Abstract:
An improved 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 a selected portion of the leaf spring between the axle and the front leaf spring mount, a rocker pivotally attached to the front leaf spring bracket assembly, and a rocker head connected to an end of the rocker for engaging a lower 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. An adjustable rigid link extends between the rear support assembly and the front rocker support assembly.

Description:
BACKGROUND OF THE INVENTION 
     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 an improved traction device for limiting wrap-up of a leaf spring of a motor vehicle during acceleration. 
     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 contribute to rear wheel “hop”. 
     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. Bolt-on traction bars decrease leaf spring wrap-up, help to prevent rear wheel hop, and aid in improving rear wheel traction during acceleration. Additionally, the bolt-on traction bars are typically relatively inexpensive and easy to install. 
     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. 
     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. 
     In U.S. Pat. No. 5,354,092, issued to 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. 
     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 restricts 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. 
     As can be seen, there is a need 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 
     A traction device for a motor vehicle is provided, where the traction device comprises an adjustable link having a first attachment eye on an end of the adjustable link and a second attachment eye on an opposite end of the adjustable link; a rear support assembly positioned proximate to a rear axle and an adjacent portion of a leaf spring, where the rear support assembly comprises a rear support attachment means for attaching the rear support assembly against a lower surface of the leaf spring, and a rear attachment means for pivotal connection with the second attachment eye of the adjustable link; a front rocker support assembly that comprises the following: a front leaf spring bracket assembly removably attached a selected portion of the leaf spring between the axle and the front leaf spring mount, the leaf spring bracket assembly positioned against the lower surface of the leaf spring; a rocker subassembly pivotally attached to the front leaf spring bracket assembly, the rocker subassembly extending in a forward direction and terminating with a rocker head that bears on the lower surface of the leaf spring; and front attachment means for pivotal connection with the first attachment eye of the adjustable link. 
     In addition, a traction device is provided for limiting wrap-up of a leaf spring of a motor vehicle under acceleration, where the vehicle has a rear axle and the leaf spring has a front leaf spring mount in front of the rear axle and a rear leaf spring mount to the rear of the rear axle. The traction device comprises: a rear support assembly positioned proximate the rear axle, where the rear support assembly comprises: a flanged bracket bolted in place adjacent the leaf spring opposite the rear axle, and a rear mount bracket extending downwardly from a flanged bracket, with the rear mount bracket providing, at its lower end, an attachment means for connecting another member to the rear support assembly; a front rocker support assembly attached to a portion of the leaf spring between the axle and the front leaf spring mount, where the front rocker support assembly further comprises: a front leaf spring bracket assembly abutting a lower surface of the leaf spring; a rocker subassembly supported for pivotal movement by the front leaf spring bracket assembly, the rocker subassembly extending in a forward direction for a selected distance and terminating with a rocker stop for engaging a lower surface of the leaf spring to limit pivotal movement of the rocker subassembly; and a rocker attachment means for attaching a rigid link to the rocker; and a rigid link extending between the attachment means of the rear support assembly and the attachment means of the front support assembly. 
     A method for limiting wrap-up of a leaf spring on acceleration of a motor vehicle is also provided, where the method comprises the steps of: providing a traction device comprising a rear support assembly; a front rocker support assembly further comprising a front leaf spring bracket and a rocker pivotally attached to the front leaf spring bracket, with the rocker having a rocker head abutting a bottom surface of the leaf spring; and a rigid link extending between an attachment means of the rear support assembly and an attachment means of the rocker; selecting a portion of the leaf spring between an axle and a front leaf spring mount; removably attaching a front leaf spring bracket subassembly to the bottom surface at the selected portion of the leaf spring without disengaging the front leaf spring mount from the vehicle; and removably attaching the rear leaf spring bracket subassembly to the bottom surface of the leaf spring immediately adjacent the axle; wherein torque exerted by the wheels longitudinally along the rigid link forces the front leaf spring bracket subassembly downwardly while the rocker head exerts an upward force against the bottom surface of the leaf spring with the rocker head serving as a fulcrum to redirect the force downwardly against the leaf spring. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawings, description, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the traction device adjacent to a leaf spring supporting a rear axle of a motor vehicle, according to an embodiment of the invention; 
         FIG. 2  is another view of the traction device shown in  FIG. 1 , according to an embodiment of the invention; and 
         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, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description of the of the present invention, like numerals and characters designate like elements throughout the figures of the drawings. 
     Referring to  FIG. 1 , an improved traction device  20  may be attached to a standard leaf spring L and a rear axle A. The rear axle A may support a wheel W in contact with a road surface S. The leaf spring L may include 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 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. 
