Note: Descriptions are shown in the official language in which they were submitted.
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POSITIVE LOCKING TRAILER TAIL
s This invention relates to a hydraulically operated tailgate for load
supporting beds of
transportation vehicles, and more particularly to a tailgate whose hydraulic
lift mechanism has the
effect of holding the tailgate positively locked in position when the tailgate
is in its raised position,
parallel and roughly planar to the main deck of the transport vehicle.
to
BACKGROUND OF THE INVENTION:
Many types of trailers have previously been manufactured for the
transportation of large
equipment over the road. The equipment is usually loaded onto the trailer from
the rearward end
is of the trailer and as such an improvement which had originally emerged in
the art is to provide
a loading ramp of some sort attached to the rear of the trailer. It is known
in the prior art to
provide swingably mounted tailgates on the rear of flat deck semi-trailers and
trucks, such that
the tailgate can selectively be operated and used as a loading and unloading
ramp for the trailer
vehicle. Some examples of tailgates which selectively form loading ramps by
means of folding
2o relative to a main section of the tailgate can be found in U.S. Patent
2,727,781 to D'Eath, U.S.
Patent 2,776,063 to Larson and U.S. Patent 2,797,960 to Endres et al. These
prior art tailgates
however are intended to be used by folding them into an upright position,
either perpendicular
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or in any event above the plane of the main portion of the truck trailer when
in the raised position.
This blocks the rear of the load carrying area of the vehicle and these types
of tailgates are not
readily used in a substantially level load carrying position.
There have also been contemplated in the prior art telescopically extensible
ramps for facilitating
the loading of vehicles, such as that disclosed in U.S. Patent 460,196 to
Chase and U.S. Patent
2,611,466 to Biggert et al. A telescopically extensible loading ramp however
is limited in utility
insofar as when it is in its retracted position the ramp cannot be used as a
portion of the load
carrying bed.
to
It has been contemplated in the prior art as well then, to provide swingably
movable sections of
the rear of a load carrying bed trailer, such that the swinging section can be
lowered to the
ground, thus forming a ramp to allow for the loading of the truck, and then
raised into a position
parallel and approximately planar to that of the main load carrying bed such
that the ramp itself
is in its raised position provides additional length on the trailer on which
the load can be distributed
or carried. An example of a trailer with a hinged ramp tail is disclosed in
U.S. Patent 5,215,426
to Bills, Jr.
Hydraulic power actuation of the raising and lowering of the ramp section of
the trailer is known
2o in the art. A hydraulic fluid pressure cylinder has in the past been used
to lift the ramp section
of such a trailer by pushing out/extending the piston rod of the cylinder to
raise the ramp section,
such hydraulic cylinder operating either individually, or along with some type
of linkage
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mechanism used to decrease the angle from which the hydraulic cylinder needs
to operate in order
to lift the ramp section. A push hydraulic would be used to elevate such a
ramp section, and then
by releasing the hydraulic cylinder the weight of the ramp would cause the
piston rod to retract
inside the hydraulic cylinder and lower the ramp section into its loading
position. The problem
with hydraulic mechanisms such as this used to raise and lower such a trailer
ramp to and from
a planar load-bearing position is that the piston rod is extended into its
extended position to raise
the ramp to its upper position and hold it there. The piston rod of the
hydraulic cylinder then
ends up bearing a great deal of weight transferred thereto through whatever
type of linkage
mechanism is used, and the rod can be weakened or bent by the combination of
such weight and
to additional shocks created by road conditions as the trailer is moved.
One solution to attempt to relieve the considerable strain on the extended
piston rod of the
hydraulic cylinder holding the ramp section in its raised position has been to
add a mechanical
locking device which can be locked into place to firmly anchor the ramp
section in position once
is it is raised. For example, U.S. Patent 4,305,694 to Chan, wherein the
hydraulic actuating
mechanism displacing the ramp extension simultaneously mechanically locks the
tailgate to the
frame of the semi-trailer vehicle. However, in that case the hydraulic piston
which is used to
actuate the mechanical lock is in its extended position when the lock is
engaged, and as such there
is the potential that mechanical forces could be communicated back to that
piston rod again. As
2o well, this very concept of a separately actuated lock requires additional
equipment to be added
to the trailer, increasing the cost and complexity of manufacture and
maintenance.
