Gas spring

A gas spring 20 having a piston 23 slidably disposed within a cylinder 21 sealed with air 25, with one end of the cylinder closed, having a rod 22 fixed to the piston 23, having cylinder grooves 29 extending in an axial direction of the cylinder formed on the inner periphery of the cylinder so that an extension side damping force is generated in an extension process in the cylinder grooves, and having one end of the cylinder and the rod fitted to a vehicle body with the other end fitted to a rear door pivoted on the body, wherein the cylinder grooves are formed in both-side movable areas X and Z excluding a locking area Y in a stroke area of the piston.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a gas spring to be used for opening and closing 
of a rear door of a four-wheel drive or vehicle, which includes vans, 
station wagons and other type of vehicles. 
2. Description of Related Art 
In the vehicle, generally there is provided a rear door (an opening and 
closing member) which is pivoted around a horizontal axis or a 
perpendicular axis next to vehicle body (main body), with a gas spring 
provided between the rear door and the body so that the force required for 
opening the rear door is reduced by a repulsive force (assisting force) of 
the gas spring. 
Among such types of gas springs, there is one, as disclosed by the Japanese 
Utility Model Application Laid-open Publication No. 63-80346, where the 
rear door is connected to the body pivotally around a horizontal axis, and 
a guide pin is provided in a cylinder of the gas spring, and a guide 
cylinder is extended to cover the cylinder from the both-sides and is 
disposed in a rod, a guide groove is extended in a direction of extension 
and compression stroke of the gas spring and is formed in the guide 
cylinder, and the guide pin is engaged with an engagement stage of the 
guide groove, to thereby restrict the extension stroke of the gas spring 
so as to adjust the extent of opening of the rear door in two stages. 
According to the gas spring described in the above publication, however, it 
is necessary to provide the guide pin and the guide cylinder, which 
results in an increase in the number of parts and an increase in the 
number of assembly process as well as the cost to manufacture. 
SUMMARY OF THE INVENTION 
The present invention is provided overcomes the disadvantages of the above 
structure, and it is an object of the present invention to provide a gas 
spring which enables an adjustment of the extent of opening of the opening 
and closing member in a plurality of stages without incurring an increase 
in the number of assembly steps and production cost increase. 
According to the present invention, a piston is slidably disposed within a 
cylinder in which a gas is sealed with one end of the cylinder closed. A 
rod fixed to the piston projects from an open end of the cylinder. 
Repulsive force means for generating a repulsive force for biasing the rod 
to the extension direction is provided within the cylinder. Cylinder 
grooves extending in an axial direction of the cylinder are formed on the 
inner periphery of the cylinder. An extension side damping force is 
generated in the extension process in the cylinder grooves, and one of the 
cylinder and the rod is fitted to a main body with the other fitted to an 
opening and closing member pivotally provided in the main body. The 
cylinder grooves are formed in both-side areas excluding a predetermined 
area in the stroke direction of the piston.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
(A) A first embodiment 
Embodiment of implementation of the present invention will be explained 
below with reference to the drawings. 
FIG. 1 is a side cross sectional view showing a first embodiment of a gas 
spring relating to the present invention. FIG. 2 is a cross sectional view 
along a II--II line in FIG. 1. FIG. 3 is a cross sectional view along a 
III--III line in FIG. 1. FIG. 4 is a side view showing the surrounding of 
a rear door of a vehicle with the gas spring shown in FIG. 1. 
A gas spring 20 shown in FIG. 1 is used on a vehicle, and is used 
particularly as a gas spring of laternal open-door type. This gas spring 
20 has a piston 23 fastened to one end of a rod 22 and slidably disposed 
within a cylinder 21 with one end of the cylinder 21 closed. A bracket 24 
of the cylinder 21 is fitted to a vehicle body 2 as a main body and the 
other end of the rod 22 is fitted to a rear door 4 of the vehicle as an 
opening and closing member, as shown in FIG. 4. The rear door 4 is 
attached to the body 2 pivotally around a vartical axis 6. 
As shown in FIG. 1, air 25 (or a nitrogen gas or the like) as gas is sealed 
in the cylinder 21, and a rod guide 26 and a gas seal 27 are disposed at 
an open end of the cylinder 21. Movement of the rod 22 along with the 
above-described sliding of the piston 23 is guided by the rod guide 26, 
and leakage of air 25 is prevented by the gas seal 27. A fine volume of 
oil sufficient to maintain a satisfactory sealing and lubrication of the 
gas seal 27 is sealed within the cylinder 21. 
