Cylinder cushion seal

A synthetic plastic cushion seal for an expansible chamber motor usable with either an air or oil pressurized medium, the seal having reduced friction characteristics, being of a concise configuration and utilizing radial and axial channels to facilitate medium flow during pressurization of the associated motor chamber.

BACKGROUND OF THE INVENTION 
Expansible chamber motors using pressurized air or hydraulic oil commonly 
utilize cushioning structure to prevent deleterious impact of the piston 
components with the motor heads at the termination of a stroke. Such 
cushion structure usually includes a passage defined in a motor head, 
usually concentric with the cylinder, through which exhausted medium 
passes. This exhaust passage receives a valve member affixed to piston 
structure as the piston approaches the head wherein the valve member 
restricts the flow of exhaust medium through the passage slowing the rate 
of flow of the exhausting medium and utilizing such medium for cushioning 
purposes at the termination of the piston stroke. 
Such cushioning apparatus normally utilizes an annular seal within the 
passage opening which cooperates with the piston mounted valve member to 
seal the valve member with respect to the passage during the cushioning 
phase. Bleed means having a regulatable restricted flow communicate with 
the cylinder chamber adjacent the head allowing the cushioning medium to 
be exhausted at a controlled rate thereby permitting the piston to move 
through its full stroke, yet at a reduced velocity, to control the 
engagement between the piston components and the motor head. 
When pressurizing the chamber, the pressurized medium is imposed upon the 
cushioning apparatus, and it is known to construct the passage seal ring 
in such a manner that medium flow about the seal is permitted to 
pressurize the adjacent motor chamber, and initiate piston movement. 
Various seal configurations have been utilized to improve the operating 
and life expectancy of cushion seal apparatus, including seal rings, and 
typical cushioned expansible motor constructions are shown in the 
assignee's U.S. Pat. Nos. 2,719,510 and 2,804,052 and in U.S. Pat. Nos. 
2,704,996; 2,710,595; 2,755,775; 2,853,974; 3,267,815; 3,626,807; 
3,805,672 and 4,088,061. 
Presently available cushioning apparatus of the aforementioned type often 
impose friction upon the piston structure which increases the pressure 
required to initiate piston movement, and such seals are often of the lip 
seal type which necessitates that the pressurized medium be sufficient to 
raise the lip seal before significant flow through the seal is possible. 
Also, known cushioning apparatus is relatively expensive to manufacture, 
and is not of such a concise configuration as to readily permit the 
associated motor head to accommodate bleed off structure. Further, the 
installation of cushion structure of the known type into expansible 
chamber motors is relatively complex and time consuming, and if the 
assembly is not properly achieved failure of the cushion structure will 
readily occur. 
It is an object of the invention to provide cushion seal structure for an 
expansible chamber motor wherein the seal has improved friction reducing 
characteristics and permits pressurized medium to bypass the seal at lower 
pressures than usual. 
A further object of the invention is to provide a cushion seal for an 
expansible chamber motor wherein the seal results in a shorter cycle time 
lag during operation and the seal may be readily assembled into a 
permanent groove within the motor head and is maintained therein by the 
normal configuration of the seal. 
An additional object of the invention is to provide a cushion seal for an 
expansible chamber motor which is formed of a synthetic plastic material, 
is economical to manufacture and has a long effective operating life, and 
is capable of permitting relatively high medium flow rates to circumvent 
the seal during pressurization of the adjacent cylinder chamber. 
In the practice of the invention the head of an expansible chamber motor 
includes a concentric fluid passage through which pressurized medium 
enters the associated cylinder chamber, and is exhausted therefrom. An 
annular groove defined in this passage receives a synthetic plastic 
cushion seal, such as formed of urethane, and the seal includes an inner 
bore generally of conical configuration which cooperates with a 
cylindrical valve member mounted upon the piston structure which enters 
the passage as the piston approaches the cylinder head. 
The seal includes a radial face adapted to engage and seal against the 
passage groove during exhausting of the pressurized medium, and bleed 
passages formed in the head permit the pressurized medium which has 
produced a cushioning effect to be bled from the cylinder at a controlled 
rate. 
