Note: Descriptions are shown in the official language in which they were submitted.
10~4074
1 BACKGROUND OF THE INVENTION
The present invention relates generally to a compressible
fluid suspension unit. More specifically, the present invention
relates to a suspension strut for assembly in a vehicle suspen-
sion system wherein such suspension system is subjected to large
weight differentials resulting from loaded and unloaded condi-
tions of the vehicle.
To improve riding qualities of any motor vehicle, it is
desirable to provide suspension springs that haue a low spring
10 rate. These low spring rates result in soft springs which
cushion the vehicle ride but which have the disadvantage of
causing excessive and objectionable deflection of a vehicle body
when it is loaded in an extreme manner.
Because of the massive loads carried by off-highway vehicles
such as large earthm~ving dump trucks and the like to which the
present invention is applicable, the weight differential be-
tween the loaded and unloaded conditions varies greatly.
Consequently, a suspension designed to ride well in the
loaded condition would be unduly stiff when riding empty. Con-
20 versely, a suspens,on designed to ride well in the unbadedcondition will be unduly soft when riding in the loaded condition
which in turn results in well recognized safety and operational
problems with respect to the vehicle.
The problem therefore in providing a suspension system that
will accommodate the off-highway vehicle in the loaded condition
is that of having the vehicle subjected to an unduly stiff
suspension and ride during unloaded use. This results in a
hard ride which is obviously uncomfortable to the driver and
iU840'74
1 passengers in view of the inability of the suspension system
to absorb road shock which in turn results in excessive stress
being transmitted throughout the entire vehicle structure. This
condition has obvious deleterious affects on the vehicle body
and tires, the latter being subjected to excessive sidewall
flexing, bruising and heat buildup which in turn decreases their
useful life. The above situation indicates the need for a sus-
pension system that provides similar ride characteristics in
an off-highway vehicle at both ends of its load scale, that is
10 in a loaded and unloaded condition. Such characteristics are
provided by the double liquid spring arrangement to be described
in which two separate spring constants are provided for accom-
modating the various loading conditions of an off-highway vehicle.
The prior art includes various types of suspension springs
such as leaf spring, rubber, pneumatic and single rate or single
stage liquid springs. However, none of the prior art structures
have been able to provide a spring which will accommodate the
requirements of an off-highway vehicle operation contemplated by
the present invention in which a large weight differential is
20 encountered through loaded and unloaded conditions. Corre-
spondingly, it is necessary that a spring or suspension system
having such a capability be of reasonable size so as to be
copacetic within the general confines of a vehicle structure,
none of which has been effectively accomplished in the prior art
structures.
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10~4074
1 SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to
provide a suspension system that will provide similar ride
characteristics to a vehicle and particularly an off-highway
vehicle at both ends of a loaded and unloaded operational scale.
Another object of the present invention is to provide a
suspension system for an off-highway vehicle which will provide
improved stability thereto resulting in a smoother ride in both
a loaded and unloaded condition which improves driver comfort
10 and control and necessarily the safety factor attendant thereto.
A further object of the present invention is to provide a
suspension system that is simple in design and has a minimum
number of moving parts resulting in long service life and low
maintenance costs.
Still another object of the present invention is to provide
the aforesaid suspension system which can be designed to fit
current vehicle requirements.
A still further object of the present invention is to pro-
vide the aforesaid suspension system which minimizes dynamic
20 loads being transmitted to the vehicle structure which in turn
lowers the induced stresses in such vehicle.
In summary, the present invention generally provides two
liquid springs connected together in axial alignment and which
respectively have different spring constants to accommodate an
off-highway vehicle in either a loaded or unloaded condition.
