Abstract:
A control arm used as a suspension link within a vehicle suspension system has two similar members. Each member has a substantially W shaped cross section and circular endplates. The endplates are coupled together with bushings that include a compressible member. During normal loading, this bushing arrangement keeps the two members spaced apart. This allows each member to bend and flex when subjected to longitudinal forces. As transverse loading occurs, the two members are caused to move together, and eventually abut one another. This abutment greatly increases the overall strength of the control arm, allowing it to withstand severe transverse forces without buckling.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to linking members coupling a frame or structural member of a vehicle to a wheel housing. More specifically the present invention relates to a control arm used in an independent suspension system that provides sufficient flexibility when needed, yet provides adequate and increasing support during loading which otherwise may cause the control arm to buckle. 
     2. Description of the Related Art 
     In most vehicles today, the structural foundation is either a traditional frame, or unibody member. Most other components are then coupled or affixed to this foundation. Where unibody construction is used, subframe elements are often added to provide additional support and attachment points. For example, the vehicle&#39;s wheels are coupled to the structural foundation by a moveable support. The wheels can then be attached to this moveable support using a wheel drum as an intermediary. Many other components are similarly attached using appropriate attachment structures. Alternatively, this coupling can be connected directly to elements of the frame. 
     During movement or operation, various forces will be imparted on the vehicle. All of these forces will eventually be transferred to the subframe through all related components. In the case of the vehicle&#39;s suspension system, forces will be directed through the moveable support member, causing many different stresses and loads. These forces are most easily described with respect to the well understood orientation of the vehicle, where the frame or body is in a substantially horizontal position, with a centerline (or central axis) extending between the front and rear of the vehicle. 
     The most common forces a vehicle encounters is simply vertical displacement of the wheel housing. Such movement is induced by the vehicle encountering various bumps or obstacles in the road. These bumps or obstacles are expected and must be dealt with by the vehicle&#39;s suspension system. Since it is undesirable to impart this motion to the passenger cabin, various shock absorbers and springs are incorporated to deal with these forces. The link between the subframe and the wheel drum housing freely pivots in this direction thus causing substantially all vertical forces to be handled by the springs and shock absorbers. 
     Longitudinal forces are also imparted on the wheel housing as the vehicle travels. This results in various forces being presented to all components of the suspension. Lastly, tension loading occurs as force is applied to the wheel by pulling it away from the vehicle center line and transverse loading occurs in an opposite direction, pushing the wheel towards the center line of the vehicle. 
     In the vehicle&#39;s suspension system, all of the components must appropriately carry each of these loads. This load handling requirement is in addition to the basic function of attaching the wheels and allowing the vehicle to operate. Thus, each component of the system must be specifically engineered for its particular purpose, and must cooperate with all other components. 
     In a rear independent suspension system, the assembly coupling the wheel drum housing to the frame or rear cradle consists of a number of control arms. The control arms are required to accommodate all of the above-referenced forces encountered by the associated wheel. Vertical forces are primarily dealt with by springs and/or shock absorbers which cooperate with one or more of the control arms. As previously suggested, the control arms are hinged to allow free movement in the vertical direction. Thus, all vertical forces are transferred to the springs or shocks. 
     The wheel, as described, is also subjected to various longitudinal, transverse, and tensile forces. Various combinations of the forces imparted on the wheel will be applied to the control arms. The net result is that the control arms themselves will be subjected to longitudinal, transverse and tensile forces resulting from forces being applied to the wheel. Whatever force or combinations of forces is applied to the wheel (and wheel drum housing), the resultant force that is applied to each of the control arms must be appropriately handled by that component. As such, each control arm and its elastomer bushings are configured to handle the forces applied to it, dependent upon the direction of the force. It is to be understood that it is the resultant force that is applied to the control arm, in the longitudinal, tensile or transverse direction with respect to the part itself, that is being discussed with respect to the various responses that the control arm will achieve. 
