Abstract:
A modular suspension system for short distance repositioning tractors, often referenced as terminal tractors, isolating the shock and impact of a retractable fifth wheel and rear axle from the frame of the terminal tractor by the arrangement of a rear axle and fifth wheel boom having lift cylinders between them and joining the rear axle, a lift arm assembly and a trailing arm assembly as a singular modular unit, isolated from the frame of the terminal tractor by elastomeric bushings at a forward location and pivot point on the terminal tractor frame, with a secondary suspension located at the rear of the singular modular unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   None 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   A suspension system for short distance repositioning tractors, often referenced as terminal tractors, isolating the shock and impact of a retractable fifth wheel and rear axle from the frame of the terminal tractor by the arrangement of a rear axle and fifth wheel boom having lift cylinders between them and joining the rear axle, a lift arm assembly and a trailing arm assembly as a singular modular unit, isolated from the frame of the terminal tractor by elastomeric bushings at a forward location and pivot point on the terminal tractor frame, with a secondary suspension located at the rear of the singular modular unit. 
   2. Description of Prior Art 
   Typically, a terminal tractor has a short wheelbase of between 110 and 116 inches. It is a cab over engine design with a one person cab, offset far to one side of the chassis. It has a medium duty diesel engine with an automatic transmission and a high reduction rear axle, the automatic transmission and the high reduction rear axle allowing the tractor to start and move a heavy load with a relatively low horsepower engine. The terminal tractor is only intended for short haul purposes in a truck depot or a yard where trailers are to be moved for short distances to and from a loading area. The steering axle is suspended from the frame with semi-elliptical leaf springs, while the rear axle is typically solidly mounted to the frame using mounting brackets and large capscrews to secure the axle. The fifth wheel, used to attach to the trailer, is mounted on a pivoted bracketry, generally referenced as a boom, which raises through hydraulics and lifts a loaded trailer or chassis for a short distance during the transport in the yard or depot. 
   Current industry standards in suspensions have the rear axle directly mounted to the frame of the tractor. The current standards in boom attachments use steel or bronze bushings rotating on a nominal 2″ diameter pivot shaft which floats in round holes in the frame rails, usually called sockets, near the center of the vehicle. Double acting hydraulic cylinders mounted between the frame and the boom provide a 50,000 to 70,000 pound lift capacity at the fifth wheel. Because of the extreme difference in axle weight between the unloaded condition (approximately 4,000 lbs.) of the terminal tractor and the loaded condition (approximately 30,000 lbs.), finding a working suspension that performs under both conditions has been a challenge. 
   The domestic terminal tractor manufacturers have been trying to develop a dependable working suspension for the rear axle of terminal tractors for several years. In the early 1980s, rubber block suspensions were attempted to cushion the frame from the shocks of ground impacts, but they provided very little flexibility. Since about the middle 1980s, several manufacturers have offered versions of conventional spring suspensions fitted to provide limited flexibility in empty and light load conditions and to settle the frame on rubber bumpers above the axle under heavy load conditions. This system is complex and expensive, but seems to be the best suspension alternative to date. Since 1992, a company named Capacity has offered a rear axle air suspension option, featuring a large A-frame under the chassis, connected to a central frame cross-member approximately below the boom attachment point near the center of the vehicle. The rear axle and lift cylinders attach to the rear ends of the A-frame below the chassis. Air springs between the axle and the frame allow vertical movement of the rear axle relative to the frame, lift the boom from the A-frame, independent of the chassis, which allows effective isolation of the chassis from vertical movement of the rear axle and boom. A bushed single front attachment of the A-frame suggests allowance of side-to-side rotation of the axle relative to the frame. However, solid mounting of the lift cylinders to the fifth wheel boom, solidly pinned to the frame through a steel pivot shaft and bushings prevents side-to-side suspension rotation and creates extreme high stress loads at the A-frame connection, pivot shaft mountings and bushings. The cost, weight and complexity of this suspension are significant and it has proven to be expensive to maintain and service. This type product accounts for only a small percent of the market. 