More specifically, each liquid spring includes a cylinder pre-
charged with a hydraulic fluid such as of the silicon variety
and which includes a displacement rod slidably mounted in the
~0~4074
cylinder end nonadjacent to the other cylinder. The two
liquid springs have different spring constants by means of
varying the displacement rod diameters with respect to the
cylinder volumes. Each spring absorbs loading through travel
of its respective displacement rod into its cylinder cavity
so as to further compress the hydraulic fluid contained
therein. With the free ends of the displacement rods of
the two springs assembled between the chassis and body portions
of an off-highway vehicle, the aforesaid spring constants of
the two liquid springs operationally accommodate the vehicle
in a loaded and unloaded condition.
Thus, the present invention is broadly defined as a
composite suspension strut adapted for connection to vehicles
experiencing a wide range of loading conditions, the composite
suspension strut comprising: first and second cylinder means,
each of the first and second cylinder means having a compressible
hydraulic fluid sealed therein and the cylinder means being
axially aligned one to another in end-to-end relation, the
first and second cylinder means being integrally connected to
one another and having open adjacent end portions providing
communication therebetween and a piston means disposed in the
? open adjacent end portions and being reciprocably slidable
therein; first and second displacement rod means, the first and
second displacement rod means having end portions concentrically
disposed within the non-adjacent ends of the first and second
cylinder means respectively and being reciprocably slidable in
a sealed manner through the non-adjacent ends to cor.tpressibly
displace the hydraulic fluid therein and the ratio of the total
internal volume of the first cylinder means to the volumetric
displacement per unit of axial length of the first displacement
rod means being different from such corresponding ratio of the
second cylinder and second displacement rod means so that the
10840'74
combination of the first displacement rod and first cylinder
means forms a first liquid spring having a first spring constant
and the combination of the second displacement rod means and
second cylinder means forms a second liquid spring having a
second spring constant, the latter spring constant being dif-
ferent from the first spring constant.
The foregoing and other objects, advantages and
characterizing features of the present invention will become
clearly apparent from the ensuing detailed description of
an illustrative embodiment thereof, taken together with the
accompanying drawings wherein like reference characters
denote like parts through the various views.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a fragmentary side view in plan of an off-
highway vehicle wheel assembly showing the suspension strut
of the present invention in an assembled disposition;
Fig. 2a is a fragmentary, longitudinal view in
section of one of two similar liquid springs connected together
with a floating piston disposed therebetween taken along Fig.
2a-2b of Fig. l;
Fig. 2b is a fragmentary, longitudinal view in
section of a second liquid spring which is connected to the
liquid spring shown in Fig. 2a;
Fig. 3a is a fragmentary, longitudinal view in
section of a liquid spring adapted for connection to a second
liquid spring; and
1084V74
'
1 Fig. 3b is a fragmentary, longitudinal view in section of
' a liquid spring to be connected to the liquid spring shown in
Fig. 3a and to be separated therefrom by a fixed barrier inter-
face.
DETAILED DESCRIPTION OF THE PREF~RRED EMBODIMENT
Heretofore, springs generally known as liquid and compres-
; sible solid springs, have been suggested for various applications
where mechanical springs,such as, coil or leaf springs, have
been used and in applications where mechanical springs could
10 not be used because of their physical limitations. In aliquid or solid spring, a relatively lightweight displacement
rod is accelerated when the spring is actuated, to compress
the hydraulic fluid contained within a cylinder means, whereas
in a mechanical spring the entire mass of the spring is moved
to some degree in each cycle so that the natural frequency of
a liquid or solid spring is much higher than a coil spring,
enabling it to be operated at much higher velocities. A liquid
or solid spring ~s much more compact and much smaller than a
mechanical spring which will carry the equivalent load. Con-
20 versely, a liquid or solid spring of a given size will carrymany times the load of the same size mechanical spring.
Liquid or solid springs have been used between two rela
tively movable parts, the container or cylinder means being
connected to one of these parts and the displacement rod being
slidable within such cylinder means being connected to the
other movable part. When a force or load is applied to one
of the two relatively movable parts, the displacement rod is
forced inwardly of the cylinder means, compressing the medium
1084074
1 therein. When the force of the load is relieved, the liquid
expands returning the displacement rod and the part, to which
it is connected, to the initial position.
