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Description  |
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TECHNICAL FIELD
This invention relates to a suspension system for a work vehicle, and, more
particularly, to a suspension system which may be readily changed to
selectively provide optimal characteristics for high speed vehicular
operation or low speed vehicular operation.
BACKGROUND ART
In high speed vehicular operation (especially when significant vehicular
weights are involved) a vehicle suspension system capable of load sharing
between longitudinally separated wheels is necessary to prevent the
subjection of terrain induced impact loads on the vehicle chassis, reduce
the load carrying capability of individual support wheels, and maintain a
stable chassis orientation regardless of the terrain. The following U.S.
patents illustrate typical longitudinal load sharing capability for high
speed vehicles: U.S. Pat. Nos. 3,254,738; 3,740,070; 3,879,052; 4,047,736;
4,230,341; and 4,420,167.
Low speed, work vehicles in contradistinction to high speed vehicles,
additionally require lateral side to side load sharing for maintaining
maximum tractive engagement with the terrain. Such work vehicles often
have an implement attached either to the front or rear end of the chassis
whose purpose is, depending on the application, to exert either an upward
or downward penetrating force on the earth. In such instances maximum
force on the implement can be exerted by vertically pivoting the entire
vehicle's chassis about the frontmost or rearmost (depending on the
mounting location of the implement and the desired direction of force
application) ground engaging member which usually constitutes a wheel.
Such vehicle chassis pivoting can only be accomplished if longitudinal
load sharing is not permitted between ground engaging members adjacent the
chassis end in question and the remaining ground engaging members. None of
the above patents has such implement application force maximizing
capabilities.
Only recently has the inherent tractive advantage of track laying vehicles
been combined with the high speed travel capability of wheel equipped
vehicles to provide a work vehicle supported on and driven by elastomeric
belts. In general, such work vehicle includes on each lateral side of its
frame, wheels arranged in supporting relation to its frame and entrained
within such belt with at least one of such wheels being frictionally
engaged with the belt. With the advent of such work vehicle, both high
speed mobility and low speed draft work may be optimally accomplished with
one vehicle. However, use of a high speed suspension system on a belted
vehicle also necessitates maintaining engagement between the belt and
entrained wheels for all configurations assumable by those wheels in order
to guide the belt and prevent it from being thrown from its entraining
position around same. None of the above described patents has such belt to
wheel engagement assurance provisions.
U.S. Pat. No. 3,254,738 ('738) provides the desired side to side load
sharing and certain aspects of longitudinal load sharing between
wheels/idlers using hydraulic circuits exclusively without any mechanical
connection of the wheels. The '738 patent lacks provisions for maximizing
the vehicle's capability of exerting penetration force on attached
implements by virtue of the vehicle's longitudinal load sharing between
wheels; and provides the side to side load sharing in a very complex
hydraulic manner.
To take full advantage of a belted vehicle's high speed travel capabilities
as well as its tractive advantages in low speed work applications, its
suspension system must be able to provide the dynamic characteristics best
suited for the operational mode selected (be it high speed or low speed)
and do so with a minimum of complexity.
DISCLOSURE OF THE INVENTION
The present invention is directed to overcoming one or more of the above
problems.
There is provided a suspension system which is readily adaptable to a high
speed, vehicular traveling mode and a low speed, vehicular work mode. The
suspension system has two suspension mechanisms which are arranged on
opposite lateral sides of and in supporting relation to a vehicular frame
with each suspension mechanism including a vehicle support apparatus, a
rear idler wheel assembly, a drive wheel assembly elevated above the rear
idler wheel assembly, an elastomeric belt entrained about the vehicle
support apparatus and the wheel assemblies and in frictional engagement
with the drive wheel assembly, a rear resilient strut connected between
the frame and the rear idler assembly, a front resilient strut connected
between the frame and the vehicle support apparatus, and a recoil strut
connected between the frame and support apparatus for maintaining a
predetermined belt tension. Each vehicle support apparatus includes a
front idler wheel assembly rotatably connected to one end of a pivoting
beam, a roller wheel assembly pivotally connected to the opposite end of
the pivoting beam, and a wheel juncture device to which the rocking bar is
pivotally connected.
