Abstract:
A gas spring assembly includes a gas spring and a linear electric motor which assists in operation of the gas spring. A coil assembly for a linear electric motor is mounted to a body of the gas spring. The coil assembly generates a magnetic field which interacts with a magnet mounted to a piston. Driving the magnet within an electric field assists in driving the piston of the gas spring. To assist in operation of the gas spring while reducing the packaging space of the gas spring.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a gas spring, and more particularly to a gas spring utilizing a linear electric motor assist.  
         [0002]     Biasing members known as pneumatic or gas springs, which for convenience can be referred to as counterbalance links are becoming more and more common in commercial articles, particularly in the automotive industry, but they are being used in many other fields wherever the need is present to provide a counterbalance force for closure units, such as lids, doors and cabinet fronts. Gas spring replacement for mechanical spring fittings is also becoming prevalent. In the automotive field, for example, pneumatic springs are used to assist in opening and supporting trunk lids and lift gates. In such applications, the counterbalance spring assemblies are compressed when the lid is closed, and they extend under differential pressure force acting on the piston when the lid is opened.  
         [0003]     In many of applications, a relatively high internal cylinder pressure is required to cause the spring to extend. These high operating pressures impose stringent sealing requirements for the pneumatic spring components which may add to the complexity of the manufacturing process.  
         [0004]     Accordingly, it is desirable to provide a gas spring which includes an assist mechanism to increase the effectiveness of the gas spring without greatly increasing the packaging space required.  
       SUMMARY OF THE INVENTION  
       [0005]     The gas spring assembly according to the present invention provides a gas spring and a linear electric motor which assists operation of the gas spring.  
         [0006]     A gas spring assembly has a main body and piston. A coil assembly for a linear electric motor is mounted to the gas spring to generate a magnetic field which interacts with a magnet pack mounted to the piston. When the linear electric motor is activated the force created by the magnet pack will assist in starting the piston in motion. As the piston and magnet pack approach the full compression or extension position the magnetic field created by the coil assembly is switched to drive the magnet pack in an opposite direction. Ending motion of the piston is also cushioning by reversing the magnet pack when the piston reaches the end of travel.  
         [0007]     The present invention therefore provides a spring assembly where a linear electric motor assist in performing the work and is efficiently packaged. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0009]      FIG. 1  is a diagrammatic view of a gas spring installed on a moveable closure member showing three positions of the counterbalance;  
         [0010]      FIG. 2  is a longitudinal sectional through a gas spring designed according to the present invention; and  
         [0011]      FIG. 3  is a longitudinal sectional through a gas spring according to an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]      FIG. 1  illustrates a general view of a gas spring assembly  10  designated as a counterbalance link. The gas spring assembly  10  is schematically illustrated in an intermediate position (II) between a compressed condition (I) and an extended condition (III) as an example of a counterbalance for a moveable closure member  11  of a vehicle  13 . The gas spring assembly  10  may, of course, be used in many other applications. A linear electric motor  14  is used to assist in compressing, extending, and cushioning the gas spring assembly  10 .  
         [0013]     Referring to  FIG. 2 , the gas spring assembly  10  includes the linear electric motor  14  and a gas spring  16 . The gas spring  16  includes a main body  12  which is preferably cylindrical. The body  12  has a closed end  15  on which is mounted an attachment fixture (illustrated schematically at  17 ). The opposite end of the main body  12  is closed off by an end plug  18  which defines an aperture  20  to allow linear passage of a piston rod  22  along a gas spring axis A. The piston rod  22  includes an attachment fixture (illustrated schematically at  24 ). It should be understood that various attachment fixtures such as fixed threaded connections and movable connections such as ball joints will benefit from the present invention.  
         [0014]     The linear electric motor  14  includes a coil assembly  26  which is mounted to the gas spring  16 . The linear electric motor  14  produces a linear force assisting the gas spring  16  in operation. As the body  12  is cylindrical, the coil assembly  26  is tubular to best fit around the main body  12 . Other complementary geometries for the body  12  and coil  26  will also benefit from the present invention. The body  12  and/or piston rod  22  are preferably made of a non-magnetic material so as not to interfere with the functioning of the linear electric motor  14 .  