     The improved traction device  20  may include 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  may cooperate with a leaf spring axle bracket  26  to receive the leaf spring L therebetween. U-bolts  28  may encircle the axle A. Threaded ends  30  of the U-bolts  28  may extend through apertures  32  in the flanged bracket  24 . The U-bolts  28  may be held in place by nuts  34 . Parallel tabs  36  may project downwardly from the flanged bracket  24 . The flanged bracket  24  may include 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  may 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  may be 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  may provide a convenient mounting location for a shock absorber (not shown). 
     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  20  according to applicant&#39;s invention may include 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 may provide further flexibility and adjustability in implementation of the improved traction device  20 , according to applicant&#39;s invention. 
     Referring to  FIG. 1  and  FIG. 2 , the rigid link assembly  52  may be employed to connect the rear end support assembly  22  with the front rocker support assembly  82 . The rigid link assembly  52  may have 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  may be threaded into a rigid bar  60  at the rear end  54  of the rigid link assembly  52 , and a front eye connector  62  may be threaded into the rigid bar at the front end portion  56  of the rigid link assembly  52 . The rigid bar  60  may be 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  may be turned one direction to increase the distance between the eye portions of the eye connectors  58 ,  62  or the rigid bar  60  may be turned the opposite direction to shorten the distance between the eye portions of the eye connectors  58 ,  62 . An external hex fitting  64  may be provided to permit easy adjustment of the rigid bar  60 . 
     It will be understood that the rigid link assembly  52  described herein is well known in the art. A rotatable bushing may be 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. 
     Referring now to  FIG. 1 ,  FIG. 2 , and  FIG. 3 , the front rocker support assembly  82  may include a rocker subassembly  84  pivotally attached to a front leaf spring bracket subassembly  86 . The rocker subassembly  84  may be formed by a pair of identical, generally triangular plates  88  permanently arranged in parallel relationship to a cylindrical spacer (not shown) with an axial channel therethrough. The axial channel may be aligned with a pair of aligned pivot bolt apertures, identified here by way of example as  89 - 89  and  90 - 90 , near one corner of each of the triangular plates  88  for pivotal movement of the rocker subassembly  84 . The number of pairs of aligned pivot bolt apertures may be arbitrary and dependent upon the size of the triangular plates  88 . The rocker subassembly  84  may also have a plurality of pairs of aligned link positioning apertures, identified here by way of example as  91 - 91 ,  92 - 92 ,  93 - 93 ,  94 - 94 , and  95 - 95 , along a side common with the pivot bolt apertures  89 - 89  and  90 - 90 . The number of pairs of aligned link positioning apertures may be arbitrary and dependent upon the size of the triangular plates  88 . The aligned link position apertures may be positioned in a downwardly extending portion of the parallel triangular plates  88 . In  FIG. 3 , the front eye connector  62  of the rigid link assembly  52  may be attached to the rocker subassembly  84  by a nut-bolt assembly  98  disposed through the eye of the eye connector  62  and a selected pair of aligned link positioning apertures ( 91 - 91 ,  92 - 92 ,  93 - 93 ,  94 - 94 , and  95 - 95 ) as designated above. The rocker subassembly  84  may further include a transverse rocker head  100  located at the third corner of the parallel triangular plates  88 . The transverse rocker head  100  may bear on the lower surface  69  of the leaf spring L. 
     The rocker subassembly  84  may be pivotally attached to the front leaf spring bracket subassembly  86  in a manner described below. The front leaf spring bracket subassembly  86  may include a generally horizontal plate  70  having a lower surface  71  from which two identical substantially parallel elongated plates  110  depend. The horizontal plate  70  may be removably secured against the lower surface  40  of the leaf spring L by a plurality of U-bolts  73  that each extend from the horizontal plate  70  over a spring leaf upper surface  69  and back to the horizontal plate  70 . Each U-bolt  73  may be inserted through holes  74  in the horizontal plate  70  and secured thereto. For example, the ends of each U-bolt  73  may be threaded to receive a nut  75  and washer so that it may draw the horizontal plate  70  against the lower surface  40  of the leaf spring for secure positioning without removal of either end of the leaf spring L. Other means of removably securing the horizontal plate  70  of the front leaf spring bracket subassembly  86  against the leaf spring L without departing from the scope of the invention. 
     Referring again to  FIG. 3 , the elongated plates  110  of the front leaf spring bracket subassembly  86  may be spaced apart a distance sufficient to allow the triangular plates  88  of the front rocker subassembly  84  to be inserted therebetween without frictional binding. The pair of elongated plates  110  may have a plurality of pairs of upper aligned apertures, indicated by way of example as  112 - 112  and  114 - 114 . A selected pair of upper aligned apertures ( 91 - 91 ,  92 - 92 ,  93 - 93 ,  94 - 94 , or  95 - 95 ) may receive a nut-bolt assembly  120  that may be inserted through the selected upper aligned aperture and both the selected pair of aligned pivot bolt apertures ( 89 - 89  or  90 - 90 ) in the triangular plates  88  and the axial channel of the cylindrical spacer, so as to allow the rocker subassembly  84  to pivot freely about the nut-bolt assembly  120 . 
