Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to king pins for use in
tractor trailer fifth wheel couplings and more particularly
to a king pin designed to obviate dangerous mis~coupling of
tractor trailers.
A well known widely used fifth wheel coupling comprises
an axially movable spring loaded plunger at the closed end
o~ a slot in the usual fifth wheel plate. The plunger has
an enlarged head on one side of which is a rack engaging a
gear sector integral with a jaw pivoted at one side Or the
slot. In normal operation the operator backs the tractor
until the king pin enters the slot and engages the plunger
head moving it forwardly against the loading of its spring.
'L'his causes the rack on the plunger head to drive the sector
on the jaw to swing the latter across the slot and in so doing
it triggers a bolt clear of a cletent cbstruction in a slot in
an operating lever permittlng a spring to slide ~he bolt
behind the jaw and lock it i-n its closed positionO
The king pin i~self has a first upper cylindrical
portion) an intermediate cylindrical portion of reduced
diameter and a lower cylindrical portion which defines a flange.
When the jaw is in its closed position it defines with the
plunger head a vertical opening whose upper cylindrical portion
is recessed to substantially closely encompass the upper
portion of the pin and a lower cylindrical portion of reduced
diameter to substantially closely encompass the intermedia~e
portion o the pin, with the flange of the pin being disposed
beneath the cooperating plunger head and closed jaw to prevent
vertical separation of the pin from the fifth wheel plate.
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In accordance with the 1982 standariz2d specification
for fifth wheel king pinsg (SAE J700b in the 1982 SAE Handbook,
page 37.19) the upper cylindrical portion of the king pin is
speciEied as having a diameter of 2.875 + 0.005 in.; the
intermediate por-tion having a diarneter of 2.000 ~ 0.005 in~
and the lower portion or flange as having a diameter of
2.8125 + 0.015 in., which is to say that the diameter of the
flange is less than the diameter of the upper portion o-f the
pin.
With a coupling arrangement as described above,
sho~lld the trailer landing wheels be inadvertently extended
too Ear so that the lower ~lange, rather than the upper part
oE tlle k:Lng pin, is allgned with the upper recessed end of
~he plunger head, when ~he tractor is backed up the Elange
engages the upper end of the plunger head causing it to
operate in a normal fashion inclu~ing closing of the jaw and
the triggering of the bolt into locking position behind the
jaw. Unless an operator looks very carefully at the coupling,
he will no~ notice that instead of the king pin flange being
beneath the opening defined by the plunger head and closed
jaw it ls actually seated within the recess at the upper end
of ~he openîng and is free to separate vertically from the
fifth wheel plat~ whenever road conditions dictate. Usually
the connection is sufficiently secure ~hat the driver can
safely enter traffic at an initial slow speed and, if the
road is smooth, he ~an accelerate safely to highway speed,
but the moment the road becomes rough there need be only
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slight relative vertica~ movement between the tractor and
trailer to enable the pin flange to jump out of the shallow
recess whereupon the out of-control trailer can careen into
traffic flow resulti~g in almost certain severe bodily injury.
Inspection of the coupling following such an accident reveals
nothing extraordinary except that the pin apparently vertically
separated from the fifth wheel plate without damage to either
the pin or coupling mechanism1 it not heretofore having been
realized ~hat the actual problem was as is described above,
that is, the elevated pin flange caused the jaw to close and
lockg not around the pin9 but beneath it.
The SAR standard Eor king pins has been unchallged
since at least January 1940, (see page 788 9 1960 SAE Handbook)
but the statistics on the number of accidents that may have
been caused by the above descr:ibed fault are unknown, it only
having been recently determined as a result of litigation that
such accidents can and have occurred.
It is the broad object of the present invention to
so construct a king pin of a trailer that the foregoing type
of accident cannot occur.
