Abstract:
A rotary damper for a vehicle trailing arm suspension mechanism includes a housing defined by a body molded of a reinforced plastic and defining a fluid filled cavity in which a multi-bladed rotor is disposed to form plural fluid filled damper chambers. The rotor is connected to a shaft which is part of a linkage of the suspension system and the housing is operably secured to the vehicle frame. The rotor may also be formed of a molded plastic or cast or otherwise fabricated metal which is covered with an overmolded layer of plastic. The rotor tips may include elastomer seal strips or as cast seal strips and providing a slight interference fit with the housing cavity surfaces. Fluid sealing between the rotor and the body and housing cover plates is provided by the separate or integral seal strips or by clearances small enough to restrict fluid flow except through flow restricting passages and damping action control valves.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to a hydraulic rotary damper, particularly adapted for a vehicle trailing arm suspension system, and wherein components of the damper are formed of composites including components formed of all reinforced plastic or components formed of metal which are overmolded with plastic materials at wear and seal surfaces. 
     BACKGROUND 
     Rotary dampers are typically used in automobile suspension systems, including trailing arm type suspensions, in particular, to damp the oscillatory motion of the suspension linkage. However, rotary dampers have rather lengthy seal lines or potential fluid leakage paths across the damper rotor between the fluid filled chambers of the damper. Accordingly, rotary dampers require relatively precise fits between parts and precise surface finishes of the respective parts to provide minimal fluid leakage and to avoid degraded damper performance. However, in mass produced automotive vehicle applications, for example, the manufacturing cost associated with forming the damper components of precision cast metal parts or machined metal parts is undesirable. It is to overcome the problems related to cost effective manufacture of rotary dampers which also provide required performance characteristics that the present invention is directed. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved rotary suspension damper for a vehicle suspension system. 
     In accordance with one aspect of the present invention, a rotary damper is provided which includes a rotor having a core portion constructed of powder metal and which includes a plastic overmolded layer on the hub and blades of the rotor, a housing constructed of reinforced plastic and molded over a metal valve ring assembly. Elastomeric seals are provided to retain a hydraulic damping fluid within the housing of the rotary damper. Internal fluid leakage between the rotor end faces and the side plates of the damper housing, as well as fluid leakage between the rotor tips and the body of the housing is controlled by dimensional clearances and by selecting a fluid with a viscosity to minimize fluid flow. 
     In accordance with another aspect of the invention, a rotary damper for a vehicle suspension system is provided with a rotor having a core portion of reinforced plastic formed over a metal hub, a body molded from reinforced plastic molded over a metal reinforcing ring assembly wherein the inner surface of the body and the outer surface of the rotor are both provided with plastic overmolded wear surfaces. The plastics used for the overmolded wear surfaces of the rotor and the body are preferably of different compositions and are different than the compositions of the core portions of the rotor and the body. Elastomeric seals retain the damping fluid within the device and ribs may be provided along the sides and end faces of the rotor and on inwardly extending projections of the body to control fluid leakage between rotor chambers. 
     In accordance with a further aspect of the invention, a rotary damper is provided for a vehicle suspension system wherein the rotor and body are each formed of long fiber reinforced plastics, the body is molded over a metal ring assembly and elastomeric seals provide sealing to contain fluid within the damper and to control fluid flow around the damper rotor. 
     The present invention further provides an improved rotary damper for a vehicle suspension system according to the above-mentioned improvements and which is further characterized by improved flow control valves for controlling the flow of hydraulic damping fluid in a way to allow the damper to react differently to torque caused when the vehicle wheel is raising (jounce) and when the wheel is lowering (rebound). The improved rotary damper may be tuned by selecting a proper valve seat, including selection of fluid passages in a valve seat plate and the configuration of valve disks so as to control flow through the valves. 
     Those skilled in the art will further appreciate the above-mentioned advantages and superior features of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a portion of a vehicle including a trailing arm type wheel suspension and a rotary damper in accordance with the invention; 
     FIG. 2 is a top plan view of one preferred embodiment of a rotary damper in accordance with the invention; 
     FIG. 3 is a central section view taken generally along the line  3 — 3  of FIG.  2 . 
     FIG. 4 is a section view taken generally along the line  4 — 4  of FIG.  3 . 
