Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: CROSS SHAFT FOR SEMTI'RAILER LANDING GEAR
FIELD OF THE INVENTION
This invention pertains to landing gears for highway transport trailers.
More particularly, this invention pertains to a cross shaft extending between
the legs of the landing gear under a semitrailer.
BACKGROUND OF THE INVENTION
A semitrailer is not always parked on even ground, and therefore the loads
carried by the two legs of a landing gear are not always equal, and the two
legs of the landing gear are not always extending in a perfect parallel
alignment. Also, when a loaded trailer is raised on its landing gear, the leg
on the far side of the crank lags behind the leg on the near side because of
the torsional deflection in the cross shaft. It is believed that this
torsional
deflection in the cross shaft together with uneven parking surfaces
contribute to cause an unbalance in the loads carried by the two legs of a
landing gear and a deflection in the frame supporting the landing gear to
the trailer.
It is believed that when the legs of a landing gear do not extend in a perfect
parallel alignment, an axial tension or a compression stress is generated in
the cross shaft, causing gear friction inside the telescoping mechanisms of
the legs. In these cases, a larger than normal torque is required to raise or
to lower the telescopic legs of the landing gear. It is believed that these
large torques have been the major cause of failure of cross shafts on
landing gears.
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Another contributing factor to explain the failures of cross shafts on the
landing gears of semitrailers is believe to be directly related to the
handling
of trailers. Generally, a highway trailer belongs to a pool of trailers, and
is
often hauled by several trucks during a same week. A trailer is normally
dropped off by one truck at a depot, for unloading and reloading, and
picked up later by another truck for delivery to a new destination. A trailer
is also often hauled along one segment of a delivery route by one truck and
along a next segment by another truck.
The fifth wheels of tractor trucks are not all at the same height, and it is
common for a truck operator to try to hitch a trailer that sits too low for
the
fifth wheel of his/her truck. When the trailer fails to reach the fifth wheel,
the truck moves ahead causing the trailer to slide down on the rails of the
truck and to fall back on its landing gear. The leg on the crank side of the
landing gear is locked in place by the gearing system of the crank.
However, the leg on the far side of the crank, that is the passenger-side leg,
is held in place by the stiffness of the cross shaft. Again, if the ground is
uneven and higher under the passenger-side leg of the landing gear, the j erk
applied to this leg is transmitted directly to the cross shaft, often breaking
the cross shaft.
The cross shaft between the legs of a landing gear of the prior art is made
of a continuous cylindrical pipe, and therefore, one of the legs of the
landing gear must be removed to replace a broken cross shaft. The
replacement of a cross shaft represents substantial repair expenses, a loss
of revenue for the truck operator, a loss of productivity for the trailer and
a missed delivery schedule for the recipients of the goods contained in the
trailer.
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Examples of landing gears having continuous cylindrical cross shafts are
illustrated and described in the following documents:
US Patent 2,232,187 issued to F.M. Reid on Feb. 18, 1942;
US Patent 2,885,220 issued to T.B. Dalton on May 5, 1959;
US Patent 3,201,086 issued to T.B. Dalton on Aug. 17, 1965;
US Patent 3,518,890 issued to B. Eastman on July 7, 1970;
US Patent 3,596,877 issued to B. Eastman on Aug. 3, 1971;
US Patent 3,632,086 issued to E. Mai on Jan. 4, 1972;
US Patent 3,861,648 issued to J.J. Glassmeyer on Jan. 21, 1975;
US Patent 3,880,403 issued to J.J. Glassmeyer on Apr. 29, 1975;
US Patent 4,004,830 issued to J.T. Belke on Jan. 25, 1977;
US Patent 4,205,824 issued to E. Mai on June 3, 1980;
US Patent 4,402,526 issued to L.C. Huetsch on Sep. 6, 1983;
US Patent 5,538,225 issued to E. VanDenberg on Jul. 23, 1996.
Because of all the expenses and inconveniences associated to the
replacement of a broken cross shaft, it is believed that a need exists for a
cross shaft for a landing gear that can resist uneven and shock loads and
that can be installed quickly without having to remove one leg of the
landing gear.
SUMIVIARY OF THE INVENTION
In the present invention, however, there is provided a landing gear having
a telescopic cross shaft with at least four loose-fit joints therein whereby
axial and bending stresses on the cross shaft are substantially reduced. The
telescopic cross shaft is made of square hollow tubing and the engagement
thereof over the cylindrical stub shafts of the landing gear produces voids
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within the tubes and excessive material around the perimeter of the tube to
better absorb torsional stresses.
