Composite radial seal

A composite radial seal for sealing the rod end of a hydraulic cylinder or suspension strut is disclosed. The composite seal includes a high abrasion resistant elastomeric seal ring having an elongated body. The body has a pressure end and a non-pressure end, with the pressure end having a U-cup configuration and a first dynamic seal lip and the non-pressure end having an enclosed annular cavity and a second dynamic seal lip. The cavity contains and is filled with a highly resilient energizer ring. Seal also includes an integral anti-extrusion ring that is bonded to the non-pressure end of the seal ring body adjacent and on the non-pressure side of the second seal lip to prevent extrusion of the seal lip into a clearance gap between a rod and a head of the cylinder or strut.

TECHNICAL FIELD 
The present invention relates generally to seals for sealing hydraulic 
cylinder rods and the like and more particularly to an improved composite 
radial seal for such use. 
BACKGROUND ART 
U-cup radial seals have been used for many years in high pressure 
applications, such as hydraulic cylinders, suspension struts and the like, 
to seal around the reciprocating rods of such cylinders or struts and 
prevent the escape of hydraulic fluid. Such U-cup seals come in many 
shapes and styles and have included separate elements that have 
contributed to their sealing ability. For instance, some use separate 
energizer springs, in the form of rubber O-rings or the like. Such rubber 
springs are typically located between the legs of the U-cup seal. Because 
such rubber O-ring springs are exposed to the hydraulic fluid in the 
cylinder, the selection of rubber material is dictated by its 
compatibility to the hydraulic fluid. As a result, its functional 
characteristics as a spring may suffer in such selection. Also, dynamic 
pressures on and movements of the seal can dislodge the rubber spring from 
its intended position and reduce its effectiveness. Other U-cup seals have 
been utilized with separate anti-extrusion rings, which are intended to 
prevent the seal lips of the seal from extruding into the annular gap 
between the cylinder rod and the cylinder housing or head as the result of 
the high pressures in the cylinder or the reciprocating movement of the 
rod. However, such separate anti-extrusion rings may be assembled in the 
wrong location or inadvertently left out during assembly. Other U-cup 
seals are provided with two axially spaced seal lips. High fluid pressure 
may become entrapped between these two lips. This can result in fluid loss 
due to leakage past the second seal lip on the non-pressure side of the 
seal. 
The present invention is directed to overcoming shortcomings of the prior 
U-cup seals with respect to separate components to obtain improved sealing 
performance and to fluid loss problems. 
DISCLOSURE OF THE INVENTION 
In accordance with one aspect of the present invention, a composite radial 
seal for sealing about a rod a hydraulic device is provided with a high 
abrasion resistant elastomeric seal ring having an elongated body. The 
body has a pressure end and a non-pressure end, with the pressure end 
having a U-cup configuration and a first dynamic seal lip and the 
non-pressure end having an enclosed annular cavity and a second dynamic 
seal lip. The cavity contains and is filled with a highly resilient 
energizer ring. Seal also includes an integral anti-extrusion ring that is 
bonded to the non-pressure end of the seal ring body adjacent and on the 
non-pressure side of the second seal lip to prevent extrusion of the seal 
lip into a clearance gap between a rod and a head of the hydraulic device.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring more particularly to the drawings, a composite radial seal 
embodying the principles of the present invention is generally indicated 
at 10 in FIG. 1 and is of a type for sealing the rod end of a hydraulic 
device, such as a suspension strut partially shown in cross-section at 12. 
Strut 12 includes a cylindrical rod 14 and an annular head 16. The rod 14 
has an outer sealing surface 18. Sealing surface 18 is suitably finished, 
as by chrome plating, in order to provide it with a smooth surface 
texture, high hardness and corrosion resistance. Head 16 has a stepped 
bore 20 for receiving the rod therethrough. Stepped bore 20 has bearing 
portion 22, having a close fit relation with the rod, and a clearance 
portion 24, having a somewhat larger diameter to eliminate its contact 
with the sealing surface 18 of the rod 14, as it is on the non-pressure 
side of the seal 10. A predetermined clearance gap "G" is thereby created 
between the sealing surface 18 of the rod 14 and the clearance portion 24. 
Head 16 also includes an annular groove 28 located between the bearing and 
clearance portions 22,24 of the stepped bore 20 for mounting the seal 10. 
As best shown in FIG. 2, the composite seal 10 includes a high abrasion 
resistant elastomeric seal ring 30, a highly resilient energizer ring 32 
and an integral anti-extrusion ring 34. 
Seal ring 30 has an elongated body 36 having a pressure end 38 and a 
non-pressure end 40, the pressure end 38 being the end exposed to fluid 
pressure in the suspension strut 12 and the non-pressure end 40 being the 
end exposed to atmospheric pressure through the clearance gap "G". 
The pressure end 38 is provided with a U-cup configuration 42 with an inner 
axially extending leg 44 and an outer axially extending leg 46 that are 
separated by an annular pressure cavity 48 that is open to the groove 28 
(FIG. 1). The inner leg 44 is formed shorter than the outer leg 46 to 
provide an annular passage 50 to the pressure cavity 48 for communicating 
fluid pressure in the strut 12 to the cavity 48. Referring again to FIG. 
2, the inner leg 44 is equipped with a first dynamic seal lip 52 that 
protrudes radially inwardly therefrom for dynamic sealing engagement 
against the sealing surface 18 of the rod 14. The outer leg 46 is provided 
with a static seal lip 54 for static sealing engagement against the groove 
28. 
The non-pressure end 40 is provided with an enclosed annular cavity 56 and 
a second dynamic sealing lip 58 that protrudes radially inwardly therefrom 
for dynamic sealing engagement against the sealing surface 18 of the rod 
14 in a similar fashion to the first lip 52. 