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Another method of hydraulically raising and lowering the ramp section of the
trailer is disclosed
by Bills Jr. The Bills, Jr. apparatus is operated by the hydraulic shifting of
the rear axle of the
trailer, moving that axle back and forth beneath the hinged section of the
trailer tail. It is the
purpose of that invention as claimed to allow for the redistribution of the
weight carned on the
trailer by the positioning of the rear axle at varying spacings behind the
first axle on the trailer.
The ramp is lowered into the loading position by retracting the rear axle all
the way into its
position right behind the front axle of the trailer. The ramp lowers, the
trailer is loaded, and the
rear axle is pushed back into a position somewhere beneath the ramp portion of
the trailer for
transport of the load. In the case of this trailer, however, the unloaded
weight of the trailer itself
to is high, due to the additional steel structure which is used to slide the
rear axle of the trailer back
and forth. In addition, the number of moving parts in the actuating mechanism
and accompanying
superstructure make the trailer harder to manufacture, and more difficult and
more costly to
maintain.
is Hydraulic actuation of load-bearing ramp tails is preferred to manual or
other methods of raising
and lowering such trailer ramps. The load bearing aspect of the ramp tail is
important as it
increases the available length of the trailer to haul longer or larger pieces
of equipment, as
compared to those trailers with telescoping ramps or ramps which fold into an
upright position.
The problem which the present invention seeks to overcome is the load strains
placed on the
2o hydraulic mechanisms used in the prior art.
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SUMMARY OF THE INVENTION:
It is the object of the present invention to provide a trailer with a ramp
tail with an improved
hydraulic lifting mechanism to move the ramp tail between its upper and lower
positions.
It is a further object of the present invention to provide an apparatus in
which the hydraulic
cylinders used to raise and lower the ramp tail are in their stronger
retracted position while the
ramp tail is in its load carrying upper position.
to It is the further object of the present invention that this hydraulically
actuated ramp tail be held
positively locked in its raised planar position by the lifting linkage itself,
rather than by additional
mechanical pins or the like such as has been contemplated in the prior art.
It is the further object of the present invention that in order to hold the
raised ramp in positively
is locked position with minimal stress on the hydraulic mechanism including
the hydraulic cylinders
used therein, the hydraulic cylinders be in their retracted positions when the
ramp is in its raised
position and the linkages between the trailer, the ramp and the hydraulic
cylinders be such that
a maximum of the load-bearing downward forces exerted on the ramp under load
be
communicated from the ramp into the trailer frame, and a minimum of such
forces exerted on the
2o hydraulic cylinders used to raise and lower the ramp.
The invention accomplishes these obj ects comprising substantially a frame,
having rearward and
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forward ends, with attachment means on the forward end of the frame for
connecting the trailer
to a prime mover; one or more ground-engaging axle assemblies attached to the
frame; a ramp
tail having rearward and forward ends, the forward end of the ramp tail being
hingedly connected
to the rearward end of the frame such that the ramp tail is selectively
moveable between an upper
position wherein the ramp tail is approximately horizontal, and a lower
position wherein the ramp
tail is inclined downward and rearward towards the ground; two or more bending
linkages, each
said bending linkage comprising two linkage arms pivotally joined together in
a linkage joint, each
said bending linkage pivotally attached at one end to the trailer at a trailer
attachment point
between the ground and the point of attachment of the ramp tail to the frame
and at the other end
to to the ramp tail at a ramp tail attachment point and wherein the distance
between the trailer
attachment point and the ramp tail attachment point when the ramp tail is in
its upper position is
the ramp hypotenuse and said bending linkages when in alignment are longer
than the ramp
hypotenuse; one or more hydraulic cylinders attached such as to exert force on
the linkage joints
so as to bend said bending linkages, oriented such that by retracting the
hydraulic cylinders the
is ramp tail is raised to its upper position and an over-centre lock is
created by the bending linkages,
and by extending the hydraulic cylinders the ramp tail is moved to its lower
position, said ramp
tail first raising slightly above the horizontal as the linkage arms come into
alignment and the
over-centre lock is overcome.
