Abstract:
A tunable hydraulic bushing mounts a steering gear to a vehicle frame member. The bushing is filled with a fluid and includes an inertia track and a pressure valve separating first and second fluid chambers or cavities. The inertia track provides uninterrupted fluid communication between the first cavity and the second cavity. The pressure valve is movable between an open position, which allows fluid communication though the pressure valve between the first cavity and the second cavity, and a closed position, which blocks fluid communication though the pressure valve between the first cavity and the second cavity. The pressure valve may be configured to be closed during loads induced by smooth road shake and open during loads greater than smooth road shake.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/164,142, filed May 20, 2015, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure generally relates to bushings for mounting steering gears or steering assemblies to vehicle frames. 
       BACKGROUND 
       [0003]    Vehicular steering systems translate directional commands of an operator into steerable wheels, which are in contact with the road, of a vehicle. 
       SUMMARY 
       [0004]    A tunable hydraulic bushing for mounting a steering gear to a vehicle frame member is provided. The bushing is filled with a fluid and includes at least an inertia track and a pressure valve separating first and second fluid chambers or cavities. The inertia track provides uninterrupted fluid communication between the first cavity and the second cavity. 
         [0005]    The pressure valve is movable between an open position, which allows fluid communication though the pressure valve between the first cavity and the second cavity, and a closed position, which blocks fluid communication though the pressure valve between the first cavity and the second cavity. The pressure valve is configured to be closed during loads induced by smooth road shake and open during loads greater than smooth road shake. 
         [0006]    The above features and advantages, and other features and advantages, of the present subject matter are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the disclosed structures, methods, or both. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic, isometric view of a portion of a steering assembly for a vehicle. 
           [0008]      FIG. 2  is a schematic, isometric view of a hydraulic bushing that may be used to mount the steering assembly to a frame of the vehicle. 
           [0009]      FIG. 3A  is a schematic, cross-sectional view of the bushing illustrated in  FIG. 2 , taken generally along line  3 - 3  of  FIG. 2 , showing the bushing in a closed state. 
           [0010]      FIG. 3B  is a schematic, cross-sectional view of the bushing illustrated in  FIG. 3A , showing the bushing in an open state. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring to the drawings, wherein like reference numbers correspond to like or similar components whenever possible throughout the several figures, there is shown in  FIG. 1  a portion of a vehicle (not numbered). In particular,  FIG. 1  shows a steering assembly  10  for the vehicle. A frame  12  is schematically shown in  FIG. 1  and broadly illustrates the structural chassis elements to which the steering assembly  10  is mounted. 
         [0012]    While the present disclosure may be described with respect to specific applications or industries, those skilled in the art will recognize the broader applicability of the disclosure. Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” et cetera, are used descriptively of the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims. Any numerical designations, such as “first” or “second” are illustrative only and are not intended to limit the scope of the disclosure in any way. 
         [0013]    Features shown in one figure may be combined with, substituted for, or modified by, features shown in any of the figures. Unless stated otherwise, no features, elements, or limitations are mutually exclusive of any other features, elements, or limitations. Furthermore, no features, elements, or limitations are absolutely required for operation. Any specific configurations shown in the figures are illustrative only and the specific configurations shown are not limiting of the claims or the description. 
         [0014]    A rack-and-pinion steering gear  14  translates rotational movement of a steering wheel (not shown) into lateral movement of a pair of tie rods  16 . In the configuration illustrated in  FIG. 1 , the steering gear  14  is a power steering gear and includes an electric motor (not numbered) that selectively amplifies forces transferred to the tie rods  16 . Although the steering assembly  10  is illustrated as rack-and-pinion, other configurations may alternatively be utilized within the scope of the disclosure herein. 
         [0015]    The steering gear  14  is mounted to the frame  12  via first and second bushings  20 . One or more bolts  24  fixedly attaches each bushing  20  to the frame  12 , such that the bushings  20  selectively provide varying degrees of relative movement between the frame  12  and the steering gear  14 . The first and second (or left and right) bushings  20  may be substantially identical, mirrored, or tailored to specific characteristics of each side. 
         [0016]    An outer housing or can  26  encapsulates the interior of the bushings  20 . The can  26  may be pressed, welded, adhered, or otherwise solidly attached to the steering gear  14 . 
