Patent Publication Number: US-2010116607-A1

Title: Dual seal rod guide assembly with low friction disc

Description:
TECHNICAL FIELD OF INVENTION 
     The invention relates to a damper guide assembly for a rod of a motor vehicle strut. More particularly, this invention relates to a guide assembly which minimizes internal friction and abrasion due to radial movement of the rod. Magneto-rheological (MR) fluid is filtered through the porous rod guide, and dual seals on either side of the bearing contain this carrier fluid, thus lubricating the bearing. A low friction disc is disposed between the tubular housing and the flexible assembly to reduce friction induced wear. 
     BACKGROUND OF INVENTION 
     A magneto-rheological (MR) strut is a type of damper used in vehicle suspensions to absorb shock and as part of the load bearing structure. The MR strut is a hydraulic vibration damper which uses MR fluid together with a device that generates a magnetic field. A typical MR fluid contains ferromagnetic particles suspended in a low viscosity fluid. When the MR fluid is subjected to a magnetic field, the ferromagnetic particles align parallel to the magnetic field, changing the apparent viscosity of the fluid. Therefore, the damping effect of the MR strut can be adjusted by varying the strength of the applied magnetic field. 
     In U.S. Pat. No. 6,840,358, incorporated by reference, Kos, et al. details the structure of a motor vehicle strut and a rod guide assembly for the strut. The rod is slidable in the housing and is held in alignment by a guide assembly. Features of the guide assembly include a compliant member adjacent a sleeve, a seal, a seal cover and a retainer attached to the housing. This rod guide configuration is limited by the ability of the single seal to resist abrasion from the MR fluid at the operating temperatures of the strut. A second limitation of this design is that the upper and lower face seals allow radial travel of the rod guide relative to the rod guide housing, resulting in face seal wear. 
     In U.S. Pat. No, 6,883,649, also incorporated by reference herein, Lun discloses a closing system for use with a MR damper. The closing system provides rod lubrication by using an internal filter to remove the microparticles from the MR fluid, and lubricating the system with MR carrier fluid. 
     It is desired to have a rod guide assembly for a MR strut which separates the temperature performance and abrasion resistance of the seals, while providing rod lubrication without the need for lubricant replenishment. It is also desired to reduce wear due to friction caused from radial movement of the rod. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention, a guide assembly for a rod of a motor vehicle strut provides dual seals to separate the functions of temperature performance and abrasion resistance, the primary seal and the buffer seal. The primary seal withstands the entire temperature range of operation of the MR strut. The buffer seal prevents the microparticles in the MR fluid from abrading the bearing, allowing only clean carrier fluid to lubricate the bearing and the primary seal. The porous rod guide acts as a filter, allowing only clean carrier fluid of the MR fluid to pass through to the bearing. The rod guide flexible assembly is a one piece molded assembly made from two inserts with a flexible member in between. The flexible assembly outer insert has an outer diameter seal which may be molded to the flexible assembly or a separate o-ring. The outer diameter seal provides sealing contact between the flexible assembly and the rod guide housing. 
     The low-friction disc, disposed between the rod guide flexible assembly and the rod guide housing, reduces surface friction caused by radial movement of the rod. Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       This invention will be further described with reference to the accompanying drawings in which: 
         FIG. 1  is an exploded view of dual seal rod guide assembly with low friction disc. 
         FIG. 2  is a cross-sectional view of dual seal rod guide assembly with low friction disc. 
         FIG. 3  is a cross-sectional view of the flexible assembly. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In accordance with a preferred embodiment of this invention, referring to  FIGS. 1-3 , a rod guide assembly  10  about an axis A for a rod  12  of a motor vehicle strut is shown. The rod guide assembly  10  includes a tubular rod guide housing  14 . The tubular housing  14  has a first end  16  and a second end  18 . The first end  16  is configured with a clearance hole to accept the rod  12 . A low friction disc  38  has a first surface  37  in contact with the inner face of the first end  16  of the housing  14 . The disc  38  is preferably made of Teflon, however any material that would reduce friction on the inner face of the first end  16  of the housing  14  would be acceptable. Rod  12  passes through the center of the disc  38 . The second surface  39  of the disc  38  is in contact with the rod guide flexible assembly  20 . The disc  38  isolates the inner face of the first end  16  of housing  14  and the rod guide flexible assembly  20 , reducing friction caused by radial movement of the rod  12 . The rod guide flexible assembly  20  comprises a flexible member  22  molded between an inner insert  21  and an outer insert  23 . The outer insert  23  is molded to an outer diameter seal  24 , which seals the flexible assembly  20  to the rod guide housing  14 . The flexible assembly  20  provides at least one opening for carrying a fluid. A primary seal  26  is positioned coaxially, along the same axis A, within the flexible assembly  20 . The inner diameter of the primary seal  26  is in seal able contact with the rod  12 . The outer diameter of the primary seal  26  is in seal able contact with the inner insert  21  of the flexible guide assembly  20 . A rod guide  28  is adjacent the primary seal. The rod guide  28  is made of a porous material that is compatible with MR fluids, preferably powdered metal. The rod guide  28  is disposed adjacent the primary seal  26  and coaxially within the flexible assembly  20 . The rod guide  28  is a barrier to the ferroelectric microparticles in the MR fluid, allowing only the MR carrier fluid to pass through. The MR carrier fluid provides excellent lubrication between the rod  12  and the primary seal  26  as well as for the bearing  32 . Bearing  32  is located coaxial and internal the rod guide  28 . Bearing  28  and MR carrier fluid for lubrication of bearing  28  are contained axially between primary seal  26  on one end and buffer seal  30  on the other. Buffer seal  30  has an inside diameter adjacent the rod  12  and an outside diameter adjacent the rod guide  28 , and provides a barrier to the ferroelectric microparticles in the MR fluid. The buffer seal  30  prevents abrasion of the bearing  32  and the primary seal  26  by ferroelectric microparticles in the MR fluid. The annular retainer  34  is disposed adjacent the buffer seal  30  and coaxial the tubular housing  14 . The inside diameter of annular retainer  34  is adjacent rod  12 . The retainer  34  is configured such that the outside diameter can be press fit into internal groove  36  of housing  14  proximate housing second end  18 . When retainer  34  is in position it acts to engage rod guide flexible assembly  20  to housing first end  16  with disc  38  therebetween. Installation of retainer  34  completes the rod guide assembly  10  by holding all of the aforementioned elements of the assembly  10  in place relative to each other. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.