Abstract:
A subframe mount capable of having its rate adjusted is disclosed. Subframe mount is configured with damping regions configured to removably receive inserts that would modify rate upon insertion. In this configuration, subframe mount may have its rate adjusted without removal from the motor vehicle. In certain configurations, the subframe mount provides the ability to tune the rate in multiple directions, providing an enhanced motor vehicle development tool.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to subframe mounts, and in particular a subframe mount capable of rate adjustment without removing the mount from the subframe. 
         [0003]    2. Description of Related Art 
         [0004]    Motor vehicles are generally constructed with a unibody frame that serves, among other things, to support the engine. Many motor vehicle designs today also include a subframe assembly attached to the unibody. The subframe assembly provides additional support to the engine, which may be mounted on unibody in the vicinity of the subframe. Generally, a mounting provision, usually in the form of a subframe mount, is disposed between the unibody and the subframe. These mounts typically provide a mechanical buffer between the unibody and the subframe. 
         [0005]    A primary function of subframe mounts is to dampen vibrations between the subframe and the unibody. This damping is desirable to prevent vibrational damage to the subframe and to inhibit the transfer of vibrations to the passenger compartment. Vibrations may be caused by engine operation or uneven road surfaces. Typically, damping can be achieved by constructing the subframe mounts from an elastomeric material, which provides some degree of compliance to the mounts. The degree of compliance, or stiffness, of the subframe mount will govern what frequencies of vibrations the subframe mount can dampen. 
         [0006]    Generally, the stiffness of the subframe mount is called the rate. During motor vehicle development, the subframe mount rate needs to be adjusted or tuned to optimize the damping effect. Typically this is performed by constructing many different subframe mounts having varying rates and testing those mounts on a vehicle until the optimal rate is achieved. Since testing typically occurs with an assembled motor vehicle, changing a mount with an undesirable rate typically requires removing the engine, removing the subframe from the unibody, removing the mount, replacing the mount with a new mount having a different rate, and replacing the engine. Each of these steps is a laborious process, leading to long development time for optimizing the subframe mount. 
         [0007]    Adjustable rate subframe mounts are generally known in the art, typically to enable a motor vehicle to select a rate during operation of the vehicle. For example, U.S. Pat. No. 3,730,462 to Dick, teaches a tunable subframe mount assembly. The subframe mount assembly in the Dick design includes an inner cylindrical bushing and an outer cylindrical bushing. The outer cylindrical bushing is shaped like a cage, including a pair of axially spaced bars and a pair of axially extending bars positioned on opposite sides of the cylinder of the outer bushing. Concentric layers of metal cages having a similar shape as the outer bushing and separated by resilient bodies are disposed between the bushings, and the resilient material is positioned only between the axially extending portions. 
         [0008]    For the Dick design, the subframe mount assembly is most stiff in the vicinity of the axially extending bars. The varying rates of the subframe mount are fixed within the mount, and stiffness tuning is available only by changing the orientation of the subframe mount. This design does not provide for modifying the rate of the subframe mount without modifying the orientation of the subframe mount. In other words, in order to change the rate, the subframe mount would have to be removed from the subframe and re-oriented. 
         [0009]    In an alternate approach, Japanese Publication Number JP58106237 to Yoshida teaches a subframe mount having adjustable vibration damping characteristics. The subframe mount includes a metal frame containing a hollow shaft centrally disposed within the metal frame. An elastic member is disposed between the hollow shaft and the metal frame. Two hollow parts or voids are formed within the elastic member on opposite sides of the hollow shaft so that the spring constant of an axis passing through the hollow parts is reduced. A worm is engaged with a worm wheel that is fixedly attached to the metal frame. This worm gear is configured to rotate the metal frame so that the hollow parts may be positioned at different orientations so that the axis of reduced spring constant may be changed depending upon the driving conditions (for example, idling versus normal driving). 
         [0010]    In the Yoshida design, the stiffness tuning is achieved by virtue of a worm gear rotating the mount, so that re-orienting the hollow parts with respect to the frame repositions the axis having the lowest spring constant. The selection of the orientation is altered during use of the mount. 
         [0011]    Therefore, a need exists in the art for a subframe mount capable of having its rate adjusted without removing the mount from the motor vehicle to adjust the rate or re-orienting the mount. 