   The following United States patents were discovered and are disclosed within this application for utility patent. In U.S. Pat. No. 6,209,895 to Mueller, an axle suspension is provided for a wheeled vehicle having an axle suspension pivotally engaged with the frame with a rubber bushing acting as cushion along with a shock relating between the frame and rear axle mount. In U.S. Pat. No. 6,135,483 to Metz, a fifth wheel suspension system is disclosed wherein the frame has three separate pivotal mounting locations, having a first pivotal mount located between the frame and a rear axle support arm having an attached rear axle, with a bushing for a cushion and a shock, similar to Mueller, supra. This suspension system also contains pivotal mountings between the frame and two fifth wheel lift arms, with a hydraulic cylinder between the rear axle support arm and the base of the fifth wheel. This still relates shocks of the rear axle directly to the fifth wheel and also to the three pivotal connections to the frame. 
   Several patents use air suspension systems in a variety of pivotal mounting mechanisms for fifth wheels, including U.S. Pat. No. 2,821,409 to Chalmers, U.S. Pat. No. 3,380,758 to Granning, U.S. Pat. No. 5,388,849 to Arsenault, U.S. Pat. No. 4,279,430 to Tagg, and U.S. Pat. No. 5,639,106 to Vitale. Those using rubber bushings for cushion between related pivotal components having fifth wheel application included U.S. Pat. No. 4,162,799 to Willetts, U.S. Pat. No. 5,346,247 to Snyder and U.S. Pat. No. 5,655,788 to Peaker. None of the suspension systems include a singular pivot point between the frame, the rear axle and the fifth wheel boom which singularly isolate the frame from the rear axle and the fifth wheel boom, yet provide a secondary suspension between the frame and the fifth wheel boom under heavy load as well as a no-load situation. 
   SUMMARY OF THE PRESENT INVENTION 
   The unitized fifth wheel and rear axle suspension provides a completely new approach to isolating and protecting the chassis from ground impacts and road shocks for terminal tractors and other tractor applications. Recognizing the inherent relationship between the rear axle and a fifth wheel boom on adjustable height fifth wheel vehicles with lift cylinders between them, the unitized suspension joins the rear axle, a boom assembly and a trailing arm suspension assembly as a single modular unit. This unit is isolated from the frame of the terminal tractor by specialized elastomer pivot bushings at the forward location and pivot point. It is also suspended at a secondary location at the rear of the frame by a choice of suspension mechanisms including a single transverse leaf spring, two longitudinal leaf springs, two coiled springs with a track bar or two air springs with a track bar. The transverse leaf spring is the secondary suspension mechanism most discussed in the preferred embodiment. 
   The primary objective of the unitized suspension is to provide enhanced protection to the terminal tractor chassis from ground impacts and road shocks under both loaded and unloaded conditions. A second objective of the unitized suspension is to provide a single pivot engagement between the frame, the rear axle, lift arm assembly and trailing arm suspension of the unitized suspension, with a secondary suspension between the unitized suspension assembly and the frame. A third objective of the unitized suspension is to isolate the lift mechanism from the chassis frame by placing the lift mechanism between the rear axle and the lift arm assembly without direct attachment to the frame. 

   
     DESCRIPTION OF THE DRAWINGS 
     The following drawings are submitted with this utility patent application. 
       FIG. 1  is a side view of the lift arm assembly and fifth wheel plate. 
       FIG. 2  is a top view of the lift arm assembly and fifth wheel plate. 
       FIG. 3  is a side expanded view of the trailing arm assembly and rear axle. 
       FIG. 4  is a side view of the trailing arm assembly. 
       FIG. 5  is a side view of the trailing arm assembly and lift arm assembly connected together as the modular suspension system with the hydraulic lift arm fully raised. 
       FIG. 6  is a top view of the trailing arm assembly. 
       FIG. 7  is a top view of the lift arm assembly and the trailing arm assembly attached to the frame of a terminal tractor. 
       FIG. 8  is a rear view of the lift arm assembly in a lowered position and trailing arm assembly attached to the frame of a terminal tractor with phantom lines showing the tractor tires attached to the rear axle. 