     FIG. 5 is a section view similar to FIG. 3 of a first alternate embodiment of the present invention; 
     FIG. 5A is a perspective view of the rotor for the damper shown in FIGS. 5 through 7; 
     FIG. 6 is a section view taken generally along the line  6 — 6  of FIG. 5; 
     FIG. 7 is a section view taken generally along the line  7 — 7  of FIG. 5; 
     FIG. 8 is a central section view similar to the section views of FIGS. 3 and 5 of a second alternate embodiment of a rotary damper in accordance with the invention; 
     FIG. 9 is a section view taken from the line  9 — 9  of FIG. 8; and 
     FIG. 10 is a section view taken from the line  10 — 10  of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the description which follows, like parts may be marked throughout the specification and drawing with the same reference numerals, respectively. The drawing figures may not be to scale and certain elements may be shown in schematic or generalized form in the interest of clarity and conciseness. 
     Referring to FIG. 1, there is illustrated a portion of a wheeled vehicle  20  including a frame or body member  22  supporting a trailing arm type wheel support member  24 . Wheel support member  24  supports a rotatable wheel hub  26  and brake rotor  28 . Trailing arm support member  24  is suitably mounted on frame member  22  for oscillatory movement about an axis  25  and is suitably connected in a conventional manner to an elastomer type spring  30  by a shaft  34 . Spring  30  is disposed in a tubular support member  32  and is fixed to shaft  34  which is secured for rotation or oscillation with the trailing arm support member  24 . Shaft  34  is shown to have a square cross section but other configurations forming a coupling between shaft  34  and the components, including spring  30 , coupled to the shaft may be provided. 
     Shaft  34  is also connected to a rotary damper unit, generally designated by the numeral  36 , which is operable to damp oscillatory movement of the wheel support member  24  to act in the manner of a so called shock absorber, for example. Damper unit  36  includes a housing  38  having a laterally projecting boss portion  40  secured by a fastener  42  to a member  44  secured to the frame member  22  to prevent rotation of the housing of the damper unit about the axis  25 . 
     Referring now primarily to FIGS. 2,  3  and  4 , the damper unit  36  includes a generally rectangular body  46  and opposed generally planar cover plates  48  and  50  forming the housing  38 . The boss  40  preferably comprises spaced apart boss portions  48   a  and  50   a  on cover plates  48  and  50 , as shown in FIG.  2 . The cover plates  48  and  50  are secured in assembly with the body  46  by suitable mechanical fasteners  52  comprising machine screws, for example. 
     Referring now primarily to FIGS. 3 and 4, the body  46  further includes an encapsulated, generally cylindrical metal ring member  54  comprising circumferentially spaced apart, generally cylindrical, valve seat plate parts  56 ,  58  and  60  which are provided with suitable ports to allow fluid flow therethrough in a manner to be described in further detail herein. A rotor  62  is mounted within a cavity  70  formed by the body  46  and includes three circumferentially spaced radially projecting blades  64 ,  66  and  68  which cooperate with the body to form fluid filled damping chambers  70   a ,  70   b ,  70   c ,  70   d ,  70   e  and  70   f . Rotor  62  includes a square cross section central bore  67  which receives square cross section shaft  34  therein and non-rotatable relative to the rotor. The radial outermost tips of the blades  64 ,  66  and  68  fit within the cavity defining the chambers  70   a - 70   f , as shown in FIG. 3, with a very small clearance or a line-to-line fit against the chamber walls  72   a ,  72   b  and  72   c  of body  46 . Body  46  includes radial inwardly projecting seal bosses  74   a ,  74   b  and  74   c  which are dimensioned to have very close tolerance or line-to-line fits against a hub part  63  of rotor  62 . A gas charged accumulator  78  is disposed in a cavity  80  formed in body  46  and is operable to maintain a fluid fill within the chambers  70   a - 70   f  and to compensate for thermal expansion and contraction of a suitable hydraulic fluid, such as a synthetic base oil or a water and glycol solution, which at least partially fills cavity  80  and all of the chambers  70   a - 70   f  when the damper  36  is placed in a working condition. Fluid is contained within the damper  36  by suitable annular o-ring type seals  81  mounted in suitable grooves in the side plates  48  and  50 , FIG. 4, and engageable with cooperating reduced diameter portions of the rotor hub portion  63 , as shown. Peripheral elastomer seals  82 , FIG. 4, are disposed in suitable grooves in the body  46  and in sealing contact with the side plates  48  and  50  when they arc assembled to the body. 
