Method for filling pressurized gas into a cylinder device

A cylinder device including a main body defining a cylinder therein, a cap member secured to the main body for closing one end of the cylinder, a piston working in the cylinder and having a piston rod passing through the cap member to project out of the main body, and a seal member surrounding the piston rod and being urged to abut with the inner surface of the cap member. There is provided a cavity between the cap member and the seal member, and an opening formed in the cap member for communicating the cavity with the outside.

BACKGROUND OF THE INVENTION 
This invention relates to a method of filling pressurized gas into cylinder 
devices, particularly applicable to hydraulic dampers or gas springs. 
For filling gas under pressure into cylinder devices such as hydraulic 
dampers or gas springs there have been proposed various techniques, 
drilling a gas filling hole in the wall of the cylinder device, filling 
the gas into the cylinder through the hole and, thereafter, plugging the 
hole; and such as, as shown in U.S. Pat. No. 4,114,866, pressing a seal 
member inwardly against the force of a spring, thereby forming a gas 
filling passage between the seal member and the cylinder, filling the gas 
under pressure into the cylinder through the gas filling passage, and 
releasing the pressing force applied from the outside to outwardly 
displace the seal member thereby closing the gas filling passage. There 
are shortcomings in the former technique in that it is troublesome to 
drill the gas filling hole, that it is necessary to weld the gas filling 
hole after inserting the plug into the hole, and that it is not possible 
to adjust the pressure of the gas being filled or to refill the gas. In 
the latter technique, the construction of a gas filling apparatus 
incorporating a pressing member for pressing the seal member is 
complicated and, further, the pressing member must be actuated 
simultaneously with the supply of the gas under pressure, and thus the 
operational procedure is complicated and troublesome. Further, it has been 
proposed as an improved procedure in the latter technique, to omit the 
pressing member by utilizing the pressure of the gas being filled for 
inwardly displacing the seal member, thereby forming a gas filling passage 
along the outer surface of the seal member. However, the outer surface of 
the seal member usually is engaged with the inner surface of the cylinder 
or of a cap member closing one end of the cylinder by the force of a 
spring and, in the initial condition, the pressure of the gas will act on 
a very limited annular area of the seal member defined between the outer 
diameter of the piston rod and the inner diameter of the central opening 
of the cap member passing therethrough the piston rod and, therefore, it 
is difficult to inwardly displace the seal member without applying a high 
pressure. 
SUMMARY OF THE INVENTION 
An object of the invention is to overcome the shortcomings of the last 
mentioned technique and, to provide a method for filling pressurized gas 
into a cylinder of the type including a main body defining a cylinder 
therein, a cap member secured to the main body and closing one end of the 
cylinder, a piston working in the cylinder and having a piston rod passing 
through the cap member to project out of the main body, a seal member 
surrounding the piston rod and being urged to abut with the inner surface 
of the cap member. There is provided means defining a cavity between the 
cap member and the seal member, and an opening in the cap member to 
communicate the cavity with the outside of the device. 
Preferably, the cavity has an annular configuration and is defined by an 
annular recess formed in the inner surface of the cap member or in the 
outer surface of the seal member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The cylinder device or the hydraulic damper illustrated in FIGS. 1 and 2 
comprises coaxially arranged outer and inner cylinders 1 and 2 which 
define therebetween an annular chamber 3. The lower ends of cylinders 1 
and 2 are closed by a cap 5. A chamber 4 is defined in the cylinder 2 and 
is divided into chambers 9 and 10 by a piston 8 which will be described 
hereinafter. Oil 7 is filled in the chamber 4 and in the lower portion of 
the chamber 3. The oil 7 in the chamber 3 communicates with the oil in the 
chamber 4 through an opening 6 formed through the cylinder 2. The piston 8 
is provided with passages 11 and a disc valve 12 which controls the oil 
flow passing through the passages 11 thereby generating a damping force 
during upward and downward movement of the piston in the cylinder. A 
piston rod 13 is secured to the piston 8 and extends through the oil 
chamber 9, a rod guide 14, a seal member 15 and a cap member 16 to project 
outside of the damper. A mounting ring 17 is secured to the outer end of 
the piston rod 13. The cap member 16 secured to the upper end of the 
cylinder 1 defines a chamber 18 on the inner side thereof and between the 
rod guide 14 which is secured to the upper ends of the cylinders 1 and 2. 
