Retractable shock absorber

A hevy duty, retractable, hydraulic, telescopic shock absorber of the type employed on fire engines, artillery vehicles and the like includes a valve arrangement for venting the main cylinder to hold a floating absorber piston in any working position. The shock absorber includes a passageway between a damping fluid reservoir and the cylinder chamber. The passageway is in open communication with the cylinder chamber when the floating piston is in an extreme position. A valve closes the passageway when the floating piston is in a position other than the extreme position.

BACKGROUND OF THE INVENTION 
The invention relates to a retractable, hydraulic, telescopic shock 
absorber. 
One such shock absorber includes a cylinder in which a piston, provided 
with passages is connected to a piston rod which can move through a 
cylinder cover and in which the piston divides the cylinder in two 
chambers. The cylinder chamber remote from the cylinder cover is by means 
of one or more passages in connection with a reservoir for the damping 
medium located outside the cylinder. In the other cylinder chamber is 
disposed an annular second piston freely slidable over the piston rod. 
Seals are provided between the second piston and the cylinder wall as well 
as the piston rod. The second piston has a rest position adjacent the 
cylinder cover. A pressure medium supplied from outside the shock absorber 
between the cylinder cover and the second piston serves to move the second 
piston in a direction remote from the cylinder cover. 
Such a shock absorber is the subject of Dutch Patent 133 120 and is used 
for vehicles, such as fire, artillery and similar vehicles, in which it is 
necessary to obtain a stationary situation by suppression of the action of 
the springs of the vehicle such that a rigid connection is obtained 
between the coach-work of the vehicle and the wheels, as well as for 
amphibian vehicles for retracting the set of wheels to obtain a lower 
travelling resistance. The shock absorbers are typically arranged in 
parallel to the springs of the vehicle with the cylinder of the shock 
absorber fixed to the wheels and the piston rod connected to the chassis 
of the vehicle. 
In shock absorbers without a second piston, the air present in the cylinder 
or liberated from the damping liquid is carried out through a passage with 
limited cross section between the cylinder and the reservoir in or near 
the cylinder cover. However, such a connection for venting is not 
allowable in shock absorbers having a second piston because the pressure 
medium supplied from outside the shock absorber between the cylinder cover 
and the second piston would escape to the reservoir with retraction of the 
shock absorber. 
SUMMARY OF THE INVENTION 
In accordance with the principles of the invention, a shock absorber is 
provided with means whereby the venting action of the cylinder can still 
take place notwithstanding the presence of a second piston. The shock 
absorber includes a passageway of limited cross section between the 
reservoir and the cylinder chamber adjacent the cover. The passageway is 
in open communication with the cylinder chamber when the second piston is 
in a first position against the cylinder cover. Valve means are provided 
to keep the connection closed when the second piston is in a position 
remote from the cylinder cover. 
Further in accordance with the principles of the invention the valve means 
includes a valve member. The position of the valve member is determined by 
means of a slide on which the pressure medium acts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS: 
The hydraulic, telescopic shock absorber of FIG. 1 includes a cylinder 1 in 
which a piston 3 connected to a piston rod 4 and provided with passages 2 
can be moved. The piston rod 4 extends outwardly through the cylinder 
cover 5. The piston 3 divides the cylinder into two chambers 6 and 7, of 
which the chamber 7 via passages 8 in the bottom of the cylinder is in 
connection with the reservoir 9 located around the cylinder 1 and used for 
the damping liquid. 
The cylinder chamber 6 contains a piston 10 which is freely slidable over 
the piston rod 4 and is sealed against the cylinder wall as well as to the 
piston rod by means of packing rings 12 and 11. 
The cylinder cover 5 is provided with a passage 13 which debouches on the 
one side above the free piston 10 into the cylinder and is at the other 
side in connection with the bores 14 and 15 in a screw nipple 16 to which 
is connected a conduit-pipe 17. 
The bore 15 is also in connection with a chamber 18 in which a differential 
slide 19 can move, displacing a ball 20 finding an end position on a seat 
21 and closing herewith a bore 22, which bore is in connection with the 
reservoir 9 via a tubular channel 23. 
A spring 24 exerts an upwardly directed force on ball 20 and the slide 19. 
A cross bore 25 with limited cross section provided above the seat 21 
debouches in the cylinder chamber 6 just below the free piston 10 when it 
is in the position as shown in FIG. 1. 