     In operation, the damper  36  damps oscillatory movement of the trailing arm support member  24  and wheel  26  about axis  25 . As shaft  34  deflects about axis  25 , the rotor  62  rotates to transfer fluid between respective pairs of the chambers  70   a - 70   f . For example, if rotor  62  is deflected in a clockwise direction, viewing FIG. 3, fluid is transferred through suitable passages in the body  46 , not shown, from chambers  70   b ,  70   d  and  70   f  to chambers  70   c ,  70   e  and  70   a , respectively, by way of valves supported on the valve plate parts  56 ,  58  and  60 , in a known manner. Rotation of the rotor  62  in the opposite direction transfers fluid from chambers  70   a ,  70   e  and  70   c  to chambers  70   f ,  70   d  and  70   b , respectively, also in a known manner. 
     It is desired to minimize damper fluid leakage between the aforementioned chambers across the outer tips of the rotor blades  64 ,  66  and  68  and between chambers at the rotor hub  63  and also between chambers at the rotor opposed end faces or side edges. In this regard, the fabrication of the rotor  62  and the body  46  of cast or fabricated metal would require relatively extensive machining to provide the dimensional tolerances required to minimize unwanted fluid leakage between the chambers  70   a - 70   f  formed between the rotor and the body. However, in accordance with the present invention, the damper  36  according to FIGS. 2,  3  and  4  includes a rotor  62  having a core portion  65  which may be formed of sintered metal, preferably iron, with a suitable plastic overmolded layer  69  defining the entire exterior surface of the blades  64 ,  66  and  68 , hub  63  and including those portions of the blades and hub which are in very close proximity to the wall surfaces  72   a ,  72   b  and  72   c , the projections or bosses  74   a ,  74   b  and  74   c  and the housing cover plate surfaces  48   b  and  50   b , FIG.  4 . Plastic lined cavities  65   a  in blades  64 ,  66  and  68  provide relatively constant wall thickness for core portion  65 . 
     Still further, the body  46  is preferably formed of a molded plastic which is operable at all elevated temperatures to which a vehicle including the damper  36  may be normally disposed. The body  46  may be formed of a temperature resistant nylon or a polyphthalamide which is suitably filled with reinforcing fibers of selected materials which may include glass or mineral fibers, for example. Moreover, the body  46  is reinforced by the metal ring member  54 , Tubular metal sleeves  84 , FIGS. 2 and 3, extend between the opposite side faces of the body  46  to receive the fasteners  52  and to provide sufficient strength to prevent distortion of the body due to fastener overtightening or due to material creep. The cover plates  48  and  50  may be formed of metal, such as aluminum, or molded plastic of the same composition as the body  46 . 
     One particular advantage of the configuration of the rotor  62  is that the porosity of the sintered metal core  65  can be controlled to provide enhanced bonding of the plastic overmolded layer  69  to the metal core. Moreover, by injection molding the body  46 , and the rotor  62  to provide the overmolded plastic layer  69  on the rotor, dimensional tolerances may be maintained such that very small clearances are provided between the opposed rotor side or end faces  62   a ,  62   b , FIG. 4, and the faces  48   b  and  50   b  of the housing cover plates  48  and  50 . Moreover, the radial outermost tips of the rotor blades  64 ,  66  and  68  may also be dimensioned such that very small clearances are provided between the blade tips and the body wall surfaces  72   a ,  72   b  and  72   c . Still further, fluid viscosity may be selected to minimize fluid leakage flow through all of the clearance spaces between the rotor  62  and the body  46  and between the rotor and the cover plates  48  and  50 . 
     Referring now to FIGS. 5,  6  and  7 , a first alternate embodiment of a rotary damper in accordance with the invention is illustrated and generally designated by the numeral  136 . The damper  136  is substantially like the damper  36  with the exceptions noted herein. Accordingly, a detailed discussion of all of the components of the damper  136  will not be undertaken in the interest of conciseness. The damper  136  includes a body member  146  substantially like the body member  46  and reinforced by molding the body  146  over a metal ring part  54 . Fastener receiving sleeves  84  are also molded in or inserted in suitable bores in the body  146  in the same manner as for the body  46 . 
