Abstract:
An electrical coupling assembly for a damper, the coupling assembly including a base and a rod received through the base. The rod has a threaded connector end and a conductor extending through the rod from the connector end. The coupling assembly further includes a conductive nut threaded onto the connector end of the rod and a plug housing including a ground lead and a power lead, the power lead being electrically coupled to the conductor. The coupling assembly has a conductive member engaging the plug housing and the nut, the conductive member being electrically coupled to the ground lead. The coupling assembly is particularly suited for use in a strut having an outer tube coaxial with the inner tube and connected to the rod and the wheel suspension assembly of the vehicle so as to absorb the side loads applied to the strut. In such a strut, the piston rod is “upside down”, with the piston at the top and the coupling assembly at the bottom, where it is fully exposed to environmental dirt, moisture, contaminants, temperatures and road induced shocks.

Description:
TECHNICAL FIELD 
     The present invention relates to electrical coupling assemblies, and more particularly, to electrical coupling assemblies sufficiently rugged to be used in vehicle magnetorheological shock absorbing systems. 
     BACKGROUND OF THE INVENTION 
     Certain types of shocks, struts and other damping components used in vehicle shock absorbing systems have damping characteristics which can be varied to adjust the damping component to prevailing conditions. The damping characteristics may be varied to account for a number of factors, such as ambient temperature and the weight distribution, speed, and cornering status of the associated vehicle. Such dampers have generally contained adjustable valving, which introduces complexity and extra cost. 
     Recently, however, a new type of adjustable dampers are being introduced. Magnetorheological fluid dampers, also known as MR dampers, damp shock forces sustained by the vehicle by transmitting the forces to a piston which is pushed through a chamber filled with magnetorheological fluid. The piston is provided with an electric coil, and the flow of electric current in the coil may be controlled to vary the properties of the magnetorheological fluid pumped by the piston through an orifice in or adjacent the piston. In this manner the flow of magnetorheological fluid through the piston, and thereby the amount of damping, is controlled. 
     The piston that is pushed though the magnetorheological fluid is mounted onto the end of a rod, and electric current is provided to the coil in the piston from the end of the rod opposite the piston by means of an electric conductor in the rod. The conductor is electrically coupled to a connector, or coupling assembly, mounted on one end of the damper. The coupling assembly receives a plug that delivers power from the vehicle&#39;s electrical system. In this manner, the coupling assembly connects the vehicle&#39;s electrical system to the coil in the damper. However, existing coupling assemblies are difficult to assemble, lack robustness, and may not be fluid-tight to prevent water or other contaminants from contacting the wires or otherwise impairing the operation of the damper. And this is true even though the typical automotive strut is constructed with the piston at the bottom of the piston rod, with the opposite end of the rod projecting through a shock tower opening into the vehicle engine compartment. A coupling assembly for such a typical strut is thus at least somewhat protected from the outside environment. 
     But in order to relieve side loads on a damper piston rod, some struts are provided with an outer tube bearing a bracket adjacent its lower end for attachment to a vehicle wheel suspension assembly and which is closed at its lower end by a strut base. One end of the piston rod is fixed to the middle of the strut base, and the rod projects upward into an inner tube containing the piston and fluid. The top of the inner tube is fixed to the vehicle body, so that the rod and piston thus move axially together with the outer tube and wheel assembly in opposition to the inner tube and vehicle body. Side loads applied to the strut are received by bearing elements between the inner and outer tubes; and very little of these side loads are thus applied to the rod. A rod guide and seal assembly is provided to close the bottom of the inner tube, and the rod projects downward through the assembly. 
     An electrical conductor from a coil in the piston in such a strut exits the bottom of the rod; and the coupling assembly in such an “upside down” structure must therefore be placed at the bottom of the strut. In this position low in the vehicle suspension, out of the protective structure of the vehicle body, the coupling assembly is fully exposed to dirt, moisture and other contaminants, as well as extreme temperatures and physical shocks at the higher frequencies and amplitudes of the vehicle wheel rather than those of the vehicle body. 