         [0017]    Referring now to  FIG. 2 , and with continued reference to  FIG. 1 , there is shown an isometric view of one of the bushings  20 .  FIG. 2  illustrates the interior portions of the bushing  20  with the can  26  shown only in phantom and with end caps hidden from view. Note that the bushing  20  is shown in generally the same orientation as  FIG. 1 , such that the vertical axis in both figures generally represents movement upward and downward relative to the vehicle and the horizontal axis generally represents lateral movement. 
         [0018]    A mount hole  28  cooperates with the bolt  24  to mount the bushing  20 —and, therefore, the steering gear  14 —to the frame  12 . A body  30  provides the structural support between the mount hole  28  and the can  26 . In some configurations, the body  30  may be made of elastomeric rubber. For example, and without limitation, for applications in larger vehicles, such as full size pickup trucks, the body  30  may have a durometer generally between 400-800 newtons per millimeter (N/mm). However, other vehicles may have durometer ranges from 200 to 50,000 N/mm. 
         [0019]    A first chamber or first cavity  31  and a second chamber or second cavity  32  are formed between the body  30  and the can  26 . The first cavity  31  and the second cavity  32  are filled with a fluid—generally an incompressible fluid—such that the bushing  20  may be referred to as a hydraulic bushing. 
         [0020]    On the left and right sides of the bushing  20  are snubbers  34 , which may be attached to the can  26 . The snubbers  34  define or limit the amount of lateral travel that may occur between the body  30  and the can  26 . Therefore, the snubbers  34  may be tuned to control the displacement between the frame  12  (via the bolt  24 ) and the steering gear  14  (via its attachment to the can  26 ). 
         [0021]    As lateral loads are introduced between the steering gear  14 , such as by the tie rods  16 , and the frame  12 , the body  30  of the bushing  20  attempts to flex and come into contact with the snubbers  34 . However, because the first cavity  31  and the second cavity  32  are filled with fluid, displacement of the body  30  is limited unless the fluid can freely move between the first cavity  31  and the second cavity  32 . 
         [0022]    Referring also to  FIG. 3A  and  FIG. 3B , and with continued reference to  FIGS. 1-2 , there are shown cross-sectional views of the bushing  20  taken generally along a line  3 - 3  of  FIG. 2 .  FIG. 3A  shows the bushing  20  in a closed state, such that flow is limited between the first cavity  31  and the second cavity  32 .  FIG. 3B  shows the bushing  20  in an open state, such that maximum flow is allowed between the first cavity  31  and the second cavity  32 . 
         [0023]    A plurality of inertia tracks  38  link the first cavity  31  and the second cavity  32 . The inertia tracks  38  are relatively narrow pathways between the first cavity  31  and the second cavity  32  and allow small amounts of fluid to pass between the first cavity  31  and the second cavity  32  at low flow rates. 
         [0024]    In the configuration shown, each of the inertia tracks  38  is substantially the same size and passes through the body  30  along a planar arc, such that the whole inertia track  38  is viewable in  FIGS. 3A and 3B . However, the inertia tracks  38  may also be lengthened or stretched by passing through the body  30  at an angle relative to the view plane of  FIGS. 3A and 3B . The inertia tracks  38  are illustrated at the bottom of the bushing  20 , but may be located at the top. 
         [0025]    The inertia tracks  38  are always open, such that fluid may move back and forth to allow slight lateral movement of the body  30  within the can  26 . However, because the inertia tracks  38  are narrow, the inertia tracks  38  will not allow large, fast displacements of the body  30 . Under steady state loads, the inertia tracks  38  allow equalization of pressure within the fluid in the first cavity  31  and the second cavity  32 . 
         [0026]    The inertia tracks  38  may be tuned to allow specific frequencies and amplitudes of displacement of the body  30 . The track length, width and number of inertia tracks  38  can be tuned to allow certain frequencies and force amplitudes to be dampened or cancelled by the bushing  20 . 
         [0027]    One specific benefit of the inertia tracks  38  of the bushing  20  is the ability to attenuate or eliminate smooth road shake (SRS) vibrations of the vehicle. In some vehicles driving at highway speeds, tire or wheel imbalances may cause smooth road shake at between 10-18 Hz vibration. Smooth road shake is often felt in the floor or seat (or both) of the vehicle, which may be bothersome to the operator of the vehicle. The inertia tracks  38  may be tuned to attenuate smooth road shake for the specific vehicle into which the bushings  20  will be placed. 
