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i
CRAWLBR BgLT VEHIChE
BACKGR~UND OF THE INVENTION
Z . Field of the Invention
The present invention relates generally to crawler-belt type
vehialas, and more particularly to an improvement -in "half-
crawler vshiales ° which include front wheels with pneumatic tires
and rear crawlers.
2 . Description of the Related Art
The so-called half-crawler vehicles are known from, for
example, Japanese Patent Laid-open Publication No. 60-143189
disclosing an °off-road vehicle" and Japanese Patent Laid-open
Publication No. 59-164270 disclosing a "four-wheel drive
vehicle".
The off-road vehicle disclosed in th,e above-mentioned 50-
1x3189 publication comprises a pair of left and right balloon-
tired front wheels attached to the front portion of the vehicle's
base frame structure or chassis r a pair of left and right rear
balloon-tired wheels attached to the rear portion of the chassis,
a pair of left and right idler wheels (infiermediate wheels) , and
a ~pair of left and right rubber-made crawler belts each passing
around and operatively connecting the associated rear wheel and
idler wheel.
Tile four-wheel dxiva vehicle disclosed in the above-mentioned
59-164270 publication comprises a pa~.r of. left and right front
wheels attached to the front portion of the chassis, a pair of
lef t and right rear balloon-tired wheels attached to the rear
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portion of the chassis, a pair of left and right idler wheels, and
a pair of left and right rubber-made crawler belts each passing
around and operatively connecting the associated rear ~,rheel and
idler wheel. This four-wheel drive vehicle also includes a pair
of left and right lower tired rollers (function~.ng as equalizers )
each provided between the associated rear wheel and idler wheel.
Each of the lower rollers is attached to the chassis via a support
bracket and abuts against the inner su~:faae of the associated
crawler belt to press the belt against the road surface or
ground.
Generally, with these half-crawler vehicles as disclosed in
the 60-7.43L89 and 59-7.64270 publications, high controllability
is required on soft grounds such as a snow-covered road or
ground, and high running performance is iies~.red even on a fresh
snow-covered untrod ground.
Tn order to meet these requirementa, it is necessary to
appropriately examine and set the ground pressure with which the
front wheel tires and crawler belts contact the ground. When the
ground pressure of the front wheel tires i.s relatively low, these
tires sink into a snow-covered or muddy ground with a small
sinking depth, which would lead to each front wheel tire sinking
into the soft ground over a relat~.vely small area thereof as
viewed sideways (projected area of sunk front-wheel portions).
This, in turn, provides a small steering resistance, so that
ther~ can not be produced a necessary frictional force for
properly steering of the front 'wheel tires . Too small steering
resistance would make it difficult to provide sufficient
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controllability over the vehicle on a soft ground.
When the ground pressure of the front wheel tires is
relatively high, these tires sink into a snow-covered or muddy
ground with a great gink~.ng depth and ar~~ eub~ected to increased
resistance of the snow or mud, which would lower the sharp-
turning capability of the vehicle. This is often-a serious
problem particularly on a fresh-snow-covered untrod ground.
Similarly, when the ground pressure of the crawler belts is
relatively low; these belts sink into a snow-covered or muddy
ground with a small sinking depth, whale taken the ground pressure
of the crawler belts is high, these bolts sink into a snow-
covared or muddy ground with a great sinking depth. Too great
sinking depth of the crawler belts would lead to a great running
resistance and hence Lower running performance of the vehicle.
This is often a serious problem particularly on a fresh-snow-
covered untrod ground.
Further, in the off-road vehicle disclosed in the 60-143189
publication, intermediate wheels functioning as driving wheels
ate disposed between the front wheels and the idler wheels, and
a vehicle engine~is provided between the front wheels and the
intermediate wheels.
Generally, the half-crawler vehicles, running on snow-
covered or muddy soft grounds, require a large driving force of
their crawlers and hence are equipped with a large-sized and
heavyweight engine. Thus, in each of such half-crawler vehicles,
the mounted position of the heavyweight engine would have a great
effect on the wheel load ( part of the vehicle' s weight acting on
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the wheels).
Furthermore, because the vehicle's running performance on the
snow-covered ground depends on the ground pressure of the front
wheels and crawler beltm as noted earl.i~er, the wheel load would
have a significant effect as a factor determining the ground
pressure. Namely, it is absolutely nec~ssary to minimize the
overall weight of the vehicle, in order to allow the vehicle to
appropriately run on a snow-covered, muddy or other sort of soft
ground.
As another example of the half-crawler vehicle, 4 "tire-
driven crawler belt is disclosed in Japanese Utility lKodei
Publication No. HEI-8-8891. On the inner surface of each of the
vehicle's crawler b~lts, there is foamed a pattern of raised and
recessed portions for contact with the treads of the tires. The
pattern of raised and recessed portions forms a multiplicity of
oblique channels as esaapeways for muddy Water. Namely, water
and mud drawn between the tire treads and the inner surface of the
crawler belts are forced out ar discharged along the oblique
channels by the channels narrowing in width as the crawler belts
bend along the curved surface of the tires and also by the pattern
of raised and recessed portions being compressed by the tires.
The disclosed half-crawler vehicle permits an efficient escape
of muddy water and such, in a situation where the crawler belts
do not sink deep into the soft ground.
However, the crawler belts, running on a snow-covered, muddy
ar other sort of soft ground, often sink deep into the soft
ground. In such a case, snow or mud drawn between the tire treads
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and the crawler belts can not be let out efficiently. Reduced
efficiency in letting out the snow or mull would reduce frictional
ra$iatanca between the tires and crawler belts, which in turn
would result in reduced affiaiancy in driving force transmission
from the tires to the crawler belts .
In particular, on a fresh-snow-cov~sred untrod ground, the
tires and crawler belts of th~ half-crawler vehicle sink deep
into the soft ground, so that a great amount of snow may ba drawn
into the inner surface area of the crawler belts . If the snow is
drawn into and compressed between the tires and the crawl~r
belts, it may easily turn into ice, wh~.ch would significantly
reduce the frictional rasi~stanae between the tires and the
crawler belts. Further, the tires and crawler belts, sunk deep
into the fresh-snow-covered untrod ground, would present
increased running resistance, so that the vehicle requires a
greater driving force. The reduced frictional resistance between
the tires and the crawler belts would have a significant adverse
effect on the running performance of the half-crawler vehicle.
Furthermore, in the above-mentioned crawler belt vehicle
disclosed in Japanese Patent Laid-open Publication No. 59-
164270, each of the ~.ower rollers presses the associated crawler
belt in a point-to-point contact, and hence the ground contact
area of the crawler belt is quite sma7:l. In order to increase the
ground contact area of each of the crawler belts to thereby
attain an inereaaed ground adhesion force ("grip"), it is
necessary to provide a relatively' large number of the lower
rollers in the longitudinal direction of the cra~rler belt, which
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would however increase the structural complexity of the vehicle .
As one possible apprasoh to increase the ground adhesion
force with a relatively simple construction, there has been
proposed a crawler as shown in Fig. 25. Tn this proposed crawler
100, a rubber-made crawler belt 103 passes around and operatively
connects two vehicle wheels I01 and 102, and the crawler belt 103
is pressed against a ground via a slider 104 (equivalent to the
equalizer) of predetermined length normally urged downward by a
spring 105. 8y the Crawler belt 103 being pressed against the
ground via the slider 104 of predetermined length, the ground
contact .area and adhesion force can be increased to a
considerable degree.
However, the proposed crawler 100 presents the problem that
frictional resistance between the crawler belt 103 and slider i04
undesirably increases because they are constantly in sliding
contact with each other. Increase in the frictional resistance
between the crawler belt 103 and slider 104 leads to increased
resistance to the movement of the crawler belt 103, Which would
shorten the life of the crawler belt 103 due to the resulting
frictional heat. The frictional resistance between the crawler
belt 103 and slider 104 can be lowered by only reducing the urging
or pressing force of the spring 104, but such reduced pressing
force of the spring 104 can not achieve a sufficient ground
contact force of the crawler belt 103.
An improves crawler belt addressing 'the forego~,ng problems
is disclosed i.n, for example, Japanese Utility Model Publication
No. 52-28258. Thi~3 improved crawler belt has a plurality of side
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~r".".. ;
guide protrusions formed thereon along the opposite longitudinal
edge portions and spaced apart from each other in the
longitudinal direction of the belt. U-shaped reinforoing metal
pieces are embedded in the Individual s~lde guide grotrusions as
well as in flat belt portions between the protrusions. The side
guide protrusions function to prevent the tires from being
aocidentally detached from the crawler belt, and the reinforcing
metal pieces function to increase the rigidity of the crawler
belt against its lateral bending.
When the side gu~.de protrusions area subjected to a force,
applied from the tires, pressing the crawler belt in the
laterally outward direction, a bending moment oocura at the base
of the guide protrusions: Bending rigidity of the reinforc~,ng
metal pieces has a direst effect on that of the side guide
protrusions. Therefore. in order to effectively avoid accidental
detachment of the tires from the crawler belt, it is necessary to
enhance the bending rigidity of the reinforcing metal pieces.
The bending rigidity may be enhanced by increasing the thickness
of the metal pieces, which would however result in an increased
2Q thickness (base gang~) of the crawler belt. The increased
thickness would make the orawler belt difficult to bend, thus
increasing the running res~,stanae to the crawler vehicle.
Further, in the half crawler vehicle disclosed in Japanese
Patent paid-open Publication No, b9~16~270, the chassis and
wheels are connected with each other via a suspension including
springs or dampers . When the half crawler vehicle is travelling
along a slope, the chassis inclines laterally so that a portion
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of the body above the suspension is dlsplacect toward the bottom
of the slaps. As a consequence, the vehicle would lose the weight
balance and can not be operated appropriately.