In one aspect of the present invention corresponding chambers in the front
struts are selectively fluidly connected for low speed operation and,
during high speed operation, are fluidly segregated and respectively
fluidly connected to separate accumulators.
In another aspect of the present invention one of the chambers defined by
the rear strut's components is, during high speed operation, fluidly
interconnected with an accumulator and a chamber defined by the recoil
strut's components and is, during low speed operation, fluidly isolated
from the connected recoil strut's chamber and accumulator.
In yet another aspect of the present invention a chamber of a pry-out strut
connected between the wheel juncture device and one end of the pivoting
beam is, during high speed operation, fluidly connected with both another
chamber of the pry-out strut and an accumulator and, during low speed
operation, is fluidly isolated.
During high speed operation, the suspension system mechanisms operate
independently with each providing longitudinal load sharing between its
wheel and roller assemblies and each ensuring continued belt entrainment
of the wheel and roller assemblies for various degrees of recoil strut
retraction. During low speed operation, however, the suspension system
mechanisms laterally load share, ensure application of maximum force on
attached implements by preventing each idler wheel assembly from sharing
load in the longitudinal direction, and maintaining the ability to permit
recoil of the front idler assembly when the entraining belt's tension
rises above a predetermined level.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a right side elevational view of a vehicle employing a suspension
system constructed in accordance with the present invention and a
fragmentary portion of a front-mounted implement such as a bulldozer
blade;
FIG. 2 is a diagrammatic and enlarged right side elevational view of the
front end portion of the suspension system shown in FIG. 1 with portions
shown broken open or in broken lines to better illustrate details of
construction thereof;
FIG. 3 is a diagrammatic view similar to FIG. 2 with many of the components
deleted in order to show certain laterally inwardly spaced elements
otherwise hidden in FIG. 2;
FIG. 4 is a semi-schematic view of the vehicle's front struts and their
fluid interconnections;
FIG. 5 is a semi-schematic view of one lateral side of the vehicle
suspension illustrating a rear strut and its fluid interconnection with a
recoil strut;
FIG. 6 is a semi-schematic view of a pry-out strut and its fluid
interconnection with an accumulator; and
FIG. 7 is a semi-schematic view of an intermediate strut and its fluid
interconnection with an accumulator.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIG. 1, an elevational view of a vehicle 10 of the endless
track laying type is shown having a chassis 12 which includes a
longitudinally extending main frame 14 and an operator's station 16
disposed at the longitudinal front end of the chassis 12. The chassis 12
is resiliently supported by a suspension system 18 which includes left
hand and right hand suspension mechanisms 20 and 22, respectively. Since
the left hand suspension mechanism 20 (not shown from the vantage point of
FIG. 1) is a mirror image of the right hand suspension mechanism 22, only
the right hand suspension mechanism 22 will be discussed hereinafter.
The suspension mechanism 22 includes a drive wheel assembly 24 rotatably
mounted about a fixed axis 26 on the main frame 14 at a position elevated
above the terrain, a vehicle support apparatus 28, a rearward guide roller
assembly 30 disposed longitudinally rearward from the support apparatus
28, a rear idler wheel assembly 32 longitudinally disposed between the
drive wheel assembly 24 and the rear guide roller assembly 30, and means
33 for resiliently connecting the rear idler wheel assembly 32, the rear
guide roller assembly 30, and vehicle support apparatus 28 to the vehicle
main frame 14. It is to be understood that pivot axes described hereafter
shall constitute longitudinal axes through pins or other similar
connecting members well known to those skilled in the art.