     Tension loading forces (pulling away from the frame) are typically minimal and need not be considered separately, as longitudinal and transverse forces are the major considerations for the control arms. During longitudinal loading (which generates torque on the control arm), it is desirable to have soft torsional modes in the rear most control arm, which is also referred to as a suspension link. In other words, rigid resistance under longitudinal loading is undesirable, as this would cause these forces to be felt by the passengers. Therefore, if the suspension link is compliant and able to twist in response to the torque generated, the forces are absorbed and not passed on. Conversely, transverse loads (compression loads) (forcing the control arm towards the frame) can be rather extreme and could cause the suspension link to buckle. This makes it difficult to design a suspension link which is adequately compliant in the longitudinal direction and sufficiently strong in the transverse direction. 
     Various suspension systems have been provided to address the longitudinal forces imparted by a vehicle in motion. For example, U.S. Pat. No. 5,662,348 issued to Kusama et al. on Mar. 20, 1996, discloses a one-piece suspension arm wherein the portion of the suspension arm subject to the most longitudinal stress has been bent at each end to provide a more rigid frame. Kusama et al. utilizes less material, hence making the suspension arm lighter while imparting sufficient resistance to longitudinal forces. However, this design does not necessarily provide for the soft torsional bending which would be desirable in a suspension link. Furthermore, Kusama et al. fails to address the relatively high transverse forces which are also imparted. 
     As such, there exists a need to provide a control arm having soft torsional modes while providing adequate support during high transverse loading. 
     SUMMARY OF THE INVENTION 
     The present invention provides a two-piece control arm for use as a suspension link, particularly in a rear independent suspension system. The present control arm is also applicable to various other control arm positions in both a front and rear independent suspension system. In a preferred embodiment, each piece of the control arm has a substantially W-shaped cross-section over a majority of its length. Other cross-sectional shapes can be provided to accomplish the same results. The ends of each piece of the control arm are configured to mate with one another in a male/female relationship. A compressible bushing and tubular insert are provided at each of these end points so as to form a developed gap between edges of each of the two pieces by keeping them spaced at a fixed distance. A tubular end section of the second piece is slid over the tubular end section of the first piece. Both are then expanded, causing them to lock together. The frictional engagement between the two end sections causes the two pieces to lock together and remain spaced apart. As higher levels of transverse loading are applied to the suspension link, during vehicle operation the two pieces begin to flex and move together. When the loading ceases, the resiliency of metal returns the two pieces to their original position and redevelops the gap. 
     During use, the two-piece control arm is capable of responding differently depending upon the type of stresses that are placed on it. Specifically, the part has relatively “strong” characteristics in response to certain stresses while having softer characteristics in response to other stresses. 
     During longitudinal loading (generating torque on the control arm) of the two-piece control arm, each piece of the control arm remains separate and twists or moves independently, responsive to the loading stresses. During transverse loading of the two-piece control arm, the pieces of the control arm are caused to compress towards one another and if the transverse loading is sufficient, they will contact one another. Such contact may occur at each extreme edge as well as a middle planar portion. As the two pieces of the control arm come together, the control arm as a whole becomes substantially stronger and is able to withstand very high transverse loads. 
     This two-piece control arm is advantageous in that it can handle loading in all three directions with the appropriate level of support, yet during the most severe transverse loading, provides more support than a one-piece stamping of more than twice the thickness. This allows the control arm to be manufactured using less material, and hence achieving significant cost reductions. Furthermore, the stock material used can be significantly thinner than previously used, allowing less expensive stock material to be purchased and utilized. The use of this thinner material also eases manufacturing burdens in that less effort is required to stamp the pieces out of the stock material. Yet despite all of these reductions, a stronger and more adaptable control arm is produced. 
     By way of example, traditional one-piece suspension link control arms are formed from tubular stock. The tubular stock is typically 2 to 2½ times more expensive than sheets or blanks of the same material. In the present process, a single press stroke forms both pieces of the control arm. Conversely, the tubular stock must be bent and shaped. Then various attachment mechanisms must be coupled to it. This is not trivial in that bending and shaping tubular material is difficult, time consuming and expensive. In the end, when the price of material and the cost of manufacturing are taken into account, a traditional control arm will cost about three times more than a two-piece control arm and will not work as effectively. 
     It is an object of the present invention to provide a two-piece control arm that becomes stronger as increasing transverse forces are applied to it. 