In addition, the crawler baits of the half-crawler vehicles
generally suffer fro~a considerable resistance to a sideslip, and
this sideslip resistance would act as a braking factor and xeduae
the vehicle's small-turning capability.
Further, according to the disclosure of the above-mentioned
~TEI-8-8891 publication, the half-crawler vehicle includes front
wheels with pneumatic tires mounted on a front portion of the
chassis, rear wheels with pneumatic tires mounted on a arear
portion of the chassis , intermediate wheels with pneumatic tires
disppsed between the front and, rear wheels , and half crawler
belts each passing around and operatively connecting the
associated front and rear wheels. This half-crawler vehicle is
based on a front-and-rear-wheel (four-wheel] drive where the
driving force from the vehicle engine is delivered to both the
front wheels and the =esr wheels .
The disclosed half-crawler vehicle is designed in such a
manner that the crawler belts are attached to the intermediate
and rear wheels only when the vehicle ie to run on an off-road
such as a soft ground; for normal smooth roads. the crawler belts
can be removed or detached from the wheels so as to afford better
running performance and riding comfort. however, the effective
radial length of each of the rear and intermediate wheels,
measured from the wheel's center to the ground, significantly
varies depending on whether the crawler belt ie attached thereto
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or not; namely, the effective radial length varies exactly by the
thickness (base gauge) of the crawler belt a greater thickness
of the crawler belt yields a greater variation in the effective
radial length.
Additionally, because the half-orav~rler vehicle disclosed in
the HEI-8-8891 publication Zs based on the front-and=rear-wheel
drive, it is necessary that the rotating speeds of the front and
rear wheels be adjusted to accurately coincide with sash other
when the crawler belts are removed. In other words, if the
rotating speeds of the front and rear wheels do not agree with
each other, some effective measures must be made between the
driving systems for the front and rear wheels to avoid
inconveniences.:
Also, the front wheel tires may be replaced with larger-
7.5 diameter tires in orders to enhance they running performance of the
vehivle 1n accordance with the running surface conditions. In
such a ease as wall, some effective measures must be made between
the driving systems for the front and rear wheels .
SUI~IARX OF THE INVENTION
The applicants of the present application studied in detail
various characteristics of crawler belt vehicles that are
required for enhanced controllability and running performance on
a snow-covered, muddy or other sort of soft ground and has
finally succeeded xn setting the ground pressure of the front
wheels and crawler belts to respective appropriate values to
accomplish these goals.
A first aspect of the present invention provides
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a crawler belt vehicle which comprisesa a pair of front wheels
maunted on a front portion of a chassis and each provided with a
pneumatic tire: a pair of tear wheels mounted on a rear portion
of the chassis and each provided with a pneumativ tare; a pair of
intermediate wheels mounted on the chassis between the front
wheels and the rear wheels; and a pair of crawler belts each
passing around the rear wheel and the intermediate wheel, wherein
ground pressure of the tires of the front wheels is set within a
range of 0.1 - 0.15 kgf./cmz, and ground pressure of the crawler
IO belts is set within a range of 0.44 - 0.05 kgf/cmz. Hy thus
setting the ground pres~9ure of the front wheel tires and crawler
belts to respective appropriate values, the controllability and
running perforcnanae of the vehicle an a so~~ft ground, particularly
on a fresh-snow-covered ground, can be improved to a significant
degree.
Here, "ground contact areas" determining the ground pressure
of the front wheel tires and crawler belts are measured as
follows by placing the crawler belt vehicle on a flat hard road
surface
(1) ground contact area of the (rant wheel tires = area
over which the front wheel tires are in Contact with the road
surface
(i.e., area of a portion of the tires flattened by
the road surface) ; and
(2) ground contact area of the crawler belts = area over
which the crawler belts are in contact with the road surface
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( area of a portion of the belt in contact with
the road surf ace ) X ( width of the belt )
A second aspect of the present invention provides a crawler
belt vehicle which comprises: a pair of front wheels each
provided with a pneumatic tire; a pair of rear wh~els each
provided with a pneumatic tire: a pair of intermediate wheels
provided between the front wheels and the rear wheels: a pair of
crawler belts each passing around the rear wheel and the
intermediate wheel: and an engine posit~.oned between the
intermediate wheels and the rear wheels.
By thus positioning the engine between the front and rear
ends of the crawler belts, i.e., between the rear and
intermed3ata wheels to thereby place 'the vehicle's center of
I5 gravity nearer to the rear end thereof. This arrangement
achieves appropriat~ loads on the front wheels. As a
consequence, the driving mechanisms located between the engine
and the crawler belts can be reduced in length and hence in
weight, which could substantially reduce a total weight of the
vehicle and enhance the vehicle's running performance on a soft
ground
Further, the engine is provided in such a manner that at least
part of the engine is located within loops of the crawler belts
as viewed sideways . Hy thus positioning part of the heavy engine
below the upper portion of the crawler belts, the center of
gravity of the vehicle is lowered, to 'thereby achieve a stable
running condition of the vehicle.
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i
A third aspect of the present invention provides a crawler
belt vehicle which comprises a a pair of front wheels mounted on
a front portion of a chassis and each provided with a pneumatic
tire; a pair of rear wheels mounted oxi a rear portion of the
chassis and each provided with a pneumatic tire; a pair of
intermediate wheels mounted on the chassis between the front
wheels and the rear wheels; and a pair of crawler belts each
passing around the rear wheel and the intermediate wheel, driving
force being delivered from the tires of the rear wheels to the
crawler belts by frictional resistance between the tires and the
crawler belts, wherein each of the craw,.er belts has a plurality
of discharge openings for letting out foreign substances,
including snow or mud, drawn into an inner surface area of the
crawler belt.
The discharge openings are formed along opposite longitudinal
edge portions of each of the crawler belts . lPreferably, each of
the crawler belts comprises left, central and right belt members
disposed in parallel relation to each other and connected
together at locations spaced agart from each other in a
longitudinal direction of the crawler. belt , so as to form a
plurality of the discharge openings along the opposite
longitudinal edge portions of the crawler belt .
With this arrangement, the snow or mud drawn into an area
between the tires and Crawler belt can be let out efficiently
through the discharge openings, so that the eff~,aiency in
transmitting the driving force from the tires to tha crawler
belts can be-maintained at a sufficient level Without reduoing
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the neoessary frictional resistance between the tires and the
crawler belts.
A fourth aspect of the present invention provides a crawler
belt vehicle which comprises: a pair of Brawler belts each
passing around a pair of wheels mounted on a chassis; and a pair
of equalizers each pressing one of tha craw~.er belts against a
ground, whe~cein each of the equalizers includes a slider of a
predetermined length for pressing the crawler belt against the
ground, and each of the crawler belts has a plurality of low-
Friction members projecting into sliding contact With the slider
and spaced apart from each other in a longitudinal direction of
the orawler belt. The friction members are lower in friction
coefficient than the cra~rler belt, anCl each of the sliders is
positioned at a distance from the crawler belt via the low
friction members.
The slider of each of the equalizers presses the crawler belt
against a ground by means of the low-friction members . Because
the slider is positioned at a distance from the inner surface of
the crawler belt, no frictional resistance ocoura therebetween.
By thus reducing the frictional resistance between the equalizer
and the crawler belt, the crawler can :run with reduced running
resist8nce and frictional heat. fihe reduced frictional heat
prolongs the lif a of the crawler belt . Resides , by the crawler
belt being pressed, via the slider of pre4etermined length,
against the ground with an appropriate forca, an increased grip
or ground adhesion of the crawler belt is guaranteed.
Preferably, a portion of each of 'the low-friction member~g
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slidably contacting the slider has a circular shape so as to
reduce its area of contact with the slider. Further, each of the
low-friction members is made of a material, selected from among
a group of low-friction resin, low-friction rubber, steel and
aluminum, the material being lower :Ln friction resistance
coefficient than the crawler belt, and each of the sliders is
made of low-friction resin lower in friction resistance
coefficient than the crawler belt.
Examples of the low-friction resin include poly vinyl
chloride (PVC) and polytetrafluoroethylene resin (Teflon:
trademark). The low-friction rubber may be made by kneading
together a rubber material similar to that of the crawler belt
and polypropylene resin powder. Alternatively, the low-friction
members may be made of the low-friction rubber lows= in friction
resistance coefficient than the crawler belt, while the slider
may be made of stae?. or aluminum.
A fifth aspect of the present invention provides a crawler
belt passing around a plurality of pneumatic tires and made of a
flexible material, which comprises: a plurality of aide guide
protrusions fo~Cmed on an inner surface of th~ crawler belt along
opposite longitudinal edge portions thereof and spaced apart from
each other in a longitudinal direction of the crawler belt; and
a plurality of reinforcing Cross members embedded iri the crawler
belt in such a manner that at least one of the reinforcing cross
members being disposed between every adjacent pair of the side
guide protrusions.
With the reinforcing cross members each embedded i.n the belt
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between adjacent side guide protrusions, each of the guide
protrusions'is effectively protected by two ad~soent reinforcing
cross members spaced apart from each other in the longitudinal
direction of the belt. Thus, the reinforcing cross members,
funct5.oning to increase the rigidity of the side guide
protrusions, can be reduced in diameter" which makes it possible
to substantially reduce the thickness (base gauge) of the crawler
belt. Ae a oonsequenee, the bending rigidity of the side guide
protrusions can be enhanced without increasing the thiokneas of
the crawler belt. The reduced thickness of the crawler belt
would reduce the bending res~.etanoe of the crawler belt and
thereby reduce the running resistance of the crawler belt
vehicle.
