Abstract:
An integrally cast aluminum subframe for a vehicle suspension system has control arm connections that avoid high stress in the connections. Mounting studs may be an integral part of the subframe casting or may be subsequently joined to the subframe. Bushings of the articulations of the control arms are joined to the mounting studs from one side only, so that the flexing of the connection that was present in the prior art clevis connection is avoided. Consequently, the articulation is retained between a head of the mounting bolt and the mounting stud.

Description:
BACKGROUND OF THE INVENTION 
     This application is related to co-pending application U.S. serial number, filed concurrently herewith. 
     The present invention relates in general to a rear subframe for a multi-link vehicle suspension and, more specifically, to the articulating connection of control arms to a cast aluminum subframe. 
     The vehicle frame supports the vehicle body and, together with other components, such as control arms, springs, and shock absorbers, comprises the suspension system which permits up and down wheel movement without up and down movement of the body. Due to the many forces to which the frame is subjected, it is important that the frame have high stiffness. The vast majority of vehicle frames have been fabricated from steel because of its high strength, high stiffness, and reasonable cost. However, there are also concerns for minimizing the weight of a frame, based mainly on a desire to improve fuel economy. 
     Integral castings of aluminum or aluminum alloys may be used as vehicle frames or more typically subframes, cradles, and cross members (i.e., frame sections). Aluminum is able to provide good stiffness and can provide a significant reduction in weight. A hollow cross section (e.g., box or tubular) of the subframe members is used to further improve stiffness and reduce weight. 
     Control arms are swinging levers that provide the links between the subframe and the wheels (or more typically the steering knuckles attached to the wheels). The frame or subframe must provide articulating mounts for the control arms. A common type of control arm is known as the A-arm, in which each arm has two connection points with the subframe and one connection point with the wheel. The subframe articulations typically include a clevis arrangement. 
     In a clevis, it is necessary to include clearance between the flanges and the control arm bushing to permit insertion of the bushing between the flanges. After tightening of a clevis bolt, the flanges flex toward the bushing to close-off the clearance. In an aluminum casting, however, flexing of the flanges may lead to high stress. 
     SUMMARY OF THE INVENTION 
     The present invention has the advantage of providing an integrally cast aluminum subframe with control arm connections that avoid high stress in the connections. 
     In one aspect, the invention provides a subframe for a vehicle which is adapted to receive articulations (e.g., bushings) of control arms for attaching vehicle wheels. The subframe comprises a substantially hollow left side-rail, a substantially hollow right side-rail, a front cross-member, a rear cross-member, lower control arm connections on the left and right side-rails, a left-side upper control arm connection on one of the cross-members, and a right-side upper control arm connection on the one cross-member. At least one of the upper control arm connections comprises a respective mounting stud, the stud including a bore extending substantially parallel to the side-rails and adapted to secure at least one of the articulations of an upper control arm using a bolt, whereby the articulation is retained between a head of the bolt and the mounting stud. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a first embodiment of a subframe according to the present invention. 
     FIG. 2 is a top view of a prior art clevis connection. 
     FIG. 3 is a side view of the subframe of FIG.  1 . 
     FIG. 4 is a side cross-sectional view of a mounting stud and control arm articulation according to one preferred embodiment of the present invention. 
     FIG. 5 is an exploded, perspective view of an alternate embodiment of the mounting stud. 
     FIG. 6 is an exploded, perspective view of another alternate embodiment of the mounting stud and articulation for both linkages of a control arm. 
     FIG. 7 is a perspective view of another preferred embodiment of the subframe of the present invention employing mounting studs for connecting both the upper and lower control arms. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a cast aluminum subframe  10  includes a left side-rail  11 , right side-rail  12 , rear cross-member  13 , and front cross-member  14 . Bosses  15  located at each corner of subframe  10  provide connection points to the vehicle body and/or to other frame components. 
     A lower control arm  16  and an upper control arm  17  are pivotably mounted to subframe  10 . Lower control arm  16  includes a wheel carrier connection  30  (such as a ball joint) and linkages  31  and  32 . Each linkage includes a bearing hole (e.g., bearing hole  33  at the end of linkage  31 ) for receiving a bushing (e.g., bushing  26 ). Lower control arm  16  is mounted to left side-rail  11  by conventional clevis connections  20  and  21 . Clevis  20 , for example, forms an articulation comprising flange  22  with bolt-hole  23 , flange  24  with bolt-hole  25 , bushing  26 , linkage  31 , a bolt  27 , a nut  28 , and washers  29 . 
