Sealing system for road wheel suspension

A hydropneumatic suspension unit includes a large diameter flanged road arm spindle which is bolted to the vehicle hull; a road arm has one end rotatably mounted on the road arm spindle and another end mounting a road wheel; a gravity oriented oil barrier is defined with a free volume enclosed within the road arm to submerge a sealing system for an in-arm mechanically operated pneumatic spring which has a gas volume trapped behind the oil barrier to support the sprung mass of the vehicle; the seal system is defined by a pair of spaced O-rings and a packing ring which seals the outer surface of a reciprocating rod that displaces the seal oil barrier to vary gas compression and produce a resultant force equivalent to pressure times the area of the rod to counteract vertical forces on the road wheel.

FIELD OF THE INVENTION 
This invention relates to a self-contained externally mounted 
hydropneumatic suspension with gas spring and integral damper; more 
particularly to such units having an in-arm gas spring with means for 
sealing the high pressure pneumatic spring volume of the unit. 
DESCRIPTION OF THE PRIOR ART 
Hydropneumatic suspension systems for multiple wheeled vehicles have a 
hydropneumatic suspension unit (HSU) for each individual wheel. These 
HSU's in the past consisted of a gas-fluid spring to support the weight of 
the vehicle and a restriction to the fluid flow to damp the vehicle. These 
HUS's were either hull mounted or built into the road arm. 
Such hydropneumatic suspension systems have utilized either hull mounted or 
in-arm self-contained HUS's. These systems are capable of retrofitting 
existing vehicles which do not contain a suitable hydraulic supply. They 
are also suitable for new applications where a high performance suspension 
is required at a reduced size, weight, and cost. They depend on the 
integrity of their seals, their ability to dissipate heat, and their 
spring rate at and near the static position to maintain the height and 
attitude of the vehicle despite changes in the ambient and operating 
conditions. 
One such in-arm unit is set forth in co-pending U.S. Ser. No. 361,944, 
filed Mar. 25, 1982 now U.S. Pat. No. 4,447,073 and assigned to the same 
assignee. The in-arm pneumatic spring produces an output force for each 
vertical position of the road wheel as a function of the initial gas 
volume and pressure; the adiabatic expansion or contraction of this gas 
volume; the road arm geometry; and the non-linear mechanism which controls 
in response to road arm displacement both the effective arm length at 
which the pneumatic forces act and the displacement of the piston which 
varies the gas volume. The resultant shaped spring characteristic provides 
improved static and dynamic suspension system performance. An in-spindle 
damper is located remotely from the gas volume and is operated 
independently of the spring mechanism. A non-linear cam which is an 
integral part of a rotating crankcase housing actuates a piston pump which 
increases crankcase fluid to a pressure which is a function of the road 
arm's direction of rotation, displacement, and velocity; and of the 
pressure-flow characteristics of the hydraulic control system components. 
The in-spindle damper absorbs energy as a function of this pressure and 
the friction characteristics at various road arm velocities of the rotary 
damper. The resultant shaped damper characteristic provides improved 
dynamic suspension system performance. 
The heat generated by the friction damper is transferred to crankcase fluid 
which is pumped through the damper via integral hydraulic components. This 
heat is then transferred by the circulating fluid to the large mass and 
area crankcase housing and then to the surrounding atmosphere, and to the 
large mass spindle and directly through the large area mounting flange to 
the vehicle hull; thus, efficiently absorbing and dissipating the heat, 
minimizing the temperature build-up, and isolating the pneumatic spring 
from the effects of varying excessive operating temperatures. The spring 
has a piston which is operated by a slider crank mechanism to vary 
compression of a trapped volume of gas. The seal assembly for the gas 
volume is carried by the piston and seals the high pressure gas directly. 
An object of the present invention is to provide an improved lubricated 
seal system for the gas spring of an in-arm pneumatic suspension unit; the 
seal system having a gravity oriented oil barrier that lubricates a set of 
seals and traps a gas volume behind the oil barrier so that it is 
displaced by a slider crank positioned rod to compress the gas volume. 
Another object of the present invention is to provide an in-arm 
hydropneumatic suspension unit with a slider crank positioned rod 
relatively positioned within a road arm which carries a set of seals fixed 
therein to relatively slide with respect to and seal the outer surface of 
the rod; the road arm has an oil volume disposed and oriented by gravity 
to a position which submerges the set of seals within an oil barrier that 
is interposed between a rod displacement cavity and a high pressure gas 
spring volume within the road arm to trap the gas behind the oil so as to 
isolate the set of seals from the gas volume and whereby the rod will be 
sealed within the oil barrier and will displace the oil barrier to vary 
the gas volume to vary the load capacity of the suspension unit. 
