Abstract:
A hydraulic mount provides passive rate dip performance through use of a secondary orifice track-mass resiliently constrained within a first orifice track for reciprocating movement within the first orifice track under conditions such as engine idle, and constrained against reciprocating motion within the first orifice track for conditions imposing large amplitude, low frequency loads on the mount.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to resilient mounts of the type used in motor vehicles, and more particularly to resilient mounts using a hydraulic fluid.  
         BACKGROUND OF THE INVENTION  
         [0002]    It has long been the practice in motor vehicles, such as automobiles and trucks, to suspend engines and other heavy components that generate vibrations when operating on resilient mounts that isolate and damp the vibration from reaching the passenger compartment of the vehicle. It is desirable in such circumstances to provide a mount that is relatively soft for low amplitude higher frequency vibrations, such as those produced while an engine is operating at idle speed. Making the mount too soft, however, results in a structure that may not be capable of damping the motion of a heavy mass, such as the engine, when the vehicle is traveling over a bumpy road.  
           [0003]    The competing requirements for a mount that is soft enough to isolate low amplitude vibrations generated by an engine at idle, and yet is robust enough to damp and limit the movement of an engine relative to the vehicle chassis when the vehicle is encountering a bumpy road surface, have caused the designers of resilient mounts to employ hydraulic fluid flowing between multiple chambers within the mount, together with judiciously sized orifice tracks and fluid valve arrangements providing fluid communication between the chambers, to provide mounts that exhibit different dynamic stiffness characteristics dependent upon the magnitude and frequency of the vibratory input to the mount. Such mounts are known as controlled rate dip mounts.  
           [0004]    The construction of prior resilient controlled rate dip mounts, has required relatively complicated internal chambering, track configurations, and valve arrangements that result in considerable and undesirable complexity and cost to achieve acceptable rate dip performance of the mount. In addition, physical constraints imposed by prior mount constructions require that compromises be made that result in less than ideal performance of the mount at one or more of the operating conditions.  
           [0005]    What is needed, therefore, is an improved resilient mount, offering a more straight-forward construction and improved passive dip rate performance, in comparison to prior hydraulic mounts.  
         SUMMARY OF THE INVENTION  
         [0006]    Our invention provides an improved hydraulic mount through use of a secondary orifice track-mass resiliently constrained within a first orifice track for reciprocating movement within the first orifice track under conditions such as engine idle, and constrained against reciprocating motion within the first orifice track for conditions imposing large amplitude, low frequency loads on the mount.  
           [0007]    In one form of our invention, a hydraulic mount includes a resilient hollow body defining a primary and a secondary fluid chamber separated from one another by a partition having a first orifice track therein providing fluid communication between the primary and secondary fluid chambers. The first orifice track has a wall thereof defining a first opening into the primary fluid chamber and a second opening into the secondary fluid chamber. The hydraulic mount also includes a secondary orifice track-mass body disposed within the first orifice track and sealed to the wall of the first orifice track for limited reciprocating movement within the first orifice track. The secondary orifice track-mass body defines a second orifice track therein providing fluid communication through the secondary orifice track-mass body for passage of fluid received from the first fluid orifice track.  
           [0008]    The hydraulic mount may include a stop for limiting reciprocating movement of the secondary orifice track-mass body within the first orifice track.  
           [0009]    The secondary orifice track-mass body and second orifice track may reciprocate with fluid movement in the first orifice track above a first resonant frequency of the mount, and provide fluid communication for passage of fluid between the primary and secondary fluid chambers at a second resonant frequency of the mount below the first resonant frequency of the mount.  
           [0010]    Our invention may also take the form of a method for operating a hydraulic mount having a resilient hollow body defining a primary and a secondary fluid chamber separated from one another by a partition having a first orifice track therein providing fluid communication between the primary and secondary fluid chambers with the first orifice track having a wall thereof defining a first opening into the primary fluid chamber and a second opening into the secondary fluid chamber.  
           [0011]    The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a cross section taken along line  1 - 1  in FIG. 2, showing an exemplary embodiment of a hydraulic mount, according to our invention;  
         [0013]    [0013]FIG. 2 is a cross section taken along line  2 - 2  of FIG. 1, showing structural details of a partition and a secondary track-mass body of the exemplary embodiment of a hydraulic mount of FIG. 1;  
         [0014]    [0014]FIG. 3 is a perspective illustration of the flow path for fluid through the mount of FIG. 1;  
         [0015]    [0015]FIG. 4 shows an exemplary embodiment of a secondary track mass, according to our invention, in the mount of FIG. 1;  
         [0016]    [0016]FIG. 5 shows a lower track plate that forms part of the partition shown in FIG. 2; and  
         [0017]    [0017]FIG. 6 shows a cross section of the partition of FIG. 2, without the secondary track-mass body. 