       SUMMARY OF THE INVENTION 
       [0012]    A subframe mount capable of rate adjustment without disengaging the subframe mount from the subframe is disclosed. The subframe mount generally includes a housing into which an insert having a known rate may be removably inserted. The insert is generally selected from a group of possible inserts of different rates. 
         [0013]    In one aspect, the invention provides subframe mount having a rate, the subframe mount comprising a housing and at least one compartment provided in the housing, wherein the housing is configured to adjust the rate of the subframe mount by selecting a removable insert having a first rate from a group of inserts having different rates and positioning the removable insert in the compartment. 
         [0014]    In another aspect, the removable insert comprises a damping material. 
         [0015]    In another aspect, the removable insert comprises a frame disposed on an exterior of a portion of the damping material. 
         [0016]    In another aspect, the removable insert comprises a single damping material. 
         [0017]    In another aspect, the removable insert comprises multiple damping materials. 
         [0018]    In another aspect, the multiple damping materials are separated by a plate. 
         [0019]    In another aspect, the invention provides a method of optimizing a subframe mount rate, the method comprising: providing a subframe mount system comprising a housing and a group of inserts of various stiffnesses, wherein the housing is configured to removably receive at least one of the group of inserts of various stiffnesses; associating the housing with a subframe of a motor vehicle; selecting a first insert from the group of inserts, the first insert having a first stiffness; positioning the first insert within the housing to form a first assembled subframe mount; associating the first assembled subframe mount to a motor vehicle frame; and testing the damping effect of the first assembled subframe mount. 
         [0020]    In another aspect, the method further comprises the step of removably securing the first insert to the housing. 
         [0021]    In another aspect, the method further comprises the steps of detaching the motor vehicle frame from the first assembled subframe mount; removing the first insert from the housing; selecting a second insert from the group of inserts, the second insert having a second stiffness; positioning the second insert within the housing to form a second assembled subframe mount; attaching the motor vehicle frame to the second assembled subframe mount; and testing the damping effect of the second assembled subframe mount. 
         [0022]    In another aspect, the method further comprises the step of securing the second insert within the housing. 
         [0023]    In another aspect, the housing is configured to receive at least two inserts along a single axis, and the group of inserts comprises a plurality of pairs of inserts of various stiffnesses, wherein both inserts of each pair have the same stiffness. 
         [0024]    In another aspect, the invention provides a subframe mounting system for determining the optimal rate of a subframe mount for a motor vehicle, the system comprising: a housing made of a rigid material; the housing including at least one compartment for removably receiving an insert; a group of inserts, where each insert of the group of inserts has a unique stiffness; wherein the stiffness of the housing may be altered by selecting an insert from the group of inserts and positioning the selected insert within the compartment. 
         [0025]    In another aspect, the housing is configured to receive at least two inserts along a single axis. 
         [0026]    In another aspect, the group of inserts comprises a plurality of pairs of inserts, wherein each insert in the pair has the same rate. 
         [0027]    In another aspect, each insert comprises a damping material. 
         [0028]    In another aspect, the damping material comprises an elastomeric material. 
         [0029]    In another aspect, the insert comprises at least two different damping materials, wherein each damping material has a different stiffness. 
         [0030]    In another aspect, a plate separates the different damping materials. 
         [0031]    In another aspect, the damping material is associated with a frame. 
         [0032]    In another aspect, the insert is configured to be secured within the compartment. 
         [0033]    In another aspect, the invention provides a kit for testing the rate of a subframe mount comprising a plurality of interchangeable inserts configured to be received within a housing of a subframe mount, wherein a first insert of the plurality of interchangeable inserts has a first stiffness and a second insert of the plurality of interchangeable inserts has a second stiffness. 
         [0034]    In another aspect, the plurality of interchangeable inserts includes at least one pair of inserts having substantially the same stiffness. 
         [0035]    In another aspect, each insert comprises a damping material. 
         [0036]    In another aspect, the damping material comprises an elastomeric material. 
         [0037]    In another aspect, the damping material is associated with a frame. 