       FIG. 9  is a rear view of the lift arm assembly in a fully raised position and trailing arm assembly attached to the frame of a terminal tractor with phantom lines showing the tractor tire attached to the rear axle. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A modular suspension system  10  adapted to a terminal tractor having a frame  600 , shown in  FIGS. 1–9  of the drawings, comprises a lift arm assembly  100  having a fifth wheel plate  300 , a trailing arm assembly  200  attaching to a rear axle  500 , the trailing arm assembly  200 , having a front segment  202  and a rear segment  204 , having the front segment  202  pivotally connecting to the frame  600  of the terminal tractor at two pivot bushing socket tubes  610  housing elastomeric trailing arm pivot bushings  210  which rotate on a common axis, with the elastomeric trailing arm bushings  210  holding an enforced longitudinal position of the trailing arm assembly  200  while allowing limited vertical movement and side-to-side rotation of the trailing arm assembly  200  relative to the frame  600 . The lift arm assembly  100 , which includes a front segment  102  and a rear segment  204 , is joined at the front segment  102  to the trailing arm assembly  200  by two larger diameter composite bushings  110  rotating on the outer surface of the pivot bushing socket  212  of the elastomeric trailing arm pivot bushings  210 , the elastomeric trailing arm pivot bushings  210  isolating the trailing arm assembly  200  and the lift arm assembly  100  from the frame  600 , with at least one lift cylinder  400  forcing the lift arm assembly  100  from the trailing arm assembly  200  to forcibly elevate and lower the lift arm assembly  100  and the fifth wheel plate  300 . The at least one lift cylinder may be a hydraulic cylinder, a pneumatic lift device or mechanical lift device, but is shown in  FIGS. 5 and 9  as hydraulic cylinders. 
   The trailing arm assembly  200 , shown in  FIGS. 3–6 , includes a rear portion  220  which supports bracketry, preferably two end housings  222  behind the rear axle  500  which secure ends  272  of a spring means  270  having a center  273 , preferably a transverse leaf spring  274  having two ends  275  and a center  277 . The transverse leaf spring  274  stabilizes the side to side location of the rear axle  500  and the lift arm assembly  100  and provides controlled vertical and side to side rotational movement, with the spring means  270  or transverse leaf spring  274  being adjusted to a preferred ride character. 
   The trailing arm assembly  200  also mounts a lower lift cylinder mount  410  of the at least one lift cylinder  400  at a lift cylinder mounting attachment  290  positioned in front of the rear axle  500 . Preferable would be the use of two lift cylinders  400  in tandem, as shown in  FIG. 9 . The lift cylinder  400  has an upper lift cylinder mount  420  which is pivotally mounted to a lift cylinder mounting attachment  152  in the lift arm assembly  100  in front of the fifth wheel plate  300 . The lift cylinder  400 , when activated, extends, raising the rear segment  104  of the lift arm assembly  100  and the fifth wheel plate  300 , further lifting a trailer or chassis attached to the fifth wheel plate  300 , transferring the lifting forces to the lift arm assembly  100  and trailing arm assembly  200  and isolating these forces from the frame  600  of the terminal tractor by the composite bushings  110 , the elastomeric trailing arm bushings  210  and the spring means  270 . 
   The lift arm assembly  100 , shown in  FIGS. 1–2 ,  5  and  7 , further comprises at least two longitudinal rails  120  connected by at least two lateral rails  130 , each longitudinal rail  120  having a front end  140  and a rear end  150 , the rear end  150  including fifth wheel plate mounting brackets  142  between which is attached the fifth wheel plate  300  by pivot pins  144 . The rear end  150  also includes the lift cylinder mounting attachments  152  located in front of the fifth wheel plate mounting brackets  142 , attaching to the upper lift cylinder mounts  420  of the at least one lift cylinder  400 . The front end  140  includes two pivot bushing housings  160  containing two lower mounting blocks  162  and two upper mounting blocks  164  which respectively attach with endcap retaining bolts  165  to two upper endcap mounting blocks  167  and two lower endcap mounting blocks  169  of two endcaps  166 , within which the composite pivot bushings  110  are secured. The lift arm assembly is further stiffened and held in desired relation by secure longitudinal and lateral bracing, in this case a welded top plate  125 , which fully encloses the top of the lift arm assembly. 