In the bottom of the reservoir 9 is provided a bore 26 having an outlet in 
the reservoir 9 located at some distance from the bottom thereof by means 
of extension pipe 27. The bore 26 is closed at its other end by means of a 
valve 29 loaded by a spring 28, in which the spring 28 is supported by 
means of a plug 30 with a bore 31. The valve 29 operates as a safety valve 
to relieve high pressures that may occur in the reservoir 9 as a result of 
the relatively high pressure of the pressure medium causing possible 
leakage along the free piston 10 via the cylinder room or along the seat 
21 to the reservoir 9. This leakage may be caused by wear after a long 
use. The extension pipe 27 assures that a minimum of damping medium supply 
remains in the revoir. 
The working of the shock absorber shown in FIG. 1 is as follows. During the 
normal operation of the shock absorber, the free piston 10 remains in the 
highest position, adjacent against the cylinder cover 5 and the piston 3 
can move up and down in the cylinder 1. During the outgoing stroke, 
damping liquid is pressed from the cylinder chamber 6 through the passages 
2 in the piston 3 into the cylinder chamber 7. The shortage of damping 
liquid in cylinder chamber 7 due to the outgoing piston rod volume is 
supplied from the reservoir 9 via the passages 8. During the ingoing 
stroke of piston 3, damping liquid flows from cylinder chamber 7 via 
passages 2 in piston 3 into the cylinder due to the entrance of the volume 
of the piston rod 4 pressed through passages 8 into the reservoir 9. 
Dependent on the damping required, the passages 2 and 8 can be provided 
with special damping means which are active in one or both flowing 
directions. During this action, the cross bore 25 is in free connection on 
one side with cylinder chamber 6 and on the other side with the bore 22, 
as the ball 20 is lifted from the seat 21 under influence of the spring 
24. With the ball 20 lifted, the cylinder chamber 6 is in free connection 
with the reservoir 9 via the passage 23. 
The over-pressure in the cylinder generated during the shock damping action 
caused a little overflow of damping liquid into the reservoir 9 due to the 
limited cross section of the bore 25, in which overflow the air present in 
the top of the cylinder is also led away. 
For blocking of the in and out spring movements of the vehicle a medium 
under pressure is supplied through the conduit pipe 17 which is connected 
to the screw nipple 16 and in which the medium acts via bores 15, 14 and 
13 onto the free cylinder 10, which is pressed downwardly. It should be 
noted, however, that the same liquid used for the pressure medium may also 
be used as the clamping medium. 
At the same time the slide 19 connected with the bore 15 will move the ball 
20 against the working of spring 24 until the ball 20 finds a rest 
position against seat 21 and closes bore 22. 
After the cross bore 25 is passed by the piston 10 the pressure medium will 
act onto the lower side of slide 19 via this bore but the slide 19 will 
stay in its position, due to the difference in surface pressures above and 
below the slide. 
At a further inward movement of the free piston 10 the piston touches 
damping piston 3 and subsequently either brings the damping piston 3 to 
the bottom of the cylinder chamber 7 or, if used on an amphibian vehicle, 
draws the cylinder upward until the bottom of said cylinder strikes the 
damping piston 3. Thereafter the damping piston 3 is blocked and 
accordingly a fixed connection is achieved between the set of wheels and 
the coach-work of the vehicle, the springs of the vehicle being retracted. 
After removing the pressure medium from outside the shock absorber and the 
subsequent release of the springs of the vehicle, the free piston 10 will 
be returned to its upward position as shown in FIG. 1 by means of the 
damping piston 3 and also due to the influence of the pressure of the 
damping medium. The ball 20 by means of spring 24 is lifted from the seat 
21 and the cross bore 25 comes again in open connection with the reservoir 
9. 
The arrangement of FIG. 2 is provided with a cylindrical slide 19a with a 
ball 20a, which ball has a rest position against a seat 21a and closes the 
connection between the cross bore 25 and the outlet 23. 
In the embodiment according to FIG. 3, a cylindrical slide 19b can against 
the working of a spring 24b,close bore 25. 
For a further understanding of the embodiments according to FIGS. 2 and 3 
reference may be made to the description of the embodiment of FIG. 1. 
It will be obvious to those skilled in the art that numerous modifications 
of the present invention can be made without departing from the spirit and 
scope of the present invention.