Alternatively, at least one of the reinforcing cross members
I5 map be disposed at a bottom of each of the side guide protrusions
and between every ad~saent pair of the side guide protrusions.
This arrangement even further increases the mechanical strength
of the side guide protrusions, so that the reinforcing cross
members can be further reduced in diameter, which makes it
possible to further minimize the thickness (base gauge) of the
crawler belt.
A sixth aspect of the present invention provides a crawler
belt vehicle Which comprises : a pair of front wheels mounted on
a front portion of a chassis sad each provided with a pneumatic
tire; a pair of rear wheels and a pair of intermediate wheels
mounted on a rear portion of the chassis via a rear suspensiono
a pair of arawlex belts each passing around the rear wheel and the
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intermediate wheel; a vertically pivotable swing arm extending
rearward from the chassis; a pair of rear-wheel driving shafts
connected to a front end portion of the swing arm; a pair of
subbeams connected to the front end portion of the swing arm for
vertical .pivotal movement and extending forward from the front
end portion; a pair of intermediate-wheel axles connected to
front ends of respective ones of the subbeams ; the intermediate
wheels mounted on respective ones of the intermediate-wheel
axles ; and the rear wheels mounted on distal ~nd portions of the
rear-wheel driving shafts as driving wheels. Relative to the
chassis, the intermediate and rear wheels are movable vertically
but immovable laterally.
The rear wheels are mounted in such a manner that they are
movable relative to the chassis in the vertical direction but not
in the lateral direction. Thus, the center of gravity of the
chassis would not move. relative to the rear wheels in the lateral
direction of the vehicle . As a result , the weight balance of the
chassis is maintained and the controllability of the vehicle is
not influenced. Further, although during sharp-turning movement
of the crawler belt vehicle, there may b~e produced force causing
the crawler belts to slip sideways relative to the rear wheels ,
the half-crawler vehicle of the present invention can positively
make use of the side slip of the crawler belts to thereby enhance
its sharp~turning capability to a signjLfioant degree.
Further, becaus~ the two subb~ams are vertically pivotably
connected to the swing arm and the .intermediate wheels are
mounted on the intermediate-wheel axles fixed to the front end
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i
portions of the forward extensions of the eubbeame, the t'vo
intermediate wheels can vertically move independently of each
other. This allows the intermediate wheels to smoothly move up
and down in accordance with ups and downer of a ground. Therefore,
when the crawler belt vehicle is running an a ground with
numerous ups and downs, the chassis is allowed to move up and down
slowly due to the smooth, independent, vertical movement of the
intermediate wheels . As a result , good around followability and
hence good riding conform are afforded 1by the invention:
IO Furthermore, when the crawler belts are driven via the rear
wheels as driving wheels, the reactive force produces soma moment
in the crawler which would lift the intermediate wheels . Thus ,
the crawler can easily get over a pile of snow or mud lying ahead
of the crawler, so that the running performance of the crawler
belt vehivle can be significantly enhanced on the snow-covered
or muddy ground .
Each of the subbeams is retractably expandable in a
travelling direction of the crawler belt vehicle so as to adjust
a tension of the crawler belt.
Tha subbeams are interconnected by means of a pivotable arose
rod near predetermined locations thereof where the intermediate-
wheel axles are mounted. A~ noted earlier, during sharp-turning
movement of the crawler belt vehicle, there may be produced force
pausing the crawler belts to slip sideways relative to the rear
2b wheels, Consequently, some moment is generated in the subbeams
which would bend them laterally. By interconnecting the subbeams
via a cross rod, the bending rigidity of the subbeams van be
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increased. Also, the subbeants are connected at their proximal
ends to the swing arm and interconnected at their distal or front
ends, ,so that the wheel alignment between the rear and
intermediate wheels can be reliably maintained. so as to improve
straight drive stability and steering responsiveness.
A seventh aspect of the present invention provides a' crawler
belt vehicle which comprises : a pair of front wheels mounted on
a front portion of a chassis and each provided with s pneumatic
tire, the front wheels being driven via a vehicle engine; a pair
i0 of rear wheels mounted on a rear portion of the chassis and each
provided with a pneumatic tire, the rear wheels being driven via
the v~hicle enginea a pair of intarmedieite wheels mounted on the
chassis between the front wheels and the rear wheels and eaah
provided with a pn~umatic tire s and a pair of Crawler belts each
passing around thB rear wheel and intermediate wheel, driving
force being transmitted from the tires of the rear wheels to the
crawler belts by frictional rssistanae between the tires of the
rear wheels and intermediate wheels and the crawler belts; and a
speed changing mechanism provided either between the engine and
front-wheel driving shafts or between the engine and rear-wheel
driving shafts. With this arrangement, the crawler belt vehicle
is capable of smooth running irrespective of presence or absence
of the crawler 'belts and a diameter of the front wheels .
In addition, baoause the speed changing mechanism is provided
between the engine and the front-wheel driving shafts or between
the engine and the rear-wheel driving shafts, the rotating speed
of the front wheels and rear wheels can be changed promptly and
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easily. This pe~Cmits smooth running of i:he arawier belt vehicle.
irrespective of presence or absence of the crawler belts and the
diameter of the front wheels .
BRIEF DESCRIBTTON OF THE DRAWINGS
Fox better understanding of the prEjsent invention, various
preferred embodiments will be descaribsd hereinbelow with
reference to the aaaompanying drawings, in which:
Fig. 1 is a sid~ view of a crawler belt vehicle in accordance
with an embodiment of the present invention:
Fig. 2 is a plan view of the crawler belt vehicle of Fig. 1
with its cabin and luggage carrier omitted for clarity of
illustration;
Fig. 3 is an enlarged side view showing details of a. rear
suspension of the crawler belt vehicle of Fig. 1;
Fig. 4 is a graph showing a variation in projected area
measurement of a portion of the vehj:cle' s front wheel tire
sinking into a fr~sh-snow-covered ground;
Fig. 5 is a graph showing a variation in turning performance
of the crawler belt vehicle on a fresh-snow-covered ground;
Fig . 6 Zs a graph showing a variation of traction or pulling
performance of the crawler on a snow-covered ground;
Fig. 7 is a graph showing a variation in running performance
of the crawler belt vehicle;
Fig. 8 is a view showing part of i:he inner surface of the
crawler belt, employed in the present invention, in an unfolded
state;
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Fig. 9 is a sectional view of the crawler belt taken along the
line IX - I% of Fig . 8 ;
Fig. 10 is a sectional view of an egualizers employed in the
present invention;
F.ig. 11 is an expanded perspective view of the equalizer'of
Fig. 10;
Fig. 12 is an enlarged sectional view of the equalizer taken
along the line XII - XII of Fig, 10;
Fig. 13 is a view showing a manner in which foreign
substances, such as snow or mud, drawn into an inner surface area
of the crawler belt are let out through discharge openings:
Fig. 14 is a sectional view showing a modification of the
crawler belt employed in the present invention;
Fig. 15 is a view showing part of the .inner surface of a
modified crawler belt in an unfolded state;
Fig. 16 is a sectional view of the crawler belt taken along
the line XVI - XVI of Fig. 15;
Fig. 17 is a sectional view of the orawler belt taken along
the line XVII - XVIi of Fig. 16;
Fig. i8 is a sectional view showing a modification of the
crawler belt of Fig . 17
Fig. 19 is a view schematically showing driving units for the ,
front and rear wheels of the vehicle;
Figs. 20A to 20D are diagrams explanatory of exemplary
operation of a front-wheel driving unit and a rear-wheel driving
unit of the crawler belt vehicle;
Fig. 21 ie a perspective view showing details of a rear
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,,
___.___ .~ r.~..~..~~ __ _ .~~..a..~.T~.~~.~M"u~.~..___~.__..~._. ..._._~ _...
_
CA 02476482 2004-09-O1
suspension of the vehicle:
Fig. 22 is an exploded perspective view showing how a cross
rod is attached to interconneot left and right subbeams in the
rear suspension;
Fig. 23 is a plan view of the rear suspension;
Fig. 24A is a view showing how the rear suspension of the
present invention operates;
Fig. 24B is a view showing how a conves~t3.onal rear suspension
operates; and
Fig. 25 is a view showing a crawler proposed as an approach
to increase its ground adhesion foroe'with s relatively simple
construction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows a crawl~r b~lt vehicle 1'in accordance With a
preferred embodiment of the present invention, which is a so-
called half-crawler vehicle including left and right front wheels
with pneumatio tires and left and right rear crawlers.
As shown more specifically in Figs. 1 and 2, the crawler belt
vehicle 1, .which is based a four-wheel drive, comprises a ahassi.s
4 having a front cabin 2 and a rear luggage carrier 3 both fixedly
mounted thereon. a pair of left and right driving front wheels 5,
a pair of left and right driving rear wheels 6 , a pair of left and
right idler intermediate wheels 7 each disposed between the front
and rear wheels 5 and 6, a pelt of left and right aqualizerg 8
each disposed between the rear and intermediate wheel 6 and 7,
and a pair of left and right crawler belts 9 each passing around
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,..
CA 02476482 2004-09-O1
and operatively connecting the associated rear and intermediate
wheel 6 and ? .
Each of the front, rear and intermediate wheels 5, 6 and 7 is
fitted with a rubber-made pneumatic balloon tire. The front
wheels 5 are greater in diameter than the rear ancY intermediate
wheels 6 and ?. ~n the rear portion of the chassis 4, a vehicle
angina 11 with a transmission lla is mounted by means of a pair
of brackets 4a.