     
    
     DETAILED DESCRIPTION  
       [0018]    [0018]FIG. 1 illustrates an exemplary embodiment of a hydraulic mount  10 , according to our invention. The hydraulic mount  10  includes a resilient hollow body  12  defining a primary fluid chamber  14  and a secondary fluid chamber  16 , separated from one another by a partition  18  formed by an upper orifice track plate  20  and a lower orifice track plate  22  that are joined together to form the partition  18 . The resilient hollow body  12  includes an upper resilient member  11 , fabricated from natural rubber or a similar elastomeric material, and a diaphragm  13 , also fabricated from natural rubber or a similar elastomeric material. The upper resilient member  11  and the diaphragm  13  are assembled with the partition  18  in a fluid tight manner to form the primary and secondary fluid chambers  14 ,  16 .  
         [0019]    The upper and lower orifice track plates  20 ,  22  each include complimentary channels therein, which are aligned when the upper and lower plates  20 ,  22  are joined together, to define a first orifice track  24 , having a wall  26 , in the partition  18 . As shown in FIGS. 1 and 2, the first orifice track  24  provides fluid communication between the primary and secondary fluid chambers  14 ,  16 , with the wall  26  of the partition  18  defining a first opening  28  into the primary fluid chamber  14  and a second opening  30  into the secondary fluid chamber  16 .  
         [0020]    A secondary orifice track-mass body  32  is disposed within the first orifice track  24 , and sealed to the wall  26  of the first orifice track  24 , as described in greater detail below, for limited reciprocating movement within the first orifice track  24 . The secondary orifice track-mass body  32  defines a second orifice track therein, in the form of a through bore  33 , providing fluid communication through the secondary orifice track-mass body  32  for passage of fluid received from the first fluid orifice track  24 . The through-bore  33  in the secondary orifice track-mass body  32  forms an orifice having an effective orifice area smaller than an effective orifice area of the first track  24 .  
         [0021]    The mount  10  includes a first and a second attachment device  34 ,  36  disposed along a mount axis  38  extending through the resilient hollow body  12  for receiving a load applied along the mount axis  38 . The first attachment device  34  of the mount  10  is in the form of a threaded stud  42  extending from a base  44  that is bonded to the upper end of the resilient hollow body  12 . The second attachment device  36  in the exemplary embodiment of the mount  10  is also a threaded stud  46  extending from a mount housing  40  attached to the partition  18 .  
         [0022]    As shown in FIG. 3, the first orifice track  24  defines a first track axis  48  extending between the first and second openings  28 ,  30 . The first track axis  48  includes a transverse section  50  extending transverse to the mount axis  38 , as indicated by arrows  52  that extend in opposite directions from the transverse section  50 . The secondary orifice track-mass body  32  is disposed within the transverse section  50  of the first orifice track  24 , for reciprocating movement transverse to the mount axis  38  along the first track axis  50 , as indicated by the arrows  52 .  
         [0023]    It should be noted, however, that the second orifice track-mass can be located anywhere within the first orifice track  24  and move in other directions relative to the mount axis  38 . In other embodiments of our invention, it may be desirable to have the first orifice track  24  define a curvilinear, circular, or other geometric shape. The track-mass  32  may be positioned in a curved section of the first orifice track  24 , rather than in a straight section, as is the case in the exemplary embodiments of the invention specifically described herein. Dependent upon the shape and orientation of the first orifice track  24  relative to the mount axis  38 , in other embodiments of our invention, the track-mass  32  may reciprocate along an axis that is parallel or coincident with the mount axis  38 , or along an axis that is transverse to the mount axis  38  at an angle other than the generally parallel and orthogonal relationship between the transverse section  50  of the first orifice track axis  48  and the mount axis  38  illustrated in the exemplary embodiments expressly disclosed herein.  
         [0024]    As shown in FIG. 4, the secondary orifice track-mass body  32  includes an elongated central member  54  defining the through bore  33 . The central member  54  of the exemplary embodiment is fabricated from a material such as nylon. The central member  54  is bonded to a resilient tethering member  56 , of a material such as natural rubber molded around the central member  54 . The secondary track-mass body  32  is configured to have a vertical dimension that fits closely to the top and bottom walls of the first orifice track  24 , to provide a sliding seal between the track-mass body  32  and the top and bottom surfaces of the wall  26  of the first orifice track  24 , so that substantially all fluid flowing between the primary and secondary fluid chambers  14 ,  16  of the mount  10  must pass through the through-hole  33  forming the second orifice track.  