As can be appreciated fromthe above, a liquid spring is
highly desirable in suspension applications wherein high levels
of loading is experienced in the suspension system which in
turn must be assembled within a limited space. However, a
single liquid spring having a fixed spring constant cannot
satisfy all of the demands placed on a suspension system in a
10 vehicle such as one of the off-highway variety in which a wide
range of loading conditions is experienced by the suspension
system.
Referring now in detail to the illustrative embodiments
depioted in the accompanying drawings, there is shown in Fig. 1
an exemplary application of the composite strut forming the
present invention. Asshown therein, an off-highway vehicle
shown in fragmentation and generally indicated at 10 has a body
portion 12 supported on an independent axle 14 and tire 16. An
off-highway vehicle such as a large dump truck having a load
20 carrying body 12 is pivoted at 18 and is urged to pivot there-
about by a hydraulic cylinder means 20. The present invention
is concerned with the suspension strut 22 disposed between the
vehicle body and independent axle 14. As fully discussed here-
inabove, the suspension strut is provided to absorb the trans-
mission of shock between axle 14 and body 12. As further
discussed hereinabove, however, such shock absorption and
cushioning of the vehicle is dependent upon the spring constant
of strut 22 and the loaded condition of vehicle 10. It is to
1(J~4074
1 further to be understood that the placement of strut 2~ is by way
of example and that other similar struts would be correspondingly
placed at other suspension points in vehicle 10.
Referring now to the strut shown in Fig. 2a, a first cylin-
der means 24a is axially aligned and integrally connected to the
cylinder means 24b shown in Fig. 2b. Each of the cylinder means
and its respectively associated structure is similar and for
purposes of description will be indicated by similar numerical
designations and different letter suffixes corresponding to the
10 cylinder structure shown in Fig. 2a and that shown in Fig. 2b.
As shown in Fig. 2a, cylinder 24a includes a displacement
rod means 26a having an end portion concentrically disposed
within the end of cylinder 24a which is nonadjacent to cylinder
24b. Displacement rod 26a is reciprocably slidable in a sealed
manner through such end portion of cylinder 24a to compressibly
displace hydraulic fluid contained therein. The cylinder 24a
further includes an end portion generally shown as 28a which
includes a housing member 30a concentrically disposed within the
end of the cylinder. Such housing member is held in sealed
20 engagement with respect to the cylinder by means of a shear ring
32a and associated cap and sealing gasket 34a and 36a, respect-
ively, Housing member 30a is further sealed with respect to
the cylinder by means of an 0-ring 38a placed in an annular
groove in the housing member adjacent to the inner surface of
the cylinder. A filler valve 40a and associated passages is
provided in housing member 30a for purposes of precharging the
cavity of cylinder 24a with a compressible hydraulic fluid. In
addition, the displacement rod 26a is slidable within the housing
30a and is sealed with respect thereto by means of the packing
--8--
10~40~4
1 gland arrangement generally indicated as 42a which is known in
the prior art. The packing gland assembly 42a serves to main-
tain hydraulic pressure within the cylinder cavity while allowing
sliding movement between displacement rod 26a and housing 30a
without leakage therebetween resulting.
A dampening head means 44a is affixed to the inner end
portion of displacement rod 26a for generation of dampening
forces during telescopic movement of the displacement rod 26a
relative to the cylinder 24a. The dampening head 44a further
10 includes metering orifices 46a to provide controlled passage
of hydraulic fluid through the dampening head during movement
thereof with the displacement rod through the cylinder. As
further shown in Fig. 2a, the outer or left side of the damp-
ening head includes a bumper pad 48a which is similar in
construction and function to the bumper pad 50a. Both bumper
pads are made of elastomeric material and serve to cushion the
displacement rod at respective ends of its stroke or travel.