For the crawler belt vehicle 1 according to the present
embodiment, the ground pressure of the front wheel tires is set
within a range of 0.3 - 0.15 kgf/om2 and the ground pressure of
the crawler belts 9 is set within a range of 0.04 - 0.05 kgf/rm~.
If the ground pressure of the front wheel tires 5 in the
crawler belt vehicle 1 running on a snow-covered, muddy or other
sort of soft ground is lower than 0.1 kgf/cm2, these tires 5 sink
into the soft ground with a too small sinking depth, which would
lead to the front wheel tires sinking into the soft ground over
a relatively small pro jected area. This results an a too small
steering resistance, making it difficult to provide sufficient
controllability of the crawler belt vehicle on the soft ground.
if the ground, prr~ssure of the front wheel tires 5 is higher
than 0.15 kgf/cmi, these tires 5 sink into the soft ground with a
too great sinking depth and'henoe are subjected to increased
resistance of the snow or mud, which would reduce the sharp-
turning capability of the vehicle. This is often a serious
problem particularly on a fresh-snow-covered untrod ground.
Similarly, if the ground pressure of the crawler belts 9 is
_22,_
CA 02476482 2004-09-O1
lower than 0.04 kgf/cm', these belts 9 sink into the soft ground
with a too small sinking depth, while if the ground pressure of
the crawler belts 9 is high, these belts 9 sink into the soft
ground with a too great sinking depth. With a too small sinking
depth of the crawl~r belts 9, a predetermined frictional force
necessary for smooth running of the crawler belt vehicle 1 would
not be provided so that the vehicle 1 can never run in a good
condition. With a too great sinking depth of the crawler belts
9, running resistance from the ground Would become excessive so
that the vehicle can not run in a good condition. These are often
serious problems particularly on a fresh-snow-covexed untrod
ground.
Therefore, it is preferable to set the ground pressure of the
front wheel tires 5 and crawler belts 9 within the abova-
I5 mentioned respective ranges. To this end, the entire engine 11
with the transmission lla is provided between the front and rear
ends of the crawler belts 9 in the present ambodirnant .
Spevifically, it is preferable that the engine 11 ba looated
between the respective canters of the rear and intermediate
wheels 6 and 7. Most preferably, the engine 11 is provided. at
such a location that the ratio of a first distanoe, L1 between the
center C of the engine crank shaft and the center of the rear
wheels 6, to a second distance D2 between the center C of the
engine crank shaft and the center of the intermediate wheels T is
2 : 1. Further, the first distance LI is about 30 % of a third
distance (wheelbase) L3 between the center lines of the' front and
rear wheels 5 and 6.
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CA 02476482 2004-09-O1
As further seen from Fig. 1, the angina 11 with the
transmission 11a is provided in such a manner that part of the
engine 11 is located within the loops of the crawler halts 9 as
viewed sideways. By thus locating part of the heavy engine lI
below the upper portion of the crawler belt 9, the center of
gravity of the vehicle is considerably lowered, to thereby
achieve a stable running oondition o~ the crawler belt vehicle 2.
The luggage carrier 3 is fixed to the rear portion of the
chassis 4. Reference numerml 14 represents a muffler, 15
represents a Beat for a vehicle driver or crew, 16 a steering
wheel, 17 a change-gear lever, 18 an accelerator pedal, 19 a
brake pedal, 21 a side brake, and 22 a front fender.
Fig. 2 iss a plan view of the crawler belt vehicle 1 of Fig. 1
with its cabin 2 omitted for clarity of illustration -the luggage
carrier 3 is shown in imaginary line°.
A front suspension 25, steering unit 30 and front wheel
driving unit 40 are mounted on a front portion of the chassis 4 ,
and a rear suspension b0 and rear wheel driving unit 60 are
mounted on a rear portion of the chassis 4.
The steering un~.t 30 includes a tie rod 31 far delivering a
steering force from the steering wheel 16 (shown in ~.maginary
line) to the front wheels 5, a pair of left and right knuckle arms
33 connected to opposite ends 32 of the tie rod 31, and a pair of
left and right kingpins 34 each connecting the knuckle arm 33 and
front-wheel axle 5a.
The front wheel driving unit 40 includes s front propeller
shaft d1 extending forward from the transmission lla, a
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differential gear 42 for the front wheels oonnected to the front
propeller shaft 41, and a pair of left and right front-wheel
driving shafts 43 each connecting the differential gear 42 and
front-wheel axle 5a. Reference numeral 44 represents a gearbox
provided on an intermediate portion of the front propeller shaft
41, which contains a mechanism for changing the ro~ati-ng speed of
the front wheels 5 and a clutch mechanism for connecting or
disconnecting the engine power to or from the front wheels 5 as
w~Lll be later described.
The rear cusp~nsion 50 includes a swing arm 51 vertically
pivotably mounted on a rear portion of the chassis 4, two
connecting memb~rs 52 lying between rear ends of two rearward
extensions of the swing arm 51, a pair of left and right subbeams
53 vertically pivotably connected to the ends of the connecting
members 52, a pair of intermediate-wheel axles 56 rotatably
oonneoted to front ends of two forward extensions of the subbeams
53, the intermediate wheels 7 each mounted on the associated axle
56, and two pairs of left and right oil dampers 81 and 82. The
oil dampers 81 and 82 will be later described in detail in
relation to Fig. 3. Reference numeral 5 represents a pivotable
cross rod connecting the left and right subbeams 53.
Similarly to the front wheel driving unit 40, the rear wheel
driving unit 60 includes a rear propeller shaft 61 extending
rearward from the transmission lla, a differential gear 63 for
the rear wheels connected via a universal point 62 to the rear
propeller shaft 61, and a pair of left and right rear-wheel
driving shafts 64 connected to the differential gear 63. The
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CA 02476482 2004-09-O1
left anB right rear wheels 6 are connected to the .left and right
rear-wheel driving shafts 64, respectively.
The differential gear 63 for the rear wheels and rear-wheel
driving shafts 64 are provided coaxially with the above-mentioned
connecting member 52 for pivotal movement therewith, to thereby
constitute part of the rear suspension 50. The -rear-wheel
driving shafts 64 are rotatably threaded through i~he connecting
members 52.
fig . 3 is an enlarged side view showing details of the rear
suspension 50. In the rear suspension 50, the subbeams 53 are
suspended from the luggage carrier 3 via the first and second oil
dampers (shock absorbers) 81 and 82 connected to proximal (rear)
and distal (front) end portions of the subbeams 53.
The tension of the crawler belts 9 is adjustable by means of
i5 the subbeams 53. More specifically, each of the subbeams 63
includes a beam member 54 suspended via the oil dampers 81 and 82 ,
a beam extension 55 provided for forward/rearward sliding
movement along the front portion of the beam member 54, and a
turnbuckle 57 couplj.ng the beam member 54 and beam extension 55
in such a manner to permit a sliding adjustment thereof. This
Way, the tension of the crawler belt 9 can be adjusted by the
associated turnbuckle 57. The beam extension 55 carries the
intermediate-wheel axle 5.
Each of the first oil dampers 81 supports the associated
(left or right) rear-wheel driving shaft 64 (sae Fig. 2) in a
suspended fashion via a bracket 83. Each of the second oxl
dampers 82 supports the associated beam member 5~i at the distal
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CA 02476482 2004-09-O1
i
end portion thereof (near the intermediate-wheel axle 56) in a
suspended fashion via a bracket 84.
Now, a description will b~ given about experimental results
on the running performance of the above-described crawler belt
vehicle 1, with reference to Figs. 4 to 7. Dote that the
experiment Was carried out on a flat snow-covered ground and the
running performance of the vehicle 1 was determined on the basis
of the vehicle driver ° g feeling .
Various conditions of the crawler belt vehicle 1 in the
experiment were as follows:
( a ) total weight of the vehicle 1: about 500 kg t '
(b) total weight of the engine l~, with the transmission
liar about 50 kg
(v) diameter of the tire on each front wheel 5: 33 inch
(about 838 mm)
( d) width of the tire on each front wheel 5 : 12 inch ( about
305 mm)
(e) diameter of the tire on each of the rear and
intermediate wheels 6 and 7: 500 mm
(f) distance betweon the canters of the front and rear
wheels 5 and 6 : 2 ; 050 mm
(g) di~3tanae between the centers of the rear and
intermediate wheels 6 and 7: 900 mm
(h) width of each crawler belt 9: 400 mm
Furth~r, the "ground contact areas°' determining the ground
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CA 02476482 2004-09-O1
pressure of the front wheels 5 and crawler belts 9 were measured
as follows by placing the crawler belt vehicle 1 on a flat hard
road surface:
(1) ground contact ar~a of the front wheel tires ~~ area
over whioh the front wheel tires era xn contact with the road
surface
(i.e., area of a portion of the tires compressed flat by
the road surf ace )
(2) ground contact area of the crawler belts ~ area over
which the crawler belts are in oontact with the road surface
(area of a portion of the belt iri contact with the road
surface ) X (width of the belt )
Fig. 4 is a graph showing a variation in projected area
measurement of portions of the front wheels tire sunk into a
fresh-snow-oovered ground, where the horizontal axis (abscissa)
represents ground pressure (kgf/cmi} of the front wheel tires and
the vertioal axis (ordinate} represents a pro~eated axes of the
sunk tire portions (cm$} (sunk front-wheel firs portions).
Density p of the fr~sh snow was 0.10 g/cm3. Sol~.d straight line
A in the graph shows a relationship between the around pressure
of the front wheel tires and the projected area of the sunk tire
portions as viewed from the front o~ the tires, while dotted
straight line B shows a relationship between the ground pressure
of the front wheel tires and the projected area of the sunk tire
portions as viewed from the side of th~ tires.
