Abstract:
A traction device for a motor vehicle provides a rear support assembly positioned proximate to a rear axle and an adjacent portion of a leaf spring and a front rocker support assembly. The front rocker support assembly includes a front leaf spring bracket assembly attached to the front leaf spring eye, a pivot stop extending across the upper surface of the leaf spring at a predetermined distance rearward from the leaf spring eye for engaging an upper surface of the leaf spring to limit pivotal movement of the front rocker support assembly relative to the front end of the leaf spring, and a rocker pivotally attached to the front leaf spring bracket assembly. An adjustable rigid link extends between the rear support assembly and the front rocker support assembly.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Background  
         [0002]     This invention relates generally to suspension systems of high performance motor vehicles. More specifically but not by way of limitation, the present invention relates to a traction device for limiting wrap-up of a leaf spring during acceleration of a motor vehicle.  
         [0003]     2. Discussion  
         [0004]     Conventional leaf springs are widely used in rear-wheel drive vehicles. During acceleration, the leaf spring is subject to twisting forces which are opposite in direction to the acceleration of the drive wheels. The opposed twisting forces are commonly referred to as “wrap-up” and often contributes to rear wheel “hop”.  
         [0005]     In an effort to minimize leaf spring wrap-up and rear wheel “hop” on acceleration, a number of devices have been designed to minimize leaf spring wrap-up and rear-wheel hop during acceleration. One of these is a simple bolt-on traction bar. A rigid bar, generally of steel, has a mounting pad on one end for attachment to the point at which the rear axle meets the leaf spring assembly. A rubber “snubber” at the other end is used to attach the rigid bar to the front eye of the leaf spring. The length of the bar extends forward from the mounting pad to a point under the front leaf spring eye. During acceleration, the counter-rotation of the rear axle is arrested when the snubber meets the spring eye.  
         [0006]     Bolt-on traction bars decrease leaf spring wrap-up, help to prevent rearwheel hop, and aid in improving rear wheel traction during acceleration. Additionally, the bolt-on traction bars are typically relatively inexpensive and easy to install.  
         [0007]     Several other devices have been devised which represent improvements over the bolt-on traction bar. One such device is the ladder bar and another is the 4-link system. The ladder bar device comprises two mounting assemblies. One end of each mounting assembly is welded to the rear axle housing and the other is welded to a forward point of the chassis. These mounting assemblies are interconnected by a tubing structure. The 4-link system, which sometimes eliminates the conventional leaf spring from the motor vehicle, utilizes two 2-link assemblies (one on each side). One end of each 2-link assembly is welded to the rear axle housing and the other end is welded to a forward location on the chassis. Adjustable tubular links connect the rear axle housing to the chassis.  
         [0008]     Each of these improved devices reduces leaf spring wrap-up and rear wheel hop, improves traction, and adjusts the instant center (the point at which the rear wheels push the vehicle forward). The ladder bar and the 4-link system, which are more expensive than simple bolt-on traction bars, require professional installation.  
         [0009]     In U.S. Pat. No.5,354,092 (Calvert), an improved traction bar includes a rear support assembly attached to the rear axle and the leaf spring and a front support assembly pivotally attached to the front end of the leaf spring. A rigid link extends between the rear support assembly and the front support assembly. The front support assembly is attached to the front of the leaf spring by a bushing which extends through the eye of leaf spring. The front support assembly includes a pivot stop which engages the upper surface of the leaf spring and limits movement of the front support assembly relative to the front end of the leaf spring. The pivotal movement limiting means includes means for engaging an upper surface of the leaf spring in the form of a pivot stop which extends across the upper surface of the leaf spring. The front support assembly includes a pair of generally triangular pivot plates which are pivotally attached to the front end of the leaf spring. The triangular pivot plates support the pivot stop at a fixed distance from the front end of the leaf spring and provide a point of attachment for the rigid link below the front end of the leaf spring. The pivot plates are secured to one another by three bolts positioned generally adjacent to the three corners of the triangular plates. The bolts serve to provide a pivot axis for the front support assembly relative to the front end of the leaf spring, the pivot stop itself, and the location of the point of attachment of the rigid link to the front support assembly. The rigid link is adjustable in length through the use of a threaded front eye connector and an oppositely threaded rear eye connector. Rotation of the rigid link thus changes the overall length of the rigid link.  
