Abstract:
A system of linkages for a beam-type straight axle drive arrangement which accurately control the vehicle steering as well as axle location throughout its full range of suspension compression. This system can be retrofitted onto existing vehicles as a “bolt-on” retrofit kit, thereby dramatically improving the handling characteristics of such vehicles.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to automotive drive systems and, more particularly, to such drive systems of the beam-type straight axle type. 
   2. Description of the Related Art 
   Beam-type straight axle drive systems have been and still are commonly used for many different automotive applications. While simple in design, these axle types also tend to be inexpensive and very durable, making them highly desirable on utility vehicles such as pickup trucks and sport utility vehicles (SUVs) which are equipped with 4-wheel drive or, at least, power transmission to the front wheels. 
   Many types of mounting and/or suspension methods have been used to attach straight axles to vehicles. Such methods include leaf springs, radius arms with coil springs, multi-link systems with coil springs, or a combination of any of the above. Probably the most compliant and well-functioning method of mounting/suspending a straight axle to a vehicle is the multi-link system in combination with coil springs. Vehicles such as the Jeep Cherokee (XJ Model), Jeep Comanche (MJ Model), Jeep Grand Cherokee (ZJ and WJ Models), Jeep Wrangler (TJ Model), and Dodge 4×4 pickup trucks have all used this type of system with reasonable success. 
   The multi-link system of locating a beam-type straight axle commonly utilizes five different links: two upper suspension arms, two lower suspension arms, and one track bar (see  FIG. 1 ). The combination of these links enables the axle to move and articulate rather freely, while still providing a relatively stable platform for the vehicle to be suspended on. 
   Additionally, the steering system commonly utilized with this type of suspension system is the Y-type linkage (see  FIG. 1 ). This system consists of a steering drag link running from the steering box pitman arm to the opposite steering knuckle, and a steering tie rod which attaches somewhere along the length of the steering drag link and on the opposite end to the remaining steering knuckle. 
   There are substantial problems with these types of suspension and steering systems. First, suspension compression results in axle translation, thus causing the vehicle to experience bump-induced yaw. When the vehicle hits a bump in the road, the suspension system will absorb this bump by allowing the axle to travel upward closer to the vehicle frame (see  FIG. 2 ). As this happens, the track bar forces the axle toward the side of the vehicle opposite where the track rod attaches to the vehicle frame or body structure. This translation in axle location actually causes the vehicle body to move in the opposite direction (as the tires and wheels are mounted to the axle, and they will stay planted on the road surface), which is bump-induced yaw. This phenomenon creates a very unstable feel in the vehicle, possibly leading to loss of vehicle control. The problem is only exacerbated when the vehicle experiences increased suspension compression, such as during use in rough terrain. 
   Another significant problem lies with the Y-type steering linkage. As suspension compresses, the linkage changes its effective length, thus causing a toe-out situation with the tires. When the vehicle hits a bump in the road and the suspension compresses, the steering drag link and steering tie rod change relationship relative to one another (see  FIG. 3 ). They become more parallel to one another during suspension compression, thus increasing the effective distance between the steering knuckles and thereby increasing toe-out on the vehicle (bump-induced toe change). Toe-out tends to make a vehicle “wander” or “hunt” around on the road, or in other words become unstable. 
   Jeep has somewhat resolved the bump-induced toe change problem on its later-model vehicles (WJ) by attaching the steering tie rod directly to both steering knuckles, rather than one steering knuckle and the steering drag link. However, there still remains an inherent problem with bump-induced steering, or bumpsteer. Referring to  FIG. 1 , it will be noted that the endpoints of the track rod do not coincide exactly with the endpoints of the steering drag link. As the vehicle hits a bump and the suspension compresses, these two linkage units move through somewhat different arcs. As the axle translates a given distance through a given amount of suspension compression, the steering knuckle translates a different amount. Thus, the vehicle will experience some amount of steering movement due solely to hitting the bump, which is bumpsteer. 