         [0038]    Other systems, methods, features and advantages of the invention will be, or will become, apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the invention, and be protected by the following claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
           [0040]      FIG. 1  is an exploded isometric view of a motor vehicle unibody, the engine, and the subframe; 
           [0041]      FIG. 2  is an isometric view of a portion of a unibody mounted to a portion of a subframe; 
           [0042]      FIG. 3  is an exploded view of the unibody a subframe mount of  FIG. 2 ; 
           [0043]      FIG. 4  an isometric view of an embodiment of an adjustable rate subframe mount with no damping inserts disposed in receiving portions; 
           [0044]      FIG. 5  is an exploded, isometric view of an embodiment of an adjustable rate subframe mount with a pair of damping inserts; 
           [0045]      FIG. 6  is an isometric view of an embodiment of an adjustable rate subframe mount with damping inserts disposed in receiving portions; 
           [0046]      FIG. 7  is an isometric view of an embodiment of a damping insert; 
           [0047]      FIG. 8  is a cross-sectional view of the damping insert shown in  FIG. 7 , taken along line  8 - 8 ; 
           [0048]      FIG. 9  is an isometric view of an embodiment of a multiple rate damping insert; 
           [0049]      FIG. 10  is a cross-sectional view of the multiple rate damping insert shown in  FIG. 9 , taken along line  10 - 10 ; 
           [0050]      FIG. 11  is an isometric view of an embodiment of a multiple rate damping insert; 
           [0051]      FIG. 12  is a cross-sectional view of the multiple rate damping insert shown in  FIG. 11 , taken along line  12 - 12 ; 
           [0052]      FIG. 13  is an isometric view of a frame, subframe, and subframe mount of with inserts of a particular rate being inserted into the subframe mount; and 
           [0053]      FIG. 14  is an isometric view of the frame, subframe, and subframe mount of  FIG. 13  in an assembled condition. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    Generally, the invention is directed toward a subframe mount disposed between and associated with the subframe and the frame of a motor vehicle. The subframe mount is configured to allow the user to alter the rate of the subframe mount while at least a portion of the subframe mount remains attached to the subframe. The subframe mount includes provisions so any one of a group of inserts may be positioned within the mount, where each insert or pair of inserts has a different stiffness. Changing the insert or inserts within the mount alters the stiffness of the mount along at least one axis. 
         [0055]    Referring to  FIG. 1 , a motor vehicle  100  is provided. The invention can be used in connection with a motor vehicle. The term “motor vehicle” as used throughout the specification and claims refers to any moving vehicle that is capable of carrying one or more human occupants and is powered by any form of energy. The term motor vehicle includes, but is not limited to cars, trucks, vans, minivans, SUVs, motorcycles, scooters, boats, personal watercraft, and aircraft. 
         [0056]    In some embodiments, including the embodiment shown in the figures, motor vehicle  100  includes a frame  105 . Frame  105  may be any type of frame known in the art. In the embodiment shown in the figures, frame  105  includes a unibody, which generally includes the chassis of motor vehicle  100  and the body of motor vehicle  100  as a single unit. In other embodiments, frame  105  may include a separate chassis and body. For reference, frame  105  has a longitudinal axis  101  and a transverse axis  102 . Longitudinal axis  101  may be the same for frame  105  and motor vehicle  100 . Additionally, transverse axis  102  is the same for frame  105  and motor vehicle  100 . 
         [0057]    In some embodiments, frame  105  includes an engine compartment  106 . Generally, engine compartment  106  is configured to receive an engine  130 . In some embodiments, a subframe  110  may be disposed in or near engine compartment  106  to supply additional support to an engine compartment frame  108 , which may be a portion of frame  105 . The shape of subframe  110  may vary depending upon the type of motor vehicle, the type of engine, the type of drivetrain, or other factors. Typically, a subframe is substantially rectangular in shape, having two spaced apart members extending substantially parallel to transverse axis  102  and two spaced apart members extending substantially parallel to longitudinal axis  101 . In some embodiments, additional structural supports may be provided on any or all of the members to reduce vibrations. Further, in some embodiments, any of all of the members may include curved portions and/or bends, for example, to accommodate drivetrain elements or to conform to the contours of the unibody. In the embodiment shown in the figures, subframe  110  includes two members extending substantially parallel to longitudinal axis  101 . A first transverse member extends parallel to transverse axis  102  to connect the longitudinal members at or near a front of motor vehicle  100 . A second transverse member extends substantially parallel to transverse axis  102  to connect the longitudinal members at or near a rear end of motor vehicle  100 . A third transverse member extends across subframe  110  at or near a center of subframe  110 . The third transverse member is configured to extend beneath engine  130 . 