The resilient connecting means 33 respectively includes a rear strut 34,
center strut 36 and forward strut 38 which respectively connect to the
rear idler assembly 32, the rear guide roller assembly 30, and the vehicle
support apparatus 28. The rear idler wheel assembly 32 includes a
bellcrank apparatus 40 and an idler wheel 42 rotatably connected to the
bellcrank 40 which is pivotally connected to the main frame 14 about a
pivot axis 44 and is pivotally connected to the rear strut 34 about a
pivot axis 46. The guide roller assembly 30 includes a rocking beam 48 and
a pair of roller wheels 50 which are rotatably mounted on a bogie beam 52
which in turn is pivotally mounted on the rocking beam 48 about a pivot
axis 54. The rocking beam 48 is pivotally mounted on the vehicle's main
frame 14 about a pivot axis 56 and is pivotally connected to the
intermediate strut 36 about a pivot axis 58. The vehicle support apparatus
28, as better illustrated in FIGS. 2 and 3, includes a wheel juncture
device 60, a recoil guide structure 62, a front or idler wheel assembly
64, a following wheel assembly or guide roller assembly 66, and a pivoting
beam 68.
The suspension mechanism 22 also includes a recoil strut 70 having a head
end portion 72 and a rod end portion 74 which are respectively pivotally
mounted on frame 14 about a pivot axis 76 and joined to wheel juncture
device 60. As best illustrated in FIG. 3, the recoil guide structure 62
includes a first member 78 which is pivotally mounted on the frame 14
about a pivot axis 80, a second member 82 which is fixed to the first
member 78 and is pivotally attached to support strut 38 about a pivot axis
84, and a support element 86 which protrudes into and is rotatably mounted
on the second member 82 about a pivot axis 87 and has a pivot axis 88.
The wheel juncture device 60 is mounted on the support element 86 so as to
be pivotable about pivot axis 88. The pivoting beam 68 is pivotally
mounted on the wheel juncture device 60 about a pivot axis 89. The guide
roller assembly 66 includes a pair of rollers 90 which are rotatably
mounted on a bogie 92 which, in turn, is pivotally mounted on one arm 94
of the pivoting beam 68 about a pivot axis 97. The front idler wheel
assembly 64 is rotatably mounted on a second arm 96 of the pivoting beam
68 about an axis of rotation 98. A pry-out strut 100 has a rod end 102 and
a head end 104 which are respectively pivotally connected to the first arm
94 about the pivot axis 97 and to the wheel juncture device 60 about a
pivot axis
An inextensible elastomeric belt 117 is entrained about the idler wheel
assemblies 32,64, guide roller assemblies 30,66, and drive wheel assembly
24. The belt 117 is suitably tensioned by the recoil strut 70 acting
through the front idler wheel assembly 64 such that the belt 117 is
frictionally coupled with the drive wheel assembly 24. Rotation of the
drive wheel assembly 24 in the desired direction induces movement of the
belt 117 to drive the vehicle 10.
Each of the struts 34,36, and 38 described herein include, as illustrated
for the front strut 38 in FIG. 3, a cylinder 108 and a piston 110
longitudinally displaceable within the cylinder 108 and having a portion
thereof which constitutes a rod 112 extending from one end of the cylinder
108. A first and a second chamber 114 and 116 are respectively defined by
the components of the strut 34. A third and a fourth chamber 114A and 116A
are respectively defined by the components of the strut 36. A fifth and a
sixth chamber 114B and 116B are respectively defined by the components of
the strut 38 wile the components of a strut 38A (constitutes a part of the
left hand suspension mechanism 20) defined a seventh and an eighth chamber
114C and 116C. A ninth and tenth chamber 114D and 116D are respectively
defined by the components of the strut 100. The aforementioned struts 34,
36, 38 and 100 are illustrated in FIGS. 2-7. Recoil strut 70, however,
includes, by virtue of its, components' construction, only an eleventh
chamber 114E. For purposes of clarity and simplicity, fluid conduits to
the various struts have been illustrated as stub or cut-off hose members
in FIGS. 1-3 but have been schematically illustrated in full in FIGS. 4-7.