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M~ ....... __ __..
CA 02476482 2004-09-O1
The crawler belt vehicle 1 ran in the above-mentioned
conditions for evaluation of its running performance. The
experimental results were as fellows:
(a) When the ground pressure of the front wheel tires was
lower than 0.1 kgf/cm2:
The sinking depth of the front wheel tire was too small,
and
the projected area of the sunk tire port~.ons as v~.ewed
frown the front and side was small. This resulted in a reduced
grip (ground adhesion) and too small steering resistance.
( b ) When the ground pressure of the (rant wheel tires was
higher than 0 .15 kgf / cma :
The sinking depth of the front wh~el tire was too great ,
and
the projected area of the sunk tire portions as viewed from
the front and s~.de was great . This resulted in too
great steering resistance, whioh made the steering operation
cliff icult .
(a) When the ground pressure of the front wheel tires
was within a range of 0.1 - 0.35 kgf/cm2:
The sinking depth of the front wheel tire was appropriate,
and the projected area of the sinking tire portions as
viewed from the front and side was just right. This resulted in
appropriate steering resistance, which achieved good steering
performance .
_Zg_
CA 02476482 2004-09-O1
The foregoing experimental results showed that good
controllability and running performance are attainable when the
ground pressure of the front wheel tires is set within a range of
0 .1 - 0 .15 kgf / cm2
Fig. 5 is a graph showing a variation in the sharp-turning
performance of the crawler belt vehicle 1 on a fresh-eriow~oovered
ground, where the horizontal axis represents ground pressure
(kgf/cm2) of the front wheel tires and the vertical axis
represents a ratio of turning diameter to wheelbase. Density
of the fresh snow was 0.10 g/cm3. In many cases, the sharp-
turning performance of half-crawler vehicles are represented by
a ratio of turning diameter to wheelbase. The wheelbase
represents a distance between the canter lines of the front and
rear wheels. Tn general, the ratio of turning diameter to
wheelbase in half-crawler vehicles is approximately ~.3 - 3.5
1. The experimental result showed that the ground pressure of
the front wheel tires satisfying this condition is Within a range
of 0.1 - 0.15 kgf/cma.
Fig. 6 is a graph showing a variation of traction or pulling
performance of the crawler on a snow-covered ground, where the
horizontal axis represents ground pressure ( kgf /cmz ) of the
crawler belts and the vertical axis represents a value of
(generateQ driving force) - (running resistance) (kgf), i.e.,
traction. Line C is a plot obtained when the vehicle ran on fresh
enoar (density p = 0.008 g/cm3), arid line D ~,s a plot obtained When
the vehicle ran on trod (compressed) snow (density p - 0.4
glcm3) .
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CA 02476482 2004-09-O1
The experimental result of Fig. 6 showed that the value of
(generated Driving force) - (running resistance) is the greatest
when the crawler belts, set to a ground pressure within a range
of 0.04 - 0.05 kgf/cmz, ran on the fresh snow. When the ground
pressure was not higher than 0.04 kgf/cma or not lower than 0.05
kgf/cm2, the ground pressure was not suffic~.ent. This indicates
that appropriately setting the ground pressure of the crawler
belts achieves an optimal value of (generated driving force) -
(running resistance). Similar results wexe obtained
irrespective of the shape or size of lug patterns formed on the
respective treads of the crawler belts.
When the crawler belts ran on a continuous snow Cover, the
value of ( generated driving force ) - ( running resistance ) was far
greater than when the crawler belts ran on a fresh snow cover,
5.rrespeotive of the ground pressure. This showed that when the
crawler belts are to run in a very poor running condition, such
as on a untrod ground covered with fresh snow, it ie preferable
to set the ground pressure of the crawler belts within a range of
. 0.04 - 0.05 kgflcm2 because high running performance is required
under such a condition.
Fig. 7 is a graph showing a variation in running performance
of the crawler belt vehicle, where the horizontal axis represents
a wheel load rats W ( % ) of the vehicle w~sight acting on the front
wheels and the vertical axis represents running performanee
measured. Density p of the fresh snow was 0.10 g/cm9. The
experimental result of Fig. 7 Showed that setting the wheel load
rate W to 30 - 40 % achieves the highest running performance on
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CA 02476482 2004-09-O1
the fresh-snow-covered ground and suffioiently high running
performance on a continuous snow cover or muddy ground.
rn order to set the wheel load rate ~V to 30 - 40 ~, it is
preferable to design the crawler belt vehicle 1 as follows
( a) first distance L1 / third distance L3 = 0.3;
(b) ratio of first distance L1 to second distanoe L2 = 2 r
I; arid
(c) weight ratio of intermediate wheel 7 to rear wheel 6 -
4 : 6
Note that the crawler belts 9 of the present invention may be
made of a flexible material or rigid material. Further, the
engine 11 may be provided in such a manner that part or whole of
I5 the engine il is located within the loops of the crawler belts as
viewed sideways.
According to the present embodiment. as described above, the
ground pressure of the front wheel tire~a is set within a range of
0.1 - 0.15 kgf/cm~, and the ground pressure of the orawler belts
is set within a range of 0.04 - 0.05 kgf/om2. By thus setting the
ground pressure of the front wheel tires and crawler belts to
respeotive appropriate values, the controllability and running
performance of the vehicle on a snow-oovered or other sort of
soft ground can be improved to a significant degree.
In addition, the present invention is characterized by
positioning the engine between the front and rear ends of the
crawler belts, i.e. , between the rear amd intermediate wheehs to
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CA 02476482 2004-09-O1
thereby pleas the vehiole' s center of gravity nearer to the rear
end of the vehicle. This arrangement achieves an appropriate
wheel load. As a consequence, the driving mechanisms located
between the engine a.nd the orawler belts van be considerably
reduced in Length and hence in weight, w1:13ch aould substantially
reduce the total weight of the vehicle and also enhance the
vehicle's running performanoe on a soft ground.
Fig. 8 is a view showing part of the inner surface of the
crawler belt, employed in the present invention, in an unfolded
state. The top-bottom direction in this figure corresponds to
the long~.tudinal direction of the crawler belt . The crawler belt
9 is made of a flexible material such as rubber. A multiplicity
of side guide protrusions 9f are formed on the inner surface of
the belt 9 along the opposite longitudinal edges, whioh function
to guide the ~shouldar portions of the associated tires.
The crawler belt 9 comprises a belt body which inoludes left,
central and right belt members 9a, 9b and 9c extending in
parallel in the longitudinal direction of the belt 9~ and spaced
apart from each other With a pr, edetermined gap S . The left and
ventral belt members 9a and 9b are interconnected by means of a
plurality of couplers 9d, and similarly the central and right
belt members 9b and 9a are interconnected by means of a plurality
of couplers 9e. The side guide protrusions 9f are formed on each
of the left and right belts 9a and 9c in alignment with each in
the longitudinal direction of the crawl~ar belt 9 at predetermined
uniform intervals . Similarly, the left and right connectors 9d
and 9a era provided in alignment with each other in the
-33-
_..
CA 02476482 2004-09-O1
longitudinal direction of the crav~ler 'belt 9 at predetermined
uniform intervals .
A plurality of discharge openings 9g are formed in the
crawler belt 9 at predetermined uniform intervals or pitohes by
the left and right gaps S being divided by the connectors 9d and
9e. These discharge openings 9g extend through the thickness of
the crawler belt 9 and function to discharge snow, mud or other
foreign substances, drawn Into the inner surface area of the belt
9 , to outside the belt 9 .
Fig. 9 is a sectional view of the orawler belt 9 taken along
the line IX -'IX of Fig. 8. The crawler belt 9 includes a
plurality of reinforcing core members 9h, made of a metal
material, spaced apart from eaoh other by a predetermined
distance along the length of the belt 9. and each of the core
members 9h is embedded in the belt and extends in the lateral
direction of the belt from the left belt member 9a, through the
Central belt member 9'b, to the right belt member 9c. These
r~ainforcing oore members 9h function to e.dd to the mechanical
strength of the belt 9 against a force acting in the lateral
direction of the belt 9.
Fach of the couplers 9d anQ 9e is oovered, around the entire
outer surface thereof , with a lowrfriction member 9i integrally
formed With the crawler belt 9 . Reference numeral 9 j represents
a pattern of raised and recessed portions formed on the tread 9m
of the orawler belt 9, which is s so-oalled utread pattern" .
Fig. 10 is a sectional view of an equaliser 8 employed in the
present inventian, showing the equalizer 8 attached to the beam
-34-
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~.~~~.~n"~!"~~" .. .~,.~...-.... ...--,.,.__. _ ......,_.... ......
..........~.-.. ......._... _.... ........
..,x-~ea...~.~,.."..a.~-o. <p. , .. . . ez~s
CA 02476482 2004-09-O1
member 56. The equalizer 8 includes a leaf spring 71 having\ite
proximal end bolted to the underside of the beam member 56 and its
distal end pivotably connected with a base 72, a plurality of
resilient members 73 bolted to the una.erside o~ the base 72 , a
support 74 bolted to the lower ends of the resilient members 73,
and a pair of left and right sliders 75 ~~emovably attaohed to the
underside of the support 74.
The leaf spring 71 normally urges the sliders 75 downward so
as to press the crawler belt 9 against the grounQ F. The leaf
spring 71 supports the sliders 75 in such a manner that the
sliders ?5 are vert3.cally movable and also swingable in the
horizontal direction about the distal end of the spring 71. The
leaf spring 71 has a oylindrioal boss 7la on the distal end
located beyond the width of the vehicle, and the boss ?la extends
longitudinally through the crawler belt 9.