         [0058]    Generally, frame  105  includes at least one provision to mount or receive an engine. The term “engine” as used throughout the specification and claims refers to any device or machine that is capable of converting energy. In some cases, potential energy is converted to kinetic energy. For example, energy conversion can include a situation where the chemical potential energy of a fuel or fuel cell is converted into rotational kinetic energy or where electrical potential energy is converted into rotational kinetic energy. Engines can also include provisions for converting kinetic energy into potential energy, for example, some engines include regenerative braking systems where kinetic energy from a drivetrain is converted into potential energy. Engines can also include devices that convert solar or nuclear energy into another form of energy. Some examples of engines include, but are not limited to: internal combustion engines, electric motors, solar energy converters, turbines, nuclear power plants, and hybrid systems that combine two or more different types of energy conversion processes. 
         [0059]    Engines typically include mounting provisions configured to removably attach the engine to the motor vehicle, although in some embodiments, an engine may be fixedly attached to the motor vehicle, such as by welding. When engine mounts are provided, such provisions typically include bolt holes and flanges configured to receive bolts or other mechanical fasteners mechanically linking the engine to the subframe mount. Any fastening system known in the art may be used as long as both the engine and the engine mount are configured to engage with each other using the selected system. 
         [0060]    Frame  105  may not be attached directly to subframe  110 , as such a configuration could yield undesirable vibrations in the passenger compartment. Vibrations occur between the engine and the subframe during operation, typically due to normal engine operation and uneven road surfaces. Subframe mounts are typically constructed such that the subframe mounts may dampen the vibrations between the engine and subframe during motor vehicle operation. Therefore, subframe  110  includes at least one provision to attach subframe  110  to frame  105 , although in many embodiments multiple receiving provisions are included. 
         [0061]    The placement and number of the subframe mounts may vary, depending upon the type of motor vehicle, the type of engine, the shape of the subframe, and other factors. In the embodiment shown in the figures, four subframe mounts are provided, one at each corner of subframe  110 : a first subframe mount  115 , a second subframe mount  116 , a third subframe mount  117 , and a fourth subframe mount  118 . Subframe mounts  115 ,  116 ,  117 , and  118  may be removably attachable to subframe  110 , although in some embodiments at least a portion of subframe mounts  115 ,  116 ,  117 , and  118  may be fixedly attached to subframe  110 . For example, as shown in  FIG. 4 , subframe mount  115  generally includes a housing  151  having compartments  165 ,  170  configured to receive removable inserts (not shown in  FIG. 4 ). Housing  151  may be configured to be press-fitted or welded to a subframe member, as the interchangeability of the inserts allows the performance characteristics of subframe  110  to be altered without removing the entirety of subframe  110  from subframe member  115 . Housing  151  may be made of a rigid and durable material, such as metals like steel and aluminum, composite materials, or the like. 
         [0062]    In some embodiments, subframe  110  includes mount receiving portions configured so that subframe mounts  115 ,  116 ,  117 , and  118  may be associated with subframe  110  at the mount receiving portions. As shown in  FIG. 1 , subframe  110  is provided with four mount receiving portions: a first mount receiving portion  111  configured to receive first subframe mount  115 , a second mount receiving portion  112  configured to receive second subframe mount  116 , a third mount receiving portion  113  configured to receive third subframe mount  117 , and a fourth mount receiving portion  114  configured to receive fourth subframe mount  118 . In some embodiments, subframe  110  may include the same number of mount receiving portions as subframe mounts. In other embodiments, the number of mount receiving portions may be greater than the number of mounts intended to be used so that the locations of the subframe mounts may be changed. In some embodiments all mount receiving portions may be identically sized and shaped, while in other embodiments, each mount receiving portion may have a unique size and/or shape so that certain subframe mounts will only fit specific mount receiving portions. 