More specifically, it is an object of the invention
to prevent such accidents by so constructing the king pin that
even i it should be unduly elevated and able to effect closing
and locking of the jaw beneath the pin9 nevertheless the
king pin stlll cannot be partially engaged ~y the closed
jaw and thus as a result that as soon as a dr.iver moves the
tractor, the king pin drops clear of the fifth wheel and
cannot be dragged to the open road in the mistaken belief that
the king pin i5 correctly coupled to the fifth wheel~
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More specifically it is an object of the invention
to achieve the Eoregoing object by making the king pin flange
predeterminedly larger in diameter than the upper cylindrical
part of the king pin so that ei~her the flange of the king pin
canno~ enter the recess in the closed jaw and plunger head
should they have been moved sufficiently so that they close
beneath the flange (as might happen if the lower edge of
the flange merely brushed the upper edge of the plunger head)
or because of the relative vertical location of the flange,
the jaw is simply unable to close sufficiently around the
:Elange to trigger the bolt, and, thus as soon as the driver
moves the trackor, the Eront end of the -~railer, having no
attachment with the tractor, drops to the groundO
StiLl another object of the invention is to provide
a king pin with an enlarged flange wherein the pin cannot
enter the slot in -the plate unless the flange is disposed
in its proper place beneath the slot.
Other objects and their attendant advantages will
become apparent as the Eollowing detailed description is
read in conjunction with the accompanying drawings wherein:
Fig. 1 is a vertical cross sectional view of a
prior art king pin whose flange instead o being in the
illustrated normal p~antom line position is seaked in the
recess at the upper end of the opening defined by the closed
plunger head and jaw;
Fig~ 2 is an underneath plan view of the prior art
arrangement of Fig. l;
Fig. 3 shows a king pin constructed in accordance
with the present invention whose flange is seated over tha
recess defined by the closed plunger head and jaw of Figs.
l and 2;
F;g. 4 is a plan view similar to Fig. 2 except
showing the plunger and locking jaw engaging the flange of
a pin construc-ted in accordance with the invention and being
thereby prevented from closing;
Fig. 5 is a schematic side elevational view showing
a modification of the king pin of the invention;
Fig. 6 is a top plan view oE the arrangement of
Fig. 5;
Fig. 7 is an enlarged vertical cross sectional view
of the arrangement of Fig. 6 showing in full lines ~he
location oE the pin when initially disposecl iII its proper
place and in phantom lines its position when initially
positioned above its proper place;
Fig. 8 is a vertical cross sectional view of a
king pin constructed in accordance with the invention and a
modified fifth wheel plate ~aken substantially on the line
8-8 of Fig. 7; and
E'ig~ 9 is a plan view on a reduced scale of the
modified plate of Fig. 8.
Referring now to the drawings~ Figs. 1 and 2
illustrate a well known and widely used tractor trailer
coupling, the essential Eeatures of which appear in the patent
to Harris No, 1,981,233 which issued November 20, 1934. The
coupling comprises a fifth wheel plate 10 rockingly mounted
on a tractor ~y means of a transverse trunnion 12 as seen in
Fig. 5. The plate has a throat 14 having converging side
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edges leading to a slot 16 at the closed end of which is a
plunger 18 axially urged by a spring 20 towards the open end
of the slot. The plunger 18 has an enlarged head 22 on one
side edge of which are rack teeth 24 which engage the teeth
of a sector gear 26 integral wi-th a jaw 28 plvotally mownted
on a pin 30 to one side of the slot 16, the arrangement being
such that when the plunger spring is fully expanded and there
is no king pin in the coupling, the jaw 28 is swung counter
clockwise to a position along side the slot 16. When the
tractor is backed up so that the trailer k;ng pin enters
the slot 16, it engages the enlarged head 22 of the plunger
to drive it to the right in Fig. 2 against the force of the
spring. As the plunger head moves to the right, the rack teeth
drive the jaw clockwise in Fig. 2 across the slot 16 and
behind the king pin. As the jaw moves to its fully closed
pos-Ltion a corner 32 thereof engages the face of a retracted
bolt 34 which is releasably retained in i~s retracted position
by e;lgagement of a pin 35 thereon with one slde of a detent
projection 36 on the lower edge of slot 38 in a control lever
40 which is pivoted at 42 to the fifth wheel plate and provided
with a spring loaded operating rod 44 which may be pulled
against the force of its spring (not shown) to move the bolt
34 from its lock position of Fig. 2 to its jaw released
position of Fig. 4 where it is retained by engagement
of the bolt pin 35 with the opposite side of the detent
projection 35 until the bolt is again triggered by engagement
of the jaw therewith for movement into its locking position.