The inside of the cylinder 21 is divided by the piston 23 into a rod-side 
chamber 28B in which the rod 22 is accommodated and a piston-side chamber 
28A in which the rod 22 is not accommodated. Air 25 is sealed in both 
chambers 28A and 28B. The pressure of air 25 (air repulsive force) is the 
same in both the piston-side chamber 28A and the rod-side chamber 28B. 
However, since the area which receives the pressure of the piston 27 in 
the piston-side chamber 28A is larger than the area which receives the 
pressure of the piston in the rod-side chamber 28B by the amount of cross 
sectional area of the rod 22, the air repulsive force within the 
piston-side chamber 28A works as a bias force (assist force) for biasing 
the rod 22 and the piston 23 in the direction of an extension of the gas 
spring 20 in an extension process of the gas spring 20, so that the air 25 
functions as repulsive force means. 
On the inner periphery of the cylinder 21, cylinder grooves 29 are formed 
as shown in FIGS. 1 and 2. These cylinder grooves 29 are formed by 
expanding the inner periphery of the cylinder 21 outwardy in a plastic 
processing such as roll forming or the like. A collar 30 is disposed near 
the position where the rod guide 26 and the gas seal 27 are disposed in 
the cylinder 21. The piston 23 is brought into contact with the collar 30 
and a further move of the piston 23 in the extension direction is 
restricted, so that the position at which the piston 23 is brought into 
contact with the collar 30 is the maximum extension end of the piston 23. 
In the above-described piston 23, a ring-shaped groove 31 is formed in the 
outer periphery, and the O-ring 34 is engaged in this ring-shaped groove 
31 as an elastic sealing member. The O-ring 34 is closely adhered to the 
inner peripheral surface of the cylinder 21. The piston 23 is a structure 
without a passage such as an orifice for communicating between the 
piston-side chamber 28A and the rod-side chamber 28B. 
The rear door 4 is opened and closed in the range from a fully closed 
position to a fully opened position as indicated by a solid line, as shown 
in FIG. 4. In this case, the piston 23 of the gas spring 20 moves in the 
range of almost one full stroke area of the cylinder 21. The opening 
operation of the rear door 4 is carried out by an extension of the gas 
spring 20 caused by a repulsive force of air 25 within the piston-side 
chamber 28A. In this case, air 25 within the rod-side chamber 28B shown in 
FIG. 1 flows to the piston-side chamber 28A through the cylinder groove 
29, so that an extension-side damping force is generated by a resistance 
of the flow. 
The cylinder grooves 29 are formed to extend in an axial direction of the 
cylinder 21 on the inner periphery of the cylinder 21 in both-side movable 
areas X and Z excluding a locking area Y of the stroke area of the piston 
23, as shown in FIGS. 1 to 3. In other words, the cylinder groove 29 is 
not formed in the locking area Y of the cylinder 21, as shown in FIG. 3. 
In the areas X and Z, the cylinder groove 29 has a square cross-sectional 
shape, with almost a constant cross section. 
When the piston 23 is located in the movable areas X and Z, air 25 flows 
through the cylinder grooves 29. In the extension process of the gas 
spring 20, an extension-side damping force is generated by the flow 
resistance caused by the flow of air 25 within the rod-side chamber 28B 
through the cylinder groove 29, and the moving speed of the piston 23 and 
the rod 22 in the extension direction is controlled by this extension-side 
damping force, with the result that the opening speed of the rear door 4 
is appropriate. 
When the piston 23 has reached the locking area Y in the extension process 
or the compression process of the gas spring 20, air 25 does not flow from 
the rod-side chamber 28B to the piston-side chamber 28A between the O-ring 
34 mounted on the piston 23 and the cylinder 21 because the cylinder 
groove 29 is not present at that point in the cylinder 21. Therefore, the 
piston 23 and the rod 22 stop in this locking area Y, so that the rear 
door 4 stops at a position indicated by a two-dot chain line as shown in 
FIG. 6. 
The operation will be explained next. 
In the extension process of gas spring 20, the repulsive force of air 25 
within the piston-side chamber 28A shown in FIG. 1 works to the piston 23 
and the rod 22, so that the piston 23 and the rod 22 move in the extension 
direction. 