   Combining these three different issues together can cause a vehicle to handle very poorly during suspension compression, possibly leading to loss of vehicle control. A method of solving these problems is highly desirable for people who own or plan to own any vehicle utilizing these suspension and steering systems. 
   SUMMARY OF THE INVENTION 
   In brief, particular arrangements of the present invention comprise a system of linkages which accurately control the vehicle steering as well as locate the axle throughout its full range of motion in a vertical plane when experiencing suspension compression. This system can be retrofit onto existing vehicles as a “bolt-on” improvement kit, thereby drastically improving the handling characteristics of such vehicles. 
   In one particular arrangement of the present invention, a pair of upper suspension arms, one connected to each front wheel, are secured together to a central tie point, thereby forming a “wishbone”. The central tie point is attached to a frame member which attaches to the axle. This wishbone suspension and the associated steering linkage permit control of axle location in all axes while preventing any translation due to suspension compression, as is demonstrated in  FIG. 2 . 
   In another particular arrangement in accordance with the invention, the two upper suspension arms extend from the wheel mounting points to a pair of separate points fastened to the central plate which is attached to the axle, thereby providing the same effect as the wishbone of  FIG. 4  with dual connecting points for the inner ends of the upper suspension arms. As with the first-mentioned embodiment, this arrangement also serves to control axle travel in all axes while preventing axle translation due to axle suspension compression. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention may be realized from a consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is an end elevational view of a conventional Y-type multi-link suspension and steering system for locating a beam-type straight axle; and 
       FIG. 2  is an end elevational view of the system of  FIG. 1  showing the effects of suspension compression resulting in axle translation causing bump-induced yaw; 
       FIG. 3  is an end elevational view of the system of  FIG. 1  showing increased toe-out of vehicle front wheels resulting from suspension compression; 
       FIG. 4  is an end elevational view of one embodiment of the present invention, wherein the two lower suspension arms are similar to those in the existing design, but there is a single “V”-shaped upper arm called a “wishbone”; and 
       FIG. 5  is an end elevational view of another embodiment of the present invention, wherein the two lower suspension arms are similar to those in the prior art design of  FIG. 1 , but two independent upper suspension arms are utilized to create an axle-centering feature similar to the wishbone link of  FIG. 4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1-3 , a common configuration of utility vehicle suspension and steering is shown. Any left and right references are used as a matter of convenience and are determined by standing at the rear of the vehicle and facing forwardly in the direction of travel. 
   As depicted in  FIG. 1 , the multi-link system of locating a beam-type straight axle, as known in the prior art, commonly utilizes five different links: two upper suspension arms  10 , two lower suspension arms  20 , and one track rod  30 . The combination of these links interconnected in the manner shown in the drawing enables the axle  40  to move and articulate rather freely, while still providing a relatively stable platform for the vehicle to be suspended on. 
     FIG. 1  also depicts a steering system commonly utilized with this type of suspension system, known as the Y-type linkage. This system consists of a steering drag link  50  running from the steering box pitman arm (not shown) to the opposite steering knuckle (not shown), and a steering tie rod  60  which attaches somewhere along the length of the steering drag link  50  and on the opposite end to the remaining steering knuckle (not shown). 
     FIG. 2  depicts the problems presented by commonly existing types of suspension and steering systems when the vehicle hits a bump in the road. The suspension system will compress to absorb the bump by allowing the axle  40  to travel upwards and closer to the vehicle frame (in the direction of the arrow  42 ). As this happens, the track bar  30  forces the axle  40  toward the side of the vehicle opposite where the track bar  30  attaches to the vehicle frame (to the left in  FIG. 2 , represented by the arrow  44 ). This translation in axle location causes the vehicle to move in the opposite direction, thereby creating bump-induced yaw. 
     FIG. 3  depicts another problem presented by the existing Y-type steering linkage when the vehicle hits a bump in the road. As the suspension system compresses (arrow  42 ) to absorb the bump, the steering drag link  50  and steering tie rod  60  change position relative to one another, becoming more parallel. This increases the effective distance between the steering knuckles (not shown) at the ends of steering drag link  50  and steering tie rod  60  and therefore increases toe-out on the vehicle (represented by the arrows  46 ). These changes in vehicle orientation on bumpy terrain contribute to vehicle instability. 