2o The over center lock is acheived by the bending linkages and linkage arms
being of dimensions
such that the linkages themselves in their 'straight' or 'aligned' position
are longer than the ramp
hypotenuse. The ramp tail is raised by retracting the hydraulic cylinders, and
lowered by
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extending them.
A linkage cross brace could be added joining the linkage joints, while still
allowing the linkage
joints to bend, so that the movement of the linkages was mirrored.
One or more hydraulic cylinders could also be used. In embodiments employing
more than one
hydraulic cylinder, the cylinders could be controlled in tandem to further
stabilize and strengthen
the operation of the device. The hydraulic cylinders could be pivotally
attached at their one end
to the ramp tail and at their free end to the linkage joints, or in the case
of an embodiment with
to more than one linkage and a linkage cross brace, the hydraulic cylinders
could be attached at their
free end to the linkage cross brace. Offset hydraulic attachment flanges could
also be added, to
allow for the pivotal attachment of the hydraulic cylinders to the bending
linkages at a point offset
below the alignment axis of the bending linkage.
is One or more axles might be used on the trailer.
DESCRIPTION OF THE DRAWINGS:
2o While the invention is claimed in the concluding portions hereof, preferred
embodiments are
provided in the accompanying detailed description which may be best understood
in conjunction
with the accompanying diagrams where like parts in each of the several
diagrams are labeled with
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like numbers, and where:
Figure 1 is a side view of the present invention, showing the ramp tail in its
upper
position;
s
Figure 2 is a top view of the frame and structural elements of the invention;
Figure 3 is a close-up side view of the ramp tail in its lower position;
to Figure 4 is a close-up side view of the ramp tail in its upper position;
and
Figure 5 is a top view of the mechanical means of the invention, used to raise
and lower
the ramp tail.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
The present invention is a flat deck trailer with a hinged ramp tail, the
hinged ramp tail being
raised and lowered via a bending linkage that provides an over-center locked
position when the
2o ramp tail is in its raised transport position.
Turning first to Figure 1, which shows the general profile of the preferred
embodiment. The
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present invention involves a hydraulically actuated ramp tail 1 attached to
the rearward end of a
trailer 2, said trailer 2 having a flat trailer deck 3 for the loading and
hauling of heavy equipment
and the like. Located in position on the underside of the goose neck portion 6
of the trailer is a
hitch pin 4 for attachment to a standard fifth wheel power unit.
To turn to Figure 2, and the structural characteristics of the trailer 2. The
trailer 2 consists of two
main frame members 7, which in this case display toward their forward ends 8 a
jog which forms
the common goose neck feature displayed in the drawings and as illustrated in
Figure 1. Attached
across the forward ends 8 of the frame members is the trailer front beam 10,
which forms the
to front edge of the trailer 2. Similarly attached across the rearward ends 9
of the frame members
is the trailer end beam 13. Attached to the frame members 7 in positions
between the trailer deck
supports 11 and underneath the trailer deck surface 12 are one or more axle
assemblies 17 with
suspension, wheels, tires and brakes to be in contact with the ground surface
and to carry the
trailer and load.
Extending downward from the trailer end beam 13 is the rear face plate 14.
Across the bottom
edge of the rear face plate 14 is welded the rear face cross member 15, which
in the preferred
embodiment is square steel tubing. Welded back from the rear face cross member
15 to the
bottom face of each trailer frame member 7 is a rear cross member brace 16,
for additional
2o support. The trailer end beam 13, the rear face plate 14, the rear face
cross member 15 and the
rear cross member brace 16 form a solidly reinforced trailer attachment
surface, to which the
ramp tail 1 can be hingably secured and the mechanical means for raising and
lowering the ramp
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tail 1 can be operatively attached. It will be understood that the invention
could be practiced on
trailers of other basic construction without departing from the intent of the
present invention and
as such the details of the trailer offered here should not be interpreted in a
limiting, but rather in
a specifically illustrative, sense. The essential basics of the trailer itself
is that it have a frame,
s attachment means and one or more ground-engaging axle assemblies.