         [0063]    In the embodiment shown in the figures, mount receiving portions  111 ,  112 ,  113 , and  114  are configured so that subframe mounts  115 ,  116 ,  117 , and  118  may be inserted into mount receiving portions  111 ,  112 ,  113 , and  114 . Subframe mounts  115 ,  116 ,  117 , and  118  may be fitted into mount receiving portions  111 ,  112 ,  113 , and  114  using any method known in the art, such as by press-fitting, sliding with keyed elements, or the like. Subframe mounts  115 ,  116 ,  117 , and  118  may be secured within mount receiving portions  111 ,  112 ,  113 , and  114 . The securing of subframe mounts  115 ,  116 ,  117 , and  118  may be achieved using any method known in the art, such as by an interference fit, using mechanical fasteners such as screws, bolts, or the like, by welding, or with a combination of securing elements. 
         [0064]    As shown in  FIGS. 2-3 , subframe mount  115  includes provisions to allow subframe mount  115  to be securely associated with subframe  110  and with engine compartment frame  108 . Subframe mount  115  may be sized and shaped to be fitted into mount receiving portion  111 , such as by press-fitting. A mechanical fastener such as bolt  120  may be inserted through subframe mount  115  and engine compartment frame  108 . In other embodiments, other mechanical fasteners may be used, such as pins, screws, or the like. A nut  122  configured to be threaded onto a threaded portion of bolt  120  may be provided to secure bolt  120  into position so that subframe  110 , subframe mount  115 , and engine compartment frame  108  are secured together. In some embodiments, a washer  121  may be provided below mount receiving portion  111  so that the head of bolt  120  may come into contact with washer  121  and not slip against mount receiving portion  111  or the lower surface of subframe mount  115 . In other embodiments, the orientation of the mechanical fastener may be reversed, so that the head of bolt  120  may be positioned above engine compartment frame  108  and nut  121  may be positioned beneath optional washer  121 . 
         [0065]    The ability of subframe mounts to dampen the vibrations relates to the stiffness of the subframe mount. Generally, the stiffness of the subframe mount resists or absorbs the engine vibrations. A subframe mount may be designed to have different stiffnesses along different axes, so that the damping effect may be slightly or substantially different in those different directions. Such configurations may be warranted if testing reveals different levels of vibrations along the different axes. 
         [0066]    To provide damping capability, subframe mounts are commonly comprised of any spring-like material commonly known in the art, such as elastomeric materials like rubber. Alternatively, subframe mounts may be comprised of any dashpot-like material known in the art. The resultant stiffness of the subframe mount is termed the rate of the mount. The subframe mount rate may be optimized or tuned to provide the most effective damping of the vibrations. 
         [0067]    Subframe mount rate tuning generally occurs during the design process of the motor vehicle. During a typical design process, subframe mounts having a known rate are attached to the subframe and the frame. The engine is then attached to the frame via engine mounts. The engine is then operated, and the vibrations of the subframe are measured. If the rate of the subframe mount is sub-optimal, i.e., if the rate is too high or too low, then the engine, subframe, and subframe mounts are detached. New subframe mounts having a different rate than the already-tested subframe mounts are selected and attached to the subframe. The engine is re-attached to the frame, and the engine is operated for additional vibration tests. Engine removal and replacement and subframe mount removal and replacement are time consuming and laborious processes, and subframe mount optimization may require several iterations before the optimal rate is identified. This leads to a lengthy process for subframe mount rate optimization. 
         [0068]    In order to reduce the required time to obtain rate optimization, the rate of subframe mounts  115 ,  116 ,  117 , and  118  may be altered without removing at least a portion of subframe mounts  115 ,  116 ,  117 , and  118  from subframe  110 . This is achieved generally by providing a group of interchangeable inserts configured to be positioned within the housing of subframe mounts  115 ,  116 ,  117 , and  118 , where each insert or subgrouping of inserts has a unique stiffness. A user may select an insert or plurality of inserts to be received within a housing depending upon the desired stiffness characteristics. 
         [0069]    Generally, as shown in  FIGS. 4-6 , a subframe mount such as subframe mount  115  includes a housing  151 . Housing  151  generally includes an outer portion and an inner cylinder  152  configured to receive a bolt such as bolt  120  shown in  FIGS. 2-3 . Housing  151  also defines one or more compartments  155 ,  160 ,  165 , and  170 . In this embodiment, housing  151  is generally cylindrical in shape, although subframe  110  may have any shape. Compartments  155 ,  160 ,  165 , and  170  may have the shape of sections or portions of the shape of housing  151 . For example, in this embodiment housing  151  is a cylinder, so compartments  155 ,  160 ,  165 , and  170  are generally wedge-shaped. In other embodiments, compartments  155 ,  160 ,  165 , and  170  may have other shapes, such as polygons or circular, conical, or spherical sections. 
         [0070]    Some compartments may be filled with a damping material while other compartments may be empty. Inserts such as inserts  175  and  180  as shown in  FIGS. 5 and 6 , are configured to be positioned within the empty compartments. In some embodiments, such as the embodiment shown in  FIGS. 4-6 , compartments  155  and  160  are filled with a damping material such as rubber. The damping material may be secured to housing  151 , such as with an adhesive layers  161 ,  162 ,  163 , and  164 . Such a configuration allows a designer to hold the rate in one axial direction constant while the rate in the other axial direction is altered. In other embodiments, all compartments may be configured to receive inserts, or the permanently-filled compartments may be aligned with multiple axes. 
         [0071]    In the embodiment shown in the figures, housing  151  is divided into four equal compartments  155 ,  160 ,  165 , and  170 . The four compartments may divide substantially all of the interior of housing  151  save for inner cylinder  152 . In other embodiments, the number of compartments may be increased or decreased. In other embodiments, the compartments may divide only a portion of the interior of housing  151 . Four compartments allows a designer to adjust the rate of subframe  110  in two axes. For example, first compartment  155  and second compartment  160  are positioned opposite to each other along a first axis. Third compartment  165  and fourth compartment  170  are positioned opposite to each other along a second axis. 
         [0072]    Each compartment  155 ,  160 ,  165 , and  170  is configured to receive a removable insert, such as inserts  175  and  180 . When all compartments  155 ,  160 ,  165 , and  170  are configured to receive a removable insert, adjustment tests may be performed in both axial directions simultaneously. Inserts  175  and  180  may be secured within the compartments using any mechanical fastener known in the art. In the embodiment shown in the figures, bolt or screw holes  185  and  190  are provided through housing  151  in each empty compartment. This allows a mechanical fastener such as a bolt  140  to be inserted into inserts  175  and  180  to secure inserts  175  and  180  within their respective compartments  165  and  170 . Although bolt holes  185  and  190  and bolts  140  are shown, any mechanical fastener may be used, such as detents, grooves, slides, or the like. 
         [0073]    Because the rate of the subframe mount is changed by changing the inserts, the subframe mount system or kit would typically include a plurality or group of inserts, where each insert or subgroup of inserts in the group has a different, known rate. In some embodiments, pairs of inserts having the same rate are provided so that multiple inserts may be used on the same axis, as shown in  FIGS. 5 and 6 . In some embodiments, at least two inserts or pairs of inserts having different rates are provided, though in other embodiments, more inserts or pairs of inserts having different rates are provided. 
         [0074]      FIGS. 7-12  show three different embodiments of inserts  180 ,  230 , and  430  configured to be inserted into the adjustable rate subframe mount. Both inserts generally include a frame  182 ,  251 ,  451  and a filler material or materials  183 ,  235 ,  240 ,  435 , and  440 . In some embodiments, frames  182 ,  251 ,  451  are sized and shaped to fit snugly within any of the compartments of housing  151  of any of the subframe mounts  115 ,  116 ,  117 ,  118 , such as compartment  170  as shown in  FIGS. 4-6 . In other embodiments, a particular insert may be sized to fit into the compartments of a specific subframe mount, or into a particular compartment. In other words, the inserts may be keyed to a subframe mount or compartment. 
         [0075]    Because, in some embodiments, all of the inserts provided with an adjustable subframe mount system may be interchangeable with each other, frames  182 ,  251 , and  451  may be substantially similarly sized and shaped. Frames  182 ,  251 , and  451  may be made of a rigid and durable material, for example metals such as stainless steel or aluminum. In some embodiments, the material of frames  182 ,  251 , and  451  are the same material as housing  151 . In other embodiments, the material of frames  182 ,  251 , and  451  may be made of a deformable material. In some embodiments, frames  182 ,  251 , and  451  may be eliminated from the inserts. 
         [0076]    In some embodiments, a damping material  183 ,  235 ,  240 ,  435 , and  440  is associated with frames  182 ,  251 , and  451  to define the shape of inserts  180 ,  230 , and  430 . Damping material  183 ,  235 ,  240 ,  435 , and  440  may be any type of damping material known in the art, such as an elastomeric material. A viscous material may also be used if frames  182 ,  251 , and  451  define a cavity that includes a top portion for sealing (not shown). Any type of damping material may be used. 
         [0077]    In the embodiment shown in  FIGS. 7 and 8 , a single damping material  183  is provided within frame  182 . Damping material  183  has a known stiffness. This configuration provides a single overall stiffness profile for insert  180 . 
         [0078]    Alternatively, in the embodiment shown in  FIGS. 9 and 10 , two different damping materials  235  and  240  are provided. Each damping material  235  and  240  has a different stiffness. For example, first damping material  235  may be a relatively soft rubber while second damping material  240  may be a relatively hard rubber, or vice versa. This configuration provides a more complex stiffness profile for insert  230 . A more complex stiffness profile allows a designer to more finely tune the rate of the subframe mount. 
         [0079]    When multiple damping materials are provided in a single insert, the materials may be separated by an optional rate plate  245 . Rate plate  245  is a rigid plate, which in some embodiments may be made of the same material as frame  251 . Rate plate  245  may be positioned a distance  250  away from an outer wall of housing  251 . Rate plate  245  essentially separates insert  230  into two concentric sections. The two sections may be relatively equal in volume or relatively different in volume, depending upon distance  250 . 
         [0080]    In other embodiments, the rate plate may be used to separate insert  230  into side-by-side sections as opposed to concentric sections.  FIGS. 11 and 12  show a side-by-side damping insert  430 . Frame  451  includes a rate plate  445  that divides frame  451  into two side-by-side sections. A first material  435  having a first stiffness is disposed in one section while a second material  440  having a different stiffness is disposed in the other section. In other embodiments, first material  435  and second material  440  may be the same material. In such embodiments, rate plate  445  may adjust the rate by increasing the stiffness of the insert. 
         [0081]    If more than two materials are provided, a rate plate may separate the materials, and at least one rate plate is provided at the interface of any two different materials or sections of material, regardless of whether or not the two sections are the same or different materials. 
         [0082]    Rate plate  245  prevents damping materials  235  and  240  from abrading each other during use. Because damping materials  235  and  240  may both be elastomeric materials, such abrasion may eventually degrade or impair the performance of the materials. Additionally, rate plate  245  provides additional stiffness, as the material of rate plate  245  is likely to be more stiff than damping materials  235  and  240 . 
         [0083]    The damping material may be secured within the frame, such as with an adhesive. For example, as shown in  FIGS. 7-8 , first damping material  183  is secured to frame  182  with a first adhesive layer  184 . In  FIGS. 9-10 , second damping material  235  is secured to a rate plate  245  with a second adhesive layer  231 . A third damping material  240  is secured to rate plate  245  with a third adhesive layer  232  and to frame  251  with a fourth adhesive layer  234 . In  FIGS. 11-12 , a fourth damping material  435  is secured to a rate plate  445  with a fifth adhesive layer  432  and to frame  451  with a sixth adhesive layer  434 . A fifth damping material is secured to rate plate  445  with a seventh adhesive layer  431  and to frame  451  with an eighth adhesive layer  433 . The adhesive used in any of adhesive layers  184 ,  231 ,  232 ,  234 ,  431 ,  432 ,  433 ,  434 ,  445  may be any type of adhesive known in the art, such as glue, UV-cured adhesive, or epoxy. 
         [0084]    Each frame  182 ,  251 , and  451  may include provisions to secure inserts  180 ,  230 , and  430 , respectively, within a compartment of housing  151 . These provisions may correspond to similar provisions provided on housing  151 , as discussed above. In the embodiments shown in the figures, bolt holes  285 ,  290  are provided through frame  182  of insert  180  ( FIG. 7 ) and frame  251  of insert  230  ( FIG. 9 ). Similarly, bolt holes  485  and  490  are provided through frame  451  of insert  430 . Bolt holes  285 ,  290 ,  485 , and  490  may extend into the filler material of the inserts. Bolt holes  285 ,  290 ,  485 , and  490  are configured to correspond to bolt holes  185  and  190  formed through housing  151 . This allows a bolt, pin, or screw to be inserted through both sets of holes, thereby securing inserts  180  and/or  230  within the compartments of housing  151 . In some embodiments, the heads of bolts  140  may rest on an exterior surface of housing  151 , as shown in  FIG. 6 . In other embodiments, the heads of bolts  140  may be recessed into housing  151  so that the exterior surface of housing  151  is relatively smooth in the vicinity of bolts  140 . 