In the description of FIGS. 4-7 hereafter, it is to be understood that the
illustrated or first position of each valve described hereafter
constitutes the position corresponding to the high speed operation mode of
the vehicle 10 and that the second (not illustrated) position corresponds
to the low speed, work operation mode of the vehicle 10. It is to be
further understood that while the valves are illustrated as being solenoid
actuated, any valve actuation is considered acceptable and within the
purview of the instant invention.
FIG. 4 is a semi-schematic illustration of the vehicle support struts 38
disposed on opposite lateral sides of the vehicle 10 and their hydraulic
interconnection with other fluid handling devices. The head end or chamber
114B and 114C of support struts 38 and 38A are respectively connected to a
first port of a valve 118 and to a first port of a valve 118A and the
second chamber 116B and 116C are respectively fluidly connected to third
and fourth accumulators 120A and 120. Each valve 118 is selectively
disposable in a first (illustrated) and a second position and includes
second and third ports. When disposed in the first position, each of the
valves 118 respectively connect the first and second ports and obstruct
fluid flow through the third port. When disposed in the second position,
each of the valves 118 and 118A fluid1y interconnects the first and third
ports. Fifth and sixth accumulators 122 and 122A are respectively fluidly
interconnected with the second port of the valves 118 and 118A.
FIG. 5 is a semi-schematic illustration of the rear support strut 34, the
recoil strut 70, and their fluid interconnection with various fluid
handling devices. The piston 110 in the strut 34 includes ports or
openings 124 which provide fluid communication between the chambers 114
and 116. A valve 126 having a first and a second port is disposable
between a first (illustrated in FIG. 5) and a second position as desired.
In its first position the valve 126 provides fluid communication between
chamber 116 of strut 34 and chamber 114E of the associated recoil strut 70
which constitutes a part of the same suspension mechanism. A first
accumulator 128 is maintained in fluid communication with chamber 114E of
the recoil strut 70. When valve 126 is disposed in its second position,
fluid communication between chamber 116 of strut 34 and accumulator 128 is
obstructed.
FIG. 6 is a semi-schematic view of the pry-out strut 100 and its hydraulic
interconnection with various fluid handling devices such as a seventh
accumulator 130. valve 132 is disposable in a first (illustrated) and a
second position and includes first and second ports which are respectively
fluidly connected to chambers 114D and 116D of the pry-out strut 100. The
accumulator 130 is maintained in continuous fluid communication with
chamber 116D of the pry-out strut 100. When valve 132 occupies the first
position, fluid communication between chamber 114D and chamber 116 of
strut 100 is provided. When valve 132 is disposed in its second position,
fluid communication between chambers 114D and 116D of strut 100 is
obstructed.
FIG. 7 is a semi-schematic of intermediate strut 36 illustrating its piston
110 having ports or openings 124 therethrough between strut 36's chambers
114A and 116A. A second accumulator 134 is in continuous fluid
communication with chamber 116A of strut 36.
Referring again to FIG. 1, a conventional front mounted implement 136 such
as a bulldozer blade, only a fragment of which is illustrated, is
connected to the main frame 14 beneath the operator's station 16. Such
implement is visible and effective to move earth or the like with movement
of the vehicle 10. It is to be understood that a similar earthworking
implement, while not illustrated, could be joined to the vehicle 10 at its
rear end for purposes of performing similar earthworking tasks.