     The improved traction device  20  may be installed according to the following procedure. A portion of the leaf spring L between the axle A and the front leaf spring mount F may be selected for mounting the front leaf spring bracket subassembly  86 . This location may be selected according to criteria which may vary from vehicle to vehicle, e.g. load distribution of the vehicle, torque produced on the rear wheels by the drive train, length of the overall leaf spring, desired performance of the vehicle under acceleration, etc. These criteria may be known in advance or may be determined by experimentation. 
     Then, the front leaf spring bracket subassembly  86  may be removably attached to the bottom surface of the selected portion of the leaf spring L that extends between the axle A and the front leaf spring mount F without disengaging the front leaf spring mount F from the vehicle. This may be accomplished by placing the U-bolts of the front leaf spring bracket subassembly  86  over the upper surface  69  of the leaf spring L so that the downwardly depending ends of the U-bolt  73  may be inserted through the holes  74  of the horizontal plate  70  held against the lower surface  40  of the leaf spring L and secured to the horizontal plate  70  by nuts  75 . The nuts  75  may be tightened sufficiently so that frictional engagement of the horizontal plate  70  against the lower surface  40  is sufficient to prevent the horizontal plate  70  from moving longitudinally along the leaf spring L. 
     The rocker subassembly  84  may in turn be pivotally attached to the front leaf spring bracket subassembly  86  by the nut-bolt combination  120  disposed simultaneously through a selected upper aligned aperture, the selected pair of aligned pivot bolt apertures ( 89 - 89  or  90 - 90 ) in the triangular plates  88 , and the axial channel of the cylindrical spacer, so as to allow the rocker subassembly  84  to pivot freely about the nut-bolt assembly  120 . 
     The rear support assembly  22  may then be attached to an area of the leaf spring L below the rear axle A by positioning the flanged bracket  24  on the lower surface  40  of the leaf spring L with U-bolts  28  encircling the axle A. The threaded ends  30  of the U-bolts  28  may extend through apertures  32  in the flanged bracket  24  and secured by nuts  34 . 
     Next, the eye of eye connector  58  of rigid bar  60  may be positioned between the parallel tabs  36  of the flanged bracket  24  and secured for pivotal movement by a nut-bolt assembly  48  inserted through the eye connector  58  and a selected pair of aligned apertures  44 - 44  or  46 - 46 . The other eye connector  62  of the rigid bar  60  may be positioned between the triangular plates  88  of the rocker subassembly  84  and secured for pivotal movement by nut-bolt assembly  98  inserted through the eye of the eye connector  62  and a selected pair of aligned link positioning apertures ( 91 - 91 ,  92 - 92 ,  93 - 93 ,  94 - 94 , or  95 - 95 ). 
     Finally, the rigid bar  60  of the rigid link assembly  52  may then be turned to lengthen or shorten the rigid link assembly  52 , so that the rocker head  100  bears on the lower surface  40  of the leaf spring L. 
     It should be noted that the previously enumerated steps for installing the improved traction device  20  on a vehicle may be performed in different orders without departing from the scope of the invention. Also, some steps of the procedure may be omitted since the improved traction device  20  may be shipped in a partially assembled state, without departing from the scope of the invention. The installation procedure is illustrative and given as an example only to better understand the device and the factors that may influence the installation. 
     In operation, force may be directed along arrow  140  during acceleration. The force directed along arrow  140  may be transferred through the rocker subassembly  84  to the front leaf spring bracket subassembly  86 . The front leaf spring bracket subassembly  86  may be forced downwardly while the rocker head  100  exerts an upward force against the lower surface  40  of the leaf spring L. With the rocker head  100  serving as a fulcrum, the force directed along arrow  140  is now applied downwardly against the upper surface  69  of the leaf spring L. 
     Referring again to  FIGS. 1-3 , Those persons skilled in the art may understand that, as the force originally applied along the arrow  140  is applied farther to the rear with respect to the front leaf spring mount F, greater benefit will be derived from the traction device of the present invention. This positioning towards the rear may be accomplished by a selected installation of the rocker subassembly  84 , extending the distance between rocker head  100  and the pivot location (nut-bolt assembly  120 ), or a combination of the two. 
     During installation of the improved 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 rocker head  100  is forced against the lower 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. 
     From the foregoing, it will be understood by persons skilled in the art that an improved traction device has been provided. The invention is relatively simple and easy to manufacture, yet affords a variety of uses. While the description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. The foregoing is considered as illustrative only of the principles of the invention. Further, because numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and numerous changes in the details of construction and combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.