         [0010]     While providing some improvement in leaf spring wrap-up, rear wheel hop, traction, and movement of the instant center forward with respect to the rear axle, the Calvert patent&#39;s effectiveness is limited by the structure of the front support assembly. The use of triangular pivot plates restrict the location of the pivot stop on the top surface of the leaf spring to a position comparatively close to the front eye of the leaf spring. Optional mounting apertures in the triangular pivot plates permit limited optional location of the threaded front eye connector of the rigid link, but additional adjustability is always helpful.  
         [0011]     Accordingly, a need remains for a traction device for motor vehicles which is more effective in preventing leaf spring wrap-up and rear wheel hop by moving the vehicle instant center forward with respect to the rear axle and, simultaneously, improving traction during hard acceleration.  
       SUMMARY OF THE INVENTION  
       [0012]     A traction device for a motor vehicle includes a rear support assembly positioned proximate to a rear axle and an adjacent portion of a leaf spring and a front rocker support assembly. The front rocker support assembly includes a front leaf spring bracket assembly attached to the front leaf spring eye, a pivot stop extending across the upper surface of the leaf spring at a predetermined distance rearward from the leaf spring eye for engaging an upper surface of the leaf spring to limit pivotal movement of the front rocker support assembly relative to the front end of the leaf spring, and a rocker pivotally attached to the front leaf spring bracket assembly. An adjustable rigid link extends between the rear support assembly and the front rocker. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  shows the traction device according to the present invention adjacent to a leaf spring supporting a rear axle of a motor vehicle.  
         [0014]      FIG. 2  is another view of the traction device shown in  FIG. 1 .  
         [0015]      FIG. 3  is a view of the front rocker assembly of the traction device shown in  FIGS. 1-2  with the rear portion cut away.  
         [0016]      FIG. 4  is a view of another traction device according to applicant&#39;s invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]     In the following description of the of the present invention, like numerals and characters designate like elements throughout the figures of the drawings.  
         [0018]     Referring generally to  FIGS. 1-2 , an improved traction device  20  works is attached to a standard leaf spring L and a rear axle A. The rear axle A supports a wheel W in contact with a road surface S. The leaf spring L includes a rear leaf spring mount R (not shown) supported by the motor vehicle chassis and a front leaf spring eye E (not shown) supported by a front leaf spring mount F (not shown) attached to the motor vehicle chassis. It will be appreciated by one skilled in the art that the standard leaf spring L, the rear axle A, the wheel W, the rear leaf spring mount R, the front leaf spring eye E, the front leaf spring mount F, and the motor vehicle chassis are typical and, therefore, no illustration is necessary.  
         [0019]     Still referring to  FIGS. 1-2 , the traction device  20  includes a rear support assembly  22 , a rigid link assembly  52 , and a front rocker support assembly  82 . Referring now to the rear support assembly  22 , a flanged bracket  24  cooperates with a leaf spring axle bracket  26  to receive the leaf spring L therebetween. U-bolts  28  encircle the axle A. Threaded ends  30  of the U-bolts  28  extend through apertures  32  in the flanged bracket  24 . The U-bolts  28  are held in place by nuts  34 . Parallel tabs  36  project downwardly from the flanged bracket  24 . The flanged bracket  24  includes at least four apertures  32  through which the U-bolts  28  extend. Front and rear flanges  38  at the forward and rearward edges of the flanged bracket  24  extend downwardly away from the leaf spring lower surface  40 . A fifth aperture  42  (See  FIG. 2 ) may be provided in the flanged bracket  24  for the leaf spring bolt, if necessary. The parallel tabs  36  are generally triangular in shape and include two pairs of aligned apertures  44 - 44  and  46 - 46  at their lower ends for receiving a nut-bolt assembly  48  to secure a rear end  54  of the rigid link assembly  52  therein. Apertures  50  (only one shown) in the front and rear flanges  38  provide a convenient mounting location for a shock absorber (not shown).  