A coil spring 19 is disposed in the chamber 18 for biassing the seal 
member 15 upwards against the inner surface of the cap member 16. An 
opening 21 is formed in the rod guide 14 for connecting the chambers 3 and 
18. The seal member 15 is formed of flexible material and receives the 
force of the spring 19 through a retaining plate 22, and the radially 
inner surface 23 of the seal member 15 slidingly engages with the piston 
rod 13. The upper surface 24 of the seal member 15 engages with the inner 
surface of the cap member 16, thereby maintaining the fluid tightness of 
the chamber 18. Thus, the seal member 15 surrounds the piston rod 13 and 
is urged to abut with the inner surface of the cap member 16. 
According to the invention an annular cavity 25 is formed between the cap 
member 16 and the seal member 15. The cavity 25 is defined by an annular 
recess 26 formed in the upper surface 24. In the embodiment of FIG. 2, the 
bottom surface 27 of the recess 26 is generally parallel with the inner 
surface of the cap member 16. The cavity 25 is connected permanently with 
the outside of the damper through an opening 28 formed between the central 
bore of the cap member 16 and the connecting rod 13 passing through the 
bore. Gas under high pressure is enclosed in the upper portion of the 
annular chamber 3. A mounting ring 30 is secured to the cap 5. 
The hydraulic damper having the construction described as above is mounted 
between, e.g. the sprung mass and unsprung mass of a vehicle by means of 
mounting rings 17 and 30. 
FIGS. 3 and 4 illustrate the process for filling high pressure gas into the 
hydraulic damper of FIG. 1. 
Firstly, the upper end portion of the damper is inserted into a filling 
container 35 of a gas filling apparatus with the mounting ring 17 not 
being mounted on the piston rod 13. A chamber 36 defined in the container 
35 is sealed by seals 37 and 38. Then, high pressure gas is supplied into 
the chamber 36 through a gas supplying port 39. The high pressure gas is 
introduced into the cavity 25 through the opening 28. The high pressure 
gas supplied into the cavity 25 acts on the seal member 15 to displace it 
against the force of the spring 19. The seal member 15 separates from the 
inner surface of the cap member 16 thereby forming a gas filling passage 
40, as shown in FIG. 4, between the inner surface of the cap member 16 and 
the upper surface of the seal member 15. The high pressure gas in the 
chamber 36 is supplied into the chamber 18 through the passage 40, and 
introduced into the chamber 3. Preferably, the pressure receiving area of 
the surface 27, the dimension of the seal member 15, and the force of the 
spring 19 are determined such that when the pressure of the gas filled 
into the chambers 3 and 18 is increased to a predetermined pressure the 
seal member 15 displaces upwardly due to the force of the spring 19, 
thereby closing the passage 40 with the upper surface 24 of the seal 
member 15 abutting with the inner surface of the cap member 16. The supply 
of the high pressure gas into the damper is stopped, and the gas under a 
predetermined pressure has been filled into the damper. 
In the above described embodiment, the cavity 25 is formed by a recess 26 
in the seal member 15. In FIG. 5, a cavity 52 is formed by an annular 
recess 51 provided in the inner surface of the cap member 16. The cavity 
52 communicates with the outside through the opening 28. In FIG. 6, a 
cavity 62 is formed by a recess 61 formed in the upper surface 24 of the 
seal member 15. The recess 61 is defined by a horizontally extending 
surface as shown in the drawing. 
FIG. 7 shows a modified form wherein a seal member 72 engaging with the 
inner surface of the cap member and with the peripheral surface of the rod 
guide also has a lip portion 71 engaging with the upper surface of the rod 
guide 14 to constitute a check valve preventing the high pressure gas in 
the chambers 3 and 18 from being introduced into the chamber 9. 
In the above described embodiments the cavity has an annular form as viewed 
in the vertical direction, but, the cavity may have any desired 
configuration and, further, a plurality of mutually disconnected cavities 
may be provided. The cavities in the embodiments is connected with the 
outside through the central opening 28. However, the cavity may be 
connected to the outside through an opening distinct from the central 
opening as shown in FIG 8, wherein an annular cavity 82 is connected to 
the outside through an opening 81 passing through the cap member 16. 
As described heretofore according to the invention, a cavity is formed 
between the inner surface of the cap member and the upper or outer surface 
of the seal member and is connected to the outside. Thus, it is possible 
to omit the seal member pressing member in the prior art gas filling 
apparatus, thus simplifying the apparatus and simplifying the gas filling 
operation. Further, the pressure of the gas for displacing the seal member 
can substantially be reduced as compared with prior art methods, thus 
enabling a reliable gas filling operation and, further, the pressure of 
gas being filled can easily be adjusted by a refilling operation.