Electrically conductive pneumatic spring

In the illustrative embodiment of a current-carrying pneumatic spring disclosed, flow of electric current between external terminals on the cylinder member and piston rod member of the spring is provided by a contact element fixed on one of the members and carrying one or more contact faces which are resiliently biased into sliding engagement with an axially elongated face portion of the other member. Flow of electric current between the external terminals may thereby be provided over a range of positions or over all positions of axial movement of the piston rod member inward and outward of the cylinder cavity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to pneumatic springs which connect mechanical parts 
movably mounted with respect to each other so as to compensate for the 
weight of one of said mechanical parts. The pneumatic spring fulfills 
besides its function as a balancing means also the function of 
transmitting electrical current between said mechanical parts. 
2. The Prior Art 
In U.S. Pat. No. 3,919,509, an electrically conductive pneumatic spring has 
been proposed which is capable of transmitting heavy currents only in one 
terminal position of the piston rod member with respect to the cylinder 
member, whereas in the other relative positions of said members only weak 
currents can be transmitted. 
The invention will be described herein below with reference to an 
application in the field of automotive engineering to which it lends 
itself advantageously, but other applications will readily come to mind. 
SUMMARY OF THE INVENTION 
The pneumatic spring according to this invention has a cylinder member 
closed at its one end and provided with a guiding and sealing unit at its 
other end, a piston rod member introduced into said cylinder member 
through said guiding and sealing unit and having an outer end outside said 
cylinder member, a first fastening element provided adjacent the closed 
end of said cylinder member, a second fastening element provided adjacent 
the outer end of said piston rod member, a first electrical connector 
provided adjacent said closed end of said cylinder member and electrically 
connected to said cylinder member, a second electrical connector provided 
adjacent said outer end of said piston rod member and electrically 
connected to said piston rod member, an electrical connection between said 
first and said second electrical connector, and a pressurized gas 
contained within said cylinder member. 
The structure defined so far is known from U.S. Pat. No. 3,919,509. 
According to the invention, an improvement in such known electrically 
conductive pneumatic springs comprises a slide contact element fixed to 
one of said members and biased into electrically conductive sliding 
contact with the other member. 
This improvement makes it possible to transmit heavier electric currents 
also in other relative positions of said piston rod member with respect to 
said cylinder member besides said above-mentioned terminal position.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
Referring initially to FIG. 1, a cylinder member 1. This cylinder member 1 
is provided at its one end with a thread bolt 20. At this end the cylinder 
member 1 is closed. On the other end of the cylinder member 1 is provided 
a guiding and sealing unit, as is known from FIG. 2 of U.S. Pat. No. 
3,919,509. A piston rod member 2 is introduced into the cylinder member 1 
through said guiding and sealing unit 4. The piston rod member 2 is 
provided with a section 21 of reduced diameter at its inner end which 
defines a radial shoulder 22 on the piston rod member 2. On the reduced 
section 21 there are provided an outer support disk 23, an apertured 
piston 3, an annular spacer member 17, a slide contact element 11 and an 
outer support disk 16 which protects the element 11 against excessive 
deflection. These parts are fixed on said reduced section 21 by a rivet 24 
attached to the outer end of said reduced section 21. The parts 23, 3, 17, 
11 and 16 provide a continuous passage for pressureized gas contained 
within said cylinder member 1 on both sides of the piston 3. A movable 
piston ring 25 is mounted between the piston 3 and the outer support disk 
23, which movable piston ring 25 provides different flow resistance for 
the gas flowing from the upper side of the piston to the lower side as 
compared with the resistance to gas flow from the lower side to the upper 
side. This construction is known and described in more detail in U.S. Pat. 
No. 3,207,498. On the outer end of the piston rod member 2 a fastening 
element 5 is fixed. This fastening element 5 consists of insulating 
plastic material and is provided with a spherically concave, annular face 
26 for constituting a universal joint with respect to a mechanical part 
having a complementary ball head. The fastening element 5 is provided with 
an inner thread 27 which is screwed on an outer thread 28 provided at the 
outer end of the piston rod member 2. A flat electrical connector 7 which 
is provided with an eyelet 29 is fixed on a frustoconical face 30 of the 
rod member by the fastening element. Electrical connection exists between 
the electrical connector 7 and the piston rod member 2 and may be enhanced 
by soldering. 