     Turning briefly to FIG. 2, a top view of clevis connection  20  is shown with bushing  26  aligned for insertion of bolt  27 . In order to bushing  26  to be able to fit between flanges  22  and  24 , a clearance  42  is provided such that the distance between flanges  22  and  24  is greater than the axial length of bushing  26 . The amount of clearance  42  may typically be about 0.5 to 2 mils. In order to securely retain bushing  26  and to apply sufficient torque to nut  28 , clearance  42  is removed by flexing of flanges  22  and  24  after installation. For an aluminum casting, this creates stress in stressed regions  43 , thus creating a potential site for cracking and failure depending upon the material specification, the flange thickness, and the amount of flexing. Thickening of the flanges adds cost and weight to the casting. 
     Returning to FIG. 1, the invention employs an improved mounting arrangement for upper control arm  17 . A mounting stud  34  and a mounting stud  35  are integrally formed in the casting of subframe  10  and preferably project coaxially in a fore and aft direction from opposite sides of front cross-member  14 . Studs  34  and  35  include central bolt-holes, such as bolt-hole  36 , and form articulations for the linkages of upper control arm  17 . Thus, upper control arm  17  includes a linkage  37  having a bearing hole  38  that receives a bushing  40 . A bolt  41  passes through bushing and into bolt-hole  36  for securing linkage  37 . Bolt-hole  36  may contain internal threads for engaging bolt  41 . 
     The other linkage of upper control arm  17  is joined to mounting stud  35  in an identical manner. Each bushing of the upper control arm is retained between the bolt heads and the mounting studs. Thus, there is no flexing of any part of the mounting stud and no stresses caused by installation of the control arm. Furthermore, with a mounting stud on each side of front cross-member  14 , loads are more evenly distributed within the subframe. 
     FIG. 3 is a side view with only the outlines of the control arm linkages at the articulations being shown. 
     FIG. 4 is a side cross-section showing one of the articulations of FIG. 3 in greater detail. In particular, bolt-hole  36  is shown threaded for receiving the threaded shank of bolt  41 . In addition, mounting stud  34  may include a recess  45  for receiving one end of bushing  40 . This increases the area against which the forces of the control arm can react, and reduces the loads applied against the bolt. The hollow cross section of cross-member  14  can also be seen in FIG.  4 . 
     An alternative embodiment in which the mounting studs are comprised of a separately formed component rather than cast integrally with the subframe is shown in FIG.  5 . Hollow cross-member  14  includes aligned (i.e., coaxial) apertures  46  and  47  for receiving a tubular stud  50 . Stud  50  can be press-fit, welded, or secured in any suitable way in apertures  46  and  47 . Stud  50  may preferably include at least one tapered end  51  or  52  to facilitate insertion into apertures  46  and  47 . Bolt-holes  53  and  54  are substantially identical to the bolt-holes of FIG. 4, for example. 
     Tubular stud  50  is preferably fabricated from aluminum or aluminum alloy of the same type as that used to form the remained of the subframe, but could be made from other material such as steel depending upon the method of attachment. 
     FIG. 6 shows an alternative embodiment similar to FIG. 5 except that a tubular stud  55  has an end-to-end through bore  56 . Thus, a single bolt  57  and nut  58  secures both articulations simultaneously. 
     FIG. 7 shows an alternative embodiment of the subframe of the present invention that takes advantage of the improved control arm attachment for both the upper and lower control arms. Specifically, a lower mounting bar  60  extends from a pedestal  61  and is substantially parallel to the side-rails. Stud ends  62  and  63  have a length adapted to receive the articulations of a lower control arm in the manner previously shown for the upper control arm. A bore  64  may be threaded or may extend all the way through mounting bar  60  according to any of the previous embodiments. Alternatively, mounting bar  60  could instead be comprised of separate mounting studs or could be attached to side-rail  11  by other means within the skill of the art, such as by bolting or welding. Mounting bar  60  would preferably also include recesses for receiving bushings in the manner shown in FIG.  4 . 
     In view of the foregoing description, a cast aluminum subframe has been shown with improved connection of control arm articulations. Thus, the subframe achieves the advantages of low weight, high stiffness, and high strength and reliability of the control arm attachment. Although A-arm control arms have been shown and discussed herein, one skilled in the art will recognize that separate linkages could be used for either or both of the upper and lower control arms within the scope of the present invention.