INDUSTRIAL APPLICABILITY
In operation, the suspension system 18 has been designed to accommodate and
traverse obstacles of approximately eight inches in height without unduly
disturbing the chassis 12 including the operator's station 16. Assuming
the suspension system 18 has been set for high speed operation and a
forward travel direction, the drive wheel assembly 24 is rotated in a
clockwise direction as viewed from the vantage point of FIG. 1 at the
desired rate of speed to propel the endless elastomeric belt 117 in a
clockwise direction. When the belt 117 and front idler wheel assembly 64
encounter an obstacle, a thrust component is longitudinally rearwardly
directed against the recoil strut 70 through the pivoting beam 68 and
vehicle support apparatus 28. The chamber 114E of the recoil cylinder 70
is continuously pressurized by fluid as shown in FIG. 5 to a pressure
level sufficient to urge the vehicle support apparatus 60 forwardly with a
relatively high nominal force of approximately 34,000 lbs. under static
conditions. The support element 86 is allowed to initially travel
rearwardly in a nearly horizontal but arcuate path about the pivot axis
87. Thereafter, the front idler wheel assembly 64 is elevated such that
the pivoting beam 68 rotates in a counterclockwise direction about the
pivot axis 89 causing the vehicle support apparatus 60 to move
incrementally rearwardly relative to the pivot axis 76 and forcing some
fluid from the recoil strut's chamber 114 into the accumulator 128 and
chamber 114E of the rear strut 34. Since the front idler wheel assembly 64
is on the front leg 96 of the pivoting beam 68, the upward movement
thereof exerts a downward force on the bogie 92 and then on the roller
wheels 90 against the interior of the belt 117. The pry-out strut 100 best
illustrated in FIGS. 1, 2, and 6 dampens or inhibits counterclockwise
movement of the pivoting beam 68 to a limited degree by expelling fluid
from chamber 116D of strut 100 into chamber 114D thereof and, at the same
time, transmitting sufficient fluid from the accumulator 130 into chamber
114D to take up the volumetric difference between the chambers 114D and
116D. With upward movement of the pivot axes 88 and 89, the piston rod 112
of the front strut 38 is moved upwardly within the cylinder 108 causing
fluid from its chamber 114B to be expelled therefrom into the accumulator
122A when the valve 118A occupies the position shown in FIG. 4. Such
upward movement of the piston rod 112 causes additional fluid to be drawn
into chamber 116B of strut 38 from accumulator 120A.
When the obstacle in question, such as a tree limb, is traversed by the
drive belt 117 to a point where such obstacle is located between the front
idler wheel assembly 64 and the front roller wheel assembly 66, the bogie
member 92 reverses from a clockwise movement relative to the pivoting beam
68 to a counterclockwise movement. As the obstacle is further traversed
and becomes located beneath the front roller wheel 90, the bogie member 92
rotates in a counterclockwise direction. At this point the obstacle is
nearly directly under the pry-out strut 100 causing a substantial upward
force component on the piston rod 102 thereof. As a result, fluid is
expelled from the pry-out strut's chamber 114D into the pry-out strut's
chamber 116D and the accumulator 130 at a progressively increasing
pressure level to yield the desired cushioning effect. Further traversal
of the obstacle causes its passage beneath the rear roller wheel 90, and
clockwise rotation of the bogie member 92. As the obstacle passes from
under the rear roller wheel 90, the bogie member 92 rotates in a
counterclockwise direction until the illustrated equilibrium position of
FIGS. 1 and 2 is reached and fluid flows from the accumulator 130 and
chamber 116D into chamber 114D of the pry-out strut 100.
Subsequently, the effective rearward travel of the obstacle under the
forward roller wheels 50 and belt 117 causes counterclockwise movement of
the rear bogie member 52. The rocking beam 48 rotates in a clockwise
direction about the pivot axis 56 causing fluid to be expelled from the
chamber 114A of strut 36 through ports 124 into chamber 116A of strut 36
and into accumulator 134 under an increasing pressure level. As the
obstacle passes under the rear roller wheels 50, clockwise moment of the
rear bogie member 52 is induced. Further traversal of the obstacle causes:
the bogie member 52 and rocking beam 48 to return to their equilibrium
positions illustrated in FIG. 1; and fluid flow reversal from that
described heretofore with respect to the strut 36.