         [0015]     Within the body  12 , the piston rod  22  is attached to a piston  28 . Assembly of the piston rod  22  within the body  12  forms a main chamber  30 . Within the body  12 , the piston rod  22  is attached to a piston  28  which engages an inner wall  25  of the body  12  to separate the body  12  into a main chamber  30  and an outer chamber  31 . The piston  28  operates as a check valve and orifice by-pass structure to provide controlled by-pass flow of gas between chambers  30  and  31 . There is a relatively free flow by-pass provided during the retraction or compression stroke and an “orifice” metered flow of gas past the piston  28  during the extension or expansion stroke. It should be understood that piston  28  may include various well-known porting, passageway and/or valve arrangements which provide for gas and oil transfer between chambers  30  and  31  as the piston rod  22  telescopes inward and outward relative to the body  12 .  
         [0016]     A magnet pack  32  for the linear electric motor  14  is mounted to the piston  28 . The magnet pack  32  is preferably mounted so that it is within the main chamber  30 . During the compression and expansion stroke the piston  28  moves relative to the body  12 . As the piston  28  moves, the size of the main chamber  30  varies. As is known, a high pressure within the main chamber  30  is required to generate the force necessary for the gas spring  16  to operate. The linear electric motor  14  assists the gas pressure in movement of the piston  28  by increasing the force generated during motion. Alternately or in addition, a lower gas pressure may be utilized in combination with the linear electric motor  14  to provide a gas spring assembly  10  of equivalent load capabilities.  
         [0017]     The piston rod  22  may be hollow in order to compensate for the volume of the main chamber  30  which is used by the magnet pack  32 . A piston chamber  34  is formed within the piston rod  22  and an internal aperture  36  connects the main chamber  30  to the piston chamber  34 . The internal aperture  36  preferably mounts a tubular member  38  which extends along the gas spring axis A to prevent a liquid oil  40  contained within the main chamber  30  from entering the piston chamber  34  of the piston rod  22  when the piston rod  22  is rotated to a downward position as illustrated in  FIG. 2 . A pre-determined quantity of the liquid oil  40  is contained within the main chamber  30  prior to assembly to provide lubrication and liquid for damping at the end of the expansion stroke as generally known. The magnet pack  32  is preferably affixed to the piston  28  around the tubular member  38 .  
         [0018]     A power source  42  is attached to the coil assembly  26 . A controller  44  is used to turn on the power source  42  which generates a current through the coil assembly  26 . The current running through the coil assembly  26  generates a magnetic field. The magnetic field drives the magnet pack  32  and the piston  28  along the gas spring axis A to assist compression and extension of the gas spring assembly  10 .  
         [0019]     Additionally, if the piston  28  is in a resting position, initiation of movement by an external source such as manual initiation by an operator may be utilized as a signal for the controller  44  to initiate generation of the magnetic field. Generating the magnetic field will drive the magnet pack  32  along the gas spring axis A. The force created by the magnet pack  32  will assist in starting the piston  28  in motion.  
         [0020]     The piston  28  has momentum in the direction of travel along the gas spring axis A. As the piston  28  and magnet pack  32  approach the full compression or extension position the controller  44  activates a switch  46  which changes the direction of current running through the coil assembly  26 . Switching the direction of the current switches the direction of the magnetic field. That is, the poles on the magnetic field are exchanged. Exchanging the poles causes the magnetic field to repel the magnet pack  32  along the gas spring axis A. During this time the opposing forces of the piston  28  and magnet pack  32  will slow the compression or extension of the gas spring assembly  10 . Thus, the linear electric motor  14  assists in cushioning the end of travel of the gas spring assembly  10 .  
         [0021]     Referring to  FIG. 3 , the gas spring  16  and linear motor assembly  14  may also be arranged such that the magnet pack  32  is mounted around the body  12  and the coil assembly  26  is mounted internally, to the piston  28 . The coil assembly  26  moves with the piston  28  during operation of the gas spring assembly  10 . Wires  48  for connecting the coil to the power source  42 , controller  44 , and switch  46  preferably includes a coil or other extension/retraction feature to allow movement of the piston  28 .  
         [0022]     The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.