Electrically conductive pneumatic spring

#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

#Other features and many of the attending advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments when considered in connection with the appended drawing in which:

#FIG. 1 shows a current-carrying pneumatic spring of the invention in elevational section;

#FIG. 2 illustrates an element of the embodiment of FIG. 1;

#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.