     Accordingly, there is a need for an electrical coupling assembly which is durable, fluid tight, and easy to assemble. There is also a need for a MR strut that can resist side loads, has a rod with a relatively small diameter, and is controllable to adjust the strut to prevailing conditions. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electrical coupling assembly which is sufficiently rugged and durable to be used in automotive applications; an electrical coupling assembly which is generally fluid-tight to protect the internal components of the coupling assembly and the associated mechanism; and an electrical coupling assembly which is relatively easy to fabricate and install. It is a further object of the invention to provide such an electrical coupling assembly in a controllable MR strut damper that has an outer tube to increase the capacity of the strut damper to resist side loads. 
     In one embodiment, the invention is an electrical coupling assembly for a damper, the coupling assembly including a base and a rod received through the base. The rod has a threaded connector end and a conductor extending through the rod from the connector end. The coupling assembly further includes a conductive nut threaded onto the connector end of the rod and a plug housing including a ground lead and a power lead, the power lead being electrically coupled to the conductor. The coupling assembly has a conductor engaging the plug housing and the nut, the conductor being electrically coupled to the ground lead. 
     In another embodiment of the invention, a magnetorheological damper for damping forces applied to a wheel suspension assembly of a vehicle includes an inner tube filled with magnetorheological fluid. The inner tube is connected to a frame of the vehicle, and a piston is located in the inner tube. A rod is connected to the piston and extends through the inner tube. The damper has an outer tube coaxial with the inner tube, the outer tube being connected to the rod and the wheel suspension assembly of the vehicle. The rod has a conductor extending along its length. The damper also includes an electrical coupling assembly connected to the rod and the conductor, the coupling assembly having a plug housing for receiving an external plug and for electrically coupling the external plug to the conductor. Other objects and advantages of the present invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation in section of a damper incorporating one embodiment of the coupling assembly of the present invention; 
     FIG. 2 is an exploded, perspective view of the coupling assembly of FIG. 1; 
     FIG. 3 is a top plan view in section of the plug housing of the coupling assembly of FIG. 2; 
     FIG. 4 side elevational view of the plug housing of FIG. 3; 
     FIG. 5 is a top plan view of the plug housing of FIG. 3; 
     FIG. 6 is a section taken at line  6 — 6  of FIG. 5; 
     FIGS. 7-9 are perspective views showing a preferred method of construction of the plug housing of FIG. 3; 
     FIG. 10 is an end elevational view of the coupling assembly of FIG. 2; 
     FIG. 11 is a section taken at line  11 — 11  of FIG. 10; 
     FIG. 12 is an exploded perspective view of an alternate embodiment of the coupling assembly of the present invention; and 
     FIG. 13 is a side elevation in section of the coupling assembly of FIG.  12 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, one embodiment of the electrical coupling assembly  10  of the present invention is illustrated in conjunction with a monotube strut  20  of a magnetorheological damping system. However, it should be understood that the coupling assembly of the present invention may be employed in a variety of magnetorheological damping applications in addition to struts, shocks or dampers, and the embodiment shown in FIG. 1 is illustrative of only a single application. The monotube strut  20  of FIG. 1 includes a piston  22  having a coil  24  around its outer surface. The piston  22  includes a pair of longitudinally extending internal orifices  26 ,  28 . The piston  22  is maintained inside an inner tube  30  and is immersed in magnetorheological fluid  32  that fills the inner tube  30 . The inner tube  30  includes a closed end  33  located near the top of the strut damper  20  as shown in FIG. 1, and an open end  31  located near the bottom of the strut damper  20 . A rod  34  is threaded into the piston  22  and extends through the inner tube  30 . The rod  34  passes through the open end  31  of the inner tube  30 . 
     The inner tube  30  is received in, and is axially movable relative to, an outer concentric tube  36 . The outer tube  36  provides structural strength to the strut  20 , and helps to accommodate side loads. A bearing sleeve support (shown schematically at  38 ) and a set of monotube seals and bearings (shown schematically at  40 ) guide the relative movement between the inner tube  30  and the outer tube  36 . The space between the inner tube  30  and outer tube  36  is not designed as a reservoir, although it is possible that some fluid  32  may enter that space. A generally cylindrical strut base  42  covers a lower end  44  of the outer tube  36 , and the strut base includes a shoulder  46  that tightly engages the open lower end  44  of the outer tube  36  to seal the open end. The strut base  42  preferably is welded to and seals the open lower end  44  of the outer tube  36 . 