As the obstacle travels under the rear idler wheel 42, clockwise movement
of the support member 40 about pivot axis 44 is induced causing the piston
110 and rod 112 of strut 34 to move further into strut 34's cylinder low.
Such movement causes fluid to be expelled from chamber 114E of the strut
34 into chamber 116 of strut 34, chamber 114 of recoil strut 70 and the
accumulator 128 as illustrated in FIG. 5. As a result, cylinder 72 of the
recoil strut 70 is urged forwardly causing vehicle support apparatus 60 to
bias the front idler wheel assembly 64 forwardly to maintain proper
tension of the drive belt 117 under the increased pressure levels
established by accumulator 128. As the obstacle passes from under the rear
idler wheel assembly 32, the above described movements of components and
fluid are reversed until the rear idler wheel assembly 32 again assumes
the equilibrium position shown in FIG. 1.
As is apparent from viewing FIG. 1, the drive wheel assembly 24 is elevated
relative to the idler wheel assemblies 32,64 and guide rollers 50,90 and
is not a part of the suspended undercarriage which must be included in the
dynamic suspension system 18 for supporting the chassis 12. Since the
drive wheel assembly 24 is not a part of the suspension system 18, no
provisions need be made to accommodate movement of the rotation axis 26
thereof resulting in simplification of the power train structure's
interconnection with the drive wheel assembly 24 and providing greater
vehicle reliability. Moreover, while other drive wheel assemblies which
are disposed at ground level are prone to ingestion of mud and debris
which can result in slippage of the drive belt relative to such drive
wheel assemblies, the elevated location of the instant drive wheel
assembly 24 provides an opportunity for gravity to clean the belt 117 and
promote frictional engagement of the belt 117 and drive wheel assembly 24
before such debris reaches the drive wheel assembly 24.
The hydraulic subsystems schematically illustrated in FIGS. 4-7 provide
optimal movement characteristics of the suspension system 18 for
relatively high rates of vehicular speed or, alternatively, movement
characteristics providing optimal tractive effort and a stable work
platforms for relatively low, working rates of vehicular speed. Soft
spring rate action of the struts 34,36,38A,70, and 100 is desired when the
vehicle 10 is traveling at high speeds and is provided by disposing the
valves 118A,126, and 132 in the positions illustrated in FIGS. 4, 5, and
6. On the other hand, when moving earth at low speeds such as through the
use of the front mounted bulldozer 136, it is desirable to move the valves
118A, and 126 to their second (not illustrated) position. Movement of
valve 132 to its second position will occur during low speed operation but
only when it is desired to exert an upward force on the bulldozer 136 for
purposes such as "prying out" a tree stump, boulder, or other object.
Referring now to FIG. 4, when the valves 118A are placed in their second
position, their first ports are respectively fluidly connected with the
chambers 114C and 114B of the struts associated therewith, fluid flow
through the second ports of valves 118A is obstructed, and the third ports
of the valves 118A are fluidly connected to their first ports, such that
the chambers 114C and 114B of the struts 38A and 38 are fluidly
interconnected and the accumulators 122 and 122A are .isolated from
accepting or providing fluid to those struts 38A and 38. The resulting
action is a "side to side" or "equalizer bar" load sharing between the
vehicle support apparatus 60 arranged on opposite lateral sides thereof.
Accordingly, when an obstacle is encountered by the vehicle support
apparatus 60 or the wheel or roller guide assemblies thereof, an upward
force on the piston 110 of strut 38 will cause fluid to be expelled from
that strut's chamber 114B and into the chamber 114C of the other strut
38A. Accordingly, when an obstacle is encountered and traversed by one
vehicle support apparatus 60, the increased force exerted on the strut 38
connected thereto will be transferred to the other strut 38A located on
the opposite lateral side of the vehicle and a downward force will be
exerted on the piston 110 of such other strut 38A to laterally "balance"
the load on the oppositely disposed vehicle support apparatus 60.
