Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3~
"DOLLY ~OR A SEMITRAILER"
BACKGROUN~ OF THE INVENTION
This invention relates to a dolly for a semi-
trailer particularly suitable for attachment to the rear of
a Eirst semitrailer so that a second semitrailer can be moved
by the same tractor unit. In recent years various appara-
tus have been proposed Eor increasing the payloacl towed by
a single tractor unit while keeping within legal restric-
tions on axle weights. Proposals have been made and carr-
ied into practice for towing one or more pup trailers be-
ind the main t,railer. Each pup trailer comprises a rear
axle and a front steerable axle coupled to a hitch for
attachment to the preceding trailer. Thus the pup trailer
follows the rear axle of the preceding trailer.
SUMMAR~ OF THE INVENTION
It is one o-bject of this invention to provide a
dolly for a semitrailer which can be used to attach a
second semitrailer to the rear of a first semitrailer tow-
ed by a single tractor unit.
Accordingly the invention provides a dolly for
a semitrailer comprising a coupling frame including a
first and a second hitch means lying on respective sides
of an axis central of the coupling frame for hitching the
coupling frame to a prime mover, a fifth wheel arrangement,
the vertical axis of which passes through the central axis,
mounted on the coupling frarne for receiving the king pin of
~ ! 9~
.,,~,
~ 2-
the semitraller, a plurality of road wheels, a support
frame mounted on the road wheels, means mounting the coupl-
ing frame on the support f-came for pivotal movement rela-
tive thereto about a vertical axis passing through the
central axis, centering means for biasing the support frame
relative to the coupling frame toward a central position
in which the road wheels lie parallel to the central axis
and means for controlling the centering means.
It is one advantage of the invention therefore
that a second semitrailer can be attached to the rear of
a first semitrailer by the dolly of the invention and tow-
ed in a safe secure manner.
It is a further advantage of the învention that
the self-steering effect of the dolly is properly control-
led so that the steering of the dolly properly follows the
movement of the trailer to which it is attached during
normal travel and also resistant to uncontrolled movements
or jack-knifing during braking, reversing or traveling
over rough terrain.
It is a yet further advantage of the present in-
vention that the dolly incorporates control means for the
self-steering which is simple, rugged and readily manually
adjustable.
With the foregoing in view, and other advantages
as will becorne apparent to those skilled in the art to which
this invention relates as this specification proceeds, the
~ ~ .
3...L~3~
-2A-
invention is herein describecl by reference to the accompany-
ing drawings forming a part hereof, which includes a de-
scription of the best mode known to the applicant and of the
preferred typical embodiment of the principles of the pre-
sent invention, in which:
~3~
--3--
DESCRIPTION OF THE l)RAWINGS
~ ___ _
Figure 1 is a schematic side elevation of a truck
including a tractor, semitrailer, the dolly of the inven-
tion and a further semitrailer.
Figure 2 is a side elevation of the dolly of
Figure 1.
Figure 3 is a section along the line 3-3 of
Figure 2.
Figure 4 is a plan view of the front end portions
of the side arms of the dolly showing the two hitches.
Figure 5 is a plan view of the rear portion of the
dolly showing the rotation locking device.
In the drawings like characters of reference in-
dicate corresponding parts of the different figures.
DETAILED DESCRIPTION
-
Referring firstly to Figure 1 the mode of use of
the dolly of the present invention is shown in schematic
form in a truck comprising a tractor unit 10, a convention-
al semitrailer 11, the dolly of the invention indicated
generally at 12 and a further conventional semitrailer 13.
The semitrailers 11 and 13 are supported at their forward
end on conventional fifth wheel arrangements indicated gen-
erally at 14, 15 and provided respectively on the tractor
unit 10 and on the dolly 12. As shown in more detail herein-
after, the dolly 12 is coupled to the rear of the semitrailer
11 by a twin hitch arrangement so that it follows the mo-
,~,
tion of the semitrailer 11 without pivoting movement about
a vertical axis at the coupling between the dolly and the
semitrailer 11. For this reason the road wheels of the dolly
12 are coupled to the frame of the dolly in such a way as
to allow steering rnovement of the wheels relative to the
frame as described in detail hereinafter.