     The rod  34  includes a threaded end  48  that protrudes through a central hole  50  in the strut base  42 , and a conductive nut  52  is threaded on the threaded end  48  to couple the strut base  42  to the rod  34 . The rod  34  is fixed to the strut base  42  such that when the outer tube  36  moves relative the inner tube  30 , the rod  34  moves axially within the inner tube  30 . The rod  34  includes a shoulder  54  that engages the strut base  42 . A washer  75  is located between the shoulder  54  of the rod  34  and the strut base  42 . A rod guide assembly  56  is located adjacent to a lower end of the inner tube  30  and receives the rod  34  therein. The rod guide assembly  56  guides the relative movement between the inner tube  30  and the rod  34 . 
     A slidable gas cup  58  is located in the inner tube  30  seals a pressure cavity  60  in the inner tube  30  that is filled with pressurized gas, such as nitrogen. The upper end of the inner tube  30  is connected to the frame of the vehicle (not shown), and the lower end of the outer tube  36  is connected to a vehicle wheel suspension assembly (not shown) by the bracket  62 . Accordingly, when an associated wheel suspension assembly transmits forces to the bracket  62  and thereby to the outer tube  36 , rod  34  and piston  22  are moved axially relative the inner tube  30 . The movement of the piston  22  within the inner tube  30  forces fluid  32  through the orifices  26 ,  28  in the piston, which damps the movement of the piston, rod  34  and outer tube  36 . As the piston  22  moves within the inner tube  30 , the gas cup  58  also moves within the inner tube  30  to accommodate the change in volume in the inner tube  30  as the rod  34  is urged into, or withdrawn from, the inner tube. 
     The piston  22  includes a coil  24  located adjacent to the orifices  26 ,  28 . The current flowing through the coil  24  can be selectively controlled to control the viscosity of the magnetorheological fluid immediately adjacent the coil. In this manner the flow rate of magnetorheological fluid  32  through the orifices  26 ,  28  as the piston  22  moves within the inner tube  30  can be controlled. A conductor  64  is electrically connected to the coil  24  and extends through the center of the rod  34 , and a shroud  66  insulates the conductor  64 . The coupling assembly  10  receives an external plug (not shown) to connect the conductor  64  to the vehicle electrical system (not shown). 
     It is desired to minimize the change in volume in the inner tube  30  as the rod  34  moves into, or is retracted out of, the inner tube. Thus it is desired to reduce the diameter of the rod  34 . However, in conventional struts the rod  34  must accommodate side loads, and thus its thickness cannot fall below a given minimum diameter. In the present invention, the outer tube  36  provides structural support to the strut damper to help accommodate sides loads, which enables the diameter of the rod  34  to be reduced. Because the diameter of the rod  34  is reduced below a prior art strut without an outer tube  36 , the change in volume in the inner tube  30  is reduced, which in turn minimizes the movement of the gas cup  58  in response to movement of the piston  22 . 
     Conventional single tube strut dampers are inverted compared to the damper illustrated in FIG.  1 . In particular, a conventional single tube strut damper is mounted such that the open end  31  of the inner tube  30  is located near the top of the strut damper and is attached to the frame of the vehicle, and the closed end  33  of the inner tube  30  is located near the bottom of the strut damper and attached to the wheel suspension assembly. However, when the outer tube  36  is used, it is preferred to orient the strut damper  20  as shown in FIG.  1 . If the strut damper  20  were inverted from the position shown in FIG. 1, the bracket  62  would have to be attached to portion  37  of the inner tube  30  that extends beyond the outer tube  36 . The welding operations that are required to attach the bracket  62  to the inner tube  30  can distort the inner tube. Furthermore, because the inner tube  30  has a smaller diameter than the outer tube  36 , it is more difficult to attach the bracket  62  to the inner tube  30 . 
     An additional problem that would result from “inverting” the strut damper  20  of FIG. 1 is that the portion  37  of the inner tube  30  that extends axially beyond the outer tube  36  would have to be lengthened to provide sufficient surface area to receive the bracket  62 . This would increase the overall length of the strut damper and make it more difficult to fit into a vehicle. Furthermore, the increased diameter of the outer tube  36  relative the inner tube  30  makes it more difficult to couple the outer tube  36  to the frame of the vehicle. 