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When the jaw and enlarged pl~nger head 22 are in
their coupling position of Figs. 1 and 2, it will be observedg
particularly in Fig. 1, that they define a vertical opening
having an upp~r cylindrical recessed part 42 and a reduced
diame-~er lower cylindral part 440 The recessed upper part
42 of the opening is of a size which is intended to substantially
closely encompass the upper cylindrical part 45 of the con-
vential king pin ~8 shown in Fig. 1 having a second reduced
diame-ter, intermediate cylindrical part 50 which is intended
to be substan-tially closely encompassed by the lower part 44
oE the opening in the jaw and plunger head when they are in
closed position.
The king pin has a lower cylindrical third part 52
defining a flange whose diameter as specified in the SAE
hanclbook referred to above is slightly less than the diameter
of the upper cylindrical part 46. When the king pin is
properly positioned relative ko fi~th wheel plate 10, the
pin occupies the phantom line position of Fig. 1 with the
upper part 46 of the pin being seated in the upper recessed
part 42 of opening defined by the jaw and plunger head of
the coupling, with the central reduced diameter part 50 of
the pin being received in lower reduced diameter part 44 of
the opening with the pin flange 52 being located beneath
the opening to prevent vertical separation of the pin and
plate 10.
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As expLained above~ should the trailer landing
wheels be extended too far Eor -the particular tractor fith
wheel plate, it is possible for the pin flange 52 to lie in
the plane of the upper portion 42 of the coupling opening.
Under these conditions the flange would engage the plunger
head in the region of the recessed portion causing the plunger~
jaw and bolt to operate in a normal manner except that instead
of encompassing the entire pin~ only the flange 52 would be
encompassed by the upper recessed portion of the opening as
shown in full lines in Fig. 1. Under these conditions the
flange 52 would rest in the recess 42 and as the operator
clrives slowly awayJ the trailer would follow in an apparently
normal manner, It may not be until the tractor trailer
comblnation is on the highway at increased speed that, upon
encountering a bump, the king pin flange could jump out of
tlle recessed upper portion o~ the opening with conseque~nt
damage and possible serious injury to other motorists,
The present invention aims to prevent the above
described type of accident by so constructing the king pin
that regardless of the condition of the jaw and bolt, ~he
flange of the pin cannot be received in the recess at the
upper end of the opening defin~d by the plunger head and
jaw in clnsed position. In accordance with the invention
this is achieved by making the flange 52 2~ as seen in Fig. 3~
predeterminedly larger than the upper cylindrical part of the
pin and any part of the opening defined by the jaw and plunger
head in closed position such thatg should the ~lange be in
a critical plane just s~fficiently below the top of the
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opening to move the jaw and bolt to closed and locked position
beneath the Elange, the 1ange 52' is of a siæe whereby it
cannot seat within the recess. In addition to this 7 the
flange is made critically oversized so that even if i~ should
abut solidly against the recessed part of the plunger head,
-the jaw will still not be able to move to its fully closed,
bolt triggering position due to the obstruction presented
by the enlarged head as can be seen in Fig. 4.
It should be understood that the flange should not
just be slightly larger than ~he upper end of the opening
but it must be of a size to positively prevent the jaw from
moving to its Eully closed positionO
In Harris patent No. 1,9811233, referred to above,
or example, it is apparent that the king pin, as illustrated
ln Fig~ ~ is machined from a cylindrical member which provides
pa:ir of Elanges, one each at the upper and lower ends o the
pin, a Eirst upper por~ion oE diameter smaller than that of
the flanges for seating in -the recessed position of the
coupling opening, and a second lower portion of lesser diameter
than the Eirst upper portion for reception in the lower
reduced dîameter portion of the coupling opening. With such
an arrangement, the lower-most flange is incidently shown as
having a slightly greater diameter than the recess in the
opening defined by the closed jaw and plunger. However,
the problem which the present invention addresses was not
recognized at the time patent No. 1,981,233 issued nor for
decades thereafter (see SAE Handbooks~ ibid) and it should be
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apparent that the flange can be somewhat larger than the recess
and stil'L operate the jaw and plunger sufficiently to trigger
the bolt for movement into its locking position.