The ramp tail itself is similarly constructed to the remainder of the trailer,
having two ramp tail
frame members 19 to which are attached a ramp tail front beam 23 and the ramp
tail end beam
25. Again the particular construction of the ramp, insofar as it does not
affect the operation of
to the bending linkages and hydraulic cylinders, is non-essential to the
invention and it will again be
understood that modifications thereto would not depart from the scope and
intent of the claimed
invention.
The ramp tail 1 is hingably attached to the trailer 2 such that the ramp tail
1 is selectively
is moveable between upper and lower positions, said ramp tail 1 being
substantially horizontal and
roughly co-planar to the trailer deck 3 when in its first said upper position
and inclined
downwardly and rearwardly with respect to the trailer deck 3 when in its
second said lower
position. In this case the ramp tail 1 is connected to the trailer end beam 13
at the ramp trailer
attachment point 26 with a commonly known pin hinging mechanism.
Bending linkages are used to join the trailer and the ramp tail and raise and
lower the ramp tail.
Each bending linkage consists of a first linkage arm 30 and a second linkage
arm 31, which in the
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present embodiment are equal in length, pivotally joined at a linkage joint
34. Each said bending
linkage is pivotally attached at one end to the trailer at a trailer
attachment point between the
ground and the point of attachment of the ramp tail to the frame and at the
other end to the ramp
tail at a ramp tail attachment point and wherein the distance between the
trailer attachment point
and the ramp tail attachment point when the ramp tail is in its upper position
is the ramp
hypotenuse RH and said bending linkages when in alignment are longer than the
ramp hypotenuse
RH.
The size of the bending linkages, namely that the bending linkage when the two
linkage arms 30,
l0 31 are straight and in alignment is larger than the ramp hypotenuse RH,
provides for a positive
over-centre lock of the bending linkages when the ramp tail is in its upper
transport position. The
bending of the bending linkages in the opposite direction then results in the
linkage arms 30, 31
coming into alignment and then overcoming the over-centre lock to lower the
ramp tail to the
ground, after first raising it slightly above the horizontal as the bending
linkages are first aligned.
is This is best illustrated in Figures 3 and 4. The only point at which the
joined first and second
linkage arms 30, 31 can reach their fully aligned straight span, which for the
purpose of this
disclosure will be referred to at that point as the center line, is above the
horizontal position of
the ramp tail 1 as that is shifted between positions. When the ramp tail 1 is
in its lower position
the first and second linkage arms 30, 31 are below center line, and when the
ramp tail 1 is in its
zo upper position the first and second linkage arms 30, 31 are slightly above
center, creating the
over-center lock.
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The present embodiment shows two bending linkages, although it will be
understood that any
number of bending linkages could be used, depending on the strength of
manufacture of each
bending linkage and on the specification and load to which the trailer and
ramp tail are to be put.
In this case the first linkage arm 30 and second linkage arm 31 are
manufactured out of hollow
structural steel tube.
One or more hydraulic cylinders are used to exert force on the linkage joints
so as to bend the
bending linkages, oriented such that by retracting the hydraulic cylinders the
ramp tail is raised
to its upper position and an over-centre lock is created by the bending
linkages, and by extending
to the hydraulic cylinders the ramp tail is moved to its lower position, said
ramp tail first raising
slightly above the horizontal as the Linkage arms come into alignment and the
over-centre lock
is overcome. The hydraulic cylinders could be attached directly to the linkage
joints in a pivotal
manner, or could be attached elsewhere in such a manner as to move the bending
linkages via the
linkage joints.
is
A linkage cross brace is also shown in this embodiment. 'The linkage cross
brace 35 is used to
hingably join the first linkage arm 30 and second linkage arm 31 of each of
the number of bending
linkages, with each bending linkage attached to the linkage cross brace 35 in
its appropriate
position for use. In this case, the two bending linkages are attached at
opposite ends of the
20 linkage cross brace 35. The first linkage arm 30 and second linkage arm 31
are joined through
their respective linkage juncture holes 34 by the linkage cross brace 35,
which is round and fits
snugly through the linkage attachment holes 34. In this manner, with all of
the bending linkages
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joined by the linkage cross brace 35, movement initiated in relation to the
linkage cross brace 35
will move each pair of linkage arms 30, 31 simultaneously and in the exact
same path and manner.
The first linkage arm 30 and second linkage arm 31 are placed onto the linkage
cross brace 35
side by side, as is shown in Figure 5. It will be understood, however, that
the first linkage arm
30 and second linkage arm 31 of each bending linkage could be spaced apart
from each other
along the linkage cross brace 35, with the positioning of the linkage trailer
attachment flanges 36
and the linkage ramp attachment flanges 38 adjusted accordingly, and that
would be contemplated
to within the scope of the present invention.
Also attached to the linkage cross brace 35 are one or more linkage cylinder
attachment flanges
40, one flange for each hydraulic cylinder 44 used in the mechanical means. In
the case of the
present embodiment, two hydraulic cylinders are used and therefore two linkage
cylinder
is attachment flanges 40 are used as well. In this case each linkage cylinder
attachment flange 40
has a round linkage flange hole 41. The linkage cylinder attachment flanges 40
are attached to
the linkage cross brace 35 spaced between the attached first and second
linkage arms 30, 31. The
linkage cylinder attachment flange 40 is manufactured and attached to the
linkage cross brace 3 5
such that the linkage flange hole 41 is below the first linkage arm 30. This
positioning of the
20 linkage cylinder attachment flange 40 and linkage flange hole 41 is shown
in Figures 3 and 4. By
offsetting the linkage attachment flanges below the center line of the bending
linkage when in its
aligned position, the behavior of the bending linkages can be further
improved.
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Attached along the inside surface of the ramp tail front beam 23 in
corresponding positions to the
linkage cylinder attachment flanges 40, such that the hydraulic cylinders 44
can be installed
between them and in parallel to each other, are the ramp cylinder attachment
flanges 42. Each
ramp cylinder attachment flange 42 has a round ramp cylinder hole 43. There is
to be one ramp
cylinder attachment flange 42 installed for each hydraulic cylinder 44 to be
used, so again in the
present embodiment two ramp cylinder attachment flanges 42 are used.
Attached to the trailer attachment surface along its bottom edge, and
specifically attached to the
rear face cross member 15, is one linkage trailer attachment flange 36 for
each first linkage arm
l0 30 used in the mechanical means - in the case of the present embodiment,
two. The linkage trailer
attachment flanges 36 are attached to the rear face cross member 15 at
positions to be joined the
first linkage arms 30. Each linkage trailer attachment flange 36 actually
consists of two flanges
extending outward from the trailer attachment surface, each having a round
trailer flange hole 37.
These two flanges are spaced apart by the thickness of the first linkage arm
30, the trailer flange
is holes 37 being in alignment and at the end of the flange 36 some distance
away from the trailer
attachment surface.
Attached along the front face of the ramp tail center beam 24 are a similax
number of linkage
ramp attachment flanges 38, attached in positions to be joined the second
linkage arms 31. Each
20 linkage ramp attachment flange 38 actually consists of two flanges
extending outward and
forward from the ramp tail center beam 24, each having a round ramp flange
hole 39. These two
flanges are spaced apart by the thickness of the second linkage arm 31, the
ramp flange holes 39
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being in alignment and at the end of the flange some distance away from the
ramp tail center beam
24.
It will be understood that the use of flanges or other means of pivotal
attachment of the hydraulic
cylinders to the trailer and the linkage joints or linkage cross brace, as
well as the attachment of
the bending linkages to the ramp tail or the trailer, could be varied to use
different attachment
methods without departing from the intent of the present invention and as such
are contemplated
within the scope of the present invention.
to Standard hydraulic cylinders would be used. It will be understood that
various attachment means
could be provided on the ends of the hydraulic cylinders and that such
attachment means and
necessary modification to the attachment of the cylinders to the device are
contemplated within
the scope of this invention. It will also be understood that other extensible
means other than
hydraulic cylinders could be used.
is
Where more than one hydraulic cylinder is used they can be linked in tandem so
that they all
operate identically.