     Thus, the strut damper  20  of FIG. 1 typically is mounted onto a vehicle such that the coupling assembly  10  is located at the bottom of the strut damper  20 . However, in this orientation the coupling assembly  10  is no longer located in the protected environment of the engine compartment, and is exposed to various environmental conditions, including standing water, salt spray and the like. Furthermore, if the strut damper  20  is dropped during installation, it is likely to be dropped on the coupling assembly  10  because the coupling assembly  10  is located on the bottom of the strut damper  20 . Thus, it is important that the electrical coupling assembly  10  be durable, robust, and fluid tight. 
     As shown in greater detail in FIG. 2, the coupling assembly  10  of FIG. 1 includes the strut base  42 , a conductive nut  52 , a spacer  72 , a plug housing  70 , and a conductive cap  74 . The structure and operation of the plug housing  70  is disclosed in U.S. application Ser. No. 09/098,868, filed Jun. 17, 1998 and issued as U.S. Pat. No. 6,007,345, the disclosure of which is hereby incorporated by reference. The assembly of the plug housing  70  is briefly discussed herein, and FIGS. 7-9 illustrate the preferred steps of forming the plug housing  70 . A power lead  78  and a ground lead  80  are formed in the shape and orientation shown in FIG.  7 . The power lead  78  includes a cylindrical connector  96  at one end. As shown in FIG. 8, a base  82  is formed as an overmold over the ground lead  80  and power lead  78 . The cylindrical connector  96  protrudes through a nozzle portion  92  of the base  82 . 
     An elastomer seal  86  is then located on a forward surface  84  of the base  82 . As shown in FIG. 9, and the elastomer seal  86  includes a forward outer surface  88  of the plug housing  70 . The elastomer seal  86  includes a ring portion  90  that fits over the nozzle  92  of the base  82 . When fully assembled, the plug housing  70  includes a body portion  100  and a forwardly extending nozzle portion  92  that is perpendicular to the body portion. The ground lead  80  protrudes through the base  82  and the seal  86  (see FIG.  8 ), and the ground lead  80  is bent flush against the elastomer seal  86  (see FIG. 9) to help retain the elastomer seal  86  in place. The portion of the ground lead  80  that is located on the forward outer surface  88  of the plug housing  70  is termed the coupling portion  102  of the ground lead  80 . 
     The plug housing  70  also includes a port  104  to receive an external plug (not shown) that couples the power lead  78  to the vehicle&#39;s electrical system. The power lead  78  extends from the port  104  through the body portion  100  and passes through the nozzle portion  92 , terminating in the cylindrical connector  96 . When the plug housing  70  is mounted on the strut  20 , the conductor  64  is received in the cylindrical connector  96  to connect the power lead  78  to the conductor  64 . In this manner, electrical power is delivered from the vehicle&#39;s electrical system to the coil  24  of the piston  22 , and the current passed through the coil  24  can be controlled. The external plug may also include a ground wire, and the ground lead  80  of the coupling assembly  10  connects the ground wire to ground, as will be discussed in greater detail below. 
     Returning to FIG. 2, the side wall  110  of the strut base  42  includes a slot  112  shaped to receive the body portion  100  of the plug housing  70  therethrough and a flange  114  which extends outwardly from the slot  112  to protect the body portion  100  of the plug housing  70 . The conductive nut  52  includes a plurality of outer threaded holes  116  spaced about its periphery, and also includes a central threaded hole  118  that receives the connector end  48  of the rod  34 . 
     The conductive spacer  72  has a pair of generally arcuate apertures  120 ,  122  and a central through hole  124 . The spacer  72  is located between the plug housing  70  and the conductive nut  52 . The spacer  72  includes a radially extending slot  126  that is shaped to receive the body portion  100  of the plug housing  70 . Finally, a cap  74  is located over the plug housing  70  to keep the components of the coupling assembly  10  in place. A pair of fasteners, such as screws  130 , are passed through a set of holes  132  in the cap  74  and the apertures  120 ,  122  in the spacer  72 , and are received in two of the outer threaded holes  116  in the conductive nut  52 . As shown in FIG. 11, the cap  74  also includes an inwardly extending arm  140  that is shaped to engage the rear surface  146  of the plug housing  70  (that is, the surface opposite the nozzle  92 ). 
