Mounting system for fifth wheels

Truck tractors are connected to their trailers by fifth wheels and several companies manufacture fifth wheel assemblies. The tractors consist of a pair of longitudinally extending beams or rails to which the fifth wheel assemblies mount. Each fifth wheel manufacturer provides several types of fifth wheels, depending upon the type of trucking service being provided. Complicating the situation is the fact that the lateral spacing between the beams will differ. As a result of these variations, different types of mounting brackets have been developed to secure the fifth wheels to the trailer frames. The drop-over bracket fifth wheel mounting assembly consists of an L-shaped angle brace which complements and is slipped over the beam of the tractor; a bracket on its top connects to the fifth wheel. The flat plate method utilizes a thick, flat plate to span across and rest upon each of the beams; it also has a top side bracket. The drop-over method resists longitudinal loads very well but has been found to develop fatigue cracks as a result of lateral and lateral overturn loads. The flat plate method has proved to be a more costly, yet more effective method of preventing fatigue cracking. The present invention combines the positive features of each individual system into a single, and unitary lightweight cast mounting assembly, thereby providing structural homogeneousity which is resistant to fatigue cracking. Since the combined bracket mounts directly to the tractor beams, it can be used from tractor to tractor if necessary, with no concern for the lateral spacing between the beams of a particular tractor.

FIELD OF THE INVENTION 
The present invention relates to fifth wheels which are demountably 
connected to truck tractors, and more particularly, to an improved 
mounting structure for securing the fifth wheel to the tractor frame. 
BACKGROUND OF THE INVENTION 
Tractor frames, to which the fifth wheels are mounted, typically comprise a 
pair of longitudinally extending C-shaped channel members that are 
supported by the wheel and axle assemblies. The channels are laterally 
spaced apart from each other and they provide a planar surface for 
resisting normal and twisting forces after the fifth wheel is secured 
thereupon and placed in operation, thereby transferring the payload of the 
trailer equally into each of the frame channels. In super heavy service 
applications, each of the channel members may even be comprised of double 
or stacked C-shaped channels. The fifth wheel can be mounted to the truck 
frame in a number of various ways, but for the sake of this discussion, 
only the fifth wheels which indirectly mount to the channels through use 
of drop-over angle brackets or flat mounting plates will be discussed. 
The drop-over method utilizes an L-shaped angle member which conforms and 
communicates with the top and vertical legs of each of the channels, 
having its vertical leg bolted to the outboard vertical side of the 
channel. The horizontal leg of the drop-over bracket, which coexists with 
the top horizontal leg of the channel, also includes an arcuately shaped 
mounting bracket which is welded thereupon. The arcuate mounting bracket 
lies generally above the top horizontal leg of the C-shaped channel and 
the exact location is a function of the variation of the width of the 
channel horizontal leg and the lateral spacing between the channels of the 
tractor frame, as will become clearer later in the discussion. The arcuate 
mounting bracket includes a horizontally aligned throughbore for accepting 
a coupling crosspin which is in communication with the fifth wheel 
framework. More specifically, the fifth wheel framework has a flange on 
one or each peripheral edge that communicates with the arcuate mounting 
bracket. In this way, flange ports on each flange can be horizontally 
aligned with the mounting bracket throughbore for pinning the fifth wheel 
to the drop over angle mounting bracket and hence, to the tractor frame. 
Although the drop-over brackets transmit lateral inertial forces which are 
caused by curving and rocking of the fifth wheel into the frame, drop-over 
arrangements are best suited for resisting longitudinal forces and moments 
caused from acceleration, deceleration, as well as the downward forces 
acting on the ramp's eccentric, to the rear of the bracket pivot center 
during coupling. In any event, the lateral and longitudinal forces will 
produce high magnitude lifting forces between the bracket and the tractor 
frame and as a result, localized forces have developed fatigue cracks 
either directly beneath the arcuate mounting bracket near the weld line, 
or between the bolt holes. 