Yet another object of the present invention is to provide an in-arm seal 
assembly for a pneumatic vehicle suspension unit having relatively 
positioned rod and seal assembly components arranged to have a gravity 
flow defined oil/gas barrier submerging the rod end and seal assembly 
within an end cavity of the suspension arm and wherein the rod end 
displaces oil from the cavity to vary gas pressure loading on the rod 
which acts directly from a gas volume across the oil barrier to produce a 
load equalizing force on the rod.

Referring now to FIG. 1, an armored vehicle 10 is illustrated. It includes 
two track laying systems 12 only one of which is shown. The system 12 
includes a track 14 guided over an idler wheel 16 and a drive sprocket 18. 
A plurality of support rollers 20 guide the upper reach of the track. The 
vehicle is suspended by a plurality of road wheels 22, spaced axially 
along the side wall 24 of the vehicle hull 26. Each road wheel 22 is 
carried for vertical movement with respect to the hull by a 
self-contained, externally mounted hydropneumatic suspension unit 28, 
hereinafter HSU 28. An adjustable track tensioner 30 is coupled between a 
compensating idler arm 32 and a spindle housing 34 of the forwardmost HSU 
or is hull mounted. 
The systems 12 are representative of track laying systems improved by the 
present invention which is equally suitable for use on other track systems 
or on wheeled vehicles. 
Each HSU 28, as shown in FIG. 2 and FIG. 3, is fixedly secured to the 
vehicle hull 26 by a large diameter road arm spindle 36 having both a 
registering diameter 38 and a mounting flange 40 with a plurality of bolts 
42 threaded to hull 26. The diameter of the spindle 36 is selected for 
purposes which will become more apparent in the text of the aforesaid 
application and is larger than diameters used in prior HSU assemblies. 
A road arm 44 having the spindle housing 34 at one end and a road wheel 
spindle 45 at the other free end 46 is supported for oscillation on the 
large outer diameter surface 48 of spindle 36 by complementary tapered 
roller bearings 50,52. The large diameter but small cross-section 
preloaded full complement tapered roller bearings 50,52 support the road 
arm both axially and radially in a construction having a minimum volume 
and a narrow width. 
A crankcase 54 is defined by the free volume enclosed within the spindle 
housing 34 and within the spindle 36. The crankcase is filled with fluid 
to the level indicated at reference numeral 56. 
A mechanically operated, single chamber gas spring 60, as shown in FIGS. 4 
and 5 having spaced bores 62, 64 is included in the road arm 44. This 
spring supports that portion of the sprung mass of vehicle 10 that acts at 
the described road wheel station. A charging valve 63 and relief valve 65 
are located on road arm 44 to supply nitrogen gas to bore 64 and to 
relieve excessive gas pressure in the unit. 
In accordance with certain principles of the present invention, a seal 
assembly 66 is axially located within oil filled bore 62. Assembly 66 
includes an inboard seal support sleeve 68 seated in bore 62 at the free 
end 46 of road arm 44 and sealed with respect thereto by an O-ring seal 
69. The support sleeve 68 is held at one end by a cylinder head 70 with an 
annular O-ring 72 therein that seals against the arm 44. A piston rod 74 
is supported in support sleeve 68 by a glide ring 76. A piston rod seal 78 
has a cone-shaped end 80 seated on support sleeve 68 to seal rod 74 in a 
gravity defined oil barrier 82 which submerges the seal assembly 66 and 
traps gas in chamber 84 to produce an initial static pressure in gas 
spring 60. The free end of rod 74 is guided by a glide ring 86 on head 70. 
Rod seal 78 is wedged by a tapered surface 88 on support sleeve 68 
radially inwardly toward the O.D. surface 90 of rod 74. Rod seal 78 also 
includes a recessed end surface 92 that yields to pack the interface 93 
between support sleeve 68 and cylinder head 70. 
As best seen in FIGS. 4 and 5, a connecting bar 94 has end 96 fastened to 
piston rod 74 by wrist pin 98 at piston rod end 100. A pin 102 connects 
wrist pin 98 to end 96. The bar 94 passes through a rectangular slot 104 
located between spindle housing walls at the closed end of bore 62. 
The other end of connecting bar 94 is fastened by a pin 105 to crank shaft 
106. 
The initial static pressure (P.sub.s) in gas spring operating on face 108 
of piston rod 74 produces a force (F) which is transmitted by connecting 
bar 94 to spindle 36. The amplitude of this force is equal to the product 
of the pressure (P), the area of face 108 (A), and the cosine of the angle 
.alpha. (cos .alpha.) included between the centerline of piston rod 74 and 
the centerline of bar 94 (as shown HSU 28 has been designed so that angle 
.alpha. equals zero degrees at the static position) or: 
EQU F=P.sub.s A cos .alpha. (1) 
The direction of this force is along the centerline of bar 94. 
