Abstract:
A truck for towing a trailer includes a vehicle frame spine, a pair of suspension assemblies extending from either side of the vehicle frame spine and each supports a drive assembly at an end distal to the vehicle frame spine. Extensible struts are positioned between the vehicle frame spine and the drive assemblies allowing selection of vehicle drive height from a driving surface. A fifth wheel assembly is supported from the vehicle frame spine located above the drive assemblies. The fifth wheel assembly includes a fifth wheel and a fifth wheel lift which varies spacing of the fifth wheel from the vehicle frame spine. Control system selects strut extension based on a selected vehicle drive height and operates the lift assembly to counteract changes in vehicle drive height and maintain a constant fifth wheel drive height relative to the driving surface.

Description:
BACKGROUND 
     The technical field relates to controlling motor vehicle aerodynamic drag. The vehicle ride height of a truck, the nominal vertical distance between the chassis of a vehicle and the ground or road surface, is adjusted as a function of trailer type and load to reduce aerodynamic drag. Control over the adjustment process is implemented through automatic and manual inputs which also mediates for road conditions. 
     The average new vehicle fuel economy for heavy-heavy long haul trucks (25+ ton loads with engine displacement ranging from 11 liters to 15 liters) in 2003 was 6.1 mpg. The annual average improvement in fuel economy for such vehicles from 1995 to 2010 was 0.88% with about two thirds of the improvement coming from changes made to the engine and transmission, and one third of the improvement coming from better aerodynamics and reduced tire rolling resistance. Engine changes have related primarily to improvements in electronic fuel injection, combustion improvements and reduction in friction. Aerodynamic improvements have included increased use of cab fairings and spoilers. Second generation radial tires exhibit some reduction in rolling resistance over the prior generation. Continued refinement of these technologies should continue to provide some gains for a few years, but continuing to meet the historical pace of year on year improvements of 0.88% a year is unlikely. 
     Vehicle aerodynamic resistance is a function of the vehicle&#39;s drag coefficient, its effective frontal area and its height above the driving surface. In truck/trailer combinations the trailer usually has a greater frontal area than the truck due to extending above the truck&#39;s height. On such vehicles aerodynamic resistance can be reduced by streamlining the truck and incorporating fairings to the truck which expand the frontal area of the truck to match the trailer but which extend the streamlining of the truck to the trailer. 
     Extending streamlined fairings from the truck to the trailer is less effective, and even self-defeating, if the trailer is not as tall as the truck and the fairings simply operate to increase the frontal area of the truck. In such cases there is more to be gained in terms of reduced drag by lowering the truck to as close to the road surface as practical. However, dynamic application of a system for changing the vehicle ride height of heavy-heavy commercial trucks has not been considered practicable. For one thing, heavy-heavy commercial trucks have been designed to operate at a specific ride height to match a fixed fifth wheel height required by most trailers. 
     Air suspension systems have become common on trucks and trailers and one of their attributes has been their ability to maintain a constant vehicle ride height. Air suspension systems allow the carrying of loads of varying weight at a constant height because the air pressure in the air spring bladders which support the load can be varied as required to level the vehicle and to bring vehicle ride height back to nominal distances. Closed loop control systems have been employed to maintain vehicle ride height. The load an air suspension carries can be adjusted over a wide range, without changing the air spring height, simply by changing the air pressure. In addition to changing the load-carrying capability, a change in air pressure also affords changing the spring rate without a significant change in the natural frequency of the suspension system. 
     SUMMARY 
     A truck for towing a trailer includes a vehicle backbone frame/frame spine, a pair of double wishbone suspension assemblies extending from either side of the vehicle frame spine and direct drive assemblies located at the ends of the double wishbone suspension assemblies distal to the vehicle frame spine. Extensible struts are positioned between the vehicle frame spine and the direct drive assemblies allowing vehicle drive height from a driving surface to be selected. A fifth wheel assembly is supported from the vehicle frame spine located above the direct drive assemblies. The fifth wheel assembly includes a fifth wheel and a fifth wheel lift assembly which is operable to vary the spacing of the fifth wheel from the vehicle frame spine. A control system selects an extension of the struts based on a selected vehicle drive height and a operates the fifth wheel lift assembly to counteract changes in vehicle drive height and maintain a constant fifth wheel drive height relative to the driving surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation of a vehicle comprising a truck and flat bed trailer. 
         FIG. 2  is a top view of a suspension assembly for mounting a drive axle to a backbone frame/frame spine. 
         FIG. 3  is a front view of the suspension assembly. 
         FIG. 4  is a top view of the suspension assembly illustrating positioning of a fifth wheel. 
         FIG. 5  is a side elevation of the suspension assembly. 
         FIG. 6  is a top view of a vehicle chassis. 
