoming in a manner comfortable to the rider, whereby a
progressive dampener 66, 68 of a unique design is employed.
Turning to FIGS. 11 and 12, a shock absorber assembly having a progressive
dampening effect is achieved by progressively decreasing the flow area
through which the by-pass fluid may route during the stroke of the piston
72. To this end, a helical, tapered passage 94 is formed in the interior
wall of the cylinder 70. This passage 94 runs along the side of the
interior wall so that when the shock absorber 66, 68 is compressed or
extended, the area of the passage 94 decreases, resulting in increased
by-pass flow restriction therethrough. This, in turn, forces an increase
of fluid to travel through the normal valving mechanism 96, thus providing
a progressive dampening effect. Varying shock speeds may determine the
amount of fluid to travel through the valving 96 and passage 94. The
passage 94 area will decrease to zero at a predetermined ending position.
This will force fluids to travel exclusively through the valving control
mechanism 96. Alternatively, the passage 94 may run the entire useable
length of the cylinder body 70. Also alternatively, as shown in FIGS. 11
and 12, there may be a pair of helical passages 94 arranged 180.degree.
out of phrase. Of course, more than two such passages 94 are possible, in
which case it is preferable to locate the passages 94 in equally spaced
circumferential increments, i.e., out of phase with each other, about the
inner wall of the cylinder body 70.
The tapered passage 94 may vary in both cross-sectional area and axial
position, depending on the suspension design and requirements. The helical
design allows for consistent flow of fluid within the shock absorber 66,
68 and results in increased piston 72 and piston ring (not shown) life.
A suspension of falling rate design, i.e., as suspension movement increases
the dampener movement decreases in its relative movement to the suspension
in jounce, will benefit due to progressive flow restriction created by the
helical tapered area passage 94. This allows for increased jounce
dampening control of the suspension system. Alternatively, a suspension of
rising design, i.e., as the suspension movement increases the dampener
increases in its relative movement to the suspension in jounce, will see
loss of dampening control in rebound. In this instance, an inverted
helical tapered passage 94, i.e., one that enlarges with continued axial
displacement, will allow for progressive and increased flow and dampening
control in rebound. Alternatively, the helical passage 94 may have a
constant cross-sectional area over a given axial | | |