The base 72 includes a flat base plate 72d, on which a pair of
front and rear brackets 72c are provided ( see Fig . 11 ) . The boss
71a of the leaf spring 71 extends between the front and rear
brackets 72c. The boss 71a accommodates therein a resilient bush
72a, and an elongate pin 72b is received in the bush 72a and
extends oentrally through the bush 72a: Th~ elongate pin 72b is
supported at its opposite ends by the braokets ?20. In this way,
the base 72 is rotatable via the brackets 72c about the pin 72c.
The support 74 is held in place by means of the side guide
protrusions 9f and supports thereon the base 72.
Fig. 11 is an expanded perspsotive view of the equalizer 8 of
Fig, 10. As shown, the support 74 includes a support base 74a
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~~~-~._~._
CA 02476482 2004-09-O1
generally in the shape of a downwar$ly-opening ohannsi, a pair of
left and right support plates 74b seoured to the opposite sides
of the support base 74a, a pair of arcuate support arms 74c
secured to the opposite sides o~ the base 74a below the support
plates 74b, and a pair of left and right rails 74d secured to the
underside of the arcuate support arms °Y4c.
The downward opening of the channel-shaped support base 74a
is closed by a reinforcing rib 74e, and Each of the left and right
support plates 74b is attached to the base 72 by means of a pair
to of the resilient members 73. The arouate support arms 74c are
formed by cutting an oval-shaped pipe in halves. Each of the
rails ?4d, Which is in the shape of an upwardly-opening box, is
secured at the top of opposed side walls thereof to the underside
of the associated arouata support arm 7~~c. The bottom of each of
T.5 the rails 74d is generally in the shape of an elongate plate
extending in the longitudinal direction (left-right direction in
the figure) of the Crawler belt 9, and the bottom has opposite end
portions bending upward. 8ach of the sliders 75 is an elongate
plate removably screwed to the underside o~ the associated rail
20 74d, which is made of a material having a lower frictional
coefficient than that of the orawler belt 9.
Fig. 12 ie an enlarged sectional view of the equaliser taken
along the line XI I - XII of Fig . 10 , showing the crawler belt
pressed downward by the slider 75 of the equalizer 8. The low-
25 friction members 9i, which are disposed at predetermined
intervals or pitches along the length of the crawler belt 9.
project in part beyond the upper and lower surfaces of the
-36-
CA 02476482 2004-09-O1
crawler belt members ( flat crawler belt port~.ons ) . The slider 75
is elidably carried on these low-frlct~.on members 9i. Thus, the
slider 75 is positioned at a distance from the. flat crawler belt
portions . Whereas ~ach of the law-friction members 9i is shown
S ass having a hollow cylindrical shape; it may be of any other shap~
as long as at least the portion of the ma..mber slidably contacting
the slider 75 is in a circular shape. Because, such a circular
shape reduc~s the area of slading contact with the slider and
hence minimizes the frictional resistance.
The following are exemplary combinations of the materials
used for the low-friction members 9i a;nd slider 75:
( 1 ) The low-friction members 9i is made of low-friction-
resin, law-friction rubber, steel or aluminum Which has a lower
frictional coefficient than the rubber-made crawler belt 9 , while
the slider 75 is made of low-friction resin having a lower
frictional coefficient than the crawler belt 9; and
(2) Tha low-friction members 9i. is made of low-friction
rubber which has a lower frictional coefficient than the rubber-
made crawler belt 9, while the slider 75 is made of steel o~
aluminum.
Examples of the low-friction resin ,include poly vinyl
chloride (PVC) and polytetrafluoroethylene resin (Teflon:
trademark). The low-friction rubber may be made by kneading
together a rubber material similar to that of the crawler belt 9
and polypropylene resin powder. Any other combination of
materials of the low-firiction members 91 and slider 75 than the
_37-
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...._.. ~~_.~. .4~_..~ _._~ ._.._~ _._.. ~_.___ .._A___~__b.~..~
CA 02476482 2004-09-O1
above-mentioned may ba employed as long as it is useful in
reducing the frictional resistance between the low-friction
members 9i and the slider 75.
The following are results of experiments using different
combinations of materials of the low-friction members 9i and
slider 75:
(Conventional Combination)
The low-friction members 9i were made of rubber, while
the slider 75 was made of hard poly vinyl chloride resin. This
combination presented a frictional ( resistance ) coefficient of
0.18.
( Combination According to an Embodiment of the Invention )
The low-friction members 9i were made of a materiel
produced by kneading together a rubber material similar to that
of the crawler belt 9 and polypropylenes resin powder, while the
slider 75 is made of rigid poly viny,3. chloride resin. This
combination presented a frictional (resistance) coefficient of
0.8.
These results showed that the combination of the present
invention presents very small frictlona,l resistance and are vary
useful far improved performance of the crawler belts in the
crawler belt vehicle 1. Partiaulasly, i~he driving capability of
the crawler belts could be significantly enhanced with the low-
friction members 9i and slider 75 using the aombinatlon of the
invention.
-38-
CA 02476482 2004-09-O1
Now, exemplary operation of the equalizers 6 and crawler
belts 9 will be described with reference to Figs . 12 and 13 . Note
that whereas only one of. the equalizers 8 and crawler belts 9 are
shown and described here, the other equalizer 8 and crawler belt
9 operate in the same manner ar the one equalizer 8 and crawler
belt 9. As shown in Fig. 12, the slider 75 of the equalizer 8
presses the crawl~r belt 9 by means of the low-friction members
91. Baeause the iow-friction members 9i are spaced apart from
each other along the length of the crawler belt 9 and each have
a lower frictional coefficient than the crawlar belt 9, anly
small frictional resistance occurs as the slider 74 slides on the
low-friction members 91.
Further, because the slider 5 is positioned at a distance
from the flat crawler belt portions, oo frictional resistance
occurs therebetween. By thus reducingi:h~ frictional resistance
between the equalizer 8 and crawler belt 9, the crawler can run
with reduced running resistance and fricaional heat. The reduced
frictional heat will prolong the life of the crawler belt 9.
Besides, by the crawler belt 9 being p~:essed, via the slider 75
of predetermined length, against the g~:ound with an appropriate
force, the grip or ground adhesion of the crawler belt 9 never
decreases. Furthermore, because the low-friction members 91 are
each in a hollow cylindrical shape, taae area o~ their contact
with the slider 75 is quite small, and thus the frictional
resistance between low-friction membexvs 91 and slider 75 can be
even further reduced.
Fig. 13 is a view showing a manner in which foreign
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CA 02476482 2004-09-O1
substances, such as snow, drawn into an inner surface area of the
crawler belt area let out through the da.scharge openings 9g. As
shown in Fig. 8, the disaharga openings 9g are each formed
between the side guide protrusions 9f adjoining in the front-rear
direction of the crawler belt 9, so 1=hat the openings 9g are
located along the opposite longitudinal. edges of the central belt
member 9b. Thus, foreign substances, such as snow or mud, drawn
into an inner surface area of the crawler belt 9 from the opposite
sides thereof through between the protrusions 9f as denoted by
inwar8 arrows, can be promptly let out through the discharge
openings 9g as shown by downward arrows before they reach the
central belt member 9b. As a eons~equenCe, foreign substances,
such as snow or mud; are effectively prevented from reaching and
clogging the tread pattern of th~ rear caheel 6 or intermediate
wheel 6. Therefore, the necessary friciaonal engagement between
the wheel tires and crawler belt is guaranteed with no
possibility of slippags therebetween, so that efficient
transmission of the driving force from the tires to the crawler
belt can be maintained.
The thus-arranged Crawler belt vehicle x was tested for its
running performance on a snow-covered ground, and it was visually
confirmed that the discharge openings 9g could effectively
function to let out snow drawn into the inner suxfacs area from
the sides of the crawler belt 9.
The discharge openings 9g can beg formed in a laterally
central portion of the crawler belt 9, in which case, however,
snow drawn into an area between the tread pattern of the tires and
-40-
s m:... ...__._ -~ . _.. . ~~ ,~~~ .~~~ -«,*-~_~*.-~ ~ .~_~. rc ...~~___. . _
__ . r..,.« m .~.~m .~ ._ ---w----_____ _
CA 02476482 2004-09-O1
the belt 9 may be readily compressed. ~.'he compressed snow could
clog the tread pattern or be firmly adhered to or even turn into
ice on the inner surface of the crawler belt 9. As a result, the
Frictional resistance bettyeen the tires and crawler belt 9 would
be lowered to cause unwanted slippage therebetwsen. Th~refore,
it is desired that the discharge openings 9g be formed along
opposite longitudinal edge portions of the crawler belt 9 as in
the illustrated exampl~ of Fig. 13.
Fig. 14 is s sectional view showing a modified embodiment of
the crawler belt 9 employed in the present invention . The lef t -
right direction in the figure corresponds to the longitudinal
direction of the crawler belt 9. This modified crawler belt 9 is
characterized in that a plurality of low-friction members 9k,
each having a columnar shape and exaending in the lateral
direction of the belt 9, are provided in spaced-part parallel
relation to each other in the longitudinal direction of the belt
9 arid that each o~ the low-frietioan members 9 is located
immediately above the associated reinforcing core member 9h an8
projects inward fram the inner surface of the belt 9. This
modified crawler belt 9 is much simpler in construction than the
above-described crawler belt 9 of Fig. 12 having the hollow
cylindrical low-friction members 91 each enclosing the
associated reinforcing core m~mber 9h.