         FIGS. 7A and 7B  illustrate a raised suspension assembly and a cooperatively lowered fifth wheel assembly. 
         FIG. 8  is a block diagram of a control system for the suspension and fifth wheel assembly. 
         FIGS. 9A and 9B  illustrate a lowered suspension assembly and cooperative elevation of the fifth wheel assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures, and in particular  FIG. 1 , a vehicle  52  is indicated comprising a truck  50  and a flat bed trailer  51  attached to be towed by the truck. The attachment of the trailer  51  to the truck  50  is made using a fifth wheel  54  which allows vehicle  52  to articulate. The fifth wheel  54  (shown in  FIG. 4 ) is installed at the back of truck  50  over the drive wheels  49 . Flat bed trailer  51  is supported by the fifth wheel  54  and on wheels  53  at a constant vehicle ride height above a driving surface  8 . A constant vehicle ride height for the flat bed trailer  51  maybe maintained by use of a suspension system including variable pressure air springs. Truck  50  though may be raised and lowered while fifth wheel  54  is maintained at a constant height to support the constant vehicle ride height of flat bed trailer  51 . Flat bed trailer  51  carries a load  55  which does not extend above the truck  50  when the truck is at its default height. This allows truck  50  to be lowered to reduce aerodynamic drag. 
     Provision for a variable vehicle ride height for truck  50  is accomplished through control of a suspension assembly  32  for the truck&#39;s drive wheels  49 . Modification of the fifth wheel  54  allows this support point for the flat bed trailer to be kept at a constant vehicle ride height.  FIGS. 2-6  illustrate the suspension assembly  32  and fifth wheel assembly  34  and their cooperative operation. Suspension assembly  32  relates to support of a particular type of vehicle frame based on a longitudinally aligned backbone or spine located down the centerline of the in the truck  50 . Suspension assembly  32  provides essentially double wishbone arrangements incorporating extensible struts  6 ,  7 . Controlling the nominal extension of the struts  6 ,  7  varies the vehicle ride height of the truck  50 . The fifth wheel assembly  34  incorporates its own extensible members allowing the height from the frame of the fifth wheel  54  to be varied concurrently with the vehicle ride height of the truck  50 . 
     Suspension assembly  32  is attached to fifth wheel assembly  34  at a fifth wheel attachment location  20  using a plurality of pins  16  that transmit the acceleration and deceleration forces of the truck  50  to the fifth wheel  54 . The suspension assembly  32  attaches a direct drive axle assembly  38  to a frame spine  36 . The backbone frame or frame spine  36  is sagittal to the truck  50 . 
     The suspension assembly  32  receives the frame spine  36  of truck  50  generally centrally and generally longitudinally through the assembly along a receiving cavity  19 . The frame spine  36  may be a light-weight, high strength tubular steel, structural composite or any other structural material frame. The frame spine  36  is received in the receiving cavity  19 . The frame spine  36  extends the length of receiving cavity  19  and is exposed at a rear end of the cavity. The position of the frame spine  36  is locked with respect to the suspension assembly  32  with a pin or other suitable means. 
     The suspension assembly  32  is configured for mounting the drive axle assembly  38 , such as an independent dual wheel direct drive axle to the frame spine  36 , however it is possible that the suspension assembly  32  can be used with other types of drive axles and rear suspensions. For example, the direct drive axle assembly  38  may have a front direct drive unit  23  and a rear direct drive unit  22  that are pivotally disposed on a spindle shaft  24 , however other numbers of drive axles are possible. The direct drive axle assembly  38  may have a cushion ride suspension  25  and be attached to the suspension assembly  32  with a walking beam  29 . When the direct drive axle assembly  38  drives over an uneven driving surface, the direct drive axle assembly  38  independently oscillates with respect to the frame spine  36  so that the wheels  49  encountering the uneven driving surface can traverse the surface while the wheels  49  not encountering the uneven driving surface remain in contact with the driving surface. 
     The left and right drive axle assemblies  38  are located mutually opposite one another and are mirror-images of each other. The front and rear axles on the direct drive axle assemblies  38  oscillate independently of one another. Together, the suspension assembly  32  and the direct drive axle assemblies  38  are attachable to the frame spine  36  to provide independent oscillation from the left side to the right side of the frame spine, and from the front set of wheels  49  to the rear set of wheels  49  associated with each direct drive axle assembly  38 . 