At the lower end of the cylinder member 1 a further flat electrical 
connector 8 having an eyelet is fixed to the cylinder member by a 
fastening element 6. The electrical connector is electrically connected to 
the bottom 9 of the cylinder member 1. The fastening element 6 has 
basically the same structure as the fastening element 5. For securing the 
fastening element 6 in its position a slit, hollow pin 32 is introduced 
into a bore 33 of the fastening element 6 and is in engagement with the 
outer thread 34 of the thread bolt 20. Alternatively the pin 32 may also 
transverse a diametrical bore of the thread bolt 20. The fastening element 
6 may also be secured to the thread bolt 20 by adhesive bonding. 
The slide contact element 11 is illustrated in more detail in FIG. 2. It 
comprises an annular body 35 and radially outwardly directed tongues 12. 
The tongues 12 are slit at their radially outer ends so as to define claws 
13. These claws 13 have contact faces of relatively soft copper, copper 
alloy, silver, or silver alloy which are in sliding contact with the 
radially inner harder steel face of the cylinder member 1. The annular 
body 35 is in electrical contact with the piston rod member 2. The tongues 
12 are radially biased in such a way as to contact the inner face of the 
cylinder member 1 under pressure. This pressure is sufficient to break a 
lubricant film which is provided on the inner side of the cylinder member 
1. The claws 13 contact the inner face of the cylinder member 1 over such 
a total contact area that the required current can be transmitted from the 
electrical connector 7 to the electrical connector 8. This contact area 
remains constant during the whole stroke of the piston rod member 2 with 
respect to the cylinder member 1. The contact area may be increased by 
reducing the angle of inclination of the tongues 12 relative to the inner 
cylinder wall. 
The cylinder member 1 is provided on its radially outer side with an 
insulating coat 10; for example, a shrunk plastic tube. The piston rod 
member 2 is provided on its section which is outside the cylinder member 1 
with an insulating shield 36 which may be a bellows of insulating 
material. 
FIG. 5 shows a station wagon 37. The cylinder member 1 is connected by its 
fastening element 6 to a ball head 38 on the fixed body portion of the 
station wagon, whereas the piston rod member is connected by its fastening 
element 5 to a ball head 39 attached to the rear gate 40. The electrical 
connector 8 is connected by a clip 41 and a cable 42 to a battery 43, 
whereas the electrical connector 7 is connected by a clip 44 to the 
heating wires provided in the window 45 of the rear gate 40. The other end 
of the battery 43 is connected to the heating wires of the window 45 by 
the electrically conductive parts of the carriage body and the gate 40. 
The gate 40 is connected to the carriage body by a pivotal connection 46. 
In the embodiment of FIG. 3, which is substantially identical with that of 
FIG. 1 as far as not described otherwise, there is provided a wire brush 
11', instead of the slide contact element 11 for breaking the lubricant 
film on the inner cylinder wall. The eyelet 29 of the electrical connector 
7 is interposed between two cup springs 18 and 19, said cup springs being 
interposed between a shoulder 36' of the piston rod member 2 and the 
fastening element 5. 
In FIG. 4, there is shown yet another pneumatic spring substantially 
identical with that of FIG. 1 as far as not explicitly stated otherwise. A 
slide contact element 15 is interposed with its annular body 35 between 
the axially outer end of the guiding and sealing unit 4 and the annular 
upper end wall 47 of the cylinder member 1. The annular body 35 is 
provided with radially inwardly directed tongues 12 which contact the 
radially outer face of the piston rod member with sufficient pressure to 
break the lubricant film on the member 2. 
Automotive applications of the electrically conductive pneumatic springs of 
the invention other than in the rear gate of a station wagon are found in 
motor hoods and trunk lids which carry external or internal lights, and 
applications outside the automotive field will suggest themselves to those 
skilled in the art. 
It should be understood, therefore, that the foregoing disclosure relates 
only to preferred embodiments of the invention, and that it is intended to 
cover all changes and modifications of the examples of the invention 
herein chosen for the purpose of the disclosure which do not constitute 
departures from the spirit and scope of the invention set forth in the 
appended claims.