Another type of anchoring assembly is the flat plate mounting assembly, and 
it offers increased fatigue cracking strength compared to the drop-over 
bracket method during the lateral and lateral overturn loads, while being 
as effective in resisting vertical loads, The flat mounting plate assembly 
consists of a rectangular, planar plate of steel which is secured flatly 
on top of each of the tractor channels, with the lateral sides of the 
plate extending slightly beyond each channel. In order to transfer loads 
from the plate into the frame, a section of L-shaped angle is used to 
support the plate directly below the overhang. Those in the art typically 
refer to this angle as the outboard angle member. The outboard angle 
member is simultaneously secured to the tractor channel and the flat 
mounting plate by bolting its horizontal leg to the bottom side of the 
mounting plate and then bolting its vertical leg to the vertical wall of 
the channel. The same arcuate mounting brackets used in the drop-over 
mounting assembly are welded to the top of the mounting plate and they are 
generally located above the top horizontal leg of the C-shaped channel: 
their relation to the frame again being a function of the channel width 
and the lateral spacing between the track channel members. The location of 
the arcuate mounting bracket, with respect to the horizontal leg of the 
channel member, does not depend upon which assembly is used. 
The flat mounting plate method of attachment offers increased fatigue 
strength when compared to the drop-over mounting assembly because the 
lateral forces and moments which work upon the arcuate mounting bracket 
are first distributed throughout the entire flat plate surface area before 
they are distributed and transferred into the outboard angle member. This 
arrangement offers greater surface area for load distribution, thereby 
decreasing the magnitude of stresses being transferred into each 
attachment bolt and into the critical areas between the anchoring bolts. 
However, one disadvantage of the fiat mounting plate arrangement is that 
it utilizes a large, thick steel plate which adds cost and weight to the 
mounting arrangement, as well as extra time and labor for assembling it to 
the tractor frame. 
SUMMARY OF THE PRESENT INVENTION 
By the present invention, it is proposed to provide a simple and economical 
fifth wheel mounting arrangement which serves to transmit both the lateral 
and longitudinal loads effectively into the vertical and horizontal webs 
of the tractor frame members. 
It is another object of the present invention to provide a lightweight 
fifth wheel mounting arrangement which incorporates the features of a fiat 
mounting plate for increased strength during lateral and lateral overturn 
loads. 
It is another object of the present invention to provide a lightweight 
fifth wheel mounting arrangement which incorporates the features of the 
drop-over angle bracket for resisting longitudinal and coupling loads. 
It is a final object of the present invention to provide an 
integrally-formed, lightweight mounting arrangement which is constructed 
as a combination of two mounting methods into a single, unitary cast 
system with at least pan of the mounting assembly formed as a drop-over 
angle bracket, while the other pan is formed as a flat mounting plate. In 
this way, when the combined mounting system is secured to the tractor 
frame, the weaknesses of each of the individual mounting arrangements, 
when operated separately, can be overcome. This means that the fatigue 
cracking problems normally found in the drop-over mounting systems can be 
eliminated while a less costly method of manufacture is employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Those in the art are familiar with the drop-over angle bracket and flat 
plate fifth wheel mounting arrangements, however, each of these 
arrangements is respectfully illustrated in FIGS. 2 and 3 so that the 
features and operations of each of these prior art mounting assemblies can 
be explained in greater detail as an aid to understanding the present 
invention. 
Referring first to FIG. 1, there is shown a tractor with a fifth wheel 
bracket mounting arrangement 5 generally mounted to tractor frame 6 and 
supporting trailer 7. Tractor frame 6 typically comprises a pair 
longitudinally extending C-shaped channel members 10 which are 
transversely spaced from each other and are supported by the suspension, 
wheel, and axle assemblies 8. The spacing between channels is not 
standardized in the trucking industry, therefore, tractor frame channel 
members 10 typically can be spaced apart from each other anywhere from 
31.5 inches to 36.0 inches, the distance being measured from the outboard 
terminal edges of the individual channel members. 