More particularly, the present invention pertains to a landing gear having
a telescopic cross shaft extending between the cylindrical stub shafts
protruding from both screw jacks of the landing gear. The telescopic cross
shaft is made of a pair of hollow square end-casing members and a hollow
square central-stem member. The end-casing members have a combined
length of less than a distance between the legs of the landing gear. The
end-casing members are slidably engaged over both ends of the central-
stem member with loose-fit connections. The end-casing members are also
respectively mounted over the cylindrical stub shafts of the landing gear
with loose-fit connections.
The square tubing has a cross-section perimeter that is much longer than
the circumference of the cylindrical stub shaft on which it is engaged. This
excess length represents excess material that is able to cave in and bundle
up for absorbing torsional stress without breaking the cross shaft. Also
because of this excess material, the shear stresses on the extreme fibres of
the tubing are substantially reduced as compared to the stress on a tight-fit
hollow cylindrical tube.
This brief summary has been provided so that the nature of the invention
may be understood quickly. A more complete understanding of the
invention can be obtained by reference to the following detailed description
of the preferred embodiments thereof in connection with the attached
drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Several drawings are included to illustrate the structure of a prior art
landing gear so that one can obtain a better appreciation of the novelty and
inventiveness of the cross shaft according to the present invention. The
drawings also illustrate four embodiments of the cross shaft according to
the present invention, in which like numerals denote like parts throughout
the several views. In the accompanying drawings;
FIG.1 is a front view of a landing gear of the prior art;
FIG. 2 is a cutaway front view of both legs in a landing gear of the prior
art;
FIG. 3 is a schematic illustration of the bending of the cross shaft when the
legs of a landing gear of the prior art rest on an uneven ground;
FIGS. 4 and 5 are schematic illustrations of the bending of the cross shaft
when the legs of a landing gear of the prior art are diverting from
each other, and converging toward each other, respectively;
FIG. 6 is a cross-section view through the cross shaft on a landing gear of
the prior art;
FIGS. 7, 8 and 9 are partial side views of one end of the cross shaft on a
landing gear of the prior art, showing various stages during a typical
failure of this cross shaft;
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FIGS. 10, 11, 12 and 13 are side views of telescopic cross shafts according
to the first, second, third and fourth preferred embodiments of the
present invention, respectively;
FIG. 14 is a cross-section view through an end of the telescopic cross shaft
according to the first preferred embodiment of the present invention,
and through a typical stub shaft of a landing gear;
FIGS. 15 and 16 are cross-section views through an end of the telescopic
cross shaft according to the first preferred embodiment after having
been subjected to excessive bending and torsional stresses
respectively;
FIG. 17 is a partial top view of an end of the telescopic cross shaft
according to the first preferred embodiment that has been subjected
to excessive torsional stresses;
FIG. 18 is a cross-section view through an end of the telescopic cross
shaft as seen along line 18-18 in FIG. 17;
FIG. 19 is a front view of a semitrailer landing gear having a cross shaft
according to the first preferred embodiment of the present invention
mounted thereto.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
While this invention is susceptible of embodiments in many different
forms, there are shown in the drawings and will be described in details
herein four specific embodiments, with the understanding that the present
disclosure is to be considered as examples of the principles of the invention
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and is not intended to limit the invention to the embodiments illustrated and
described.
Referring firstly to FIGS. 1 and 2, a semitrailer landing gear comprises a
pair of telescopic legs that are referred to herein as the driver side leg 20
and the passenger side leg 22. These legs are fastened to the frame 24 of
the semitrailer 26 and may be retained to each other by cross braces 28.
Although only certain types of highway trailers have narrow frame rails as
illustrated by label 24, this example is used herein for convenience. It will
be appreciated that the other types of trailers also have deflection in the
mounting structure of a landing gear, and therefore the following
description also applies to these other trailers.
Each of the legs 20,22 extends and retracts by means of a screw jack 30 on
which is mounted a crown gear 32. The crown gear 32 is driven by a
pinion gear 34 mounted on a transverse shaft 36. The transverse shaft 36
on the driver side leg 20 is integrated into a gear box 38 which is driven by
a crank 40. The transverse shafts 36 have respective portions thereof
extending toward each other outside the respective legs 20, 22. These
shaft portions are referred to herein as the stub shafts 42. In a landing gear
of the prior art, both stub shafts 42 are joined to each other by a continuous
hollow cylindrical cross shaft 44.