     It is another object of the present invention to provide a two-piece control arm that has soft torsional modes when longitudinal forces are applied to it. 
     It is yet another object of the present invention to provide a two piece control arm where the two pieces act independently until sufficient force is applied in a transverse direction to cause the two pieces to contact one another. 
     It is still yet another object of the present invention to provide a suspension link in a rear suspension system utilizing a two-piece control arm which increases in strength as force is applied to the control arm in a transverse direction and exhibits soft torsional modes as force is applied to the control arm in a longitudinal direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a rear cradle having a wheel drum (or disk) housing attached thereto by a plurality of control arms. 
     FIG. 2 is a side perspective view of the two-piece control arm of the present invention. 
     FIG. 3 is a sectional view of a bushing within the control arm taken about line  3 — 3 . 
     FIG. 4 is a sectional view of the two-piece control arm taken about line  4 — 4 . 
     FIG. 5 is a top perspective view of the two-piece control arm of the present invention. 
     FIG. 6 is a sectional view of the two-piece control arm taken about line  4 — 4  during normal loading stresses. 
     FIG. 7 is a sectional view of a control arm taken around line  4 — 4  during clockwise longitudinal stresses. 
     FIG. 8 is a sectional view of a control arm taken about line  4 — 4  during counterclockwise longitudinal stresses. 
     FIG. 9 is a sectional view of a control arm taken about line  4 — 4  during increased transverse loading. 
     FIG. 10 is a sectional view of a control arm taken about line  4 — 4  during high transverse loading. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the two-piece control arm  20  of the present invention is shown in the context of a rear independent suspension system  8 . The rear cradle  10  forms a portion of the frame of the vehicle. Wheel drum housing  12  supports the braking assembly and wheels for the vehicle. Wheel drum housing  12  is attached to rear cradle  10  and is aligned with the rear axle line  16 . As shown, three control arms connect the wheel drum housing  12  to the rear cradle  10 ; rear control arm  20  (suspension link  20 ), upper control arm  22 , and front control arm  23 . A spring  14  and shock absorber (not shown) are coupled to front control arm  23  to absorb vertical displacement of the wheel drum housing  12  whereas the suspension link  20  and upper control arm  22  are able to freely pivot in this direction. The front of the vehicle is indicated as shown. Suspension link  20  must be designed to handle the three disparate forces indicated. Movement of wheel drum housing  12  (with respect to the rear cradle  10 ) along the center line of the vehicle results in longitudinal forces as designated by arrow “L.” Movement of wheel drum housing  12  away from the center of the vehicle results in tension loading as indicated by arrow “Te.” Finally, movement of wheel drum housing  12  towards the center of the vehicle, results in transverse forces as indicated by arrow “T.” Generally, the longitudinal, transverse and tensile forces will be applied to wheel drum housing  12  in various combinations due to a plethora of external factors. As these forces are applied, wheel drum housing  12  is caused to react by moving with respect to rear cradle  10 . This movement, in turn, imparts forces onto all components, including the suspension link  20 . As such, suspension link  20  is independently subjected to longitudinal, transverse and tensile forces, caused by the movement of wheel drum housing  12  with respect to rear cradle  10 . Whatever force is applied to wheel drum housing  12  and whatever direction it may be applied in, it is the resultant force that is applied to the suspension link  20  that is of interest here. 
     As shown, suspension link  20  is the only control arm utilizing the present two-piece construction. Suspension link  20  benefits the most from this construction because it should have soft torsional modes when subjected to longitudinal loading yet be very stiff and structurally sound when under transverse loading. In addition, upper control arm  22  could also utilize the two-piece construction (with the appropriate bend), though it is simply shown as a tubular member. It would be advantageous to use the two-piece configuration for the upper control arm  22  because it is significantly less expensive. Finally, many suspension systems utilize more than three control arms, and as such, additional two-piece control arms can be used. Generally, front control arm  23  will remain a very rigid and very thick one piece member. This is because front control arm  23  needs to be very stiff and strong to support the shocks or springs utilized. As such, it is made much heftier than the remaining control arms. 