When the piston 23 is in the movable area X in the extension process of the 
gas spring 20, air 25 within the rod-side chamber 28B flows through the 
cylinder groove 29 into the piston-side chamber 28A, and a extension-side 
damping force is generated by the flow resistance caused by the flow of 
air 25 through the cylinder groove 29. By this extension-side damping 
force, the moving speed of the piston 23 and the rod 22 for moving in the 
extension direction by the repulsive force of air 25 within the 
piston-side chamber 28A is controlled to a proper level. Accordingly, the 
rear door 4 is opened at a proper speed from the fully closed position as 
shown in FIG. 4. 
When the piston 23 has reached the locking area Y in the extension process 
of the gas spring 20 shown in FIG. 1, air 25 does not flow from the 
rod-side chamber 28B to the piston-side chamber 28A between the O-ring 34 
mounted on the piston 23 and the inner peripheral surface of the cylinder 
21 because the cylinder groove 29 is absent in the locking area Y. 
Therefore, the piston 23 and the rod 22 stop in this locking area Y, so 
that the rear door 4 in the opening process stops at a half-opened 
position (indicated by the broken line) as shown in FIG. 4. As a result, 
it is possible to prevent an unintentional opening of the rear door 4 by 
an angle more than a required angle of 90 degrees. 
When the rear door 4 is pushed, manually for example, from the half-opened 
position to make the piston 23 reach the movable position Z of the 
cylinder 21 shown in FIG. 1, air 25 within the rod-side chamber 28B flows 
through the cylinder groove 29 into the piston-side chamber 28A because 
the cylinder groove 29 is formed in the movable area Z. By the flow 
resistance of air 25 flowing through the cylinder groove 29, the piston 23 
and the rod 22 move again in the extension direction at a proper speed 
similar to the speed in the movable area X, by the repulsive force of air 
25 within the piston-side chamber 28A. Then, the piston 23 is brought into 
contact with the collar 30 and stops there. Accordingly, the rear door 4 
is opened at a proper opening speed from the half-opened position 
(indicated by the broken line) to the fully opened position (indicated by 
the solid line) as shown in FIG. 4. 
In the compression process of the gas spring 20, since the cylinder groove 
29 is formed in the movable area Z of the cylinder 21, as shown in FIG. 1, 
when the rear door 4 is closed from the fully opened position (indicated 
by the solid line) in FIG. 4 by hand or by the self-weight of the rear 
door 4 at the time when the vehicle is parked on a sloped surface air 25 
within the piston-side chamber 28A flows through the cylinder groove 29 
and reaches the rod-side chamber 28B, so that the piston 23 and the rod 22 
move in the compression direction against the repulsive force of air 25 
within the piston-side chamber 28A. 
When the piston 23 and the rod 22 reach the locking area Y of the cylinder 
21, air 25 stops flowing from the rod-side chamber 28B to the piston-side 
chamber 28A between the O-ring 34 of the piston 23 and the cylinder 21 
because the cylinder groove 29 is not formed in this locking area Y. Thus, 
the piston 23 and the rod 22 stop in the locking area Y. Accordingly, the 
rear door 4 stops at the half-opened position (indicated by the broken 
line in FIG. 4) corresponding to the locking area Y of the cylinder 21 
even if the rear door 4 is closed by the weight of the door when the 
vehicle is parking on a sloped surface, for example. 
When the rear door 4 is opened by hand, for example, from the 
above-described half-opened position, the piston 23 and the rod 22 of the 
gas spring 20 reach the movable area X of the cylinder 21, and air 25 
within the piston-side chamber 28A flows through the cylinder groove 29 
and reaches the rod-side chamber 28B. Therefore, the rear door 4 moves in 
the compression direction by hand or by the self-weight against the 
repulsive force of the air 25 within the piston-side chamber 28A, and then 
the rear door 4 is fully closed. 
According to the gas spring 20 of the above-described embodiment, the 
following benefits (1) and (2) are obtained. 