   The trailing arm assembly  200 ,  FIGS. 3–4 , further comprises two trailing arm beams  230  having a front end  240  and a rear end  260 , each front end  240  having a lower control arm droplink  242  welded to the trailing arm beam  230 , the two trailing arm beams  230  joined at their front ends  240  by a front suspension cross member  262  and reinforced by a corner brace  244 . Each control arm droplink  242  defines a pivot bushing socket tube  246  containing the elastomeric trailing arm bushings  210 . A suspension attaching bolt  248  attaches each elastomeric trailing arm bushing  210  and each composite bushing  110  through the pivot bushing socket tube  246  and also by suspension attaching bolts  248  to suspension attaching bolt tubes  610  in the terminal tractor frame  600 . 
   The rear end  260  of each trailing arm beam  230  is welded to an axle clamp mounting plate  261  and a trailing arm weldment  266  comprising the rear portion  220  of the trailing arm assembly  200 . An axle clamp weldment  264  is secured to the axle clamp mounting plate  261  by lower clamp bolts  265  and to the rear portion  220  of the trailing arm assembly  200  by end housing retainer bolts  224  and rear cross member retainer bolts  225 . The axle clamp mounting plate  261 , rear axle clamp weldment  264  and trailing arm weldment  266  define a cavity  250  within which the rear axle  500  is secured to the trailing arm assembly  200  and clamped in place by axle clamp bolts  267 ,  FIGS. 3–4 . On an upper surface  268  of each trailing arm weldment  266  is a rear cross member and fifth wheel rest weldment  269  and a spring end housing  222  which secure the preferred transverse leaf spring  274 ,  FIG. 6 . Welded to a lower surface  232  of each trailing arm beam  230  is the cylinder mounting attachment  290  supporting the lower lift cylinder mount  410  of the lift cylinders  400  and a suspension center cross member  263  connecting the two trailing arm beams  230  and supporting the lower lift cylinder mounting attachments  290 . The end housings  222  within which are secured the ends  275  of the transverse leaf spring  274  attach to the trailing arm weldment  266  by upper clamp bolts  224 . The ends  275  of the transverse leaf spring  274  are captured in the end housings  222  by rubber spring end isolators  276 . 
   The rear axle  500 , having a pair of dual tractor tires  510  on the ends of the rear axle  500 ,  FIGS. 8–9 , further attached to the trailing arm assembly  200 , is connected to the drive train of the terminal tractor in the same manner as a common rear axle on any terminal tractor, the rear axle  500  including a rear differential  520  attaching to the drive train and including brakes, with brake actuators  530  connected to the foundation brake components contained in the rear axle  500  typically used in terminal tractor rear axles. 
   A rear loading ramp  620  of the frame  600  of the terminal tractor is designed to accommodate the modular suspension system  10  by the inclusion of a tapered approach section  622  with a suspension mounting cross member  624  located to facilitate mounting of the spring means  270  or the preferred transverse leaf spring  274 . A recess  623  in the tapered approach section  622 ,  FIGS. 8–9 , comprising a rear cross member plate  626  leading to the approach section  622 , directs a semi trailer king pin into the fifth wheel plate  300  when the lift arm assembly  100  is in a lowered position, with tail portions  301  of the fifth wheel plate  300  resting upon the fifth wheel rest weldment  269 ,  FIGS. 7–9 . 
   Other possible embodiments of the spring means  270  would include longitudinal leaf springs, coil springs with a track bar or air springs with a track bar, but would not be as simply applied as the single transverse leaf spring  274 . 
   When the modular suspension system  10  is applied to the frame  600  of the terminal tractor, five scenarios come into play. First, when the terminal tractor is unloaded and the fifth wheel plate  300  is fully lowered,  FIG. 8 , the modular suspension system  10  substantially isolates the frame from road shocks, using the elastomeric trailing arm bushings  210  and transverse leaf spring  274  as plural isolators. The tails  301  of the fifth wheel plate  300  rest upon the fifth wheel rest weldment  269  which attaches directly to the trailing arm assembly  200 , which is isolated from the frame  600  by the rear spring means  270  or the transverse leaf spring  274 , with the center  277  of the transverse leaf spring  274  attached to the spring mounting cross member  624  for lateral and vertical location and to provide vertical cushion. This maintains the fifth wheel plate  300  fully synchronized with the modular suspension system  10  and prevents unnecessary wear on the fifth wheel plate  300 , the lift arm assembly  100  and trailing arm assembly  200 . All rotational forces generated under acceleration and braking are distributed and minimized by the above isolation. 