     When the conductive nut  52  is tightened over the connector end  48  of the rod  34 , the orientation of the nut when it becomes fully tightened is not known in advance. Because the outer threaded holes  116  in the conductive nut  52  cannot be precisely located, the arcuate apertures  120 ,  122  in the spacer  72  provide a range of locations to ensure that at least one outer threaded hole is accessible through each of the apertures  120 ,  122 . The body portion  100  of the plug housing may be located at various angles within the flange  114  of the strut base  42  depending upon the orientation of the slot  126  in the spacer  72  after the spacer  72  is coupled to the nut  52 . The cap  74  includes a cutout  142  in its forwardly extending flange  144  to accommodate the range of positions of the body portion  100 . 
     As shown in FIG. 11, the threaded end  48  of the rod  34  includes a recess  150 , and the conductor  64  terminates in an end  152  inside the recess  150 . When the connector assembly  10  is mounted on the outer cylinder  36 , the nozzle  92  and cylindrical connector  96  are received in the recess  150  such that the cylindrical connector  96  receives the end  152  of the conductor  64  therein. The elastomer seal  86  helps to seal the recess  150  and the outer cylinder  36 . 
     As noted earlier, the ground lead  80  includes a coupling portion  102  that extends on a forward outer surface  88  of the plug housing  70 . When the coupling assembly  10  is assembled, the conductive spacer  72  is pressed into contact with the coupling portion  102  to electrically engage the coupling portion  102 . In this manner, the ground lead  80  is electrically coupled to the spacer  72 . Because the spacer  72  is in contact with the nut  52 , which is in turn in contact with the rod  34 , the ground lead  80  is also electrically connected to the rod  34  and portions of the piston  22 . In this manner the spacer  72 , nut  52 , rod  34  and portions of the piston  22  all act as ground. 
     Once the coupling assembly  10  is fully assembled, an external plug may be inserted into the port  104  of the plug housing  70 . The external plug (not shown) will typically include a power wire and a ground wire. Thus, when the external plug is received in the port  104 , the power wire is connected to the power lead  78 , which thereby connects the power wire to the conductor  64  and coil  24 . Similarly, the ground wire is connected to the ground lead  80  and a ground is formed by the conductive nut  52 , spacer  72  and rod  34 . 
     A preferred embodiment of the invention is shown in FIGS. 12-13. In this embodiment, the strut base  170  includes a generally cylindrical side wall  172  and a base  174  having a central hole  176  that receives the connector end  48  of the rod  34  therethrough. The plug housing  180  does not extend radially outwardly of the strut base  170 , and thus the plug housing  180  is protected by the strut base  170  (FIG.  13 ). 
     As shown in FIG. 13, a seal  181 , such as a ring seal made of rubber, synthetic rubber or another elastomer, is located radially inwardly of the conductive nut  182  and between the rod  34  and the plug housing  180 . In this embodiment, the coupling portion  186  of the ground lead  188  protrudes through the body  190  of the plug housing  180  and is located on the rear surface  191  of the body  190 . 
     The conductive nut  182  includes a generally annular groove  192  extending around its outer surface. The coupling assembly  151  includes a conductive cap  194  that fits around a lower end of the plug housing  180 . The cap  194  includes a plurality of flanges  196  shaped and located to engage the groove  192 . In this manner the coupling assembly  151  can be assembled easily by mounting the components in the illustrated positions, and then snapping the flanges  196  of the conductive cap  194  into the groove  192  in the conductive nut  182 . The conductive cap  194  includes a notch  201  to receive the body portion  190  of the plug housing  180  therein (FIG.  12 ). 
     When the coupling assembly  151  is fully assembled, the conductive cap  194  holds the conductive nut  182 , seal  181 , and plug housing  180  in close engagement. The seal  181  helps to ensure that the coupling assembly  151  is fluid tight relative the surrounding atmosphere. Furthermore, the conductive cap  194  engages the coupling portion  186  of the ground lead  188 , and thereby electrically couples the ground lead  188  to the conductive nut  182  and the rod  34 . This connects the ground lead  188  to a ground source. The nozzle  92  of the plug housing  180  is received in the recess  150  in the rod  34  such that the power lead  200  is electrically coupled to the conductor  64  in a manner similar to the embodiment of FIGS. 1-11. 
     Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention.