Note: Descriptions are shown in the official language in which they were submitted.
~ 36~38
This invention relates to hitch balls, of the type for
securing to a draw bar of an automobile, van, liqht truck or the
like, for releasable coupling to a trailer.
Because of the stresses and forces which such a hitch
ball must withstand in use, and the bearing surface that it must
present to the trailer coupling, it is conventional to make the
hitch ball of steel. They are normally made as one piece
castings, machined, die-formed or forged. They have a lower
screw threaded shank by means of which they can be bolted to the
draw bar. In use, the ball must withstand pushing and pulling
forces in substantially all directions, and impact. Moreover,
it must be capable of withstanding compressive forces deriving
from bolting it to the draw bar. Accordingly, such hitch balls
- are relatively heavy. Not only do they add significant weight
to the vehicle to which they are attached, but also the total
weight of a significant number of them leads to shipping and
haulage problems for the manufacturer of such hitch balls. In
~ efforts to reduce this weight even marginally, manufacturers
;~ have in the past resorted to such expedients as flattening the
top part of the sphere of the ball, to save metal.
It is an object of the present invention to provide a
novel hitchball which is considerably lighter in weight than the
conventional, all steel ball, but nevertheless meets
satisfactory strength and durability criteria in use.
It has now been found that a hitch ball of much reduced
weight and satisfactory strength properties can be made from
high strength reinforcing resin, using the resin as a molded
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body with a part spherical top surface, and a metal core
embedded in the body. The core has a downwardly protruding
shank extending below the body, which can be used to secure the
ball to the vehicle. It addition, the metal core presents a
bearing surface, exposed in a downward direction, and clear of
the resin body, for direct bearing and tightening against the
vehicle draw bar.
Thus according to the present invention, there is
provided a hitch ball for attachment to a vehicle, comprising:
an elongated metal core having a lower shank portion,
an upper enlarged head portion and an intermediate skirt portion
having a downwardly presented bearing surface;
an outer resinous body of high stren~th resin
composition surrounding said core, the body havin~ an upper,
substantially part spherical portion surrounding the enlarged
head portion of the core, a generally cylindrical waste portion,
and a lower collar surrounding the intermediate skirt portion of
the core;
the lower collar of said body havinq a lowermost planar
surface which surrounds the downwardly presented bearing surface
of the skirt of the core;
said downwardly presented bearinq surface being exposed
at the lowermost surface of the lower collar of the body, so as
to bear against a surface of vehicle attachment structure when
the hitch ball is secured thereto in use.
The presence of the metal core, with its exposed
bearing surface for tiqhtenin~ aqainst the vehicle attachment
~L236~3~3
bar, provides the hitch ball of the present invention with the
necessary compressive strength. Whilst synthetic resin
compositions can be found which show the necessary rigidity,
hardness and impact strength to perform as hitch ball
components, a reinforcing steel core is necessary to provide
adequate shear strength in practice. Moreover, such synthetic
resin compositions should not be put under tension or
compression when in use; otherwise, their strength
characteristics are impaired and become inadequate. The
arrangement according to the present invention provides a
compression resistant bearing surface, of at least 50,000 psi,
to take the compression forces oE tighteninq the hitch ball
against the vehicle frame. Such surface will easily withstand
the forces of tiqhtening to and releasinq from the vehicle, e.g.
by bolting, which might otherwise cause premature fatigue in the
plastic and cause the synthetic resin body to shatter.
As a result, the present invention provides a novel
hitch ball which is readily manufactured in quantity, from
relatively cheap components, and is stron~ and durable in use.
It presents si~nificant energy savings and handling conveniences
in view of its relatively light weight.