This force acts at an effective radius (r.sub.1) which is the perpendicular 
distance between the centerline of bearings 50,52 and the centerline of 
bar 94 to produce a moment around the centerline of the bearings. An equal 
and opposite moment reacts on road arm 44. The vertical sprung weight 
(F.sub.v) of vehicle 10 acts at the described HSU 28 at an effective 
radius (r.sub.2) which is the horizontal distance between the centerline 
of bearings 50,52 and the centerline of a wheel spindle 45 on free end 46 
to produce a second moment about bearings 50,52. Equating these moments to 
zero and solving for Fv yields: 
##EQU1## 
The volume of gas spring chamber 84 at any road arm position is equal to 
the initial volume (V.sub.s) at the static position (S) in FIG. 4 plus or 
minus the displacement of (X.sub.p) of piston rod 74 times its area A or: 
##EQU2## 
The pressure that corresponds to this volume is determined by the adiabatic 
expansion or compression of gas in the variable volume chamber 84 or: 
##EQU3## 
Where the factor .gamma. is the ratio of the specific heat of the selected 
gas at constant volume to the specific heat at constant pressure values 
are available in published tables. For all displacements of the road arm 
the piston rod displacement (X.sub.p), the angle (.alpha.), the effective 
connecting bar radius (r.sub.1), and the effective road arm radius 
(r.sub.2) may be determined by graphical or numerical means. Substituting 
these values in equations (2), (3), and (4) will permit the vertical force 
(F.sub.v) to be calculated for each displacement. 
In the past, damping systems of conventional in-arm suspension units have 
used restrictions to the flow of fluid between the fluid piston and the 
gas/fluid separator of a hydropneumatic spring to damp the vehicle 
oscillations as a function of piston direction of motion and velocity. 
Such restrictions absorb energy from the system and convert this energy to 
heat. The heat which is generated has to be dissipated to the surrounding 
atmosphere from the limited surface area of the arm (which may be caked 
with dried mud). The resultant increase in temperature causes increases in 
the fluid volume and the gas pressure which adversely affect the vehicle's 
height and attitude. 
The present invention has a hydraulically controlled rotary friction damper 
system 110 more specifically described in co-pending U.S. Ser. No. 
361,994, filed Mar. 25, 1982, now U.S. Pat. No. 4,447,073. System 110 is 
located remote from gas spring 60 in spindle 36, and operated 
independently of the spring drive mechanism and damps the vehicle 
oscillations as a function of road arm 44 direction of rotation, 
displacement, and velocity, pressure-flow characteristics of the hydraulic 
control system and friction-velocity characteristics of a rotary damper. 
Damper system 110 provides improved dynamic suspension system performance 
without the heat dissipation problem of conventional in-arm systems. 
Since the seal assembly 66 is submerged at all times and remote from damper 
produced heat, the glide rings 76, 86 and rod seal 78 have long life and 
do not have to seal directly against a gas volume. Thus the present 
invention is a dynamic gas (preferably nitrogen) rod sealing system which 
employs standard seal components whose function is enhanced by use of a 
gravity oriented oil barrier of unique configuration to seal between a 
high pressure oil region (oil barrier 82) and a lower pressure oil region 
(crankcase 54). 
Another embodiment of an oil submerged seal is illustrated in FIG. 6. A rod 
seal assembly 112 located in bore 62' includes a guide ring 114 in a 
support collar 116 to support a rod 74'. A piston rod seal 118 engages 
collar 116 and includes internal spring clips 120 that forces the seal 118 
into sealing engagement with the O.D. of rod 74' and the wall of bore 62'. 
A second seal support 122 has a snubber cavity 24 that attenuates the 
sealed oil pressure at seal 118. A floating rod seal 126 in support 122 is 
pressured upwardly as viewed in FIG. 6 when the piston rod 74' is stroked 
downwardly. The seal 126 includes an O-ring 128. The support 122 also 
carries a glide ring 130 at its opposite end. The seal assembly 122 
defines a dynamic, oil submerged seal for associated with the 
aforedescribed gravity oriented oil barrier arrangement to seal between a 
high pressure oil region and a lower pressure oil region. 
While the embodiment of the present invention, as herein disclosed, 
constitutes a preferred form, it is to be understood that other forms 
might be adopted. 
The embodiments of the invention in which an exclusive property or 
privilege is claimed are defined as follows: