Note: Descriptions are shown in the official language in which they were submitted.
S3~7
SELF-STEERING CONVERTER DOLLY
Field of the Invention
This invention is concerned with i~provements in and
relating to transport converter dollies of the kind employed for
releasable tandem connection of a rearward vehicle to a forward
vehicle.
Review of the Prior Art
The tandem connection together of two vehicles,
particularly a tractor/trailer combination and a second trailer,
is of continuing commercial interest, owing to the cost savings
that are possible, and accordingly there have been a substantial
number of prior proposals disclosing different equipment for
this purpose. Despite the number of such proposals that have
been made relatively few such tandem rigs are in use at this
time. A fundamental problem has been the apparent need hitherto
to accept either a certain amount of instability in the tandem
connection, or else a considerable amount of tire wear with the
forward wheels of the rearward vehicle. Thus, it is found that
if the dolly is rigidly connected to the frame of the forward
trailer, so as to form in effect an extension thereof, the rear
trailer being mounted on the dolly by a fifth wheel, then high
tire wear is obtained. If the dolly is connected to the forward
trailer so as to pivot about a vertical axis the tire wear is
reduced, but the presence of two closely-spaced vertical pivots
between the two trailers in~roduces an undesirable ins~ability
that has been known to result in the vehicles overturning or
jackknifing.
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A self-steerirlg dolly that addresses this problem is
described and claimed in our prior Canadian Patent Serial No.
1,108,203, issued 1st September 1981 to Auto Steering Trailers
Limited, comprising a dolly frame that is releasably but rigidly
connected to the frame of the forward vehicle by which the dolly
and the rearward vehicle are to be towed. A fifth wheel
connection mounted on the dolly frame releasably receives the
front end of the rearward vehicle, and the dolly runs on a pair
of road wheels mounted by respective stub axles with link means
connecting the stub axles for steering movement about their
respective axes under the effect of sideways-directed forces
applied to ~he road wheels by movement of the forward vehicle as
it is steered away from a straight line. Centering means are
connected between the link means and the dolly frame and urge
the road wheels to a centered straight ahead attitude.
Definition of the Invention
It is therefore an object of the invention to provide a
new transport converter dolly for releasable tandem connection
of two vehicles.
It is a more specific object to provide such a dolly
which will provide a stable connection between the two vehicles
and yet will minimi~e the amount of tire wear with the dolly
wheels.
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In accordance with the present invention there is
provided a transport dolly for releasable tanclem connection of a
rearward vehicle to a forward vehicle comprising:
a dolly frame;
means at the forward end of the dolly frame for
releasably connecting the dolly frame to the frame of the
forward vehicle by which the dolly and the rearward vehicle are
to be towed;
the said connecting means comprising a pair of
transversely-spaced connectors attaching the dolly frame to the
forward vehicle frame for free pitching movement between the two
frames but without substantial tilting or yawing movements
between the two frames;
a fifth wheel connection mounted on the dolly frame to5 releasably receive the front end of the rearward vehicle;
at least two steerable road wheels mounted on the dolly
frame and on which the dolly runs, the said steerable road
wheels being mounted for pivoting steering movement under the
effect of sideways-directed forces applied to the road wheels by
movement of the forward vehicle as it is steered away from a
straight line; and
cen~ering means connected between the dolly frame and
the steerable road wheels and urging the steerable road wheels
to a centered straight ahead attitude.
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The said releasable connecting means may comprise a
pair of transversely-spaced, upwardly~opening loop me~nbers
mounted on one of the frames to extend longitudinally therefrom,
and respective transversely-spaced hoo~ members mounted on the
other frame so that each hook member hooks into a respective
loop member and thereby attaches the dolly frame to the forward
vehicle frame for the said free pitching rnovement between the
two frarnes but without substantial rolling or yawing movements
between the two frames.