Examples of suitable synthetic resinous materials for
use as the body of the hitch ball include qlass reinforced
nylon, polyester reinforced with qlass, steel mica or carbon,
polycarbonate, similarly reinforced polycarbonate, reinforced
ionomeric materials (e.g. SURLYN), and the like. Typically
suitable such materials exhibit a tensile strenqth of at leas~
``; ~236~3~
150 MPa, a Dart impact str~ngth, at low temperature, of at least
3J, a flexural strength of at least 200 Mæa, and are capable of
molding or forming to a smooth surface finish. The material
should also, of course r be ade~uately weather resistant, and
resistant to the effects of lubricants~ Hitch balls ac~ording
to the present invention may be quite simply manufactured by a
compression or injection moldin~ techni~ue, applying the
synthetic resin in softened or molten condition around the
pre-formed steel core positioned in the mold. The surface of
the body may be finished by light abrasion or buffing to provide
the necessary degree of smoothness.
Preferred embodiments of the invention are illustrated
diagrammatically in the accompanying drawings, in which:
Figure 1 is a perspective view of a hitch ball
accordin~ to an embodiment of the invention, and trailer
attached complementary cup therefor;
Figure 2 is a sectional view of the hitch ball along
the line 2-2 of Fig. l;
Figure 3 is a view similar to Fig. 2, of an alternative
embodiment.
In the drawings, like reference numerals indicate like
parts.
Figure 1 shows a hitch ball 10 according to the present
invention secured to a draw bar 12 of the towing vehicle. The
hitch ball 10 is of standard size (typically 1 7/8" or 2" in
diameter), and releasably attachable to a conventional cup 14
attached to a trailer. It is lockable thereon by conventional
~23~;~1L3~
lockinc~ means 16 on the cup, to provide an articulation joint
between vehicle and trailer.
The hitch ball 10 ! as shown in Fig~ 2, includes an
outer body 18 of glass reinforced nylon and an elonqated steel
5 core embedded therein, which in this embodiment takes the form
of a conventional carriage bolt 20. The body 18 has a part
spherical upper portion 22 to fit in cup 14, and which envelopes
the head 24 of the bolt 20. The body also has an intermediate
waist 26 and a lower collar 28, terminatin~ in a lowermost
10 planar annular surface 30.
The carriage bolt includes the usual threaded lower
shank 32 which protudes below the body 18, and an intermediate
skirt formed by a jam nut 34 secured tighly a~ainst the upper
end of the threaded shank 32. The lowermost surface 36 of the
15 nut 34 is substantially flush with the lowermost surface 30 of
the body 18. Thus the collar 28 of the body surrounds the nut
34.
The hitch ball is releasably secured to the vehicle
draw bar 12 in the usual way, namely by extending the shank 32
20 of the core through a hole in the draw bar 12 and securing it
therein by means of lower washer 38 and nut 40. As the nut 40
is tightened, however, to provide the necessary firm, rigid
attachment, the compressive forces are taken by the enqagement
of the lowermost surface 36 of jam nut 34, and hence by the core
25 20 as a whole, against the draw bar 12, and not by the plastic
body 18, which is therefcre substantially free from compressive
forces derived therefrom, when in use.
~36~3~
The embodiment shown in Fig. 3 is essentially similar,
except for the use of a specially formed core 20a, instead of a
conventional carriage bolt. The core 20a has a generally
part-spherical head 42, in replacement of the carriage bolt head
24, free from sharp edges which might tend to cut the plastic
body 18 when drawing force is applied. An integral skirt 43 is
provided, with a downwardly presented lowermost surface 44, to
perform the same function as that of the jam nut 34 and its
lower surface 36 in the embodiment of Fig.2.
In a further embodiment, the jam nut 34 shown in Fig. 2
is replaced by a screw threaded circular washer having a
bevelled upper surface, which is threaded onto the shank 32 into
the same position as nut 34 and performs a similar function. It
allows the use of a normal carriage bolt, but eliminates the
sharp corners of the conventional hexagon nut 34.
The present invention thus provides a novel, simple and
economical replacement for the conventional hitch ball, with
consequent savings in weight and manufacturing costs, yet
meeting adequate criteria of strenqth and durability for its
purpose.
Whilst specific embodiments of the invention have been
described in detail and illustrated in the accompanyinq
drawings, the invention is not to be construed as limited
thereto. The scope of the invention is limited solely by the
scope of the appended claims.
