Towbar assembly

A towbar assembly wherein two individual towbars are arranged in a V-configuration between a towing vehicle and a towed vehicle. The leading ends of the towbars have special end connectors that hook around a single towing pintle so that each towbar carries approximately the same tensile loading irrespective of changes in vehicle pitch or roll attitude. Each towbar is essentially independent of the other towbar, whereby the towbar loadings are essentially in the direction of the bar longitudinal axis; bending forces are to a great extent eliminated. The invention is designed primarily for use in towing large heavy vehicles weighing in excess of fifty tons.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a towbar assembly in which two individual towbars 
are arranged in a V-configuration between the towing vehicle and the towed 
vehicle. The invention can be used in various vehicle environments. 
However, it was particularly devised for use on relatively heavy vehicles, 
such as military tanks weighing on the order of fifty tons. 
Each individual towbar includes a tube constituting the major portion of 
the towbar length, and end connectors affixed to the tube ends. An aim of 
the invention is to design the end connectors on each towbar so that each 
towbar is substantially identically loaded, at least when the vehicles are 
moving in the straight-ahead direction. This is accomplished primarily by 
designing the front end connectors so that they can simultaneously fit 
onto a single towing pintle carried by the towing vehicle. Each front end 
connector is a flat plate having a circular opening therethrough sized to 
fit over the towing pintle; one face of the plate area surrounding the 
circular opening is transversely curved so that when the front end 
connectors on individual towbars are positioned on the pintle the 
noncurved flat plate faces mate together, while the curved faces engage 
the pintle surface in nonbinding fashion. The curved surface engagement 
between the towbar end connectors and pintle permits the towbars to swivel 
around the pintle in a side-to-side direction and also in a vertical 
up-down direction. The individual towbars are subjected to minimal load 
changes when the vehicles change attitude or direction. 
A second aim of our invention is to design the towbar end connectors so 
that each towbar tube is loaded essentially in tension or compression, 
without any oblique loadings that would produce bending stresses in the 
tubes. By confining the towbar loadings to tension or compression 
loadings, it becomes possible to reduce the tube wall thickness and tube 
weight. For heavy vehicle situations, such as military tanks, the 
individual towbar weight is of some importance as regards to cost and 
effect on vehicle payload, as well as easier handling by an individual 
when making or unmaking the connections between vehicles. In battlefield 
situations, the time required to achieve towbar hook-up of a disabled tank 
to a towing tank may be an important consideration. We achieve towbar 
weight reduction by making each individual towbar separate from the other 
towbar, and also by the above-discussed end connector design for confining 
the loadings to tensile loadings or compression loadings. 
A further aim of our invention is to simplify the towbar-vehicle connection 
mechanisms insofar as possible without having to completely redesign the 
attachment mechanisms used on existing vehicles, especially military tanks 
now in the field. Our towbar design is compatible with existing towing 
pintle-hook construction found on present U.S. Army tanks, e.g., the M-60 
tank.

Referring in greater detail to FIG. 1, there is shown a tow-bar assembly 
arranged between the rear end 10 of a towing vehicle and the front end 12 
of a towed vehicle. In practice each vehicle can be a tracked military 
vehicle used by the U.S. Army under the designation M-60; such vehicles 
weigh approximately fifty tons each. The towbar assembly is required to be 
of sufficient strength to handle the towing loads under various conditions 
of vehicle turning, acceleration, pitching, rolling, etc. 
The towbar assembly comprises two identical towbars 14 and 16 arranged in a 
V-configuration between a towing pintle 18 attached to the rear end of the 
towing vehicle and to laterally-spaced hooks 20 permanently attached to 
the front end of the towed vehicle; one of hooks 20 is shown broken away 
to illustrate towbar end connector configuration. Each towbar comprises an 
elongated tube 22 constituting the major portion of the towbar length, a 
front eye member or end connector 24, and a rear eye member or end 
connector 26. The front eye members 24 on individual towbars overlap one 
another so that both of them fit the upstanding pin portion 27 of towing 
pintle 18. 
Elongated tube 22 is of circular cross section except at the end areas 
thereof that receive the eye members 24 and 26. As best shown in FIGS. 3 
and 4, front eye member 24 comprises a flat steel plate 29 configured to 
include a spade portion 28 extending into the front end of tube 22, and an 
exposed doughnut portion 30 located outside tube 22. The eye is formed by 
a circular opening 32 extending between major faces 34 and 36 of the 
plate. Tube 22 is tapered and partially flattened at its forward end to 
facially engage major plate faces 34 and 36; welding procedures are used 
to affix plate 29 to the tube. As shown, the welding may be performed 
around joint 31 between the tube mouth and plate 29, and also in circular 
access openings 33 formed in the flattened wall areas of the tube. The 
plate-tube connection may be reinforced against bending in planes normal 
to the plate by means of a reinforcement gusset 38 that extends along face 
36 of the plate and the flattened area of tube 22. Gusset 38 is welded to 
plate face 36 and the flattened area of the tube. 
The area of plate surface 36 that surrounds opening 32 has a transverse 
arcuate contour, whereas the corresponding area of plate surface 34 is 
flat, thus giving the doughnut a semi-circular transverse cross-section. 
Referring to FIGS. 5 and 6, each rear eye member 26 is formed by a steel 
rod 40 having an exterior loop section 42 and parallel end sections 44 
extending into flattened end portion 46 of tube 22. The eye member is 
affixed to the tube by welding. 