Description of the Drawin~s
Self-steering converter dollies which are particular
preferred embodiments of the invention will now be described, by
way of example, with reference to the accompanying diagrammatic
drawings, wherein:-
FIGURE 1 is a side elevation showing a tractor/trailer
combination and a second trailer employing the dolly of the
invention between the two trailers;
FIGURE 2 is a plan view from above of a dolly of theinvention, showing the centering device employed with the dolly
in an "off-centre" position, the fifth wheel connecting plate
being omitted for clarity of illustration,
FIGURE 3 is a side elevation of the dolly of Figure 2,
the centering device being in the "centered" position~
FIGURE 4 is a perspective view to show the part of
~s~
~he dolly connecting means carried by the forward vehicl~ and
its cooperation with the part thereof carried by the dolly, and
FIGURE 5 is a plan view of another form of dolly to show
the application of the connecting means of the invention to this
another dolly.
Description of the Pre~ferred Embodimen~s
Figure 1 illustrates a typical application of a transport
dolly 10 of the invention wherein the tractor 12 of a tractor/-
trailer combination has the forward trailer 14 coupled thereto via
a fifth wheel 16, while a second rear trailer 18 is coupled to the
forward trailer via the dolly. Referring now more specifically to
Figures 2 and 3 the dolly consists of a short rigid rectangular
frame 20 having a fifth wheel connecting plate 22 mounted on its
upper surface about horizontal pivots 24. The longitudinal
position of the fifth wheel plate is moved as required for adjuc~-
men~ of ~he draw bar weight that is transferred to the forward
vehicle. ~nother short ~igid rectangular dolly sub frame 26 is
moun~ed ~eneath the frame 20 and is connected thereto by a turn-
table ~earing 28 for relative rotation about a vertical steering
axis 30. A transverse trailing axle 32 carrying running wheels 34
is mounted beneath the sub-frame 2~ to the rear of the steering
axis 30 by any conventional suspension system, which in this
embodiment is illustrated as consisting of downward-extending
hangers 36 and 38 (Figure 2), springs 40 and trailing links 42 to
which the axle 32 is clamped. The suspension permits the wheels
to move up and down under control of the springs 40 and the usual
shock-absorbers (not shown), but cons~rains ~hem to run parallel
to the longitudinal centre-line of the dolly sub-frame as it
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pivots a~ollt the axis 30. In other embodiments other types of
suspension can be used without affecting the essenti~l elements
of the invention.
The dolly sub~frame remains in its "straight-ahead"
position in which the longitudinal centre lines of the dolly frame
and sub-frame are parallel to one another, and moves from that
position under control of a centering device comprising a speciallv-
shaped cam member 44 fastened to the rear end of the dolly frame.
The cam member provides a vertical cam face 46 consisting of two
symmetric mirror-image convex faces meeting at a central concave
cusp 48, this cam face cooperating with a cam follower consisting
of a roller 50 mounted by a yoke 52 to rotate about a vertical
axis 54 the yoke being fastened to a transverse bar 56 on the
sub-frame~ The bar 46 is pivoted at one end to one side-~ember
of the sub-frame about a vertical pivot 58, and has its other end
constantly urged in the forward direction by an air-spring 60
interposed between the bar and a bracket 6~ on the other side
member of the sub-frame. The cam follower roller S0 is therefore
constantly urged to maintain it engaged in the cusp 48 at which
position the wheels 34 are in a straight-ahead attitude.
The respective mountings of the cam 44 and the cam
follower roller 50 can be reversed, the cam 44 being mounted on
the dolly sub-frame 26, while the roller 50 is mounted on the dolly
frame 20.
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As long as the wheels 34 are running "straight-ahead"
they will remain in the corresponding "straight-ahe~d" or centered
position or attitude of Figure 2 with the cam roller 50 in the cusp
48. The centering device in this position provides a positive
cushioned restraining force that wi.ll oppose and damp any tendency
of the wheels to hunt or oscillate about the centered position.