(1) Since the cylinder grooves 29 are formed in both-side movable areas X 
and Z excluding the locking area Y in the stroke area of the piston 23 of 
the cylinder 21, air 25 stops flowing from the rod-side chamber 28B to the 
piston-side chamber 28A between the O-ring 34 of the piston 23 and the 
cylinder 21 (in the extension process) and air 25 stops flowing from the 
piston-side chamber 28A to the rod-side chamber 28B (in the compression 
process) when the piston 23 has reached the locking area Y, both in the 
extension process in which the piston 23 and the rod 22 move in the 
extension direction of the gas spring 20 by the action of the repulsive 
force of air 25 within the piston-side chamber 28A and in the compression 
process in which the piston 23 and the rod 22 move in the compression 
direction of the gas spring 20 against the repulsive force. Accordingly, 
the movement of the piston 23 and the rod 22 in the extension direction or 
in the compression direction stops. As explained above, since the rear 
door 4 can be stopped once in the middle of the opening or closing 
operation by stopping the movement of the piston 23 and the rod 22 in the 
extension direction or compression direction in the stroke area of the 
piston 23, the extent of opening of the rear door 4 to be opened or closed 
in the piston stroke area of the gas spring 20 can be adjusted in two 
stages. As a result, particularly when the opening and closing member is 
the lateral opening rear door 4 of the vehicle, it is possible to prevent 
trouble in traffic due to an unprepared opening of the rear door 4 by an 
angle more than a required angle of 90 degrees and it is also possible to 
prevent an unprepared closing of the rear door 4 when the vehicle is 
parked on a sloped surface. 
(2) Further, according to the gas spring structure described, since the 
extent of opening of the rear door 4 can be adjusted as explained in (1) 
above by providing the locking area Y having no cylinder groove 29 formed 
in the cylinder 21, it is possible to minimize the number of parts of the 
structure and it is also possible to reduce the number of assembly parts 
of the gas spring 20 and to reduce the cost of manufacture. 
(B) A second embodiment 
FIG. 5 is a side cross sectional view showing a second embodiment of the 
gas spring of the present invention. FIG. 6 is a cross sectional view 
along a VI--VI line in FIG. 5. FIG. 7 is a cross sectional diagram cut 
along a VII--VII line in FIG. 5. FIG. 8 is a cross sectional view along a 
VIII--VIII line in FIG. 5. In this second embodiment, portions similar to 
those in the first embodiment are identified by the same reference numbers 
and their explanation will be omitted. 
As shown in FIG. 5, in a gas spring 40, cylinder grooves 41 formed in the 
movable areas X and Z of the cylinder 21 are of the same shape. Each of 
the cylinder grooves 41 is structured by a straight section 41A having a 
constant groove cross sectional area and a tapered section 41B connected 
to the straight section 41A and having a gradually changing groove cross 
sectional area. 
These straight sections 41A and tapered sections 41B are structured in a 
square cross sectional shape as shown in FIGS. 6 and 7. The tapered 
sections 41B are formed in side end portions in the extension direction of 
the gas spring 40 in the cylinder grooves 41, and are formed in a tapered 
shape so that their cross sectional areas are gradually reduced in the 
extension direction of the gas spring 40. Each tapered section 41B has the 
same cross sectional area as the straight section 41A at a portion 
connecting to this straight section 41A. Further, it is preferable that a 
taper angle .theta. of each tapered section 41B to the axial core of the 
cylinder 21 be about one degree. 
Although each tapered section 41B of the cylinder groove is tapered in a 
groove depth direction in the example of FIG. 7, it is also possible to 
have this tapered section 41B tapered in a groove width direction, or 
tapered both in a groove depth direction and in a groove width direction. 
Accordingly, in this gas spring 40, in the extension process, when the 
piston 23 has reached the tapered section 41B from the straight section 
41A of the cylinder groove 41 of the movable area X or Z and this tapered 
section 41B is moved in the extension direction, the extension-side 
damping force generated by the air 25 flowing from the rod-side chamber 
28B to the piston-side chamber 28A through the tapered section 41B 
increases gradually, so that the moving speed of the piston 23 and the rod 
22 in the extension direction will reduce gradually. Then, the piston 23 
and the rod 22 stop slowly when the piston 23 reaches a position of the 
locking area Y or the collar 30 to which the piston 23 is brought into 
contact. 
According to the gas spring 40 of the above-described embodiment, the 
following benefits (3) and (4) can be obtained in addition to the effects 
(1) and (2) of the gas spring 10 of the above-described embodiment. 