In the present invention, the diameter of the lower
flange is made predeterminedly larger than -the recess of the
opening that no matter how much farther the plunger may be
moved to the right (in Figo 4 of the present applica-tion, say,)
the jaw 28 can never move a sufficient distarce clockwise in
Fig. 4 to its fully closed and bolt triggering position of
Fig. 2. Thus when the pin flange is accidently positioned so
as to lie in the elevated plane of the recessed part of the
plunger heacl 22 and abuts the plunger head in this region, so
long as -~he plunger can move no further to khe right in Fig. 4,
for example beyond the stop provided by the plate rib 54,
as seen in Fig. 4 the jaw 28 cannot move fully across the slot
to trigger the, release of the bolt 34. When the jaw cannot
close at all, even a cursory investigation should reveal to
the operator that the king pin is not properly connected to
the fifth wheel plate, but even if the operator does not
observe this, the instant he drives off, the trailer front end
will drop to the ground. Though this may cause some property
damage to the trailer or its contents~ this would be insignificant
relative to the damage that would occur if the trailer were
to separate ~rom the tractor on the op~n road traveling at
highway speed.
It has been found that the critical oversized
diameter need not necessarily 'be larger than the transverse
width of the slot 16~ but it is within the purview of the
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invention to make the diameter of the lower pin flange sub-
stantially larger than the wiclth oE the slot as shown at 52"
in Figso 5-9.
In Figs. 5, 6 and 7 the diameter of the pin flange
is selected to coincide with the width of the throat at a
preselect~d position 56 outwardly of the slot 16 as shown in
Fig. 6. Thus if the pin is in the correct plane, as khe fifth
wheel plate is backed under the pin the plate is pivoted about
the trunnion 12 and the enlarged flange is permitted to enter
the throat 14 of the plate as it is tilted to a horizontal
position with continued backing of the tractor moving the slot
rclative to the pin until the plunger head ~2 is engaged by
the pin and the latter locked in towing position as described
above. Cn the other hand, should the trailer be initially
too high relative to the fifth wheel plate, the flange 52"
would engage the plate at a position inwardly or to the right
oE the position 56 in Figo 6 and as the plate tends to rnove
to its horizontal position, its upper surface to either side
of the throat and slot to the right oE the position 56 would
engage the underside of the flange as shown in Fig. 7 with
the result that it would be almost impossible for the operator
not to realize that the pin has no connection at all with the
fifth wheel plate except by the frictional engagement of the
flange surface with the plate. Should the operator nevertheless
fail to realize the true state o affairs 3 the ins~ant he
drives ofE, the trailer front end would drop to the ground.
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It may be desirable to provide depending side walls
58 at the entrance of the slo~ as sho~n in Figs. 8 and 9 to
posi~ively prevent the entrance of the pin into the slot
except when -the pin is properly positioned relative to the
fi~th wheel plateO Because the walls 58 must not interEere
with the swinging of the jaw 28 across the slot, the wall~
must have a length such that they are clear of the swinging
movement o~ the jaw. To ensure this, it may be necessary to
foreshorten the throat as shown at 14' in Fig. 9. An advantage
of this arrangement is that in every case where the king pin
is initially too high, except when it is grossly above the
plate upper surEace, the king pin is prevented from jamming
beneath the fifth wheel plate tending ko lift the rear end of
the tractor o~f the ground as it is backed towards the plate~
By preventing such action right at the beginning, the operator
is made immediately aware of the problem and can adjus~ the
tra-iler landing wheels to ensure that the pin will pass into
the slot with the flange properly positioned.
Though the invention has been described as used in
conjunc~ion with the well-known swinging jaw type of coupling,
it will be apparent that the invention is susceptible for use
with any type of fith wheel coupling of the type wherein some
form of coupling member swings from a slot-clear position to
enable a king pin to enter the slot to a position across ~he
slot where the coupling member is releasably locked in place.
No change would be required in the kin pin constructed as
described herein to prevent miscoupling or partial coupling
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regardless of the type of coupling actually used. The king pin
is, however, susceptible of modification and changes without
departing from the scope and spirit of the appended claims.