     Referring to FIG. 2, two-piece control arm  20  is shown to have an elongated first control arm member  24  and a substantially similar elongated second control arm member  26 . Each member  24  and  26  terminates in circular end sections  36 . Members  24  and  26  are joined together at first bushing  28  and second bushing  30 . 
     Referring to FIG. 3, second bushing  30  is shown in a sectional view taken about line  3 — 3 . Inner cylinder  31  is inserted through first member  24  and second member  26 . A compressible member  38  surrounds inner cylinder  31  and is made from a suitable material such as rubber. The tubular inner shell  46  of first member  24  surrounds compressible portion  38 . The tubular outer shell  48  of second member  26  then surrounds tubular inner shell  46 . Tubular inner shell  46  is flared outwards, causing inner shell  46  and outer shell  48  to tightly abut one another and effectively lock together. Referring again to FIG. 2, members  24  and  26  are spaced apart from one another, leaving developed gap  32 . Transverse forces applied to control arm  20  will cause members  24  and  26  to buckle slightly, allowing them to move towards one another and abut, thus reducing or eliminating developed gap  32 . 
     FIG. 4 is a sectional view taken about line  4 — 4  in FIG.  2  and illustrates how each of the first member  24  and second member  26  has a substantially W-shaped cross-section, in the illustrated preferred embodiment. Other cross-sectional configurations can be selected to achieve the same result. Each member  24 ,  26  terminates in a first edge  40  and a second edge  42  and has disposed medially therebetween a center web  44 . The bushings  28  and  30  keep the first member  24  and second member  26  spaced substantially as shown in FIG. 4 so that the respective first edges  40 , second edges  42 , and center webs  44  of each member  24 ,  26  do not normally contact one another. 
     FIG. 5 is a top perspective view of control arm  20 . As can be seen, first member  24  has a tubular inner shell  46  extending from each end portion  36 . Correspondingly, the second member  26  has a tubular outer shell  48  disposed at each end thereof within circular portion  36 . Tubular inner shell  46  is sized to fit very tightly within tubular outer shell  48 . Once so arranged, inner shell  46  is flared to lock the inner shell  46  and outer shell  48  together in this position. 
     FIG. 6 is a sectional view of control arm  20  when no forces are being applied. As such, first member  24  is separated from second member  26  with developed gap  32  being at its maximum. As illustrated, first edges  40 , second edges  42  and contact areas  44  do not contact their counterparts between first member  24  and second member  26 , respectively. 
     FIG. 7 illustrates control arm  20  when longitudinal forces are being applied which create torque on the control arm  20  in a clockwise direction. As can be seen, first member  24  and second member  26  are able to rotate independently of one another thereby absorbing the longitudinal forces. Since first member  24  remains separate from second member  26 , soft torsional modes are imparted, thereby allowing sufficient flexibility within the suspension system. FIG. 8 simply illustrates longitudinal forces herein applied to control arm  20  in a counter-clockwise direction. 
     As shown in FIG. 9, control arm  20  is now being subjected to transverse forces. Initially, compressible member  38  absorbs these forces. As these forces increase, first member  24  is caused to move towards second member  26  as the transverse forces are sufficient to cause members  24  and  26  to begin to buckle, or more accurately flex. Respective first edges  40 , center webs  44 , and second edges  42  of both first member  24  and second member  26  move towards one another. When sufficient transverse loads are being applied, as shown in FIG. 10, first edges  40 , second edges  42  and center webs  44  are caused to abut one another. This, in effect, causes first member  24  and second member  26  to form a unitary control arm  20  wherein the developed strength of control arm  20  as shown in FIG. 10 is substantially stronger than either first member  24  or second member  26  would be alone and prevents the control arm  22  from collapsing. Once the transverse loading ceases, the resiliency of members  24  and  26  cause the control arm  20  to return to its original configuration. 
     Those skilled in the art will further appreciate that the present invention may be embodied in other specific forms without departing from the spirit or central attributes thereof. In that the foregoing description of the present invention discloses only exemplary embodiments thereof, it is to be understood that other variations are contemplated as being within the scope of the present invention. Accordingly, the present invention is not limited in the particular embodiments which have been described in detail therein. Rather, reference should be made to the appended claims as indicative of the scope and content of the present invention.