Note: Descriptions are shown in the official language in which they were submitted.
~'~0/14263 2 0 5 8 41 ~ PCT/SE90/~327
~evi~e for vehicles driven by ~çks~
TECHNICAL FIELD OF THE INVENTION AND PRIOR ART
The present invention relates to a device for vehicles driven
by two substantially parallel endless tracks, said tracks being
arranged at a mutual distance in the transversal direction of
the vehicle, so that a space extending in the longitudinal
direction of the vehicle is formed between the tracks, each
track being associated with wheels rotatably arranged about a
rear axle and arranged to bear against the track from inside
and assure the rear diverting thereof, each rear axle being by
at least one pivot lever extending forwardly pivotally arranged
relative to the chassis of the vehicle about a virtual pivot
axis being substantially parallel to the rear axle.
All types of vehicles of this kind with more than one track are
comprised, the number of the tracks could be higher than two.
However, a twin track snowmobile will hereinafter be discussed
by way of a non-limitative example.
Trac~ vehicles in general and in particular snowmobiles are
intended to be driven on an irregular ground and often on a
very rough ground. For this reason the surface of the tracks
bearing upon the ground is often made adaptable to the ground,
for instance by arranging the wheels guidinq the tracks in
resilient bogie couples. The rear diverting wheels are also
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~90/14263 2 0 ~ 8 ~ 1 ~ PCT/SE90/00327
generally, as in the device defined in the introduction,
pivotally arranged by arms with respect to the chassis, so
that the rear part of the track may be adapted to irregu-
larities of the ground, such as cavities, elevations, brows and
the like.
However, the driving features on transportation of load, either
directly on the vehicle or by towing through a tow hook, by
means of the track vehicles already known of the type mentioned
in the introduction leaves a great deal to be desired. This is
especially the case when the vehicle is driven on an uneven
ground, which is the case almost always during some part of
the drive.
The loading area of the vehicle, if there is any, is located at
the back of the vehicle, which results in the fact that a heavy
load on this loading area will cause the rear part o~ the
vehicle to sink because the rear diverting wheels may pivot
upwardly towards the chassis of the vehicle. This results in
its turn in that the front portions of the tracks tend to
relieve or at least bear at a very low pressure upon the
ground, which leads to difficulties in steering the vehicle,
and these difficulties become even greater if one of several
steering skis are arranged in front of the tracks in order to
steer the vehicle. If the vehicle is too heavily loaded it may
even happen that the steering skis in certain situations take
off from the ground, which may have very serious effects.
When any type of trailed vehicle, such as a sledge, tracking
arrangements or the like is to be trailed by the track vehicle,
this trailed vehicle is attached to a tow hook fixedly arranged
on the chassis of the vehicle. As a consequence thereof, when
driving in a hilly country, sometimes very high pressures are
generated upon the tow hook, which influences the steering
behaviour of the vehicle in a way similar to the one described
above in connection with a heavy rear load. There is an appa-
rent risk for not being able to make way for suddenly appearing
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u~g0~14263 2 ~ ~ 8 ~1 a PCT/SE90/003~7
obstacles, and it may also happen that the vehicle does not
manage to come up from a cavity as a result of the pressure
very concentratedly applied on the rear portions of the tracks.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a device of
the type mentioned in the introduction, but which to a great
extent reduces the drawbac~s described above of the previously
known devices on transportation of comparatively heavy loads on
the vehicle or by trailing.
This object is, according to the invention, obtained by
arranging means in a device of the type defined in the
introduction in said space in the region of said pivot axis for
co-operating with said levers influencing the pressure exerted
by the levers upon the rear axles downwardly towards the
ground.
The pressure upon the rear axles may, when loading a heavy load
at the back of the track vehicle in question, be increased in
advance, so that the heavy load will not weigh down the vehicle
as much as would be the case otherwise. An excellent distribu-
tion of the pressure of the tracks upon the ground over large
track surfaces is thereby obtained, so that the steering
problems described above are avoided.
By increasing the pressure exerted by the levers upon the rear
axles downwardly towards the ground on trailing a trailed
vehicle behind a track vehicle according to the invention,
correspondingly improved steering features and an increased
traction power are obtained, especially in driving in cavities,
when the track vehicle is on its way out of the cavity and the
trailed vehicle is on its way down into the same and tends to
weigh down the rear end of the track vehicle.
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A particularly pre~erred embodiment of the invention is defined
in the appended claim 8 and there are such arrangements
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'~0 ~/14263 2 ~ PCT/SEgo/~327
made, that a tow hook for towing a trailed vehicle is arranged
on the rear end of the rigid arm. owing to this it is possible
to increase the pressure exerted by the levers u~on the rear
axles downwardly towards the ground by application of forces
from the trailed vehicle on the tow hook and thus on the rigid
arm.