         [0020]     Regarding the rear support assembly  22  shown in  FIGS. 1-2 , it will be understood by one skilled in the art that the rear support assembly  22  described herein is a modification of a support assembly well known in the art. The present improved traction device according to applicant&#39;s invention includes optional aligned apertures  44 - 44  and  46 - 46  in the downwardly extending tabs  36  for attachment of the rear end  54  of the rigid link assembly  52 . The second pair of aligned apertures provides further flexibility and adjustability in implementation of the traction device  20  according to applicant&#39;s invention.  
         [0021]     Referring again to  FIGS. 1-2 , the rigid link assembly  52  has a rear end portion  54  attached to the rear support assembly  22  and a front end portion  56  attached to the front rocker support assembly  82 . A rear eye connector  58  is threaded into a rigid bar  60  at the rear end  54  of the rigid link assembly  52 , and a front eye connector  62  is threaded into the rigid bar at the front end portion  56  of the rigid link assembly  52 . The rigid bar  60  is typically constructed by welding internally oppositely threaded front and rear inserts into the ends of a rigid bar. Oppositely internally threaded ends of the rigid bar  60  permit the rigid bar to be operated like a turnbuckle. i.e., the rigid bar  60  can be turned one direction to increase the distance between the eye portions of the eye connectors  58 ,  62  or the rigid bar  60  can be turned the opposite direction to shorten the distance between the eye portions of the eye connectors  58 ,  62 . An external hex fitting  64  is provided to permit easy adjustment of the rigid bar  60 .  
         [0022]     Regarding the rigid link assembly  52 , it will be understood that the rigid link assembly  52  described herein is well known in the art. A rotatable bushing is typically deployed within the eye of the eye connectors  58 ,  62 . Because the implementation of the rigid link assembly  52  shown herein is well known to persons skilled in the art, the rigid link assembly  52  will not be described in great detail.  
         [0023]     Referring now to  FIGS. 1-2  in conjunction with  FIG. 3 , the front rocker support assembly  82  includes a rocker  84  pivotally attached to a front leaf spring bracket subassembly  86 . The rocker  84  is formed by a pair of identical, generally triangular plates  88  welded in parallel relationship to a cylindrical rocker pivot member  89 . The rocker  84  has a pair of aligned pivot bolt apertures  90 - 90  near one corner of each of the triangular plates  88 . The rocker  84  also has three pairs of aligned link positioning apertures  92 - 92 ,  94 - 94 , and  96 - 96  along a side common with the pivot bolt apertures  90 - 90 . The aligned link position apertures  92 - 92  are positioned in a downwardly extending second corner of the parallel triangular plates  88 . The pairs of aligned link positioning apertures  94 - 94  and  96 - 96  are spaced between the pivot bolt apertures  90 - 90  and the distal link position apertures  92 - 92 . In  FIGS. 1-3 , the front eye connector  62  of the rigid link assembly  52  is attached to the rocker  84  by a nut-bolt assembly  98  disposed through the eye of the eye connector  62  and aligned positioning link apertures  94 - 94 . The rocker  84  further includes a transverse rocker head  100  located at the third corner of the parallel triangular plates  88 .  