It will be appreciated that the frame 24 of a semitrailer is relatively
flexible
but resilient to accommodate the curves and crowns of roads. This frame
24 is flexible to accommodate any driving surface irregularities without
breaking. Therefore, it will also be appreciated that when the legs of a
landing gear do not rest on an even ground surface, the frame 24 of the
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semitrailer twist slightly, and the cross shaft 44 of the landing gear is
subjected to bending stresses which cause it to deform and take a shape as
illustrated in an exaggerated mode in FIG. 3.
When the cross braces 28 on a landing gear are loose or broken, the legs
20, 22 of the landing gear can sometime divert away from each other or
converge toward each other slightly, causing the cross shaft 44 to flex as
shown in exaggerated modes in FIGS. 4 and 5.
In all three cases shown in FIGS. 3, 4 and 5, an axial tension or
compression force is applied to the cross shaft in addition to a bending
moment. In the situations illustrated in FIGS. 3 and 4, an axial tension
force is set in the cross shaft 44. This axial tension force is transmitted to
the pinion gears 34, causing the pinion gear 34 in the driver side leg 20 to
climb onto or otherwisejam against the crown gear 32 on the screwjack 30
of that leg 20. In the situation illustrated in FIG. 5, an axial compression
force is set in the cross shaft 44. This axial compression force is
transmitted to the pinion gears 34, causing the pinion gear 34 on the
passenger side leg 22 to climb onto or otherwisejam against the crown gear
32 on the screw jack 30 of that leg 22. In both cases, a excessive friction
is generated between one of the pinions 34 and its respective crown gear
32, thereby increasing the torque required to operate one of the screw jacks
30.
Referring now to FIGS. 6-9, the inherent drawback with the cross shafts
44 of the landing gears of the prior art will be explained. The cross shafts
44 of the prior art are made of cylindrical tubes, as illustrated in FIG. 6.
The inside diameter of the tube 44 is substantially a same dimension as the
outside diameter of the stub shaft 42. The cross shaft 44 is locked to the
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stub shaft 42 by a bolt 50 passing through the cross shaft 44 and the stub
shaft 42. When a torque 'T' is applied to the cross shaft 44, the stress on
the cross shaft is substantially tangential to the surface of the cross shaft
44
as illustrated by arrow 'S' in FIG. 6. In other words, the torsion stress on
the cross shaft 44 is translated into a tension and shear stress in the
extreme
fibres of the material of the cross shaft. The extreme fibres referred to
herein are those fibres located farthest from the axis of rotation of the
shaft.
In a typical new landing gear, both ends of the cross shaft 44 have a pair of
aligning slots 52 for receiving the bolts 50, for mounting the cross shaft to
the stub shafts 42. In the after market cross shafts, only one pair of slots
52
are provided on one end of the cross shaft, as the installer must cut the
cross shaft and drill a hole at the appropriate location in the other end.
Therefore it is often the case where the bolt 50 extends close to the end of
the slot 52 as illustrated on FIG. 7, because the cross shaft 44 was cut too
short, because of deformation in the landing gear, because of contraction
of the cross shaft in cold weather, or because of previous deformation in
the cross shaft, beyond the yield strength thereof.
It has been observed that because the cross shaft 44 has a same inside
diameter as the outside diameter of the stub shaft 42, bending stresses 'M'
in the cross shaft 44 cause bulges 54 to appear along the side thereof.
These bending stresses 'M' also cause funnel-like deformations 56 to
appear along the open end thereof. It has also been observed that because
the bolt 50 extends through a slot 52, an excessive torque on the cross shaft
44 causes the slots to stretch out transversely, substantially as shown by the
stress point 58 in FIG. 8.
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It will be appreciated that the weak point in the cross shaft 44 of the prior
art in the case of a combined torsion stress 'T', bending stress 'M' and
axial tension or compression force 'P' is within the segment 60 between the
end of the slot 52 and the open end of the cross shaft 44.
Most failures of cross shafts that were observed, have a break that was
initiated at this segment 60, as illustrated in FIG. 9, indicating excessive
axial and circumferential stresses in that segment 60.