When the dolly is taken round a curve of sufficiently smal,l radius
and the wheels are subjected to a force with a sideways-directed
component of greater than a predetermined magnitude, then the
force of the air spring 60 is overcome and the wheels move from
the centered position to an appropriate steering position, as
determined by the internal pressure of the air spring 60 and the
cam characteristics of the cam surfaces 46. The wheels will
therefore steer around the curve, assuming for example the attitude
illustrated by Figure 2, with consequent reduction in side~ays
scrubblng of the wheels and wear of their tires and a reduction
of the possi~ y of the rear trailer overturning. ~owever, as
soon as the sideways-directed ~orce reduces below the said pre-
determined value because o~ their trailing configuration, the
wheels quickly return to the neutral straight-ahead attitude for
normal strai.ght running, this return being assisted by the urging
of the centering device.
When the trailers are to be reversed the dolly frame
and sub-frame must be latched together against pivoting motion,
and this is effected by a driver-controlled latch constituted by
a notched latch plate 88 on the dolly frame 20 that is engaged
by a movable latch member 90 on the dolly sub-frame 26 while the
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wheels are in the straighc ahead position. The latch Inember 90
is spring urged to engage the latch and is held in the unlatched
position for normal running by a pneumatic motor 92.
It is important that the dolly frame is connected to
the frame 64 of the forward trailer in a manner that will freely
permit pitching movement between the two trailers, but that will
hold the trailers securely against any relative yawing movement
and will also permit only relatively very small rolling
movements, since the latter movements could result in
instability of the trailer to an extent that overturning or
jackknifing occurs. Thus, a certain amount of rolling movement
is already accom~odated by the fifth wheel connection and the
springs 40, so that some rolling movement capability is not
19 ¦~ L~,
~` disadvantageous. To this end the ~ frame is provided at the
respective ends of its two transversely-spaced parallel
longitudinal side members with respective vertically-opening
loops 66, each of which cooperates with a respective
transversely-spaced closable vertically-upwardly opening and
extending hook member 68 that hooks into the loop, the hooks
being of the type wherein the upwardly-open mouth thereof is
closed by a respective latch member 70. Moreover, each hook is
provided with a pneuma~ical.ly-urged plunger 72 operated by a
pneumatic motor 74 that is operative while the rig is running to
engage ~he loop 66 and spring press it against the hook inner
wall, thereby preventing longitudinal "chatter" movements
between the hoop and the loop.
3S7
The two connections therefore permit the required
pitching ~otion by pivoting movement about a horizontal axis,
while yawing motion is precluded because of the transverse
spacing of the two connections. As described a~ove, only very
limited rolling movement is possible or necessary. This
particular construction employing a rigid transverse axle
permits ~he ready "retrofit" of the invention to an existing
truck, and also permits the conversion of an existing single
draw-bow type fixed wheel dolly to be converted with maximum use
of existing components. The dolly of the invention is also
suitable for use in a ~railer train of more than two trailers
e.g. between the second and third trailer of a "triple train".
Figure 5 illustrates the application of this specific
form of connection to my prior transport dolly construction in
which the steerable running wheels 34 are mounted on respective
king pins 74 connected to the two ends of the axle 32. Each
king pin comprises a stub axle on which the steerable wheels are
mounted and a forwardly-projecting arm 76, the two arms 76 being
connected for simultaneous steering movemen~ of the wheels by
adjustable-length links 78 and a central T-shaped link member
80. The link member 80 also comprises part of a centering
device for this embodiment consisting of a cam member 82 that
engages a cam follower 84 on the link member 80 and is urged
forwardly in the direc~ion of movement of the dolly by a
pneumatic motor 86.
9 _
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In other embodiments which are not illustrated each
dolly may include other non-steerable wheels after the steerable
wheels for additional load-carrying. The small amount of roll
that is to be permitted is that required to accommodate
undulations in the road. In embodiments of the kinds
illustrated the spacing between the two connectors will usually
be about 75-87cm (30-34ins), while they will permit vertical
movements of about 2.5-Scm (1-2ins), for a consequent maximum
roll angle of about 7 degrees.
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