Referring now to FIG. 2, a drop-over angle bracket mounting arrangement is 
illustrated in which an L-shaped section of angle 24 is literally 
"dropped" over or onto each of the C-shaped channels 10 and then bolted to 
the vertical web 16 of channel 10 through the series of horizontal bolts 
32. As seen, drop over bracket 24 consists of vertical leg 26 extending 
longitudinally along a length of vertical web 16, and horizontal leg 30 
resting on top horizontal flange 18 such that inside surface 29 
communicates with outside horizontal top flange surface 17. Horizontal leg 
30 is substantially co-extensive with top horizontal flange 18 of channel 
member 10, while vertical leg 26 extends down vertical web 16. An arcuate 
mounting bracket 50 is welded to the drop-over bracket horizontal leg 
outside surface 31 for securing the tractor frame to the fifth wheel 100. 
Bracket 50 is secured to fifth wheel 100 by pivotally mounting it to a 
pair of diametrically opposed fifth wheel clevises or flanges 104 and 
104A, that downwardly extend from the lower surface 102 of fifth wheel 
100. Each flange 104,104A has a respective flange port 110 and 110A, which 
is in horizontal alignment with respect to each other as well as with 
arcuate mounting bracket apertures 52,54. Referring to FIG. 2A, it is seen 
that arcuate mounting bracket 50 is interposed between the fifth wheel 
flanges 104 and 104A, and that cross pin 108 passes through the flange 
ports and bracket apertures to pivotally secure the fifth wheel to the 
mounting bracket. The cross pin 108 accepts a heavy duty clip (not show) 
on the pin shank to prevent the pin from pulling out during operation. 
For the purposes of this discussion, it is important to understand that 
with the drop-over bracket assembly 24, the arcuate mounting bracket 50 
can be interchanged for use with a single flanged fifth wheel, as shown in 
FIG. 3. In that illustration, it is seen that a recess 90 extends across 
diametrically opposed locations on the base of the fifth wheel, each 
recess terminating at a respective single, inboard flange 104. When the 
fifth wheel is assembled to the arcuate mounting bracket, the top surface 
49 of bracket 50 is in articulated connection with corresponding fifth 
wheel surface 98 such that each flange 104 is pivotally connected to the 
mounting bracket by passing cross pin 108 through respective flange ports 
110 and bracket apertures 52,54. The peripheral lip 51 on the outboard 
edge of each mounting bracket 50 retains the fifth wheel against movement 
in the lateral direction. 
With either type of mounting bracket 50, the inboard and outboard position 
of arcuate bracket 50 respective to top horizontal flange 18 will depend 
upon the spacing between the tractor channel members 10 since all fifth 
wheels are not manufactured to an industry standard between flange ports 
110,112. For example, if a narrow tractor frame is utilized, the mounting 
bracket 50 will be positioned more directly above vertical web 16 and 
closer to outboard terminal edge 23. Likewise, bracket 50 will be closer 
to inboard terminal edge 21 if a wider channel spacing is utilized. 
Upon inspection of FIG. 3, a prior art fifth wheel flat mounting plate 
assembly is shown in conjunction with the single flanged fifth wheel 
previously mentioned, although the dual flanged bracket can also be used. 
With this design, a planar, rectangular mounting plate 60, having upper 
surface 62 and lower surface 64, transverses each of the tractor channel 
members 10 and rests upon each of the channel member top horizontal flange 
surfaces 17. As seen, mounting plate 60 also extends slightly beyond each 
of the frame vertical webs 16 and this overhang or extension functions to 
distribute forces into the channel members, as will be explained shortly. 
Lower surface 64 is indirectly secured to each channel member 10 through 
use of an outboard angle member 80. The outboard angle member 80 is 
identical for each channel member and is comprised of a horizontal leg 82 
which provides a planar and co-extensive support surface 83 for the 
over-hang of flat mounting plate 60. As illustrated, plate 60 is fastened 
to angle member horizontal leg 82, as by bolts 86, and as seen from the 
cutaway, horizontal leg 82 has slotted bolt holes 68 in order to 
accommodate varying tractor frame spacings. Vertical leg 84 is similarly 
fastened to channel member vertical web 16 by bolts 32. Arcuate mounting 
bracket 50 is attached to top surface 62 preferably by welding and is 
longitudinally centered on flat plate 60. As previously explained with the 
drop-over mounting arrangement, arcuate bracket 50 is either pivotally 
connected to a single or dual flanged fifth wheel and further detail will 
not be necessary. 
In road operation, it has been discovered that each of the prior art 
mounting arrangements are well suited for specific loading applications 
unique to their type of design. In the drop-over arrangement shown in FIG. 
2, it is known that drop-over brackets 24 best provide resistance to 
longitudinal and coupling loads. These loading forces tend to act upon the 
mounting brackets in the longitudinal direction along the length of the 
tractor channels, either during the coupling operation or during 
acceleration and deceleration over the road hauling. This is best 
understood by referring to FIG. 4, where it is seen that any longitudinal 
loading "L.sub.z ", acting along the channel and on arcuate bracket 56, 
will be directly resisted by each of the mounting bolts 32. Although each 
bolt is exposed to shearing forces, the series of bolts distribute the 
forces into vertical web 16 for excellent force distribution into channel 
10. The drop-over bracket arrangement also offers resistance to vertical 
loading "V" since the forces pushing either up or down on the mounting 
bracket 50 are typically transferred from the bracket down into vertical 
web 16. It should be understood that vertical loads will not be 
transferred directly downward into the vertical member 16 if the wider 
tractor frame spacing is used since the bracket will be located more 
towards the inboard terminal edge 21 of top horizontal flange 18. In that 
case, the series of bolts 32 will experience shear and bending loading. 
However, it has been found that drop-over brackets 24 can potentially 
develop fatigue cracks on the vertical leg 26, usually in the area just 
above or in between the bolt holes from lateral or lateral over-turn 
loads. Lateral loads "L" are those which transversely push against the 
arcuate mounting bracket before they are transferred into channel member 
10. Lateral over-turn loads "L.sub.o " are those forces which also 
transversely work against mounting bracket 50 but at a fixed vertical 
distance from the trailer frame channel members 10. As seen from FIG. 4, 
lateral loads "L" transversely act against the bracket creating bending 
moments which are a distance d from the series of mounting bolts 32. The 
bending moments are equally resisted by each of the bolts 32. When the 
distance "d" is increased an incremental amount "d'" above the bracket, as 
with lateral overturn loads "L.sub.o ", the bending moments are likewise 
increased. In either case, the drop-over bracket will begin to flex in the 
area just above or between the bolts 32, thereby causing flexure stresses 
that can lead to fatigue cracking. 
The planar or flat mounting plate assembly 60, shown in FIGS. 3 and 5, 
offers increased strength to lateral and lateral over-turn loads because 
the forces acting upon arcuate mounting bracket 50 are more effectively 
distributed throughout a larger surface area before they are transmitted 
into the support angle members 80 and each individual mounting bolt 32. By 
distributing the forces from the mounting bracket into the surface area of 
the plate, the magnitude of stresses acting upon the outboard angle member 
is greatly reduced. However, flat mounting plate assembly has the 
disadvantage of making assembly to the tractor frame more time consuming 
and costly since it is much larger and heavier than the drop-over bracket 
assemblies. 
In accordance with the present invention, the advantages of each of the 
prior art mounting arrangements have been uniquely incorporated into a 
lightweight, unitary device, seen in FIG. 6. However, before proceeding 
with a detailed description of that device, it is necessary to explain 
that the present invention has been designed with the parameters that the 
fifth wheel 100 is designed for handling a 70,000 lbs static vertical 
load, and a 200,000 lbs trailing load. This means that 35,000 lbs of load 
will be present at each arcuate mounting bracket 150. Furthermore, the 
length of unitary member 120 has been set at 36 inches. This particular 
length is the most common length used in the industry although mounting 
structure lengths for other mounting bracket assemblies have been known to 
be as long as 52 inches. Only under very exact and specific circumstances 
has the mounting structure length ever been below 36 inches. In addition, 
the thickness of all plate and angle members is 3/8 inches thick, which is 
the recommended thickness for use with a 70,000 lb fifth wheel as stated 
in the Maintenance Practices Manual of the Truck Maintenance Council; this 
is not an actual standard. It is known to those in the field that fifth 
wheels with ratings of 40,000 lbs and 100,000 lbs are also commonly used. 