As shown in Fig. 2a, the displacement rod is at its outermost
position with the bumper pad 48a in abutment with a ring means
20 52a disposed in the housing member. Similarly, as shown in dotted
lines, the displacement rod and dampening head may travel inwardly
whereby bumper pad 50a would come into abutment with the outer end
surface of housing member 30a. A duct shield 54a is provided to
i~ concentrically ride over the outer wall of cylinder 24a so as to
shield the displacement rod 26a and the end portion of the cylin-
der structure from dirt and other foreign matter. As assembly
joint 56a is provided at the free end of the displacement rod 26a
which together with the assembly joint 56b on displacement rod
26b provides for connection of the combined liquid springs shown
in Figs. 2a and 2b between the chassis and body of an off-hiqhwaY
~ 10~40~4
1 vehicle all of which is generally shown in Fig. 1.
As previously stated, the cylinder 24b is connected inte-
grally in alignment with cylinder 24a and the displacement rod
and associated structure in cylinder 24b is similar to that de-
scribed in Fig. 2a. AS further shown in Fig. 2a, the adjacent
ends of the cylinders are open with respect to one another and
include a floating piston means 58 slidable in a reciprocable
manner therebetween. The abutment means or shoulder 60 limits
travel of the piston into cylinder 24a as to be more fully de-
10 scribed. The floating piston 58 further includes sealing ringmeans 62 for providing a sliding sealed relationship between
the floating piston 58 and the inner walls of the adjacent end
portions of cylinders 24a and 24b. In this manner, the piston
may float in a limited axial range between the open adjacent
end portions of the cylinders to effectively vary the internal
volume thereof. Such floating piston movements is dictated by
the relative hydraulic pressure differential in the two cylinders
which will also be more fully described hereinbelow.
The two liquid springs separately shown in Figs. 3a and 3b
2~ are substantially identical to the liquid springs described in
Figs. 2a and 2b with the exception that the springs in Figs. 3a
and 3b have cylinder cavities separated from one another through
closed adjacent portions therein. More specifically, asshown in
Fig. 3b, a shoulder means 64 protrudes inwardly at the junction
point of the two cylinder walls. A fixed barrier interface is
provided between the two cylinder cavities by means of the adja-
cent cylinder end portions 66 and 68 being held in abutment
against opposite sides of the shoulder 64 by the hydraulic pres-
sure in their respective cylinder cavities. As stated, the
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iV~4074
1 remainder of the combined liquid spring structure shown in Fig.
3a and 3b is substantially identical to that of Figs. 2a and 2b.
In describing the operation of the present invention, ref-
erence will be made to the Fig. 2 strut and the Fig. 3 strut.
Utilizing such a reference indication, it is to be understood
that the Fig. 2 strut represents the aligned connection of the
separate liquid springs shown in Figs. 2a and 2b with the float-
ing piston 58 disposed in a sliding manner therebetween through
the respective open adjacent ends of the cylinder cavities.
10 Similarly, it is to be understood that the Fig. 3 strut comprises
the aligned connection of the liquid springs shown in Figs. 3a
and 3b with a fixed barrier interface provided between the re-
spective cylinder cavities thereof by the closed adjacent end
portions 66 and 68 shown in Fig. 3b.
In regard to the hydraulic concept in both the Fig. 2 and
Fig. 3 struts, it is to be understood that the spring constant
of a liquid spring is determined by comparing the total internal
volume of the spring cylinder to the volumetric displacement per
unit of axial length of a displacement rod slidable therein. In
20 other words, as shown in detail in Fig. 2a, the hydraulic fluid
contained in cylinder 24a under an initial pressure with the
displacement rod in the outward disposition shown therein, will
become further compresses as the displacement rod 26a is urged
into the cylinder cavity as shown in dotted lines. Such com-
pression of the hydraulic fluid is caused by the additional
volume or space oddupied by the rod 26a within the cylinder cav-
ity. In this manner, each unit of axial length of the displace-
ment rod 26a displaces and compresses a corresponding amount of
hydraulic fluid with respect to the total volume of the cylinder
under initial conditions.