Another very advantageous feature of the invention is defined
in the appended claim 9 and involves that the rigid arm may be
locked in different positions with respect to the chassis of
the vehicle so as to pre-adjust said pressure upon the rear
axles. This type of means for pressure transmission upon the
rear axles is very suitable when the vehicle itself is to be
loaded.
Further advantages and advantageous features of the invention
will appear from the following description and the other
dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
With reference to the appended drawings, below follows a
specific description of a preferred embodiment of the device
according to the invention cited as an example.
In the drawings:
Fig l is a side elevation of a twin track snowmobile provided
with a preferred embodiment of the device according to the
invention,
Fig 2 is a perspective view obliquely from behind of the device
according to the invention of Fig l broken away from the
snowmobile,
Fig 3 is a side elevation of the snowmobile according to Fig l
in a position in use with-biasing of.the diverting wheels, and
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"'090/14263 2 n ~ ~ ~ 3 ~ PCT/SE90/~327
Fig 4 is a view of the device according to the invention in the
snowmobile utilized for carrying out towing work.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The device according to the invention will now be explained
with reference made simultaneously to Figs 1-3, which show an
advantageous emhodiment of the invention. The invention is
applied on a twin track snowmobile l, which moves on the ground
by means of two substantially parallel endless tracks 2, which
are driven by driving wheels connected to an output shaft of an
engine at the front diversion of the tracks. These driving
wheels are hidden in the figures by a chassis sheet 3. The
tracks 2 rest upon the ground through bearing pressure from
wheels 4 of resiliently arranged bogie wheel couples. The rear
diverting of the track is carried out by rear diverting wheels
5. Each track 2 has in this case diverting wheels 5 rotatably
arranged on a rear axle 6. Each end of the respective rear axle
6 is secured on one end of rigid pivot levers 7 extending from
the wheels 5 and forwardly. Alternatively, the wheels could of
course also be secured to the rear axle 6 and the latter be
rotatably arranged in bearings in the pivot levers 7. The other
end of the pivot levers are by torsion spring-like elements 8
connected to a rigid axle lO rotatably mounted on the chassis 9
of the vehicle by circular discs 9' (Fig 2). The rigid axle 9
is in this case divided into two axles, one for each track 2.
The rigid axle l0 has a substantially square cross section, and
the spring-like elements 8 consist of elements known from the
trademark ROSTA, said elements consisting of a square cavity in
one end 12 of each pivot lever 7, the internal corners of this
cavity square being filled by rubber elements 13, which allow
pivoting of the pivot levers about the axles lO, but constitute
a resistance to such a pivoting and function as a type of
torsion spring on the storage of potential energy. Where the
rigid axles are arranged on the chassis is shown at 14 in Fig
l, and they may be displaced by means of a screw 15 between and
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WO ~/14263 2 ~ 5 8 ~ 1 ~
secured in different positions in the longitudinal directions
with respect to the chassis 9 of the snowmobile.
Thus, the rigid axle 10 of each trac~ extends substantially in
parallel to the rear axle 6 associated therewith and defines by
means of the damping pivotability of the rigid pivot levers 7
therearound a pivot axis. The ends of the rigid axles turned to
the interior of the snowmobile extend into the space 16 between
the two tracks 2 and into a further torsion spring-like element
(ROSTA-element) 17 in the form of a short beam with a substan-
tially square cross section and inner rubber elements in the
corners. An elongated rigid arm 18 extending bac~wardly in the
space 16 is connected to the element 17. A tow hook 19 is
arranged on the outer end of the rigid arm. A member 20 pro-
vided with bores is arranged on the chassis 9 of the vehicle by
means of a locking pin 21 enabling locking of the arm 18 in
certain fixed positions with respect to the chassis thanks to
the penetration of the locking pin through a bore 22 arranged
in the arm and into the member 20 provided with bores.
When the rigid arm 18 is unloaded the rigid levers 7 will be
able to pivot freely about the pivot axis defined by the rigid
axles lO through the bearings of the circular discs 9' in the
chassis, while the rigid arm 18 follows the rigid levers in
this pivoting movement. The only exception occurs when the two
tracks travel over irregularities extending differently in the
transversal direction of the vehicle and the two rigid axles 10
turn with respect to each other. However, the torsion spring-
like element 17 will cause a certain damping of these relative
turnings.