Accordingly, dimensional parameters of the plate thicknesses and mounting 
structure lengths can vary according to the fifth wheel load ratings. 
In the preferred embodiment of the fifth wheel mounting bracket assembly of 
the present invention, shown in FIG. 6, it is seen that the mounting 
assembly generally includes a unitary mounting member 120 having a forward 
end section 122, a rearward end section 124, and a midsection 126, each 
section integrally connected together. An arcuate mounting bracket 150 is 
preferably integrally formed as part of the midsection, although it can be 
a separate component later welded to the midsection. It should be 
understood that the present invention is not limited to only the single 
flange arcuate mounting bracket 150 illustrated in FIG. 6; it can also 
utilize the dual flanged arcuate bracket 150' shown in FIG. 7. The 
preferred embodiment is cast as a single, unitary member so that the 
assembly will not require any fabrication time and attention, thereby 
saving manufacturing costs, although mounting member 120 and 120' can be 
fabricated without sacrificing performance. 
As FIG. 6 illustrates, the forward and rearward ends 122,124 are formed as 
drop over brackets 140,142, while the midsection 126 consists of a 
horizontally disposed planar mounting plate 160 interposed between and 
integral with each of said forward and rearward drop-over brackets 
140,142. An outboard support angle member 180 is simultaneously attached 
to the underside 164 of planar section 160 and to vertical web 16, thereby 
providing a transfer mechanism for stresses acting upon section 160 to 
reach channel member 10. 
The unitary member 120 is secured to each of the channel members 10 by 
first slipping or dropping the forward and rearward ends 122,124 over the 
top horizontal flange 18. Bolt holes 131 in each end must align with 
predrilled holes in channel member 10 so that bolts 132 can be inserted 
therethrough. Appropriate nuts and lock washers are used with bolts 132 to 
draw member 120 tight against channel 10. If predrilled holes in the 
vertical leg 16 are not provided, the holes can be drilled after unitary 
member 120 is positioned over channel 10. When this is completed, it is 
seen that arcuate mounting bracket 150 lies generally above top horizontal 
flange 18. The bolt holes 185 in angle member 180 can be predrilled or 
marked for drilling once top surface 162 of plate 160 is leveled. Bolts 
132 are also used to secure midsection 126 to vertical web 16. Slotted 
bolt holes 168 in the horizontal leg 182 are used to align angle support 
member 180 with the bolt holes 163 in the flat plate section 160. Bolts 
186 are used to loosely hold the support member to unitary member 120 
until bolt holes 185 on vertical leg 184 can be aligned with corresponding 
holes in the channel member. Once bolts 132 are inserted in holes 185 and 
plate 160 is leveled. bolts 186 and bolts 132 can be fully tightened in 
order to secure midsection 126 to channel 10. The drop-over brackets 
140,142 and the flat plate 160 can be predrilled before assembly is 
started. 
With the unitary members 120 thus anchored to channel member 10, and 
brackets 150 so aligned, bending and twisting of the tractor frame is 
minimized by assuring that any vertical loads imposed thereon are 
maintained in close proximity to, or directly over vertical web 16 of 
channel 10. Keeping the loads as close to the channel vertical web and 
distributing them through the large surface area of the vertical web 
contributes to the strength and reliability of the mounting system by 
minimizing bending moments. Similarly, the affects of the bending moments 
lateral and lateral over-turn loads are also minimized by assuring that 
any such bending moments imposed thereon are first distributed through the 
thick, arcuate mounting bracket 150, then along the bracket's extended 
base, into fiat plate 160, where the entire support angle member 180 
receives the same bending moments. Since plate 160 has a substantial 
longitudinal extent, the bending moments are well distributed into the 
entire support angle vertical leg 184, bolts 185, and vertical web 16. 