,,
lV~40'74
1 Therefore, in developing two different spring constants for
the two liquid springs in a single strut member, it is proposed
to vary the volume of each spring cylinder and the diameter of
each displacement rod associated therewith so as to vary the spring
constant described hereinabove. In varying the diameter of the
displacementrod the volumetric displacement of such rod per unit of
axial length thereof is obviously varied while the volume of the
spring cylinders may be varied through variation of their diameter
as well as their axial length. As shown in the Fig. 2 strut, each
10 cylinder 24a and 24b has the same diameter while having different
axial lengths in addition to the displacement rods 26a and 26b
having different diameters in order to arrive at the desired spring
constant for each spring. It is understood however that the dia-
meters of the respective spring cylinders could be different with
respect to one another.
In considering the operation of the Fig. 3 strut, reference
will be made to the Fig. 2a detail since it is identical to the
Fig. 3 strut with the exception of the floating piston 58. The
cylinders in the Fig. 3 strut are precharged with a hydraulic
~0 fluid such as silicon by use of the filler valve and passage ~
- Such precharging is desirable in order to place at least a minimum
loading on the packing gland assembly 42a and the closed cylinder
end portions 66 and 68.
The compressibility of the silicon with the rate of volume
change due to rod displacement gives the suspension a smooth oper-
ation. Such a hydraulic fluid is also desirable from the point
of view of temperature stability. For Example, a 200F. tempera-
ture change only results in a 50 p.s.i. pressure change in a
silicon fluid. The performance of the suspension unit is therefore
1~84074
1 not adversely affected by temperature changes. Moreover, tests
conducted with respect to the present apparatus over the most
dema~ding work cycles indicate a temperature rise within the unit
of only 20F. approximately.
If the cylinders of the springs shown in Figs. 3a and 3b were
identical with respect to their diameters and axial lengths, then
the Fig. 3a spring would have a higher spring constant than the
Fig. 3b ~pring due to the smaller diameter displacement rod in
Fig. 3a as the term "spring constant~ has been defined hereinabove.
10 The amount of force necessary to urge the displacement rod in Fig.
3a inwardly a unit of axial length is inversely proportional to
the spring constant as such term has been defined in this specifi-
cation. In other words, the Fig. 3a spring has a relatively high
ration of cylinder volume to volumetric rod displacement per unit
length of displacement rod when compared to such corresponding
ratio in Fig. 3b. Therefore, the spring constant in Fig. 3b would
be smaller than that in Fig. 3a while a smaller amount of force is
required to urge the displacement rod in Fig. 3b inwardly.
Therefore, in an assembled position, the spring in Fig. 3a
20 of strut 3 will become operational before ~e spring in Fi~. 3b
since the Fig. 3a spring reacts to a lesser amount of shock and
resulting force. Conceptually, the Fig. 3a spring therefore would
be generally operational during the unloaded condition of the
vehicle. Prior to such operation, hydraulic fluid initially is
in equilibrium on both sides of the dampening head or plate means
indicated as 44a in Fig. 2a. Such dampening head or plate is
loosely fit with respect to the cylinder inside wall so that upon
axial movement of the displacement rod there will not be frictional
interference between the dampening head and the cylinder. In
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iO~4074
l addition, the metering orifices 46a and the clearance between the
dampening head and the cylinder wall provide controlled passage
of hydraulic fluid pass the dampening head during movement of the
displacement rod in the cylinder which in turn creates increased
hydraulic pressure therein and the tendency of the hydraulic fluid
to flow pass the dampening head to reach a state of equilibrium
within the cylinder cavity. It can therefore be appreciated that
the dampening head in the form of a plate means with orifices 46a
as illustrated provides controlled shock absorption to the spring
lO movement of the displacement rod and the operational characteristics
of the dampening head can be controlled by the placement and design
of such orifices therein and the clearance provided with respect to
the cylinder sidewall.