Referring now to FIG. 10, the telescopic cross shaft 70 according to the
first preferred embodiment of the present invention is illustrated therein.
The first preferred telescopic cross shaft 70 is made of hollow structural
steel (HSS) or other metal having a structural grade known as ASTM A-
500 or equivalent.
The cross shaft 70 is made of three pieces. A first end-casing member 72
has inside dimensions to enclose the stub shaft 42 on one leg of the landing
gear. A second end-casing member 74 has inside dimensions to enclose the
stub shaft 42 on the opposite leg of the landing gear. A central-stem
member 76 has dimension to slide freely inside the first and second end-
casing members 72,74. The first end-casing member 72 extends about half
the length or less of the full length of the cross shaft 70. The second end-
casing member 74 extends about 4 to 6 inches. The central-stem member
76 spans between and extends inside the first and second end-casing
members 72, 74. The central-stem member 76 extends into the first end-
casing member 72 over a distance of about 6-12 inches or more.
The first and second end-casing members 72, 74 are preferably made of
HSS having an outside dimension of 1-1/4 inches by a wall thickness of
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0.100 inch. The central-stem member 76 preferably has an outside
dimension of 1.00 inch with a wall thickness of 0.125 inch.
It will be appreciated that the clearance between the first end-casing
member 72 or the second end-casing member 74 and the central-stem
member 76 is about 0.050 inch. This clearance provides a very loose
sliding fit between the central-stem member 76 and the first and second
end-casing members 72, 74. The central-stem member 76 is retained to the
second end-casing member 74 by means of a single bolt 78 extending
through both the second end-casing member 74 and the central-stem
member 76. The preferred cross shaft 70 is also affixed to both stub shafts
42 by means of bolts 50 as explained before.
The landing gear on which the preferred cross shaft 70 is installed has
cylindrical stub shafts 42 each having a diameter of 1.00 inch and a
protruding length of between about 2 to 3 inches and sometimes much
more. Therefore, the loose sliding fit mentioned above is also found in the
mounting of the cross shaft 70 to both stub shafts 42.
The advantages of the telescopic cross shaft 70 according to the first
preferred embodiment of the present invention include that fact that axial
stress therein is completely eliminated. The telescopic arrangement of the
cross shaft 70 is also advantageous for eliminating the need for a slot in the
first or second end-casing member 72, 74 to receive a mounting bolt 50.
Further, the preferred cross shaft 70 is easily and quickly installed in
replacement of a broken shaft 44 of the prior art without removing one of
the legs of the landing gear.
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The loose fit of the preferred cross shaft 70 over both stub shafts 42 and
within the mounting of its central-stem member 76 to the first and second
end-casing members 72, 74 provide flexibility to absorb a substantial
misalignment of the stub shafts 42, without causing any bending stress on
the cross shaft 70 itself. These and other advantages will be better
explained by making references to FIGS. 14-18. For convenience, the 1-
1/4 inch HSS of the first and second casing members 72, 74 are also
referred to herein as the square tubes 80.
As mentioned before the square tubes 80 are mounted to the cylindrical
stub shafts 42 with a loose mounting fit, as illustrated in FIG. 14. When
a bending force 'M' is applied to the cross shaft 70 in a similar manner as
illustrated in FIGS. 7 and 8, the wall of the square tube 80 is easily flexed
outwardly as indicated by the deformation 82 in FIG. 15 to absorb this
bending force. Because of the excess material in the square tube 80, voids
84 are created between the stub shaft 42 and the walls of the square tube
80. These voids 84 are advantageous for absorbing torsion stresses in the
cross shaft 70 as it will be explained below.
Referring particularly to FIGS. 16-18, it has been found that an excessive
torsion stress in the cross shaft 70 according to the first preferred
embodiment causes the walls of the square tube 80 under the bolt head 86
and under the nut 88 of the bolt 50 to cave in and bundle up around the
mounting hole 90. Because of this type of deformation, it has been found
that an excessive torsion force on the cross shaft 70 causes the
circumferential stresses 'C' to be directed inwardly relative to the extreme
fibres 92 of the square tube 80. It has been found that the force on the
square tube 80 is concentrated in a sector 94 around the bolt hole 90. It has
further been found that the region 94 of stress concentration is at a distance
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'A' of about 1/4 inch from the extreme fibres 92 of the square tube 80,
thereby preventing shearing the wall of the square tube 80.