Referring now to Figures 2 and 3, the dolly is
shown in detail and comprises a coupling Erame generally
indicated at 16 and a support frame generally indicated at
20. The coupling frame 16 comprises a pair of side arms 161,
162 formed of box section steel coupled by cross members
163 indicated in dotted line in Figures 2 similarly formed
of box section steel and lying at right angles to the side
arms so as to form a rigid structure lying generally in a
horizontal plane. Each of the side arms supports adjacent
its rear end a right angled flange 164, 165 which is rigid-
ly connected to the respective side arm and supports trun-
nions 166, 167 for receiving pivot pins 168 of a convention-
al fifth wheel arrangement 169 which is pivotal about a
horizontal axis lying across the dolly so as to receive and
support the forward end of a conventional semitrailer.
A liftable castor wheel 170 is mounted on the
side arm 161 in conventional manner to allow the dolly to
stand when not in use and to provide height adjustment so that
the dolly can be coupled when required to hitches for use.
The structure of the castor wheel, which is shown in
." l
~3~
Figure 2, is conventional and hence no description will be
made here.
At the forward end, each side arm 161, 162 car-
ries an end plate 171, 172 which is welded across the end
of the box section so as to close the box section and form
a rigid anchor thereto. A hitch device 173, 17~ is con-
nected to each of the end plates by suitable means such as
bolts or welding and each comprises a steel ring of rigid
structure integral with a coupling plate by which the ring
is coupled to the end 171, 172 so that the ring lies in a
horizontal plane. Such hitching rings are conventional and
are used to hitch the dolly at two spaced locations to a
prime mover which as shown in Figure 1 is the rear of the
forward semitrailer ll. I'he rings, as is well known, are
placed in a yoke 111 which has openings so that a pin can
pass through the yoke and through the opening in the ring
to provide a coupling which prevents pivotal movement about
a vertical axis but allows some movement of the frame 16
about a horizontal axis so as to accommodate any changes in
the road surfaces.
The support frame 20 comprises a rectangular
frame section 201 formed of side members and cross members
details of wnich are not shown and a top plate 202 thus
forming a rigid structure with an upper platform. The
frame section 201 is supported by conventional road springs
203, 20~ on an axle and road wheels generally indicated at
~ ~33
--6--
205. Mounted on top of the platform 202 of the support
Erame 20 is a conventional slewing ring assembly 19 which
in turn is coupled to the underside of the coupling frame
16. Thus the support frame 20 is coup]ed to the coupling
frame 16 by a bearing arrangement which allows the support
20 to pivot relative to the coupLing frame about a verti-
cal axis. Referring to Figure 3 it will be noted that the
apparatus is substantially symmetrical about a central axis
lying parallel to and between the side arms 161, 162 and
thus the pivot axis of the coupling between the coupling
frame and the support frame passes through the central axis
and also the pivot axis of the king pin of the semitrailer
mounted upon the fifth wheel similarly pivots about an axis
passing through the central axis. From Figure 2, however
~5 it will be noted that the axis of the axle of the road wheel
assembly 205 lies behind the pivot axis of the support
frame relative to the coupling frame thus when the vehicle
is moving forwardly producing a castoring action which will
act to maintain the road wheels parallel to the side arms
161, 162. However it will be appreciated that any tendency
for the coupling frame to move sideways as caused by turn-
ing of the prime mover to which the coupling frame is at-
tached will tend to cause the support frame and axle to
pivot to take up the turning movement and thus to steer
the wheels relative to the turning movement.
In order to assist the self-centering action of
--7--
the castor arrangement and to inhibit any wobbl.e whi.ch may
arise there is provided a self-centering device which acts
to bias the support frame to a positi.on wherein the road
wheels are parallel to the central axis. The self-center-
ing device is generally indicated at 18 and comprises a
cam 181 rigidly attached to the front of the support frame
20 and a cam follower 182 carried by the coupling frame 16.
the cam follower comprises a wheel 183 supported in a yoke
18~ carried upon a shaft 185 which is mounted for sliding
movement in a sleeve 192 supported by the cross members 163
of the frame 16 so as to allow displacement of the wheel
183 in a vertical direction. As shown more clearly in
Figure 3, the cam has a minimum displacement position at the
center corresponding to the position where the road wheels
lie parallel to the central axis with ramps on either side
of the central position so that as the support frame turns
relative to the coupling frame to turn the road wheels the
cam follower 182 is displaced vertically upwardly by the
ramps of the cam 181. Two plates 186 pass through a slot
in the shaft 185 to form arms extending either side of the
shaft. At the extremi.ty of each arm is coupled a respective
one of a pair of pistons 187, 188 of a pair of air cylinders
189, 190. The air cylinders act to apply biasing force to
the shaft 185 via the pistons 187, 188 thus tending to cen-
ter the cam 181 and return the road wheels to the parallel
position.
~ 3
-8-
Alr pressure to the cylinders 189, 190 is supplied
from the tractor unit 10 via a control device schematically
indicated in Figure 2 at 193. The control device 193 in-
cludes a lever 194 which controls a valve within the con-
trol device 193 (not shown) which acts to control the
level of air pressure supplied to the cylinders at 189, 190.
The lever 194 is specifically movable between two positions
which have adjustable preset pressure values, one of the
positions providing a first pressure within the cylinders
189, 190 which is suitable for use when the trailer carried
by the dolly is empty. The second position of the lever 194
provides a pressure which is suitable for use when the
trailer supported by the dolly is fully laden. The lever 194
is thus operable by the driver of the vehicle following load-
ing the trailer or unloading the trailer and before setting
off on the journey. Thus the amount of force applied when
the trailer is fully laden is substantially greater than the
force supplied when the trailer is empty. In this way the
degree of self-centering is compensated for the increased
frictional forces involved when a full load is applied to
the road wheel assembly. If desired the amount of control
over the pressure can be increased from the simple two posi-
tion switch to a more complex arrangement providing further
levels of control but this has not been found necessary in
practice and hence the most simple arrangement has been
provided for reducing the complexity to the operator while
1~.
_9_
maintaining the degree of self-centering within acceptable
bounds~
~ further control device for the self-centering
is shown at the rear of the dolly in Figure 2 and also in
S plan view in Figure 5. The cont-rol device comprises a
third air cylinder to 2]0, mounted upon an extension brac-
ket, extending from the frame 16 so that the air cylinder
210 sits within the frame without extending above the frame
to sufficient extent to interfere with the fifth wheel
arrangement 169. The air cylinders 210 includes a piston
211 carrying a pin 212 for cooperation with a plurality of
slots 213 carried in an arcuate member 214 supported upon
the support frame 20 at the rear thereof. The portion 214
is curved about the axis of the slewing ring 14 so that as
the support 20 moves relative to the coupling frame 16 the
slots 213 of the member 214 move around under the pin 212.
The cylinder 210 is attached via a further control device
schematically indicated at 215 to the braking system of the
truck. The control device 215 is arranged so that in normal
forward traveling, when the brakes of the truck are applied
to the wheels to slow or halt the vehicle, pressure is also
applied to the cylinder 210 thus moving the pin 212 verti-
cally downwardly to enter one of the slots 213. The pin
212 and the member 214 thus cooperate to lock the support
frame 20 against rotation movement relative to the coupl~
ing frame 16 so that the road wheel assembly is maintained
r ?
, ` ~
33~
-10-
in the orientation immediately prior to the application of
the brakes thus preventing ~macceptable wobbling and jack-
knifing of the dolly during brake application. The control
means 215 also includes a lever 216 which can be moved from
a first normal position described above wherein air pres-
sure is only applied during braking to a second position
in which air pressure is continually applied thus locking
the support frame 20 relative to the coupling frame 16.
The lever 216 is operable by the driver on leaving his cab
and is used for locking the dolly against rotation when re-
versing the vehicle or on other occasions, such as when go-
ing over rough terrain, when the driver considers it de-
sirable to do so.
It will be appreciated therefore that the steer-
ing function of the dolly is normally centered by the cas-
toring effect achieved by the off set of the relative a~es
of the axle and the slewing ring. The control of this cas-
toring effect is supplemented by the force from the self-
centering cam and cam follower arrangement 18 which in turn
can be controlled to apply two or more different forces de-
pending upon the load applied to the dolly or other criteria
at the discretion of the operator. Furthermore, the self-
centering aspect can be locked to cease its action during
braking of the vehicle or when otherwise necessary for
example during reversing. The dolly is therefore fully con-
trolled thus providing a means of supporting a further semi-
:" ~ .
3~
trailer in a safe and convenient manner.
Since vaious modi:Eications can be made in my in-
vention as hereinabove describecl, and many apparently wide-
ly dif:Eerent embodiments of same made withi.n the spirit and
scope of the claims without departing from such spirit and
scope, it is intended that all matter contained in the ac-
companying specification shall be interpreted as illustra-
tive only and not in a limiting sense.