In the above-d~scribed embodiments of the pr~sent invention,
, the crawler belt 9 may be made of a rigid material rather than a
flexible material. The discharge openings 9g may of any desired
chaps and size; for example, they may be in the shap~ of a
-41-
CA 02476482 2004-09-O1
circular aperture as viewed in plan. Further; the low-friction
members 9i and 9k may be of any desired shape, size, pitch and
material as long as they are maintained apart from the crawler
belt 9. Also, the low-friction members 91 and 9k may be rotatable
hollow cylinders.
As has been described, the crawler belt of the present
invention is shat&ctarized by a plurality of the discharge
openings for letting out foreign substances, such as snow or mud,
drawn into an inner surface area of the crawler belt 9. With this
arrangement , the snow or mud drawn into an area between the tires
and crawler belt can be let out e:Efiaiently so that the
efficiency in transmitting the driving force from the tires to
the crawler belt can be maintained at a~ sufficient level.
Fig. 15 is a view showing part of the inner surface of a
modified crawler belt 90 in an unfalQed state. In Fig. 15, the
crawler belt 90 is made of a flexible material, such as rubber,
and has a multiplicity of reinforcing c:rosa members 90a embedded
therein and extending in the lateral d.ireation of the belt 90.
Reference numeral 90b represents a multiplicity of side guide
protrusions formed along opposite longitudinal edges of the
crawler belt 90, which function to prevent the tires from being
accidentally detached from the belt 90. The reinforcing cross
members 90a may each be in the form of a steel rod.
The crawler belt 90 also has a multiplicity of discharge
openings 90c in corresponding relations to the side guide
protrusions 90b, each of which is located adjacent ~ to the inner
aide of the associated side guide protrusion 90b. As in the
-42-
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above-described embodiment, these discharge openings 90c are
through-holes for letting out foreign, substances, such as snow
or mud, drawn into an a.nner surface area of the crawler belt 90.
A rod-shaped connecting member 90d spans the central part of eaoh
of the discharge openings 90c. The left and right side guide
protrus5.ons 90b, discharge openings 90c and connecting members
90d are in alignment with each other in the lateral direction of
the crawler belt 90 and spaced apart from each ether by a
predetermined distance in the longitudinal direction of the
crawler belt 90.
Fig. 16 is a sectional view of the crawler belt 90 taken along
the line XYI ~ XVI of Fig. 15, where the reinforcing cross member
90a extends substantially across the entire width of the orawler
belt 90 to thereby increase the lateral rigidity of the belt 90
and the rigidity of the proximal end portion of the side guide
protrusions 90b against a lateral bending force. That is, each
of the side guide protrusions 90b is protected by a pair of the
reinforcing cross members 90a embedded in spaced apart relation
to each other in the longitudinal direction of the belt 9.
Reference numeral 90e represents a pattern of raised and recessed
portions ( tread pattern ) forme4 on the tread of the crawler belt
90.
Fig. 17 is a sectional view of the crawler belt 90 taken along
the line XV'II - XVII of Fig. 16, shoring how each of the
rainforaing crass members 90a is provided centrally between the
side guide protrusions 90b spaced apart of each other in the
longitudinal direction (left-right direction in the figure) of
-43-
CA 02476482 2004-09-O1
t°"~
the crawler belt 9.
With r~farence to Fig. 1?, the following paragraphs describe
exemplary operation of the crawler belt 90 arranged in the above-
mentioned manner. WTith the re~.nforoing crass members 90a each
embedded in the belt 90 between adjacent side guide protrusions
90b, each of the guide protrusions 90b is effectively protected
by two ad~aaent the reinforcing crass members 90a spaced apart
from each other in the longitudinal direction of the belt 9.
Thus, the reinforcing cross members 90a, function~:ng to increase
the rigidity of the side guide protrusions 90b, can be reduced in
diameter, which makes it possible to substantially reduce the
thickness abase gauge) H of the crawler belt 90. As a
consequence, the bending rigidity of the side gui4e protrusions
90b can be enhanced without increasing the thickness H of the
I5 crawler belt 90.
Fig. 18 is a sectional view similar to Fig. 17 but showing a
modification of the crawler belt 90 illustrated in Figs. 15 to
17. This modified crawler belt 90 is characterized in that the
reinforcing crass members 90a are embedded in the belt 90 not
only between adjacent side guide protrusions 90b but also at the
bottom of each side guide protrusion 90b. According to this
modification, each of the side guide protrusions 90b is
reinforced by cooperation of three reinforcing cross members 90a,
i. e. , ont only by the members 90a located on both sides thereof
but also by the member. 90s located at the bottom thereof . Thus ,
each of the re5.nforcing cross member 90a may be of smaller
diameter than in the embodiment of Flgs . 15 to 17 , and hence the
CA 02476482 2004-09-O1
thickness H of the crawler belt 90 can be even further reduced.
Wlth these reinforcing cross members 90a, the crawler belt 90
of Fig. 18 presents an enhanced rigidity against bending and
twisting fore~s so that local resilient deformation of the belt
90 can be effectively avoided. As a result, a greater effective
ground contact area of the crawler belt 90 is prov5.ded, which
would lead to a reduced ground pressure of the belt 90.
Accordingly, the crawler belt vehicle With the thus-constructed
belt 90 will present enhanced running performance on a soft
ground.
As a further modification, a plurality of the reinforcing
cross members 90a rnay be provided between every ad~aeent side
guide protrusrions 90b. The reinforcing cross members 90a may bs
made of any desired material, such as metal or hard plastic
material, which provides enhanced rigidity of the crawler belt
90.
With the reinforcing cross members 90a embedded in the belt
90 between adjacent side guide protrusions 90b, each of the guide
. protrusions 90b is effectively protected by the reinforcing cross
members 90a.spaced apart from each other in the longitudinal
direction of the belt 90. Thus, the reinforcing cross members
90a, functioning to increase the rigidity of the side guide
protrusions gob, can be rgducad in diameter, which makes it
possible to substantially reduce the thickness (base gauge) H of
the crawler belt 90. As a eonsaquance, the bending rigidity of
the aide guide protrusions 90b can be enhanced without increasing
the thickness H of the crawler bait 90.
~tm .. .. . . ,.. ., ., ., >." .r. ,.,nr....m..wa*x.rmnm.~a<.- BF...
.d~',r'w'..~RS9~f~~7~'~T"!2'.PA7F? .-.;'f'~'~'~'.-F~b.S~.iupkR
Xr&T0.'niP%~!kR~'T2tiM 'N'MM ~'° ~ .vit .:w..,.wv....~",..._.,...-.....-
..e.."....... _.,.., ._.__.-.,...
CA 02476482 2004-09-O1
Fig. 19 it a view schematically show~,ng in detail driving
units 40 and 60 for the front and rear wheels of the crawler belt
vehicle 1 shown in Fig. 2.
The front-wheel driving unit 40 inoludes the front prop~llsr
shaft 41 extending forward from an output section 11b of the
transmission lla, and the front-wheel differential gear 42 is
connected to the front propeller shaft 41. The left and right
front~wheel driving shafts 43 connect between the differential
gear 42 and the respeotlve front-wheel axles 5a (Fig. 2). The
gearbox 44 is provided on an intermediate portion of the front
propeller shaft 42 between the engine 11 and the front-wheel
driving shafts 43. and this gearbox 44 contains the mechanism 45
for changing the rotating speed of the front wheels 5 and the
clutch meohanism 46 for connecting or diseonneoting the engine
power to or from the front wheels 5.
The reax-wheel driving unit 60 includes the rear propeller
Shaft 61 extending rearward from the output section Iib of the
transmission ila, and the rear-wheel differential gear 63 is
connected via the universal joint 52 to the rear propeller shaft
61. The left and right rear-wheel driving shafts 64 are
vonnected to the differential gear 63 to drive th~ rear wheels 6.
Reference numeral 66 represents constant velocity joints mounted
on the front and rear propeller shafts 41 and 61..
The following paragraphs describe exemplary operation of the
front-wheel driving unit 40 and rear-wheel driving unit 60, with
reference to Figs. 20A to 20D.
In Fig. 20A, the front wheels 5 are provided with small-
-46-
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~.,~m~,.m m._.~..__ _. _..._ . _ .....__._
CA 02476482 2004-09-O1
diameter tires, the crawler belts 9 are attached is th~
respective predetermined positions, the clutch mechanism
and 46
is in the "connecting" position. In this case, the speed
changing mechanism 45 is set at speed stage I such that
the
rotating speed of the front wheel's small-diameter tares
coincides with that of the crawler 9, so that the crawler
belts
belt vehicle 1 is allowed to run smoothly
via the front and rear
wheels 5 and G being driven via the
front and rear propeller
shafts 41 and 61, respectively.
In Fig. 208, the front wheels 5 are
provided with large-
diameter tires, the crawler belts 9 are attaohea in the
respective predetermined positions, the clutoh mechanism
and 46
is in the "connecting" position. In this case, the speed
changing mechanism 45 is set at speed stage II such that
the
rotating speed of the front wheel's largedi,ameter tires
coincides with that of the crawler
belts 9, so that the crawler
belt vehicle 1 is allowed to run smoothlyvia the driven front
and
rear wheels 5 and 6.
In Fig. 20C, the front wheels 5 ar e provided With large-
diameter tires, they crawler belts are removed from the
9
predetermined positions, and the clutch mechanism 46 i.s in the
°aonnecting" position. In this case, the speed changing
mechanism 45 is set at speed stage 1<I such that the rotating speed
of the front wheel's large-diameter tires coincides with that of
the crawler belts 9, so that the crawler belt vehicle 1 is allowed
to run smoothly via the driven front and rear wheels 5 and 6.