         [0024]     Still referring to  FIGS. 1-3 , the front leaf spring bracket subassembly  86  includes two identical substantially parallel elongated plates  110  having three pairs of aligned apertures. Aligned apertures  112 - 112  are located at one end of the elongated parallel plates  110 . Aligned pivot stop apertures  114 - 114  are located distal from the leaf spring eye apertures  112 - 112 . Rocker pivot bolt apertures  116 - 116  are located between the leaf spring eye apertures  112 - 112  and the pivot stop apertures  114 - 114 . A leaf spring bushing insert  120  disposed within the aligned leaf spring eye apertures  112 - 112  supports a leaf spring bushing  122  inserted into the front leaf spring eye E of the leaf spring L.  
         [0025]     In use, the front leaf spring bracket subassembly  86  encloses the front leaf spring eye E and the leaf spring bushing  122  between ends  124  of the elongated parallel plates  110 . The front leaf spring eye E is supported by the leaf spring bushing  122  which is, in turn, supported by the leaf spring bushing insert  120 . The ends of the elongated parallel plates  110  and the front leaf spring eye E contained therebetween are attached to the mating front leaf spring mount F (not shown) on the vehicle chassis. The front leaf spring bracket assembly is secured to the front leaf spring mount F by a nut-bolt combination  126 .  
         [0026]     Still referring to  FIGS. 1-3 , a pivot stop  128  is disposed within the aligned apertures  114 - 114  and secured in place by a nut-bolt combination  130 . Although the pivot stop  128  shown in  FIGS. 1-3  is a cylindrical metal sleeve, it will be understood by one skilled in the art that the pivot stop  128  could also be a welded bar.  
         [0027]     Still referring to  FIGS. 1-3 , the front leaf spring bracket subassembly  86  is attached to the rocker  84  by a rocker pivot bolt nut-bolt combination  132  disposed simultaneously through aligned apertures  116 - 116  in the elongated parallel plates  110 , the cylindrical rocker pivot member  89  in the rocker  84 , the aligned apertures  90 - 90  in the plates  88 , and cylindrical spacers  134 .  
         [0028]     Referring now to  FIG. 3 , when properly installed, the elongated parallel plates  110  bracket the front end of the leaf spring L and position the pivot stop  128  adjacent the upper surface  40  of the leaf spring L at a predetermined distance from the front leaf spring eye E. During acceleration, force is directed along arrow  140 . The force directed along arrow  140  is transferred through the rocker  84  to the front leaf spring bracket subassembly  86 . The front leaf spring bracket subassembly  86  rotates on the rocker pivot bolt-nut combination  132  so the pivot stop  128  moves along arrow  142  and the force which was originally directed along  140  is now applied to the surface of the leaf spring L.  
         [0029]     Referring again to  FIGS. 1-3 , the aligned apertures  114 - 114  for the pivot stop  128  and the bolt-nut combination  130  are positioned generally rearward with respect to the rocker pivot bolt-nut combination  132 . It will be understood by one skilled in the art that, as the force originally applied along the arrow  140  is applied farther to the rear with respect to the front leaf spring eye E, greater benefit will be derived from the traction device of the present invention.  
         [0030]     During installation of the traction device  20  of the present invention, it is possible to pre-load either wheel W by initially adjusting the front rocker support assembly  82  so the pivot stop  128  bears downwardly on the upper surface  40  of the leaf spring L while the vehicle is stopped. Moreover, selective adjustment of left and right traction devices can adjust for traction differences between the left wheel and the right wheel of a vehicle.  
         [0031]     Referring now to  FIG. 4 , shown therein is another traction device  220  according to the present invention. The traction device  220  has a front rocker support assembly  282  which differs from the front rocker support assembly  82  of the traction device  20  shown in  FIGS. 1-3 . Otherwise, the structure of the traction device  220  (cut away) is the same as that of the traction device  20 . the front rocker support assembly  282  includes a rocker  284  pivotally attached to a front leaf spring bracket subassembly  286 . The rocker  284  is formed by a pair of identical, generally triangular plates  288  welded in parallel relationship to a cylindrical rocker pivot member  289 . The rocker  284  has a pair of aligned pivot bolt apertures  290 - 290  near one corner of each of the triangular plates  288 . The rocker  284  also has three pairs of aligned link positioning apertures  292 - 292 ,  294 - 294 , and  296 - 296  along a side common with the pivot bolt apertures  290 - 290 . The aligned link position apertures  292 - 292  are positioned in a downwardly extending second corner of the parallel plates  288 . The pairs of aligned link positioning apertures  294 - 294  and  296 - 296  are spaced between the pivot bolt apertures  290 - 290  and the distal link position apertures  292 - 292 .  