     The damper  136  includes a rotor  162  having a hub  163  and circumferentially spaced radially projecting blades  164 ,  166  and  168  of generally the same configuration as the rotor  62 . The rotor  162  has a core portion  165  formed of glass fiber or glass fiber/mineral reinforced polyphthalamide or poly-ether sulfone. Alternatively, the core  165  may be formed of aluminum. The core  165  is molded over a metal hub  163   a  having a suitable square cross section bore  167  for receiving the shaft  34 . The rotor  162  is also provided with a plastic layer  169  molded over and encapsulating the core portion  165 . As shown in FIG. 5A, the rotor  162  may be provided with suitable ribs projecting from the surface of the layer  169  and extending radially along the opposite sides of the rotor blades  164 ,  166  and  168 , see FIG. 6 also. Transverse ribs  171   a , one shown in FIG. 5A, may also extend across the tips of rotor blades  164 ,  166  and  168 . The aforementioned ribs may be dimensioned to form a slight interference fit with corresponding surfaces  48   b  and  50   b  of the cover plates and the surfaces of the body  146  delimiting fluid chambers  170   a - 170   f.    
     The damper  136  is also provided with an overmolded layer  172  on the surfaces of the body  146  which define the chambers  170   a - 170   f . The overmolded layers  169  and  172  may be unfilled or self-lubricated polyamide-imide, unfilled polyphthalamide or polyether-ether ketone. The plastic used to overmold the layer  169  on the rotor  162  should be different from that used to provide the overmolded layer  172  on body  146 . 
     Referring briefly to FIG. 7, a typical damper fluid flow control valve assembly associated with the ring part  54  is illustrated and comprises opposed deflectable disks  180  and  181  which are secured to each of the valve plate portions  56 ,  58  and  60 , by a nut and bolt assembly  183 , respectively. The plate portion  56  is shown in FIG. 7 by way of example. The disks  180  and  181  and transverse passages in the plate portions  56 ,  58  and  60  covered by the disks allow differential reaction to torque caused when the trailing arm support member  24  is raising an attached wheel or when the wheel is lowering. For example, when rotor  162  is moved clockwise viewing FIG. 5, fluid may flow from chamber  170   b  to  170   c  through passages  156  which are only partially blocked by disk  180 . However, when rotor  162  moves in the opposite direction fluid flow from chamber  170   c  to  170   b  is permitted only through smaller passages  157 , since passages  156  are blocked by disc  181 . 
     Referring now to FIGS. 8,  9  and  10 , a second alternate embodiment of a rotary damper in accordance with the invention is illustrated and generally designated by the numeral  236 . The damper  236  includes a body  246  similar in most respects to the body  46  and a rotor  262  similar to the rotor  62  except as described herein. Body  246  is shown as being molded over and encapsulating the ring  54  in the same manner as provided for in the dampers  36  and  136 . 
     The rotary damper  236  is characterized by the rotor  262  comprising a rotor core part  263  which is molded over a metal hub part  263   a  having a suitable bore  267  for receiving the shaft  34 , not shown in FIGS. 8,  9  or  10 . The rotor core  263  is preferably formed of long fiber reinforced plastic, such as Isoplast thermoplastic resin, nylon PA6/6 or polyphenylene sulfide. The rotor  262  includes circumferentially spaced radially projecting blades  264 ,  266  and  268 , the radially outermost tips of which are provided with transverse grooves in which are fitted elastomeric seal strips  271 , FIG.  8 . Elastomer seal strips  273  are also fitted in transverse grooves formed in radially inwardly extending projections or bosses  274   a ,  274   b  and  274   c  of body  246 , as also shown in FIG.  8 . 
     The body  246  is formed of molded plastic of one of the types previously mentioned for the damper bodies of the embodiments previously described. The body  246  includes an encapsulated ring  54  and continuous peripheral fluid containment seals  292 , FIG. 9, which are disposed in opposed peripheral grooves in the body  246  and are in fluid tight sealing engagement with surfaces  48   b  and  50   b  of the housing cover plates  48  and  50 , as shown in FIGS. 9 and 10. Suitable o-ring seals  291  disposed in suitable grooves in cover plates  48  and  50  and are engageable with the rotor hub  263  at opposite sides thereof, as shown in FIG. 9, to prevent fluid leakage out of the damper  236 . As with the damper  136 , it is preferable that the rotor  262  and body  246  be molded of dissimilar plastics but of one of the types mentioned hereinbefore. 
     In all of the embodiments described above. The plastic molding or overnolding may be carried out using techniques known to those skilled in the art and with enough precision in dimensional control to eliminate the need for machining the seal surfaces between the rotor and the body and between the rotor and the housing side plates of the embodiments disclosed. The construction and operation of the rotary dampers  36 ,  136  and  236  is believed to be understandable to those of skill in the art based on the foregoing description. Although preferred embodiments have been described in detail herein and certain materials specified, those skilled in the art will also recognize that various substitutions and modifications may be made without departing from the scope and spirit of the appended claims.