The aforementioned towing pintle 18 (FIG. 1) is of conventional 
construction. As shown in FIG. 7, the towing pintle includes a mounting 
plate 48 welded or bolted to the vehicle, a U-shaped member 50 having a 
shaft extension 52 swivel mounted in a circular bore 54 in member 50, and 
a pintle closure member 56 connected to member 50 by means of a transverse 
pivot pin 58. The pintle can rotate around shaft axis 59 to accommodate 
roll motions and changes in roll attitude between the towing vehicle and 
towed vehicle. 
Closure member 56 is provided with a manually-operable latch 60 swingable 
around a transverse pivot 62. In its illustrated position latch 60 abuts 
shoulder 64 on member 50 to retain closure member 56 in a locked position. 
Clockwise pull on handle portion 65 of the latch around pivot 62 
disengages the latch from shoulder 64, thus enabling member 56 to be swung 
in a counterclockwise arc around pin 58 for obtaining access to pin 27. 
Pin 27 has essentially a circular cross section of appreciable diameter to 
provide the necessary strength for withstanding towbar loads in the arrow 
68 direction. The bight space between pin 27 and the base area of member 
50 is relatively short, e.g., about 13/4 inches, to minimize undesired 
cantilever effects. 
As noted above, pintle assembly 18 is of a conventional known design now 
used in U.S. Army vehicles, e.g., the M-60 tank. We have designed our 
towbars especially to fit this standard pintle design. As shown 
fragmentarily in FIG. 7, the individual towbars are arranged so that the 
front eye members 24 overlap one another when the circular openings 32, 32 
are fitted on the circular cross-sectioned pin 27. The individual towbars 
are juxtaposed so that the flat faces 34 on the respective plates 29 mate 
with one another, thus causing the cross-section of the doughnut assembly 
to be circular. The doughnut cross section is sized to substantially fill 
the bight space between pin 27 and the base area of member 50 without 
binding between the pintle and either towbar. In this connection, it will 
be appreciated that the towbars should be free for vertical swing motions, 
as designated by arrows 70; the towbars should also be free to swing in 
side-to-side directions to accommodate vehicle turn maneuvering. The 
side-to-side motions and vertical swing motions sometimes occur 
simultaneously. By providing a circular transverse cross-section on the 
doughnut assembly, i.e. the overlapped eye members, it is possible to 
accommodate the desired towbar motions while at the same time achieving a 
force loading line-of-action that is substantially along the towbar axis 
for each towbar. The symmetry of the towbar assembly relative to the 
common pulling point 27 causes the individual towbars to have 
substantially the same loading. The loads in each case are essentially in 
the tube's axial direction so that bending loads are minimal. Tubes 22 can 
thus have a reduced wall thickness and lowered weight. 
The rear end of each towbar can be anchored to the towed vehicle in various 
ways. FIGS. 8 and 9 show an anchorage mechanism that has been used on 
military vehicles; the rear end connector on our towbar (FIGS. 5 and 6) is 
designed for use with this specific anchorage mechanism. Mechanism 20 
includes a base 72 having a forwardly-projecting wall 74 that fits within 
the U-section 76 of a hook structure 77; a transverse connector pin 78 
allows the hook structure to swing around the pin 78 axis. The tip end of 
hook structure 77 is equipped with laterally-extending wings 79 that 
overlie the loop portion 42 of the towbar end connector when it is in its 
operative position. To initially connect the towbar to hook 77 it is 
necessary to orient the towbar at right angles to the plane of the hook so 
that the long dimension 43 of the loop 42 space registers with the long 
dimension 80 of wings 79; after the towbar is moved to lower its loop 42 
onto hook 77 the towbar can be swung to its FIG. 1 operative position. The 
towbar is connected to the towed vehicle first, i.e., before connection to 
the towing vehicle. 
The structure of hook mechanism 20 enters into our invention only in the 
sense that we have devised the cooperating towbar end connector to fit the 
hook structure without any intervening clevis members or articulation 
devices that would add to system complexity and/or serve as weak zones in 
the towbar system. Our towbar system is operable in spite of possible 
variations in spacing between hook mechanisms 20 from one vehicle to 
another. 
FIG. 2 illustrates a variant form that hook mechanism 20 could take. In 
this case the U-shaped hook includes a vertical shaft 21 that enables the 
hook to swing in a horizontal arc, thereby enabling the towbar force line 
of action to pass through shaft 21 and thus provide a lessened bending 
load on the hook mechanism. 
A major feature of our invention is the construction of the towbar front 
connector shown in FIGS. 3 and 4, which enables two towbars to be 
connected to a common pintle pin 27 in the fashion shown in FIG. 7. The 
individual towbars are capable of being substantially equally loaded 
because of their symmetrical orientation to the pintle pin 27. At the same 
time the individual towbars are not rigidly or permanently fixed to one 
another, as by cross braces, welding or the like. Therefore each towbar 
acts independently in essentially pure tension or compression; one towbar 
does not apply oblique loads to the other towbar, as might produce a 
bending action. When the vehicles are both moving in the straight-ahead 
direction, the towbars are each loaded in tension. Should the towing 
vehicle execute a turning maneuver, the towbar at the inner side of the 
turn will experience a compression loading, whereas the other towbar will 
continue to be in tension. The separate connections of the respective 
towbars to the towing pintle serves to preclude undesired bending loads in 
either towbar. 
There are ancillary benefits in making the towbars separate from one 
another. Thus, by making the towbars separable we achieve ease of 
handling, due to the low weight of each individual towbar. The separable 
towbars also have advantages in regard to low storage space requirements. 
Some economies in inventory requirements are possible because each towbar 
has the same construction; each towbar is interchangeable with the other. 
We wish it to be understood that we do not desire to be limited to the 
exact details of construction shown and described for obvious 
modifications will occur to a person skilled in the art.