With respect to the Fig. 3, strut, the Fig. 3a spring will
continue to compress upon loading of the vehicle until the hy-
draulic pressure in the cylinder of Fig. 3a is substantially
engaged. As can be seen from the fixed nature of the clo~ed end
portions 66 and 68 of the strut 3 springs, fluid pressure in the
respective springs exist independent of one another. It is further
20 to be noted that in operation of the Fig. 3 strut, that a smooth
transition takes place between the op~ration of the Fig. 3a spring
and the Fig. 3b spring due to the operation of the Fig. 3b spring
being initiated before the fig. 3a spring has bottomed out. Such
a smooth transition may avoid any spike in the ride characteris-
tics of the vehicle in any loading situation. It is anticipated
that both cylinder cavities in the strut 3 will be precharged to
an equal amount. However, it is within the scope of the present
invention that there could be different initial prechargings in
the cylinder cavities of strut 3 which could be employed to vary
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lV~4074
the operational transition and characteristics between the two
liquid springs therein all of which can be specifically designed
for a particular vehicle application.
A slightly different operation takes place in strut 2 as
compared to strut 3 in view of the floating piston 58 as compared
to the clo~ed cylinder end portions 66 and 68 in strut 3. In
strut 2, the liquid spring having the smaller diameter displace-
ment rod 26a has a higher spring constant than that corresponding
to displacement rod 26b. However, due to the floating piston 58
lO hydraulic pressurebuildup in cylinder cavity 24a has an affect
on the hydraulic pressure in the cavity of cylinder 24b. Assuming
that both cavities of cylinders 24a and 24b are precharged to the
same degree, for example in the neighborhood of 1000 psi, the
smaller diameter displacement rod 26a will function and move in-
wardly first with a lightly loaded or empty vehicle. The displace-
ment rod 26a enters the cavity of cyliner 24a and the pressure
therein will ultimately rise urging the floating piston 58 to the
right into the cavity of cylinder 24b causing a commensurate hy-
draulic pressure increase therein. As displacement rod 26a starts
20 to bottom out, displacement rod 26a will assume further loading as
it enters the cavity of cylinder 2~b causing additional pressure
increase therein and consequently urging the floating piston 58
back into the cavity of cylinder 24a to thereby cause a soft tran-
sition between the two liquid springs shown in Figs. 2a and 2b.
However, when the floating piston reaches the shoulder or abutment
means 60a, the cavity in cylinder 24b becomes the sole support for
providing the desired suspension to a loaded vehicle. As can be
appreciated by one skilled in the art the exact placement of the
floating piston 58 in the cylinders 24a and 24b can be varied so
--15--
4074
1 as to provide suspension characteristics adaptable to any particular
vehicle. In addition, it is within the scope of this invention that
different initial charging pressures could be provided to the cavi-
ties of cylinders 24a and 24b in strut 2 which could result in the
initial condition of floating piston 58 being in affirmative engage-
ment with abutment means 60a.
From the foregoing, it is apparent that the objects of the
present invention have been fully accomplished. As a result of
this invention a suspension system is provided which imparts
10 similar ride characteristics to an off-highway vehicle in both a
loaded and unloaded condition. As a result thereof, improved
stability and a smoother ride in such a vehicle is encountered
which necessarily improves driver comfort and control of the vehicle.
Moreover, the suspension system described herein above as consti-
tuting the present invention has a minimum number of moving parts
which are only the displacement rods and in the Fig. 2 strut, the
floating piston 58. Such a minimum number of mbving parts results
in long service life and low maintenance costs. As is to be ap-
preciated from the flexibility in varying the displacement rod
20 diameters, cylinder diameters, cylinder lenqths and cylinder pre-
charging pressure, the suspension system envisioned in the present
invention can be designed to fit specific requirements of a parti-
cular vehicle. A primary benefit of the present invention, however,
resides in the fact that the present suspension system minimizes
the dynamicloads being transmitted to the vehicle in all operational
conditions.
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