     The suspension assembly  32  includes a left sub-frame  42 A and a right sub-frame  42 B that are attached to a suspension tube  18 . Sub-frames  42 A,  42 B respectively incorporate upper frame members  4 ,  5  and lower frame members  9 ,  10 , where the upper frame members  4  and  5  are common parts and where frame members  9  and  10  are common parts. The upper frame members  4 ,  5  and the lower frame members  9 ,  10  may be generally clevis-shaped or Y-shaped (essentially A-arms) with upper ends  44  attached to the suspension tube  18 , however other shapes are possible. The upper and lower frame members  4 ,  5 ,  9 ,  10  can be made of cast iron, compacted graphite iron, structural composite, manufactured steel or any other material that provides the structural strength and material properties for the vehicle service loads. The sub-frames  42 A, B are essentially double wishbones usually constructed with equal length A-arms. 
     The suspension tube  18  may be a high strength, light-weight steel tube with an inside diameter that is slightly larger than an outside diameter of the frame spine  36 , however other configurations are possible. The sub-frames  42 A,  42 B, are pivotally attached to the suspension tube  18  with the hinge pins  16  and  17  at clevis hinges for the upper frame members  4 ,  5  and the lower frame members  9 ,  10  respectively. The pins  16  extend beyond the clevis and are used to attach to service loads, such as the fifth wheel assembly  34 . Hinge rings  15  are concentrically attached to the suspension body  18 , for example with retainers  21 , and receive the hinge pins  17 . 
     Opposite the upper ends  44 , lower ends  45  of the sub-frames  42 A,  42 B are received in a receiving structure  12  and pinned with hinge pins  17  and lock nut (not shown). The receiving structure  12  may be a box having a parallelogram-shape, however other configurations are possible. Receiving holes  13 ,  14  are disposed through the receiving structure  12  for receiving direct drive axle assemblies  38 . Here a pivot of walking beam  29  is pinned in place with a king pin  11 . In the receiving holes  13 ,  14  the walking beam  29  is generally parallel with the frame spine  36  and rotates in a plane parallel to the frame spine. 
     Each sub-frame  42 A,  42 B may mount four wheels  40  to the frame spine  36  on one side (left or right) of the frame. Each suspension assembly  32  may mount eight wheels  49  to the frame spine  36 , generally with an even amount of wheels on each side (left and right) of the frame spine. It is possible that some vehicles may be equipped with two or more suspension assemblies  32  on the extended frame spine  36  with a one piece rigid architecture or a frame made of multiple piece members joined together with hinged articulation. 
     Hydraulic/pneumatic struts  6 ,  7  extend from the suspension body  18 , generally centrally between the clevis-shaped upper frames  4 ,  5  to the receiving structure  12 . A first end  46  of the struts  6 ,  7 , attaches to a hinge ring  15  with hinge pins  17  and lock nuts, and a second end  48  of the struts  6 ,  7  attaches to the receiving structure  12  with pins  17 A. The struts  6 ,  7  dampen the pivotal movement of the receiving structure  12  of the sub-frames  42 A,  42 B with respect to the frame spine  36 . The pivotal movement of the sub-frames  42 A,  42 B with respect to the suspension body  18  results in movement of the receiving structure  12 , which accommodates the oscillation of the direct drive axle assemblies  38 . Hydraulic fluid may be pumped/withdrawn into the struts  6 ,  7  or air pressure varied to change the default extension of the struts and thereby raise or lower the frame spine  36  as shown in  FIGS. 9A  (lowered) and  7 A (raised). If chosen, the front end elevation of truck  50  may be varied by changing the extension of front air springs  74 . 
       FIGS. 9A , B and  7 A, B illustrate details of the construction of the fifth wheel assembly  34  and the operation of the fifth wheel lift mechanism  47 , which is usually based on air bladders or air springs. The fifth wheel lift mechanism  47  in turn passes through a cradle  80  and rests on a base  84  which is supported from the pins  20 . The fifth wheel  54  and cradle  80  are positionally stabilized relative to the base  84  by an anchor  75  supported from the bask which is linked to the fifth wheel and cradle respectively by a scissor action linkage including an upper stabilizer arm  82  and a lower stabilizer arm  81 . The upper and lower stabilizer arms  82  and  81  are pivotally connected to the anchor  75  at one end and to the fifth wheel  54  or cradle  80  at their ends distal to the anchor. Fifth wheel assembly  34  provides that the fifth wheel  54  be supported by the four air springs of the fifth wheel lift mechanism  47 . Inflation of the fifth wheel lift mechanism  47  counteracts lowering of the frame spine  36 , which occurs upon retraction/contraction of the struts  6  and  7 . Deflation of the fifth wheel lift mechanism  34  in turn counteracts extension of the struts  6  and  7  to maintain the fifth wheel  54  at a constant vehicle ride height. 