         [0032]     Still referring to  FIG. 4 , the front eye connector  62  of the rigid link assembly  52  is attached to the rocker  284  by a nut-bolt assembly  298  disposed through the eye of the eye connector  262  and aligned positioning link apertures  294 - 294 . The rocker  284  further includes a transverse rocker head  300  located at the third corner of the parallel triangular plates  288 . The front leaf spring bracket subassembly  286  includes two identical elongated parallel plates  310  having three pairs of aligned apertures. Aligned apertures  312 - 312  are located at one end of the elongated parallel plates  310 . Two pairs of aligned pivot stop apertures  314 - 314  and  314 ′- 314 ′ are located distal from the leaf spring eye apertures  312 - 312 . Rocker pivot bolt apertures  316 - 316  are located between the leaf spring eye apertures  312 - 312  and the pivot stop apertures  314 - 314 . A leaf spring bushing insert  320  disposed within the aligned leaf spring eye apertures  312 - 312  supports a leaf spring bushing  322  (not visible in  FIG. 4 ; see  FIGS. 1-2 ) inserted into the front leaf spring eye E of the leaf spring L.  
         [0033]     In use, the front leaf spring bracket subassembly  286  encloses the front leaf spring eye E and the leaf spring bushing  322  between ends  324  of the elongated parallel plates  310 . The front leaf spring eye E is supported by the leaf spring bushing  322  which is, in turn, supported by the leaf spring bushing insert  320 . The ends of the elongated parallel plates  310  and the front leaf spring eye E contained therebetween are attached to the mating front leaf spring mount F (not shown) on the vehicle chassis. The front leaf spring bracket assembly is secured to the front leaf spring mount F by a nut-bolt combination  326 .  
         [0034]     Still referring to  FIG. 4 , a pivot stop  328  is disposed within the aligned apertures  314 - 314  and secured in place by a nut-bolt combination  330 . Although the pivot stop  328  shown in  FIG. 4  is a cylindrical metal sleeve, it will be understood by one skilled in the art that the pivot stop  328  could also be a welded bar.  
         [0035]     Still referring to  FIG. 4 , the front leaf spring bracket subassembly  286  is attached to the rocker  284  by a rocker pivot bolt nut-bolt combination  332  disposed simultaneously through aligned apertures  316 - 316  in the elongated parallel plates  310 , the cylindrical rocker pivot member  289  in the rocker  284 , the aligned apertures  290 - 290  in the generally triangular plates  288 , and cylindrical spacers  334 .  
         [0036]     Referring now to  FIG. 4 , when properly installed, the elongated parallel plates  310  bracket the front end of the leaf spring L and position the pivot stop  328  adjacent the upper surface  40  of the leaf spring L at a predetermined distance from the front leaf spring eye E. During acceleration, force is directed along arrow  340 . The force directed along arrow  340  is transferred through the rocker  284  to the front leaf spring bracket subassembly  286 . The front leaf spring bracket subassembly  286  rotates on the rocker pivot bolt-nut combination  332  so the pivot stop  328  moves along arrow  342  and the force which was originally directed along  340  is now applied to the surface of the leaf spring L.  
         [0037]     The pivot stop  328  can optionally be located in a aligned apertures  314 ′ in the elongated parallel plates  310  so the pivot stop moves along arrow  342 ′ to apply the force originally directed along  340  to the surface of the leaf spring L at a point still farther to the rear.  
         [0038]     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.