     FIG. 4  depicts a steering linkage system  101  of the present invention which eliminates the noted problems to which existing steering systems are prone. A steering link (not shown) extends from the pitman arm  110  on the steering box of the vehicle (also not shown) back to a steering idler  120 . This steering idler  120  provides a pivot which is substantially coincident with the frame pivot  132  of a wishbone  130 , thereby minimizing relative motion between the steering idler  120  and the pitman arm  110  as the wishbone  130  is moved up and down throughout the vehicle&#39;s range of suspension travel, from full compression to full extension. A steering drag link  100  extends from the steering idler  120  to a steering bellcrank  140 . The pivot of the steering bellcrank  140  is substantially coincident with the axle pivot of wishbone  130 ; therefore there is no relative motion between steering bellcrank  140  and steering idler  120  as wishbone  130  is moved up and down throughout the vehicle&#39;s range of suspension travel. Tie rods  150  extend from steering bellcrank  140  to each of the steering knuckles (not shown). In this manner, there is no relative motion between steering knuckles (not shown) and steering bellcrank  140 , as they all attach to axle  40  via the frame pivot  132  and mounting plate  134 . 
   It is not necessary that the steering idler  120  be coupled by a pivot on the wishbone  130 . In an alternative embodiment, a sliding idler would be equivalent in result to the pivoted idler  120 . This is because the idler is used to transmit motion from pitman arm  110  to the bellcrank  140  via the steering link and steering drag link  100 . All that is required is that the idler be unaffected by motion of the wishbone. This result can be accomplished equally well by the idler  120 , whether its coupling to the wishbone  130  is by means of a pivot or a slider. 
   With this system, all relative motion between linkage components is eliminated by making all relative pivot points substantially coincident with one another. Bump-induced toe change and bump-induced steering change are therefore completely eliminated. 
   This wishbone linkage can attach in one of two ways: two attachment points on the vehicle frame  142  and one attachment point on the axle  40  (as shown in  FIG. 4 ) or reversed, with one attachment point on the frame and two attachment points on the axle. This wishbone linkage may also be located either on the top of the axle (as shown), or on the bottom of the axle utilizing upper suspension arms instead of lower suspension arms. The combination of two suspension arms and one wishbone allows control of the axle location in all axes without any translation due to axle suspension compression and articulation. 
     FIG. 5  illustrates another embodiment  102  of the present invention. Rather than using a single wishbone link, such as the wishbone  130  in  FIG. 4 , this embodiment incorporates two independent upper suspension arms  200  connected to frame  142 . This embodiment could also be deployed as lower suspension arms  200 ′. By angling suspension arms  200  significantly inward toward axle  40 , the suspension arms  200  provide an axle-centering feature similar to the wishbone configuration depicted in  FIG. 4 . An alternative configuration could have upper suspension arms  200  substantially parallel and lower suspension arms  200 ′ angled in relation to axle  40 . The steering linkage is very similar to that in  FIG. 4 , as the pivots of the steering idler  120  and the steering bellcrank  140  coincide with the pivots of a single suspension link. 
   Yet another alternative configuration (not shown) involves leaving commonly occurring, stock multi-link setup, such as is shown in  FIG. 1  (with two upper suspension arms  10 , two lower suspension arms  20 , and a track bar  30 ), but replacing the steering links  50  and  60  with a linkage system similar to that in  FIG. 5 . Such a configuration would have the pivots coinciding with one of the suspension arms ( 10  or  20 ) and the problems with bump-induced toe change and bumpsteer are eliminated, although bump-induced yaw would remain. 
   Although there have been described hereinabove various specific arrangements of a AUTOMOTIVE STEERING AND SUSPENSION SYSTEM in accordance with the invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited should be considered to be within the scope of the invention as defined in the annexed claims.