Referring now to FIG. 5, when valve 126 is disposed in its second position,
the position of the piston 110 of strut 34 is effectively locked in
position since fluid communication between the first and second ports of
the valve 126 is precluded. In such second position, however, the recoil
strut 70 retains its ability to absorb shock and accommodate obstacles
longitudinally encountered and/or traversed by maintaining the chamber 114
of the recoil strut 70 in continuous fluid communication with the
accumulator 128. Accordingly, upon encountering such obstacles, the
cylinder 72 of recoil strut 70 will move to further develop its associated
piston 74 and expel fluid from the chamber 114 into the accumulator 128 at
increasing pressure. Such action closely simulates a conventional recoil
system which uses springs to maintain belt tension. Moreover, when the
piston 110 of strut 34 is fixed in position, the vehicle can exert its
maximum moment about the rear idler wheel assembly 32 for purposes of
inserting an implement such as the illustrated bulldozer 136 into the
ground. Maximum penetration force thereof can be exerted only by fixing
the position of the rear idler wheel assembly 32.
Turning now to FIG. 6, the valve 132 is moved to its second position for
purposes of preventing retraction of the piston 110 of strut 100. In such
second position, fluid communication between the first and second ports on
the valve 132 are blocked to prevent fluid expulsion from the chamber 114D
of the pry-out strut 100. By preventing expulsion of fluid from chamber
114D of pry-out strut 100, the pivoting beam 68 will no longer pivot and
provide longitudinal load sharing between the front idler wheel assembly
64 and the trailing guide roller assembly 66. Accordingly, the maximum
upward force for prying upwardly on rock or other objects can be exerted
on a front mounted implement such as the bulldozer 136 by causing the
entire vehicle to pivot and exert a downwardly directed moment about the
front idler assembly 64. If, however, when the valve 132 is disposed in
its second position, a void in the terrain occurs under the guide wheel
assembly 66, the piston rod 102 of the strut 100 will move downwardly
(resisted only by the vacuum force exerted thereon from the chamber 114D)
and permit fluid in the chamber 116D to be expelled into the accumulator
130 under increasing pressure. Such increasing pressure prevents impact
engagement of the piston joined to the rod 102 and the cylinder 104 of the
pry-out strut 100.
As may be appreciated from viewing FIGS. 1 and 7, movement of the rear
roller guide assembly 30 is permitted regardless of the vehicular travel
speed. Thus, when an obstacle or terrain irregularity is encountered
beneath one or both of the guide wheels 50, the piston 110 and associated
rod 112 of the strut 36 will be biased upwardly as viewed in FIG. 7 so as
to expel fluid from chamber 114A through ports 124 and into chamber 116A
of strut 36 and accumulator 134 under increasing pressure. When the
subject obstacle disappears or when a void appears beneath the guide wheel
assembly 30, the piston 110 and associated rod 112 will be biased
downwardly until an equilibrium position is reached wherein the fluid
force in the chamber 116A equals the sum of the fluid force in the chamber
114A and the upward force exerted on the rod 112A. Fluid will be biased
into chamber 114 from chamber 116A and accumulator 134 under decreasing
pressure conditions. By proper sizing of the ports 124, a dampening action
for the strut 36 can be obtained to smooth the ride and improve
performance of the suspension system 18.
It is now apparent that a suspension system 18 has been provided which is
readily adaptable to high speed vehicular movement and to reduced, working
speeds. At high speeds independent side to side suspension characteristics
are provided, longitudinal load sharing is provided, and the belt 117 is
maintained at the desired tension to insure continued belt to wheel
engagement thus preventing the belt 117 from being disentrained from the
drive, idler, and guide wheels. On the other hand, optimal suspension
characteristics are provided for the low speed, vehicular working mode in
which lateral side to side load sharing is desired and maximum force can
be exerted on earthworking implements attached to the vehicle. Such dual
purpose vehicle enables transportation costs thereof to be minimized while
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