(3) Since the side end portion of each cylinder groove 41 in the movable 
areas X and Z in the extension direction of the gas spring 40 is 
structured as the tapered section 41B which groove cross sectional area is 
reduced gradually in the extension direction, the extension-side damping 
force generated in the tapered section 41B increases gradually when the 
piston 23 has reached the tapered section 41B of the cylinder groove 41 in 
the extension process of the gas spring 40, so that speed of the piston 23 
and the rod 22 in the extension direction can be reduced gradually. The 
piston 23 and the rod 22 stop when the piston has reached the longest 
extension end at which the piston is brought into contact with the locking 
area Y or the collar 30. As a result, in the extension process of the gas 
spring 40, the piston 23 and the rod 22 can be stopped slowly and not 
suddenly. Therefore, it is possible to prevent undesirable vibration of 
the rear door due to a abrupt stop of the rear door 4 is stopped during 
the opening process. 
(4) Further, since each cylinder groove 41 of the cylinder 21 is structured 
by the straight section 41A and the tapered section 41B, both in a square 
cross sectional shape, the moving speed of the piston 23 and rod 22 can be 
reduced gradually when the piston 23 has reached the tapered section 41B 
in the extension process of the gas spring 40, as compared with the case 
where the straight section 41A and the tapered section 41B are in a 
triangular cross sectional shape, for example. In other words, while the 
groove cross sectional area changes suddenly in the tapered section 41B 
when the straight section 41A and the tapered section 41B of the cylinder 
groove 41 are in a triangular cross sectional shape, the groove cross 
sectional area in the tapered section 41B changes gradually when the 
straight section 41A and the tapered section 41B of the cylinder groove 41 
are in a square cross sectional shape, as compared with the triangular 
cross sectional shape. Accordingly, when the piston 23 moves the tapered 
section 41B of the cylinder groove 41 in the extension process of the gas 
spring 40, the extension-side damping force generated by the flow of air 
25 in the tapered section 41B can be increased gradually. Therefore, the 
moving speed of the piston 23 and the rod 22 in the extension direction in 
this case can be reduced gradually. As a result, it is possible to 
positively prevent the undesirable vibration of the rear door 4 which 
occurs at stopping of the rear door 4 while it is being opened. 
In the gas springs 20 and 40 of the above-described embodiment, description 
has been made of the case where the cross sectional area is almost the 
same for the cylinders 29 and 41 between the movable areas X and Z of the 
cylinder 21. However, it is also advantageous to have the cross sectional 
areas of the cylinder grooves 29 and 41 different between the movable area 
X and the movable area Z. For example, the cross sectional areas of the 
cylinder grooves 29 and 41 in the movable area X are larger than the cross 
sectional areas of the cylinder grooves 29 and 41 in the movable area Z so 
that the opening speed of the rear door 4 is faster at the start of the 
opening or the opening speed at the rear door 4 is faster at just before 
the closing. 
Further, in the above-described embodiments, description has been made of 
the case where the locking area Y has no cylinder grooves 29 and 41 is 
formed in the piston stroke area of the cylinder 21. However, it can also 
be arranged such that two or more locking areas Y are formed and the 
extent of opening of the rear door 4 is adjusted for three or more stages. 
Further, in the above-described embodiments, description has been made of 
the case where the repulsive force of air 25 within the piston-side 
chamber 28A works on the piston 23 and the rod 22 in the extension process 
of the gas springs 20 and 40. It is also advantageous if a coil spring is 
disposed as a repulsive force means between the closed end portion of the 
cylinder 21 and the piston 23 and the biasing force of the coil spring is 
applied as repulsive force to the piston 23 and the rod 22. 
Further, in the above-described embodiments, description has been made of 
the case where the gas cylinder 21 of the gas springs 20 and 40 is 
disposed in the vehicle body 2 and the rod 22 is disposed in the rear door 
4. It is also advantageous if the cylinder 21 disposed in the rear door 4 
and the rod 22 disposed in the vehicle body 2. 
Although in the above-described embodiments, description has been made of 
the case where the gas springs 20 and 40 are used as lateral open-door 
type gas springs, the gas spring may also be used as an inverted type or 
an inverted push-up type gas spring pivotting on a horizontal axis. 
As explained above, according to the gas spring relating to the present 
invention, it is possible to adjust the extent of opening of the opening 
and closing member at a plurality of stages without increasing the number 
of assembly process or incurring cost of production increase. 
Although the invention has been illustrated and described with respect to 
several exemplary embodiments, it should be understood by those skilled in 
the art that the foregoing and various other changes, omissions and 
additions may be made to the present invention without departing from the 
spirit and scope thereof. Therefore, the present invention should not be 
understood as limited to the specific modes of implementation set out 
above but to include all possible embodiments which can be embodied within 
a scope encompassed and equivalents thereof with respect to the feature 
set out in the appended claims.