Extensible strut for use in device such as a gas spring

An extensible strut such as a gas spring and having a cylinder, a rod guided by the cylinder and slidably extending through one end of the cylinder to the outside, and a locking mechanism for locking the rod at an extended position. The locking mechanism has inner and outer axially contiguous recesses formed in the outer circumference of the rod and having respectively oppositely inclining surfaces defining therebetween a ridge, a locking member selectively and rockingly movable between the inner and outer recesses and having axially spaced and radially projecting inner and outer legs, a resilient ring for snappingly locating the locking member in either of the inner and outer recesses, a retaining element secured to the cylinder for cooperating with the inner leg of the locking member when the same is in the outer recess thereby preventing the contraction of the rod, and a releasing element secured to the cylinder at the location axially outwards of the retaining element for cooperating with the outer leg of the locking member when the same is in the outer recess thereby snappingly move the same into the inner recess.

BACKGROUND OF THE INVENTION 
This invention relates to an extensible strut of the kind including a 
cylinder and a rod slidably guided by the cylinder and extending through 
one end thereof to the outside. A typical application of the strut is a 
gas spring. 
It is usually required to provide a locking device in an extensible strut 
for locking the strut at least at one predetermined length position. 
However, the locking devices heretofore proposed have a complicated 
construction and are not reliable in operation. 
SUMMARY OF THE INVENTION 
One of the objects of the invention is to provide a novel strut having a 
locking device which is simple in the construction and is reliable in 
operation. 
The extensible strut according to the invention comprises a cylinder, a rod 
slidably guided by the cylinder and extending to the outside through one 
end of the cylinder, first and second axially contiguous recesses provided 
in the outer circumference of the rod, the recesses having oppositely 
inclined surfaces defining therebetween a ridge or projecting portion, a 
locking member selectively and rockingly located in either of first and 
second recesses, the locking member having a generally V-shaped 
longitudinal cross-section and including first and second axially spaced 
and radially outwardly extending legs, resilient means for biasing the 
locking members radially inwardly whereby the locking member snappingly 
moves between the first and second recesses, a retaining element provided 
in the cylinder and projecting radially inwardly, and a releasing element 
provided in the cylinder and projecting radially inwardly by an amount 
larger than that of the retaining element, the retaining element and 
releasing element being spaced axially by an amount larger than that 
between the first and second legs of the locking member, the arrangement 
being such that when the locking member is located in the second recess 
and between the retaining and locking elements, the first leg is adapted 
to engage with the retaining element thereby preventing the movement of 
the piston rod and the second leg is adapted to engage with the releasing 
element whereby the locking member is moved to the first recess.

DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a gas spring 35 constituting a preferred application of the 
extensible strut according to the invention, and the gas spring comprises 
a cylinder 1 with one end thereof closed by a cap 3, a piston 2 slidably 
mounted in the cylinder 1, a piston rod 8 connected to the piston 2 and 
extending to the outside through one end (the right end) of the cylinder 1 
and through a seal 11 and a rod guide 9. A mounting member 4 is secured to 
the cap 3 and a mounting member 10 is secured to the tip end of the rod 8. 
A through hole or a passage 5 is formed in the piston 2 for communicating 
two chambers 6 and 7 which are defined in the interior of the cylinder 1 
and are partitioned by the piston 2. The chambers 6 and 9 are filled with 
pressurized gas. The gas pressure normally urges the rod 8 in the 
extending direction, due to the difference in the pressure receiving areas 
on the piston 2 in the chambers 6 and 7, and thus, when no external force 
acts on the rod 8 the rod 8 takes the maximum extended position. There are 
provided in the inner end portion of the rod 8 a first recess 13 and a 
second recess 14 according to the invention, and the recesses 13 and 14 
include oppositely inclined and generally symmetrical surfaces which 
define therebetween a ridge or projecting portion 30. A locking member 16 
having a generally V-shaped or U-shaped configuration and having first and 
second radially outwardly extending legs 17 and 18 is located selectively 
in either of the two recesses 13 and 14. An annular resilient member 15 
such as a ring shaped coil spring or a rubber ring is fitted on the 
locking member 16 to snappingly locate the locking member 16 in either of 
the recesses 13 and 14. In the embodiment of FIG. 1, the recesses 13 and 
14 and the locking member 16 are provided at one predetermined angular 
position with reference to the circumference of the rod, but it will be 
understood that they extend respectively in the circumferential direction 
through a desired range such as about 90 degrees. A recess 19 is formed at 
a longitudinal position nearly corresponding to that of the ridge 30 and 
at an angular position diametrically opposite to the recesses 13 and 14 
for locating the resilient member 15. 
An annular engaging member 20 having the outer diameter corresponding to 
the inner diameter of the cylinder 1 is fitted in the cylinder 1 and is 
secured thereto by an annular projection 24 formed on the inner 
circumference of the cylinder 1. According to the invention, there are 
provided on the inner circumference of the engaging member 20 a retaining 
element 21 and a releasing element 22. The retaining element 21 and the 
releasing element 22 are spaced an axial distance larger than that of the 
legs 17 and 18 of the locking member 16, and the releasing element 22 
extends radially inwardly a distance larger than that of the retaining 
element 21. Further, the retaining element 21 has a generally radially 
extending wall portion and an inclined wall portion gradually inclining 
axially and radially outwardly. 
There are also provided in the cylinder 1 spring retainers 26 and 27 and a 
coil spring 28 axially outwards of the engaging member 20. An annular stop 
29 is mounted on the rod 8 and cooperates with the spring retainer 26 to 
resiliently restrict the outward (rightward as viewed in FIG. 1) movement 
of the rod 8. Normally, the rod 8 takes the most extended position whereat 
the gas pressure acting on the piston 2 is received by the coil spring 28 
with the annular stop 29 engaging with the spring retainer 26, and the 
locking member 16 is located in the second recess 14 and between the 
retaining element 21 and the releasing element 22 of the engaging member 
20. 
In use, the gas spring 35 is mounted on e.g. an automobile with the 
mounting member 4 on the cap 3 being connected to a vehicle body and the 
mounting member 10 on the rod 8 being connected to such as a hatch back 
door. In opening the door, the gas spring 35 extends and aids the opening 
movement of the door. When the door is fully opened, the gas spring takes 
a normal fully extended position as shown in FIGS. 1 and 8 whereat the 
locking member 16 is located in the second recess 14 and between the 
elements 21 and 22 of the engaging member 20. The weight of the door may 
tend to contract the gas spring, at that time, but the first leg 17 
engages with the retaining element 21 as shown in FIG. 2 thereby 
preventing further contraction of the rod 8. The gas spring is effectively 
and reliably locked. It will be understood that FIG. 2 shows the condition 
whereat a relatively large compressive force acts on the gas spring 
whereby the locking member 16 is displaced radially outwardly against the 
force of the resilient ring 15. 
For releasing from the locked condition, firstly, the rod 8 is moved in the 
extending direction or the arrow A direction by displacing the retainer 26 
against the force of the spring 28. The releasing element 22 engages with 
the second leg 18 of the locking member 16 as shown in FIG. 3 until the 
locking member 16 rockingly and snappingly moves from the second recess 14 
to the first recess 13 as shown in FIG. 4. Thereafter, the rod 8 is moved 
in arrow B direction or the contracting direction. The second leg 18 
engages with the retaining element 21 and, in response to the movement of 
the rod 8, the locking member 16 rockingly and snappingly moves from the 
first recess 13 to the second recess 14 as shown in FIGS. 5 and 6. It will 
be understood that there is a radial gap between the second leg 18 and the 
retaining element 21 when the locking member 16 is located in the second 
recess 14 as will be understood from FIG. 6. The rod 8 can be moved in 
arrow B direction by the full stroke. When the rod moves in arrow A 
direction, the inclined wall portion of the retaining element 21 engages 
with the first leg 17 of the locking member 16 to rockingly move the 
locking member 16 in the counterclockwise direction as shown in FIG. 7, 
but the locking member 16 does not displace from the second recess 14 to 
the first recess 13 and, finally, the locking member 16 is located between 
the retaining element 21 and the releasing element 22 as shown in FIG. 8. 
The gas spring is then in the locked condition. 
The locking device according to the invention is particularly advantageous 
for use in a gas spring when the ambient temperature decreases thereby 
decreasing the pressure of the gas enclosed in the gas spring so that the 
gas spring cannot maintain the maximum extended condition by means for the 
enclosed gas. 
FIGS. 9-10 show a modified form wherein the first and second recesses are 
annular, and a plurality of circumferentially spaced locking members 16' 
are selectively and snappingly mounted in either of the recesses 13 and 
14. An annular resilient member 15' acts on the locking members 16. The 
function and operation of the embodiment is similar to the first 
embodiment. 
It will be understood that the invention is not limited to gas springs and 
may be applied to extensible struts of other types. 
According to the invention, the rod can reliably be retained with respect 
to the cylinder with a very simple construction, and can easily be 
released from the locked condition. 
It will be understood that the rod 8 of the gas spring 35 is urged in arrow 
A direction by the gas pressure and that the locking mechanism according 
to the invention acts to prevent the contraction of the rod from a 
predetermined extended condition and is released from the locked condition 
by movement to a further extended condition. Thus, it is necessary to 
provide the spring retainer 26, spring 28 and the ring 29 for preventing 
the rod 8 from adversely extending to the further extended condition. 
However, when the cylinder 1 and the rod 8 constitute a simple extensible 
strut, the spring retainers 26 and 27, the spring 28 and the ring 29 may 
be omitted. In such case, it is preferable to make the axial length 
between the retaining element 21 and the releasing element 22 sufficiently 
larger than the axial length of the locking member 16 and to provide a 
suitable marking on such as the rod for clearly distinguishing aforesaid 
predetermined extended condition at which the locking mechanism functions 
from the aforesaid further extended condition at which the locking 
mechanism is released.