Test results shown in the table below indicate that substantial stress 
reductions can be achieved with the present invention, especially in the 
lateral and vertical loading directions. In those respective directions, 
it is seen that stresses were reduced by about 92 and 65 percent, 
respectfully. Even the longitudinal stresses were reduced by about 20%. 
However, it is important to understand that these results are only 
applicable to a fifth wheel rated for a 70,000 lb load and where the 
mounting assembly is 36 inches long, and which utilizes 3/8 inch thick 
plate and angles. As mentioned, varying plate and angle thicknesses, and 
mounting assembly lengths are common, therefore, stress reductions other 
than as provided will vary accordingly. 
______________________________________ 
STRESS (KSI) 
LOAD/BRKT(KIPS) DOA STRESS DECREASE 
______________________________________ 
1. Longitudinal (31.5) 
36 20% 
2. Vertical (35) 
36 65% 
3. Lateral (12) 26.4 92% 
______________________________________ 
A second embodiment of the present invention is shown in FIG. 7. It is seen 
that the location of the drop-over bracket and the flat plate areas have 
been rearranged when compared to the preferred embodiment, although the 
respective surface areas of the drop-over brackets and the fiat plate 
areas have not been changed. As illustrated, instead of the forward and 
rearward ends 122',124' consisting of drop-over brackets, as with the 
preferred embodiment, they have been provided with flat plates 160'. As 
mentioned, it is preferable that, the summation of the individual areas of 
each flat plate 160' be equal to the area of plate 160 in the preferred 
embodiment. In this way, the second embodiment will resist lateral and 
lateral overturn forces as effectively as with the preferred embodiment. 
However, it should be understood that the individual areas of each flat 
plate 160' can be of non-equal area if it is necessary for one or both of 
the individual plates to clear appurtenances attached to the tractor. 
Minor changes in the total area will not affect the performance or the end 
results. 
In a similar fashion, instead of the midsection 126' being constructed as a 
flat plate section, it has been constructed as a single drop-over bracket 
124'. The single drop-over bracket 124' is preferably equal in 
longitudinal extent to the longitudinal extent of both of the individual 
drop-over brackets 140,142 in the preferred embodiment of FIG. 6. Because 
the surface areas of the flat plate and drop-over bracket assemblies from 
the preferred embodiment have been preserved in the second embodiment, it 
can be said that unitary, member 120' functions equivalently to unitary 
member 120 of the preferred embodiment with respect to reducing 
longitudinal, vertical, lateral and lateral overturn loads. 
In addition, it should be clear that in both embodiments, an inboard 
overhang 155 can laterally extend beyond inboard channel terminal edge 21 
in a continuous fashion along the entire longitudinal length of unitary 
mounting assembly 120 or 120'. This is best seen from viewing FIG. 8 where 
it is seen that unitary overhang 155 allows an additional anchoring device 
350 to be added to the fifth wheel mounting system, if desired. As 
illustrated, anchoring device 350 is a generally L-shaped structure that 
preferably is of one piece construction or it can consist of plate 
sections 351,353, welded together. Plate 351 is equal in thickness to 
channel horizontal leg 18 and has a horizontal extent equal to overhang 
155. Plate 353 is at least the same thickness as plate 351, although it is 
preferable to be twice as thick in order to provide for throughbore 354. 
Bolt 200 and nut 205 are used to secure the overhang 155 of member 120 or 
120' to anchoring device 350. Anchoring device 350 provides additional 
bending resistance to the inboard side of unitary member 120 or 120' to 
that already provided by each of the outboard support angle members 180 or 
180'. Anchoring device 350 can also be either two separate members at each 
end of the unitary member or it can be one unitary piece extending the 
entire longitudinal span or length of unitary member 120 or 120'. Of 
course, if anchoring device 350 extended the entire longitudinal length of 
member 120', more bolts would have to be used for securing the assembly to 
overhang 155. 
The foregoing description has been provided to clearly define and 
completely describe the present invention. Various modifications may be 
made without departing from the scope and spirit of the invention, which 
is defined in the following claims.