When pressurized medium is to be introduced into the adjacent cylinder 
chamber, the cushion seal permits medium flow therearound due to axial 
displacement of the seal ring which disengages the seal ring radial 
surface from the passage groove face. Axial channels defined in the seal 
circumference communicate with radial channels defined in the seal face 
nearest the piston wherein the channels are capable of handling a 
relatively large capacity flow of pressurized medium to initiate piston 
movement facilitating withdrawal of the valve from the head passage. 
The bore of the seal is of a conical-cylindrical configuration wherein a 
limited area of engagement exists between the seal and valve and the 
characteristics of the seal are such as to minimize frictional drag 
between the seal and valve components, and minimize the frictional 
resistance of pressurized medium flowing therearound. 
The flexible and resilient characteristics of the seal permits the seal to 
be readily deformed for assembly purposes into the motor head, yet the 
seal configuration, and the associated head groove, prevent "roll out" of 
the seal from the groove due to frictional or pressure forces thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A typical expansible chamber motor utilizing the cushion seal of the 
invention is illustrated in FIG. 1. The motor 10 includes a cylindrical 
cylinder 12 closed at each end by a head 14, and a head 16 through which 
the piston rod extends. The heads are sealingly mounted upon the cylinder 
12 by tie rods 18. 
The head 14 includes a threaded port 20 in communication with coaxial 
passage 22 in which cushion seal groove 24 is formed which receives the 
cushion seal 26. Likewise, the head 16 includes threaded port 28 
communicating with coaxial passage 30 in which annular groove 32 is 
located for receiving an identical cushion seal 26. A piston rod gland 34 
is mounted upon the head 16 by the associated tie rods 18. 
The piston 36 is affixed to the piston rod 38 by a nut 40 which maintains 
the assembly of the piston and annular valve 42 upon the rod. The 
innermost end of the rod includes valve 44, and the valves 42 and 44 are 
of a similar construction, each being of a cylindrical form and including 
a conical seal aligning surface 46. The valves 42 and 44 are fixed on the 
piston rod, and as appreciated from FIG. 1, are disposed adjacent the 
piston 36 which is sealed with respect to the inner surface of the 
cylinder 12 by the usual annular piston rings 48. 
Bleed off of the cushioning medium to the left of the piston 36, FIG. 1, is 
through bleed passage 50 which communicates with the cylinder chamber 52 
and the passage 30. The rate of medium flow through the passage 50 is 
regulated by needle valve 54 whose position is locked by the lock nut 56. 
The general operation of the illustrated expansible chamber motor and 
cushions is similar to that described in the aforementioned patents. For 
instance, pressurizing of the cylinder chamber 58 to the right of piston 
36 through passage 22 causes the piston to move toward the head 16 at a 
rate dependent upon the rate of pressurization of the medium on the right 
of the piston. As the piston moves towards head 16 the valve 42 enters the 
passage 30, coaxially aligns the cushion seal 26 with the valve due to the 
presence of surface 46, and the reception of the valve within the passage 
30 restricts the flow of exhausting medium through the passage slowing the 
rate of movement of the piston and piston rod 38. Thereupon, the rate of 
movement of the piston towards the head 16 is determined by the rate of 
flow of the medium through the bleed off passage 50, and piston movement 
will terminate upon engagement of the piston with the head 16. 
Upon the supplying of a pressurized medium to port 28 and passage 30, and 
exhausting the medium through head 14, the forces imposed upon the valve 
42 and piston 36 move the piston and piston rod 38 toward head 14 
reversing the aforedescribed procedure. Cushioning of the piston rod as it 
approaches head 14 is accomplished by reception of the valve 44 into the 
sealed passage 22. A bleed passage, not shown, may be utilized in the head 
14. 
The details of construction of the cushion seal 26 are best appreciated 
from FIGS. 2-6. The seal consists of an annular ring of synthetic plastic 
material, preferably urethane having a 70 Durometer. The seal includes an 
inner bore having a conical surface portion 60, and a cylindrical surface 
portion 62. The axial dimension of the seal is defined by an outer radial 
face 66 of a flat configuration, and the inner radial face 64 which is 
disposed toward the piston. The inner face 64 is also of a planar 
configuration, and both seal faces are disposed at substantially right 
angles to the axis of the seal. 