   A second scenario is present when the terminal tractor is being loaded while the fifth wheel plate  300  in a lowered position,  FIG. 8 , but not shown under load, which commonly occurs when the terminal tractor is being hooked to a trailer. If the trailer has a very low coupler height, the tapered approach section  622  of the rear frame cross member  626  slides under the trailer, forcing the frame  600  slightly downward on the modular suspension system  10 , and lifting the trailer until the trailer slides onto the fifth wheel plate  300 . The weight of the trailer is passed through the rear frame crossmember  626 , the spring mounting crossmember  624 , the spring means  270  or the transverse spring  274  to the trailing arm assembly  200  and the rear axle  500 . Backing on under the trailer will effect coupling. The lift arm assembly  100  would then be lifted after coupling and prior to movement, leading to the third scenario below. 
   With the loaded trailer attached and the lift arm assembly  100  fully raised, the weight of the trailer is carried through the fifth wheel plate  300 , the lift arm assembly  100 , lift cylinders  400 , trailing arm assembly  200  and the rear axle  500 . As much as 10% of the trailer weight could be carried froward to the elastomeric trailing arm bushings  210  and composite bushings  110  where it would then be carried to the frame  600 . In this scenario, nearly 95% of the load is carried by the modular suspension system  10  and not the terminal tractor frame. 
   Fourth, when the fifth wheel plate  300  is raised and the trailer is loaded during acceleration, the distribution of forces will depend on the torque being delivered to the rear axle  500 . For example, a 174 horsepower engine, generally supplied as an industry standard, under full throttle acceleration with a heavy load could generate torque in the range of 36,000 lbs/ft (based upon 458 lbs/ft×2.43:1 torque multiplication×3.58:1 reduction in low gear×9.08:1 rear axle drive ratio.) Adding an additional rotational force of approximately 25% or another 9,000 lbs./ft for the inertia of the loaded trailer at 16″ of lift height to the 36,000 lbs/ft yields approximately 45,000 lbs/ft, reduced proportionally by the length of the trailing arm assembly  200 , approximately 5 feet, for a gross weight yield of 9000 lbs/ft delivered to the elastomeric trailing arm bushings  210  at the center of the frame  600 . Without the modular suspension system  10 , the terminal tractor bucks or rises abruptly during acceleration. The modular suspension system  10  transfers the primary accelerating forces to the frame  600  of the terminal tractor at the center pivot bushing socket tube  610 , effectively balancing the effects of the accelerative forces between the front and rear suspensions and thus reducing the rise at front of the terminal tractor during acceleration and minimizing the resulting lift to the driver. 
   Fifth, when the fifth wheel plate  300  is raised and the trailer is loaded during deceleration, braking torque is the main factor in determining applied force. Under good repair and a hard braking application as much a 50,000 lbs/ft plus another 25% for kinetic energy of a loaded trailer, factoring reduction due to the nominal 5 foot length of the trailing arm assembly  200 , a braking force of approximately 12,500 lbs/ft is presented at the elastomeric trailing arm bushing  210  at the pivot bushing socket tubes  610 . Without the modular suspension system  10 , the terminal tractor would experience a hard dive at the front of the terminal tractor. With the modular suspension system  10 , the terminal tractor and driver experience a significantly less movement, with the modular suspension system  10  more equally distributing the braking force by applying this force at the pivot bushing socket tubes  610  near the center of the frame  600 , thus balancing the application of force between the front and rear axles of the terminal tractor and reducing the dive reaction at the front of the frame  600  and on the operator. 
   Reducing stress and shock loading to the terminal tractor frame reduces wear to the terminal tractor and all of its components, including the electrical system, engine, drive train and front suspension, thus prolonging the useful life of the terminal tractor and lowering cost and frequency of repairs due to stress and shock loading. 
   While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that changes in form and detail may be made therein without departing from the spirit and scope of the invention.