         [0025]    As shown in FIGS. 5 and 6, the upper and lower track plates  20 ,  22  define complimentary recesses  58  for receiving the resilient tethering member  56  of the track-mass body  32 . As shown in FIGS. 2, 5 and  6 , the mount  10  includes stops, in the form of T-shaped stop posts  60  extending from the upper and lower track plates  20 ,  22 , into the recesses  58  and first orifice track  24 , for limiting the reciprocating movement of the secondary orifice track-mass body  32  within the first orifice track  24 .  
         [0026]    As seen in FIGS.  2 - 4 , the secondary track-mass body  32  includes a pair of vertical openings  62 , or through slots, for passage of the stop posts  60 . The openings  62  and stop posts  60  are configured in a complimentary manner to provide sufficient clearance in the openings  62  for the secondary track-mass body  32  to oscillate in a reciprocating manner as indicated by the arrows  52  along the transverse section  50  of the first orifice track  24 , over a linear distance predetermined by the amount of clearance in the openings  62 , i.e. the length of the slots. The resilient tethering member  56  of the secondary track-mass body  32  provides a fluid seal between the wall  26  of the first orifice track  24  and the secondary track-mass body  32 , while allowing reciprocating movement of the secondary track-mass body  32  within the first orifice track  24 .  
         [0027]    By virtue of the structure described above, when an oscillating load of small amplitude is applied to the mount  10  through the first and second attachment devices  34 ,  36 , the secondary orifice track-mass body  32  and second orifice track  33  reciprocate with fluid movement in the first orifice track  24 . Resistance to fluid flow through the through-hole  33  is great enough, due to the through-hole being of smaller cross sectional flow area than the first orifice track  24 , and fluid friction and viscosity induced forces resisting fluid flow through the elongated length of the through-hole  33 , that there is little if any fluid flow through the through-hole  33 . In this mode of operation, our mount is well suited for providing lower dynamic stiffness at higher frequencies for improved isolation of low amplitude vibrations, such as those produced by an automobile engine at idle or during sustained constant speed operation.  
         [0028]    Should a large amplitude input be applied to the mount through the first and second attachment devices  34 ,  36 , however, the volume of fluid flowing between the first and second fluid chambers  14 ,  16  rises to a point that the ends of the openings in the secondary track-mass body  32  contact the stop posts  60 , and the fluid must flow through the through-hole  33  in traveling through the first and second orifice tracks  24 ,  33  between the primary and secondary fluid chambers  14 ,  16 . In this mode of operation, the dynamic stiffness of the mount  10  is increased significantly, and provides a mount  10  that is well suited to damping low frequency, large amplitude, vibrations, such as those that must be dealt with when an automobile having a resiliently mounted engine encounters a bump in the road causing the engine to bounce with respect to the automobile chassis.  
         [0029]    By judicious design of the components described above, a mount  10  according to our invention provides reciprocating movement of the secondary orifice track-mass body  32  and second orifice track  33 , with fluid movement in the first orifice track  24 , above a first desired resonant frequency of the mount  10 , and fluid communication for passage of fluid between the primary and secondary fluid chambers  14 ,  16  at a second desired resonant frequency of the mount  10  below the first resonant frequency of the mount  10 . A mount  10 , according to our invention, is thus well suited for providing a passive rate dip type of engine mount.  
         [0030]    While the embodiments of our invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention.  
         [0031]    For example, in the exemplary form of the mount  10  according to our invention, oriented as depicted in FIGS.  1 - 6 , the first orifice track  24  defines a generally rectangular shaped cross section thereof in the transverse section  50  of the first orifice track  24 , with the rectangular shaped cross-section defining an upper and a lower wall connected by a pair of spaced side walls, and the secondary orifice track-mass  32  includes upper and lower surfaces respectively thereof in sliding contact with the upper and lower surfaces of the first orifice track  24 , and a pair of spaced side surfaces thereof connected to the side walls of the first orifice track by the imperforate resilient tethering members  56 . In other forms of our invention, however, other cross sectional shapes and tethering configurations may also be utilized.  
         [0032]    Also, in the exemplary forms described herein, the upper and lower track plates  20 ,  22  have a slightly different height. In other forms of our invention, however, it may be preferable to have the upper and lower track plates  20 ,  22  be identical, to reduce the number of component parts required to fabricate the mount  10 .  
         [0033]    The various elements and aspects of our invention may also be used independently from one another, or in different combinations or orientations than are described above and in the drawing with regard to the exemplary embodiment. The first and second attachment devices  34 ,  36  may take many other forms, and can be oriented at an angle to one another and/or the mount axis  36  to facilitate use of our invention in a wide range of applications. We also expressly emphasize that our invention may be practiced in mounts providing resilient support of a wide variety of masses, in addition to the automotive engine mounts described herein.  
         [0034]    The scope of the invention is indicated in the appended claims. We intend that all changes or modifications within the meaning and range of equivalents are embraced by the claims.