The energizer ring 32 fills and is sealed within the enclosed cavity 56 of 
the non-pressure end 40. Ring 32 may be encased inside the cavity 56 
during the molding process of the seal ring 30 or by any other suitable 
means known in the art. 
In the embodiment illustrated in FIGS. 1 and 2, the anti-extrusion ring 34 
is carried on the non-pressure end 40 of the seal ring body 36 adjacent to 
and on the non-pressure side of the second seal lip 58, in essence, at an 
inner corner 59 of the body 36 which may be notched to receive the ring 
34. The anti-extrusion ring 34 is secured to the ring body 36 by bonding 
so as to be an integral part thereof. Ring 34 is constructed with an 
inside diameter that is only slightly greater than the diameter of the rod 
14 and an outside diameter that is marginally greater than the clearance 
portion 24 of the bore 20 of the head 16 so as to span the gap "G". Such 
outside diameter, however, is not so great as to prevent the mounting of 
the seal 10 into the groove 28 with the limited flexure afforded by the 
anti-extrusion ring 34. The described construction of the anti-extrusion 
ring 34 is able to provide backup to the second lip 58 in order to prevent 
the lip 58 from being extruded into the gap "G" as the result of high 
fluid pressure in the strut 12 and/or the reciprocating movement of the 
rod 14. 
FIG. 3 illustrates another embodiment of the present invention wherein a 
composite radial seal 10' is provided with a full anti-extrusion ring 60 
that is bonded to an end surface 62 of the seal ring body 36'. The full 
ring 60 illustrated in this embodiment may by used when a detachable end 
cap 64 is employed on the head 16' of the strut 12 so as to permit the 
installation of the seal 10' into an open ended groove 28'. 
It should be noted that the seal 10 or 10' have a radial cross-section 
height "H" in a free state, as shown in FIG. 2, that is greater than the 
radial distance "D" between the sealing surface 18 of the rod 14 and the 
bottom of the groove 28. Thus, when the seal 10 is in its operating 
position in the strut 12, as shown in FIG. 1, it is in a compressed state. 
In particular, the energizer ring 32 is loaded to exert a predetermined 
compressive force on the second seal lip 58. 
Industrial Applicability 
The seal 10 constructed in accordance with the teachings of the present 
invention advantageously provides superior sealing and longer wear life in 
high hydraulic pressure applications, such as found in hydraulic cylinders 
and hydraulic suspension struts used on large earthmoving vehicles, such 
as tractors, loaders, excavators, off-highway trucks and the like. 
As is apparent from the above description and the drawings, seal 10 or 10' 
have means for pressure energizing the first dynamic seal lip 52 and means 
for compression energizing the second dynamic seal lip 58. The pressure 
energizing means is afforded by the U-cup configuration of the pressure 
end 38, as is well known in the art. Communication of fluid pressure into 
the pressure cavity 48 is ensured in the present seal 10 or 10' by means 
of the annular passage 50. During operation of the strut 12, fluid 
pressure levels in the strut will fluctuate, as will be appreciated by 
those skilled in the art. As a consequence, the pressure energizing means 
will exert a variable force on the seal lips 52 and 54, depending on the 
fluid pressure levels existing the the strut 14 from time to time. 
The compression energizing means is afforded by the energizer ring 32 that 
acts solely on the second dynamic seal lip 58 and applies a predetermined 
constant force on such second seal lip 58. This constant force is 
preferably selected to be greater than the force exerted on the first seal 
lip 52 when the fluid pressure in the strut is below a preselected minimum 
level. One particular advantage that is achieved by this arrangement is 
that any high pressure fluid that becomes entrapped between the first and 
second lips 52 and 58 will be vented back into the strut 12 past the first 
lip 52 when the fluid pressure in the strut decreases below the selected 
minimum level, rather than escaping past the second lip 58, thereby 
reducing fluid loss from the strut 12. 
Another advantage of the present invention is that the energizer ring 32 is 
completely encapsulated within the seal ring 30. Because of this, the 
energizer ring 32 is not exposed to the hydraulic fluid in the strut or 
cylinder. This permits the selection of the material of the energizer ring 
32 to be based solely on its spring characteristics, and not on its 
compatibility with the hydraulic fluid. As a result, a softer elastomeric 
material, with a low compression set and high resilience that is 
maintained over a wide temperature band, can be used. A material, such as 
silicone rubber, with a hardness of less than 90 Shore A durometer is 
preferred. 
Likewise, the selection of the material for the seal ring 30 can be based 
on its sealing and abrasion resistance characteristics, and less so on its 
compression set and resiliency characteristics, as the latter functions 
are provided by the energizer ring 32. As a consequence, a harder, 
tougher, and higher abrasion resistant material can be used for the seal 
ring 30. Preferably, the seal ring 30 is of a material with a hardness of 
about 40 to 80 Shore D durometer. One such material is polyurethane, as is 
well known in the art. 
Lastly, the selection of the material for the anti-extrusion ring 34 can be 
based on its rigidity and bending strength in functioning to prevent the 
extrusion of the seal ring 30 into the gap "G". The ring 34 employed in 
the first embodiment depicted in FIGS. 1 and 2 must also be sufficiently 
elastically deformable to permit the seal 10 to be installed in the groove 
28. Materials, such as polyarylsulfone or nylon, with a flex modulus of 
around 400,000 p.s.i. are preferred for the anti-extrusion ring 34. 
Other aspects, objects and advantages of the present invention can be 
obtained for a study of the drawings, the disclosure and the appended 
claims.