Abstract:
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.

Description:
This is a continuation of application Ser. No. 782,012 filed Mar. 28, 1977, now abandoned. 
    
    
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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; 
     FIG. 3 shows a modified spring in elevational section; 
     FIG. 4 shows a further modified pneumatic spring of the invention in elevational section; 
     FIG. 5 shows a station wagon equipped with a spring illustrated in FIGS. 1, 3 or 4 in fragmentary elevational section. 
    
    
     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&#39;, 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&#39; 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.