The seal circumference is substantially cylindrical, and the seal is of a 
diameter less than the diameter of the associated head groove cylindrical 
surface 68. The head groove also includes an outer flat face 70 and an 
inner flat face 72, both of which are at right angles to the axis of the 
expansible motor, and the axial separation of the groove faces 70 and 72 
is greater than the axial dimension between the seal faces 64 and 66, as 
will be appreciated from FIGS. 5 and 6. 
The seal face 64 is provided with four radial channels 74 which at their 
innermost end intersect the seal bore portion 62, and at their outermost 
end each align with an axially extending channel 76 defined in the seal 
circumference. The circumference channels 76 intersect the seal face 66. 
The "corner" of the cushion seal as represented by an axial projection of 
the circumference, and a radial projection of the face 64, is removed, or 
notched, at 78, wherein a clearance or opening exists at the intersection 
of the aligned channels 74 and 76 producing a minimum of flow resistance 
between the channels. 
The cushion seal 26 is assembled into the associated head groove 24 or 32 
by deforming the seal radially and the seal may be readily installed into 
its head groove by such deformation, and will accommodate to the groove 
configuration upon release due to the resilient nature of the seal 
material. 
In use, the cushion seal 26 "floats" within the associated head groove 24 
or 32 due to the fact that the diameter of the seal is less than the 
groove diameter, and the axial seal dimension is less than the groove 
axial dimension. During cushioning, the seal bore 62 will be initially 
engaged by the piston valve surface 46, which concentrically aligns the 
seal with the piston. The frictional engagement between the seal and 
valve, which is of an interference fit, forces the seal face 66 against 
the groove face 70, FIG. 5, establishing a sealing relationship between 
the seal and the groove. Thereupon, the pressure within the exhausting 
medium in chamber 52, for instance, will maintain the seal in tight 
relationship with the groove face 70, and as the seal will be firmly 
engaging the cushion valve 42 the flow of exhaust medium through the 
passage 30 is terminated, and exhausting of the pressurized medium takes 
place through the bleed passage 50 during the final stages of cushioning. 
To reverse the motor stroke, pressurized medium is supplied to the head 16, 
and the port 20 becomes an exhaust port. Initial pressurization of the 
passage 30 will displace the piston rod valve to the right, permitting 
pressurized medium to flow between the seal 26 and the groove face 70, 
through the channels 76, and through the radial channels 74, as 
represented by the arrows in FIG. 6. This simultaneous flow of pressurized 
medium through the four circumference and inner face channels permits a 
relatively high volume of pressurized medium to flow into the motor 
chamber 52 rapidly displacing the piston 36 to the right, and upon 
clearance of the valve 42 from the seal 26, the full flow capacity of the 
passage 30 will drive the piston. 
The presence of the channels 74 and 76 assures a high "bypass" flow rate 
about the cushion seal prior to the passage 30 being fully opened, and the 
seal construction results in a low "breakout" friction and permits a short 
time lag between cycles of the piston as a lip seal relationship is not 
present between the seal and valve. As the seal produces a fluid tight 
seal with the groove face 70 and the valve 42 under the conditions of FIG. 
5, effective cushioning is produced, and the rectangular cross section of 
the seal prevents the seal from being "rolled out" of the associated head 
groove during high flow capacity through the associated passage during 
bypass as in FIG. 6. 
This type of seal requires little overall radial dimension permitting 
adequate space within the motor head for the bleed passage, which is a 
problem with small diameter size expansible chamber motors, and the molded 
urethane construction is much more economical to produce than many of the 
fabrication techniques of prior art cushion seals. 
In FIG. 7 a modified form of cushion seal 26' is illustrated wherein the 
circumferential channels are defined by flats 80 formed in the seal 
circumference intersecting the seal inner and outer faces. Also, as will 
be appreciated, the dimension of the aligned radial passages 82 
corresponds to the dimensions of the circumferential flats, and this 
construction permits a seal of small dimension to effectively bypass 
relatively large volumes of pressurized medium with little restriction. 
The aforedescribed cushion seals may be used equally well with pressurized 
oil or air type expansible chamber motors, and it is appreciated that 
various modifications to the inventive concepts may be apparent to those 
skilled in the art without departing from the spirit and scope of the 
invention.