When the rigid arm 18 is subjected to a load in the direction
of the arrow F (see Fig 2) the spring-like element 17 will try
to turn the rigid axles 10, which in their turn will try to
pivot the rigid pivot ievers 7 also in the direction of the
arrow F. As a consequence thereof it will be possible by
pressing the rigid arm 18 downwardly and loc~ing the same in a
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W~ ~/14263 2 0 5 8 41 .~ PCT/SE90/003~
certain position define~ by the member 20 to apply a pressure
upon the rear axles 6 and raise the rear end of the snowmobile,
as shown in Fig 3. The pivot levers 7 may thanks to the
spring-like elements 8 and 17 on meeting obstacles of course
pivot in the direction opposite the arrow F, and this indepen-
dently of each other, but this pivoting will be damped by the
elements 8 and 17. Analogous to this a loading of heavy load on
the loading area 23 starting in the position according to Fig 3
will cause storage of potential energy in the elements 8 and
17, while the rear end of the snowmobile sinks down to a
horizontal position, so that an even distribution of the
pressure over great parts of the track surfaces may take place
despite of the existence of an important load on the rear
loading area. Thanks to this the latter fact will not glve rise
to any lifting of the front steering ski 24 of the snowmobile
off the ground, and accordingly, an excellent steering capacity
may be maintained at the same time as the propulsion ability
will be maintained on a high level.
It would also be possible to arrange a compression spring means
25 indicated in Fig 2 by dashed lines between the rigid arm 18
and a point on the chassis instead of locking the former to the
member 20.
In the case that it is desired to attach a trailed vehicle to
the snowmobile by the tow hook 19, the rigid arm 18 is allowed
to be movable with respect to the member 20 and in a plane
substantially perpendicular to the rigid axles 10. Thus, in
this case the rigid arm 18 assures that the traction point is
moved into the space under the snowmobile to the spring-like
element 17 and through this and the spring-like elements 18 and
the rigid pivot levers transmitted to the rear axle 6 of the
wheels 5. In the position according to Fig 4 the trailed
veh~cle 26 moving downwardly will then press the rigid arm 18
in the direction of the arrow F downwardly and thereby effect
the rigid levers 7 in the same direction, so that the pressure
is more even distributed over large surfaces of the tracks 2
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and the rear part of the snowmobile is raised, so that the
front steering ski 24 remains in a good steering engagement
with the ground and the snowmobile gets a higher ability to tow
the trailed vehicle out of the cavity. When on the contrary the
trailer tends to lift the rigid arm 18 the rear wheels 5 are
also lifted with respect to the chassis, so that the rear part
of the chassis is lowered and an even pressure remains over the
surfaces of the tracks. If the tow hook in this case would be
secured directly on the chassis, the rear part of the snowmo-
bile had been lifted and the pressure on the steering ski and
the front parts of the snowmobile tracks would have been high,
while the rear portions of the tracks had taken off from the
ground. Thus, by moving the towing point of the snowmobile into
and under the snowmobile improved driving features are ob-
tained, which lead to a more secure and comfortable driving of
a snowmobile trailing a trailer. It would also be possible to
arrange other damping means than the torsion spring-like
elements 8 and 17 or add such means to the latters, such as for
example a compression spring means 25.
The invention is of course not restricted to the preferred
embodiment described above, but several possibilities to modify
it would be apparent to a man with ordinary skill in the art,
without departing from the basic idea of the invention.
The invention is for instance completely applicable to a
vehicle having no loading area on the vehicle itself as well as
a vehicle having such a loading area but not being adapted to
tow any trailed vehicle. Thus, it is not necessary that the
rigid arm has a tow hook.
~he tracXs may be more than two in numbers and it would then be
conceivable to arrange a rigid arm in each space between the
tracks. These rigid arms could if desired be interconnected at
their rear ends by a transversal element.
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' ~90/14263 PCT/SE90/00327
The expression torsion spring-like element comprises all means
allowing a turning of the part in question (rigid axle, pivot
lever, rigid arm), but in doing this store potential energy.
It would also be conceivable to arrange one single rigid
continuous axle, but in such a case the two tracks would not be
able to be adapted to irregularities in the ground extending in
the transversal direction of the vehicle.
More than two wheels could be arranged on each rear axle. One
single roll would also be conceivable instead of the two rear
diverting wheels.
It would also be possible to arrange one single rigid pivot
lever on each rear axle at a location between the wheels.
However, this could generate too important point pressures upon
the rear axle and the rigid axle. More than two pivot levers
for each track would not be impossible either.
Locking means for the rigid arm could be designed in an arbi-
trary way and it could also comprise a resilient locking with
respect to the chassis instead of a rigid one.
It would also be conceivable but hardly suitable to connect the
pivot levers rigidly to the rigid axles and accordingly omit
the elements 8. ~he same is applicable to the element 17, but
at least one of these two types of torsion spring-like elements
should then be maintained.
The circular discs could be torsion spring-like mounted in the
chassis. _
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