The bending linkages and hydraulic cylinders are mounted in place to
operatively interconnect the
2o ramp tail 1 with the trailer 2 as follows. Each of the first linkage arms
30 is attached to the
corresponding linkage trailer attachment flange 36 by the use of a pin or the
like placed through
the trailer flange hole 37 on one side, through the first linkage attachment
hole 32, and out the
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trailer flange hole 37 on the other side. Each first linkage arm 30 would be
similarly attached to
the trailer attachment surface in this manner. Each of the second linkage arms
31 is attached to
the corresponding linkage ramp attachment flange 38 by the use of a pin or the
like placed
through the ramp flange hole 39 on one side, through the second linkage
attachment hole 33, and
s out the ramp flange hole 39 on the other side. Each second linkage arm 31
would be attached
to the ramp tail center beam 24 in this manner. The hydraulic cylinders 44
would then be installed
similarly in position, with pins or the like, with the hydraulic cylinder
attachment end 46 attached
to the ramp cylinder attachment flange 42 through the ramp cylinder hole 43
and the flange holes
on the hydraulic cylinder attachment end 46. T'he flange holes on the piston
rod attachment end
l0 47 would be attached to the linkage flange hole 41 on the corresponding
linkage cylinder
attachment flange 40, again with a pin or the like. With the attachments
having been made at
these four operative points, the actuating mechanism for the raising and
lowering the ramp tail
1 is ready to operate.
is The hydraulic cylinders are operated by pressurized fluid from a suitable
source under control of
suitable control valves (not shown) all of which is generally well known in
the art.
One of the major problems experienced in the prior art was that of the
hydraulic cylinders used
to actuate such a ramp tail being in their extended position and the piston
rods therefore subj ected
2o to extreme loads and stress while the ramp tail was in its raised position,
while the hydraulic
cylinder would be in its stronger retracted position while the ramp tail was
lowered to the ground
and no strain was placed on or support was required from the hydraulic
cylinder. The present
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invention reverses this - the hydraulic cylinders are extended to their full
stroke when the ramp
tail 1 is in its lower position, and are fully retracted when the ramp tail 1
is in its raised position.
This causes less stress on the hydraulic cylinders while the trailer 2 is
under load.
With the attachment point of the hydraulic cylinders 44 to the linkage cross
brace 35 being below
the first linkage arm 30, the downward force of the loaded ramp tail
communicated onto the
hydraulic cylinder is minimized, with the remainder traveling through the
first linkage arm 30 and
being communicated into the trailer 2 and its stronger frame and suspension.
In addition, with
the hydraulic cylinder 44 in its retracted position any force that is
communicated through the
to hydraulic cylinder 44 is easily handled without strain by the cylinder
which is in its strongest
position when retracted.
To lower the ramp tail 1 to the ground the hydraulic cylinders 44 are
extended, which in turn
through movement of the linkage cross brace 35 moves the joined first and
second linkage arms
is 30, 31 down below their center line and the attached ramp tail 1 is lowered
to the ground. When
operated to raise the ramp tail 1, the piston rods of the hydraulic cylinders
44 are pulled in, thus
moving the linkage cross brace 35 and the linkage arms 30, 31 back up past the
center line and
into the above described locked position.
zo While the current embodiment speaks of a hitch pin 4 being used on the
lower surface of the
gooseneck to attach the trailer 2 to a power unit, it will be understood and
is contemplated within
the scope of this invention that modifications could be made to the front end
of the trailer
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including the use of a different hook up apparatus or the like to adapt the
trailer for use with a
different power unit, without altering the substance of the invention claimed.
The trailer of the illustrated embodiment has two ground-engaging axle
assemblies.
s
While the invention in this embodiment comprises a trailer of common goose
neck variety, it will
be understood that a foreseeable variation would be to use a conventional
flatbed trailer
configuration without a gooseneck configuration and that this is contemplated
within the scope
of the invention - that is to say the trailer 1 being of constant sufficient
height from front to rear
to to allow for the proper placement of the hitch pin or other power
attachment method. This would
result in a higher trailer which would merely mean that the ramp tail would
come down at a
steeper angle in its lower position, or could be lengthened to provide a
lengthier loading slope.
Thus it can be seen that the invention accomplishes at least all of its stated
objectives. Since
is various modifications can be made in my invention as herein above
described, and many
apparently widely different embodiments of same made within the spirit and
scope of the claims
without departing from such spirit and scope, it is intended that all matter
contained in the
accompanying specification shall be interpreted as illustrative only and not
in a limiting sense.