In Fig. 20D. the front wheels 5 are provided with large-
-47-
CA 02476482 2004-09-O1
diameter tires, the crawler belts 9 sr~ attached in the
respective predetermined positions, and the clutch; mechanism a6
ie in the "disconnecting° position. In this case, the crawler
belt vehiole 1 1s allowed to run only via the rear wheels 6 driven
by the rear propeller shaft 61.
Thus, according to the invention, the crawler belt vehicle 1
is allowed to run smoothly irrespective of the presence or
absence of the crawler belts 9 or the diameter of the front wheel
tires .
~ Fig. 21 is a perspective view showing details of the rear
suspension 50 of the vehiole 1. The rear suspension 5D inaluftes
the U-shaped swing arm 51 vertically pivotally mounted on a rear
portion of the ahassi~s 4, and two vertically movable connecting
members 52 connected between rear ends of two rearward extensions
of the swing arm 51.
The left and right rear-wheel driving shafts 64 are threaded
through the respective connecting members ~ 52 . The left and right
subbeams 53 are vertically pivotally connected to the distal ends
of the respective connecting members 52, and the intermediate-
wheel axles 56 are rotatably connected to the front ends of the
re$pectiae subbeams 53. The intermeQfate Wheels 7 (Fig. 2) are
mounted on the respective axles 56, and the driving rear wheels
6 (Fig. 2) are mounted on the respective rear-wheel driving
shafts fi4.
Further, the swing arm 51 includes a support beam 51a
extending in the lateral direction of the vehicle 1 and pivotably
connected to the chassis 4. To the support beam 51a are connected
-48-
CA 02476482 2004-09-O1
three arms, i.e., left, central and right arms 51b, 51c and 51d
extending rearward from the support beam 51a. Thus , the ss~ing
arm 51 ie in the E shape as viewed in plan. The central arm 51c
is in a tubular shape, and a housing 63a of the rear-wheel
differential gear 63 is coupled with the rear end of the central
arm 51a. The rear propeller shaft 61 connected with the rear-
wheel differential gear 63 is threaded through the central arm
51c. The rear propeller shaft 61 is also connected with the
support beam 51a of the swing arm 51 via the universal, joint 62
so that it is vertically movable together with the swing arm 51.
The connecting members 52 extending away from each other in
the lateral direction of the vehicle 1 are scoured at their inner
ends to the opposite sides of the housl.ng 63a of the rear-wheel
differential gear 63. The housing 63a and connecting members 52
together function as a beam to which are connected the rear ends
of the three arms 51b to 51d. The rear-wh~el driving shafts 64
are rotatably threaded through the respective tubu:Lar connecting
members 52; however, these connecting members 52 are not movable
in the axial direction thereof . That is, although the rear-wheel
driving shafts 64 are rotatably supported by the swing arm 5 via
the conneotiag members 52, the swing arm 51 is fixed against
axial displacement. Acoordlngly, rel.at~.ve to the chassis 4, the
rear wheels 6 are movable vertically but immovable laterally.
The rear-wheel differential gear 63, rear-wheel driving
shafts 64 and connect5.ng members 52 are provided concentrically.
The left arid right subbeams 53 have their proximal ends connected
to the outward ends of the respective connecting members 52, from
-49-
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~".~:~,~~~~,~. . ~"~ ,~ e~.~- ~ ~.~___a-v _... ._._ .. _
CA 02476482 2004-09-O1
which the subbeams 53 extend forward.
Each of the left arid right subbeams 53 is retractably
expandable in the travelling direction of the vehicle 1 in order
to permit adjustment of the tension of the associated crawler
belt 9 (Fig. 1). Each of the left and right subb~ams 53 has the
beam member 54 vertically pivotably coupled with one of the
connecting members 52. Tha beam extensions 85 are connected to
front end portions of the respective beam members 54 for sliding
movement in the front-rear direction along or parallel to the
side surface thereof and support the respective intermediate-
wheel axles 56. The intermediate wheels 7 (Fig. 2) ar~ mounted
on the respective intermediate-wheel axles 56. In this way, the
intermediate wheels 7 are movable only in the vertical direction
relative to the chassis 4.
Each of the beam extensions 55 is connected to the 'beam member
54 via the turnbuckle 57 for adjustable sliding movement relative
to the beam member 54, so that the tension of the associated
crawler belt 9 is adjusted by means of the turnbuckle 57.
Reference numeral 54a represents guides for the beam extensions
55, and reference numeral 54b represents bolts, by each of which
the beam extension 55 is adjustably attached to the beam member
54. The left and right subbeams 53 ar~ interconn~:ated by means
of a pivotable cross rod 58 near the location where the
intermediate-wheel axles 56 are connected thereto. Further,
reference numeral 51e represents reinforcing members adding to
the mechanical strength of the swing arm 51, and reference 59
represents a rear guard for protecting the rear end portion of
-50-
CA 02476482 2004-09-O1
the rear suspension 50.
Fig. 22 is an exploded perspective view showing how the cross
rod 58 1s attached to the left and right aubbeams 53. The cross
rod 58 has a pair of, point ring 58g at the axial ends thereof, and
a rubber bush 85 functioning as a damper is aompressedly inserted
in each of the point rings 58a. The cross rod is-vertically
pivotably connected, at the opposite ends, to brackets 54c of the
beam members 54 by bolts 86 each threaded through the bracket 54c
and rubber bush 85.
Fig. 23 is a p~,an view of the rear suspension 50. ~ As shown,
the rear suspension 5d supports the engine 11 with the
transmission 11a, via the brackets 4a, on the rear portion of the
chassis 4 practically at a laterally central position of the
vehicle 1.
The following paragraph describes exemplary ogeration of the
rear suspension 50 with reference to Figs. 24A and 248, of which
Fig. 24A shows how the r~ar suspension 50 of the present
invention operates while Fig. 24B shows how a conventional rear
suspension operates . Specifically, Fig. 24H shows a half-crawler
vehicle where the chassis d and rear wheels fi are interconnected
via the oil dampers 81. When the chassis 4 tilts leftward as the
half-crawler vehicle runs aJ:ong a slope, the chassis 4 above the
oil dampers 81 is displaced toward the bottoaq of the slope and
hence the center of gravity G of the chassis 4 shifts to the slope
bottom (G ~ Go) . Thus, the weight balance of the Chassis is lost,
Which Would significantly influence the controllability of the
vehicle i.
-51-
CA 02476482 2004-09-O1
In contrast, in the half-crawler vehicle of the present
invention shown in fig. 2~A, the chavsis 4 is connected With the
rear wheels 6 via the swing arm 51 against lateral displacement
relative to the rear wheels 6 , so that the center of gravity G of
the chassis ~ would not move relative to the rear wheels 6 in the
lateral direction of the vehicle. Thus, the weight balance of
the chassis is maintained and the controllability of the vehicle
1 is not influenced.
In the illustrated example of Fig. Z, the rear wheels 6 are
mounted in such a manner that they are movable xelative to the
chassis 4 in the vertical direction but not in the lateral
direotion. Consequently, during sharp turning movement of the
crawler belt vehicle I, there is producad force causing the
crawler belts 9 to slip sideway,e relative to tha rear wheels 6.
IS The half-crawler vehicle of the present invention can positively
make use of the side slip o~ the crawler belts 9 to thereby
enhance its sharp turning capability to a significant degree.
Further, because the two subbeams 53 are vertically pivotally
connected via tha connecting members 52 to the swing arm 51 and
the intermediate wheels 7 (Fig. 2) are mounted on the axles 56
fixed to the front end portions of the forward extensions of the
subbeams 53 as shown in Fig. 21, the two intermediate wheels T can
vertically move independently of each other. This allows the
intermediate wheels 7 to smoothly move up and down in accordance
Z5 with ups and downs of a ground. Therefore, when the crawler belt
vehicle 1 1s running on a ground with numerous ups and downs , the
chassis 4 is allowed to move up and down slowly due to the smooth,
-52-
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...._., ....-~.~.~N~A..~H _., ..__.... .. ..__..
CA 02476482 2004-09-O1
independent, vertical movement of the intermediate wheels 7. As
a result, good ground followability and hence good riding conform
are afforded. In addition, even where the rear wheels 6 are
mounted in such a manner to vertically move together relative to
the chassis 4, it is possible to .constrain sudden vextioal
movements of the chassis 4.
Furthermore, when the crawler belts 9 are driven via the rear
wheels 6 , the reactive force produces some moment in the crawler
which would lift the intermediate wheels . Thus , the crawler can
easily get over a. pile of snow or mud lying ahead of the crawler,
so that the running performance of the crawler belt vehicle 1 can
be significantly enhanced on the snow-covered or muddy ground.
In the above-described embodiment, the speed changing
mechanism 45 and clutch mechanism 46 (Fig. 19) may be provided
between the engine 1.1 and the front-wheel. driving shafts 43 or
between the engine 11 and the rear-wheel driving shafts 64: The
number of the speed changing stages may be chosen depending on an
intended application, and the mounting of the clutch mechanism
46 is also optional.
It is only necessary that the rear and int~rmediate wheels 6
and ? be mounted is such a manner that they are movable relative
to the chassis 4 in the vertical direction but not in the lateral
direction. For example, the rear-wheel driving shafts 64 may be
directly connected to the front end of the swing arm 51 in such
z5 a manner that they are movable only in the vertical direction and
not movable in the lateral direction, and the rear wheels 6 may
be mounted on these shafts 64. Each of the subbeams 53 only need
_53-
CA 02476482 2004-09-O1
be retractably expandable in the,travelling direction of the
vehicle 1, so as to adjust the tension of the crawler belt 9 , and
may be constructed in any other suitable manner wifihout being
limited to the above-described combination of the beam member 54 ,
beam extension 55 and turnbuckle 57.
-54-