         [0085]    In other embodiments, alternate mechanical or magnetic securing devices may be provided. For example, detents may be provided on frames  182 ,  251 , and  451  that are configured to snap into recesses formed within the compartments of housing  151  or vice versa. Frames  182 ,  251 , and  451  may include a strong magnet that may secure frames  182 ,  251 , and  451  to housing  151  if housing  151  were made of a paramagnetic or oppositely-poled magnetic material. In some embodiments, no securing mechanism may be provided. 
         [0086]      FIGS. 2-3  and  13 - 14  show one embodiment of how adjustable rate subframe mounts may be used to determine an optimal rate during the development process. Generally, for testing purposes, the tester may be provided with a subframe mount system for testing including a plurality of subframe mounts, such as subframe mounts  115 ,  116 ,  117 , and  118 , and a group of inserts having different stiffnesses, such as inserts  180 ,  230 , and  240 . Inserts  180 ,  230 , and  240  may be provided in pairs or other multiples so that multiple compartments may be fitted with inserts having the same rate. The tester may then select inserts having a known rate from the group of inserts so that testing may begin. While only subframe mount  115  is discussed, the same procedure may be applied to any of the subframe mounts used to attach subframe  110  to frame  105  and/or engine compartment frame  108 . 
         [0087]    As discussed above,  FIG. 2  shows subframe  110  attached to engine compartment frame  108  using subframe mount  115 . Subframe mount  115  is inserted into mount receiving portion  111 , and the assembly is connected together using bolt  120 , washer  121 , and nut  122 , similar to the assembly discussed above in  FIGS. 2-3 . In this assembly, two inserts according to the design of insert  180  are inserted into the empty compartments of subframe mount  115  to form an assembled mount. Inserts  180  are substantially as described above with respect to  FIGS. 7 and 8 , and have been selected from a group of inserts having known stiffnesses. The group may include any number of inserts, ranging from two to ten or even more. Vibrations tests are performed, and measurements of the vibrations experienced by subframe  110  and engine compartment frame  108  are collected and recorded. A determination is made of whether or not the stiffness profile of mount  115  having inserts  180  is optimal for the motor vehicle being tested. 
         [0088]    If the stiffness profile of mount  115  having inserts  180  does not produce the desired results, then the assembly shown in  FIG. 2  is disassembled as shown in  FIG. 3 . Inserts  180  are removed, and a new pair of inserts having a different stiffness profile is selected from the group, such as inserts  230 . As shown in  FIG. 13 , inserts  230  are positioned to be inserted into the empty compartments of subframe mount  115  prior to re-attaching subframe  110  to engine compartment frame  108 . Subframe mount  115  having inserts  230  will have a new stiffness profile and rate, wherein the new rate is different from the first rate of the mount assembly formed by when inserts  180  were inserted into subframe mount  115 . Subframe  110 , subframe mount  115 , and engine compartment frame  108  are then associated together. For example, as shown in  FIG. 14  and described above with respect to  FIG. 2 , bolt  120  may be pushed through subframe  110 , subframe mount  115 , and engine compartment frame  108  and secured in position with nut  122 . Vibration tests are performed again, and a determination is made as to whether inserts  230  produce the desired response. If so, testing is concluded. If not, the assembly is disassembled, a new set of inserts is selected from the group of inserts, and the process is repeated. The process may be repeated as often as desired by the testers. 
         [0089]    The process described above details the testing of vibration response in only one axis. To test a different axis, subframe mount  115  may be removed from mount receiving portion  111  and replaced in a new orientation so that the empty compartments are oriented on another axis. In another embodiment, subframe mount  115  may be provided with four empty compartments, so that both directions may be tested simultaneously with four inserts. It will be apparent to those in the art that various combinations of mounts with different numbers of empty compartments and inserts may be provided to test according to the preferences of the designers. 
         [0090]    While various embodiments of the invention have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.