         [0028]    At least one pressure valve  40  divides the first cavity  31  and the second cavity  32 . In  FIG. 3A , the pressure valve  40  is shown in a closed or un-actuated state. In  FIG. 3B , the pressure valve  40  is shown in an open or actuated state. While the inertia tracks  38  always allow low flow rates between the first cavity  31  and the second cavity  32 , the pressure valve  40  selectively allows high flow rates between first cavity  31  and the second cavity  32 . 
         [0029]    As best illustrated in  FIG. 2 , the bushing  20  includes two pressure valves  40 , one tending to open to the left, such that it promotes flow from the second cavity  32  to the first cavity  31 , and one tending to open to the right, such that it promotes flow from the first cavity  31  to the second cavity  32 . The viewpoint of  FIG. 3B  taken through the pressure valve  40  tending to open toward the right. 
         [0030]    In the closed state, as illustrated in  FIG. 3A , the pressure valve  40  is subjected to pressure differentials below a cracking threshold. This occurs while the bushing  20  is subjected to lateral loads between the frame  12  and the steering gear  14  below a lateral threshold. During such relatively low, or steady-state, loading conditions, fluid flow through the inertia tracks  38  is sufficient to prevent fluid pressure build up in either the first cavity  31  or the second cavity  32  from reaching the cracking threshold of the pressure valve  40 . 
         [0031]    In the open state, as illustrated in  FIG. 3B , the pressure valve  40  is subjected to a pressure differential greater than the cracking threshold. The opened pressure valve  40  creates a long, relatively wide opening between the first cavity  31  or the second cavity  32 . This situation occurs when the bushing  20  is subjected to lateral loads between the frame  12  and the steering gear  14  above the lateral threshold. 
         [0032]    For example, during cornering of the vehicle, the tie rods  16  introduce lateral loads between the steering gear  14  and the frame  12 , which bias the body  30  laterally within the can  26 . If these loads cause pressure differentials to exceed the cracking threshold, the pressure valve  40  will open. The high flow rate between the first cavity  31  or the second cavity  32  while the pressure valve  40  is open allows the body  30  to quickly move laterally until it makes contact with the snubbers  34 . 
         [0033]    The pressure valve  40  may be tuned to open during pressure buildup of specific lateral loads. In particular, the pressure valve  40  may open under laterals loads that are greater than those introduced by smooth road shake or similar, very low force, vibrations. 
         [0034]    For hydraulic bushings located elsewhere on the vehicle, or for alternative (high cracking) configurations of bushing  20 , over-pressure valves may be configured to open or actuate at very high loads. Such over-pressure valves actuate only during extreme loading conditions expected to occur a handful of times during the operating life of the vehicle. For example, over-pressure valves in a hydraulic bushing located elsewhere on the vehicle may be configured to open when the bushing is subjected to greater than 30 kilonewtons (kN) of lateral force. 
         [0035]    Contrarily, the pressure valves  40  of the bushing  20  are configured to open at significantly lower lateral loading conditions, such that one of the pressure valves is open at all loads greater than those introduced by smooth road shake and other low-level vibrations. For example, and without limitation, the bushings  20  mounting the steering gear  14  to the frame  12  may be configured such that the pressure valves  40  open at as low as 1 kN of lateral force. Therefore, the pressure valves  40  are open under relatively low loads, and are often open while the vehicle is operating, such as those occurring under minor corning or steering loads applied to the steering gear  14 . 
         [0036]    The displacement of the body  30  within the bushing  20  may be configured to allow, or create, understeer during cornering of the vehicle. For example, the body  30  and the snubbers  34  may be configured to allow between 4-7 millimeters of lateral displacement to either the left or the right. This lateral movement between the frame  12  and the steering gear  14  assists in causing the vehicle to understeer. 
         [0037]    Note that the area opened by either of the pressure valves  40  is significantly greater than the total area of the inertia tracks  38 . Furthermore, the length of the inertia tracks  38  contributes drag to fluid flowing there through, but fluid flowing passed the open pressure valves  40  is significantly less constricted. Each of the pressure valves  40  may have an area (i.e., a cross-sectional area though which fluid is capable of flowing when open) that is at least twice the combined area of the inertia tracks  38 . 
         [0038]    The detailed description and the drawings or figures are supportive and descriptive of the subject matter discussed herein. While some of the best modes and other embodiments have been described in detail, various alternative designs, configurations, and embodiments exist.