     The suspension assembly  32  with the direct drive axle  38  provides three axes of articulation to traverse roadway obstructions as well as the ability to raise and lower the truck  50 . The first independent axis of oscillation is between each of the direct drive units  22 ,  23  about the axis created by pin of the spindle shaft  24  at (the left to right direction). The second independent axis of oscillation is about pin  11  at a drive axle axis of rotation  30  (the front to rear direction, shown in  FIG. 4 ). The third independent axis of oscillation is sub-frame  42 A,  42 B of the suspension assembly  32  about the frame spine  36 . 
     Each suspension assembly  32  along the frame spine  36  independently articulates as the vehicle traverses over uneven surfaces. Further, each sub-frame assembly  42 A,  42 B, independently articulates as each side of the vehicle traverses uneven surfaces. The suspension assembly  32  reduces or eliminates the torsional loading on the frame spine  36  by allowing the independent oscillation of the front and rear drive axles, as well as independent oscillation of the left and right drive axles. Employing internal direct drive electric (shown in block diagram form in  FIG. 8 ) or high torque hydraulic motors (not shown) the dual wheel direct drive suspension assembly  32  allows front from rear and left from right rotation up to about 20 degrees both ways from the vehicle centerline. Under poor pavement conditions this allows travel through 17 inches of roadway obstructions. The struts  6 ,  7  may be employed to lower the vehicle ride height of truck  50  to a comparable degree, conditions allowing, to reduce vehicle drag while fifth wheel lift mechanism counteracts the drop in frame spine  36  height to maintain the fifth wheel  54  at a constant ride height H (shown in  FIG. 3 ). 
     Referring to  FIG. 6  frame spine  36  is shown extended forward to the location of a steering axle  43 , at each end of which are mounted front wheels  40 . Front wheels  40  support frame spine  36  along air springs  74  and may be equipped with suspension vertical travel sensors  73  which relate to automatic control modes of the system. 
     Struts  6 ,  7  may be variably and electronically controlled by automatic processes or by the operator while vehicle  52  is in motion. Higher pressure in the struts  6 ,  7  may be used to raise the overall height of the truck  50  to increase the articulation of the suspension assembly  32  or to increase the clearance of the suspension system. Lower pressure in the cylinder  6 ,  7  may be used to increase the vehicle&#39;s aerodynamics for highway use. To effect operation of the system the truck  50  may be equipped with a control system  27 . 
     Referring to  FIG. 8  a control system  27  and major truck  50  components relating to control over truck  50  operating height are illustrated. In brief, a hybrid type drive train is contemplated, illustrated here as series diesel/electric system incorporating an internal combustion engine  13  for driving a generator  14 , a hybrid inverter connected to receive power from the generator  14  and applying it to either traction batteries  31  for charging or directly to the direct drive traction motors/generators  35  installed on the direct drive axle assemblies  38  for powering drive wheels  49 . Alternatively a hydraulic system could be employed substituting hydraulic motors for the direct drive traction motors  35 , a hydraulic accumulator for the hybrid inverter  33  and traction batteries  31  and a pump for the generator  14 . 
     Control system  27  may be based on dual controller area networks based on datalink  68  and datalink  70 . The datalinks  68 ,  70  may conform to the Society of Automotive Engineers J1939 standard. A hybrid controller  37 , an engine controller  39  and an electronic system controller (ESC)  26  are connected to both datalinks  68  and  70 . An anti-lock brake system (ABS) controller  90  and a suspension controller  28  are connected only to the public datalink  70 . The ABS controller  90  can supply vehicle velocity information to the other controllers from measurements taken by service brake  41  sensors. The suspension controller  28  may be adapted both to control strut  6 ,  7  extension and to control fifth wheel lift mechanism  47  extension through a valve manifold  71 . Valve manifold  71  represents both hydraulic and pneumatic systems. It may also be used to supply air to trailer air springs  72 . In addition the suspension controller  28  monitors suspension travel sensors  73  which may be used to measure driving surface roughness. In automatic modes the suspension controller  28  can operate on vehicle speed and driving surface roughness related data to automatically set the vertical drive height of truck  50 . For example, at sustained low speeds there the system may be programmed to return to a “normal” drive height rather than a reduced, aerodynamic height. The control system  27  may be assumed to include connections to a trailer and providing for determination as to whether a trailer is present. 
     Manual input of constraint modes into the control system  27  may be implemented using mode select switches which are part of an in-cab switch pack  56 . The states of the switches are communicated to the ESC  26  over a datalink  64  and from ESC  26  to suspension controller  28  over datalink  70 . The operator may choose between settings, for example on-highway, off-highway, off-road and auto settings. In addition the truck  50  may be lowered to allow easy ingress and egress/vehicle service or the system may be turned off and the truck returned to a default “standard” height. The settings may control the levels of articulation, the vehicle height clearances, the direct drive acceleration response, the vehicle velocity limits, the steering ratios and the electronically controlled shock damping, among other settings.