It has been found also that during such deformation of the square tube 80
the voids 84 between the stub shaft 42 and the square tube 80 are reduced
in size. It is believed that because of the excess material and the voids 84
in the square tube 80, the square tube can absorb more bending and
torsional stresses than a cylindrical tube of a same inside diameter and wall
thickness.
The cross shaft 70 according to the first preferred embodiment of the
present invention has been tested thoroughly and used successfully in the
same installations where cylindrical tubes 44 failed repeatedly.
Referring now to FIG. 19, a landing gear is shown with the two legs
thereof resting on an uneven ground surface 100, with the passenger side
leg 22 being higher than the driver side leg 20 by a substantial distance 'B'.
As explained herein before, the first preferred cross shaft 70 has a
telescoping arrangement to eliminate any axial force on the stub shafts 42
and to prevent jamming the pinion gears 34 against the crown gears 32 of
the screw jacks 30. The first preferred cross shaft 70 has four loose-fit
engagements 102 therein to absorb and eliminate any bending stress
thereon from the uneven ground surface 100. The first preferred cross shaft
70 is made of square tubing having excess material and voids therein
around the stub shafts 42 to better absorb torsion loads thereon, and to
reduce or eliminate any shear stresses on its extreme fibres.
Referring back to FIGS. 11, 12 and 13, the cross shafts according to the
second, third and fourth preferred embodiments 110,112 will be described.
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The cross shaft 110 according to the second preferred embodiment is made
of two end-stem sections 120,122 extending inside a central-casing section
124. The end-stem sections are made of 1-1/4 inch square HSS tubing, and
the central-casing section 124 is made of 1-1 /2 inch square HS S tubing.
All three sections have a wall thickness of 0.100 inch.
The cross shaft 112 according to the third preferred embodiment has two
end-casing sections 130,132 that are made of 1-1/4 inch square HSS tubing
having a wall thickness of 0.100 inch, and a central-stem section 134
telescopically mounted inside the end-casing sections 130, 132. The
central-stem section 132 is made of 1 inch square HSS having a wall
thickness of 0.125 inch.
In use, the central-stem section 134 is kept centred inside the end-casing
sections 130, 132 by means of a pair of compression springs 136 fastened
respectively to the ends of the central-stem section 134 and extending
inside the end-casing sections 130, 132 against the stub shafts 42 of the
screw jacks 30. This particular embodiment of the present invention
further has an optional central band 138 affixed to the central-stem section
134 to limit the movement of the central-stem section 134 inside the end-
casing sections 130, 132 in the event where the cross shaft 112 would be
inadvertently installed without one or both springs 136.
The cross shaft according to the fourth preferred embodiment 114
comprises a pair of coupling members 140, 142 which are permanently
affixed to the stub shafts 42 by bolts for example. The telescoping portion
of the cross shaft has a stem member 144 slidably mounted in one end of
a casing member 146 and extending into the first coupling member 140.
A stem extension 148 is affixed to the other end of the casing member 146
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by a bolt 150 for example, and extends into the second coupling member
142. A spring 152 is mounted inside the casing member 146 between the
stem member 144 and the stem extension 148 for maintaining the stem
member 144 and the stem extension 148 apart from each other and into
their respective engagement with the coupling members 140, 142. It will
be appreciated that the telescopic cross shaft of the fourth preferred
embodiment 114 has six loose-fit connections 102 therein to better absorb
misalignments between the stub shafts 42. The fourth preferred telescopic
cross shaft 114 is made with the same materials as for the cross shaft of the
first preferred embodiment 70.
As to other manner of usage and operation of the present invention, the
same should be apparent from the above description and accompanying
drawings, and accordingly further discussion relative to the manner of
usage and operation of the invention would be considered repetitious and
is not provided.
While four embodiments of the present invention have been illustrated and
described herein above, it will be appreciated by those skilled in the art
that
various modifications, alternate constructions and equivalents may be
employed without departing from the true spirit and scope of the invention.
For example, although the cross shaft according to the preferred
embodiments were illustrated and described as square tubes, it is believed
that other hollow polygonal structural members such as hexagonal
members would also provide advantageous results. Therefore, the above
description and the illustrations should not be construed as limiting the
scope of the invention which is defmed by the appended claims.
