Note: Descriptions are shown in the official language in which they were submitted.
BPt57~4-047
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Title: GROUND ENGAGING ~U~U.~l MEANS FOR A VEHICLE
FIELD OF THE INVENTION
This invention relates generally to ground
engaging support means for vehicles and is particularly
concerned with a wheel or endless track for work vehicles
such as earthworking machines, agricultural machines,
military vehicles, and other vehicles used in rough
terrain.
RArRGnouND OF THE INVENTION
Wheels or endless tracks which are resilient in
character have certain performance benefits and in
particular they provide cushioning so as to offer some
resistance to vibration and jarring. While pneumatic
tires provide cushioning, they do have the disadvantage of
being susceptible to puncturing.
There have been various proposals to provide
wheels or endless tracks which can resiliently flex to
provide cushioning but which are not pneumatic. One such
proposal is disclosed in United Ringdom Patent No. 857439
which is directed to a vehicle ground engaging means in
the form of a wheel having a plurality of pieces of
flexible tubing circumferentially spaced around its
periphery and exten~ing crosswise of the direction of
travel. Although the provision of the flexible tubing is
intended to provide the wheel with some cushioning
characteristics, it is believed that tubing would not
perform altogether satisfactorily in practice. This is
because the side wall strength required of the tubing to
avoid collapsing or excessive deformation under normal
load conditions would be such that the tubing would in all
probability not flex sufficiently to provide satisfactory
cushioning.
Proposals have also been made for a non-
pneumatic but resilient vehicle wheel which has a tire
formed of a plurality of individual modular ground
engaging elements or segments. Reference may be made by
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way of example to United States Design Patents Nos.
329,413 issued September 15, lg92 to Ch~n~ler~ 342,526
issued December 21, 1993 also to Ch~n~ler and 325,209
issued April 7, 1992 to Robinson.
The present invention has been devised
specifically (although not exclusively) for use in
connection with above-ground mobile irrigation systems.
Systems of this type are used extensively in North
America, as well as in other parts of the world to
increase crop yields. A typical system includes a number
of wheeled vehicles called irrigation pivots which support
water spray equipment. The irrigation pivots are spaced
quite widely from one another across an area to irrigated
and are driven so as to advance progressively across the
area as the irrigation proceeds. Each pivot normally has
at least two wheels that are conventionally provided with
pneumatic tires.
In practice, these systems have severe flat tire
problems due to prolonged exposure to the elements, which
results in side wall cracking and corresponding losses in
air pressure. Flat tires are difficult and expensive to
repair or replace in the field. In addition, these
systems often operate in extremely difficult soil
conditions and, in many instances, require much better
traction than current pneumatic tires can provide.
Accordingly, one aim of the invention is to
provide a non-pneumatic but resiliently flexible tire
structure which is particularly suitable for application
in this field. It should, however, be clearly understood
that the invention is not limited to this particular
application.
S~M~Y OF THE INVENTION
Broadly, the invention provides ground engaging
support means for a vehicle, comprising a support movable
in a defined direction and a plurality of ground engaging
elements mounted on the support. Each element has a base
portion which is coupled to the support and a pair of
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similar tread structures which extend outwardly of the
base portion and are spaced from one another transversely
with respect to the said defined direction and offset from
one another in that direction. Each of the structures
includes a tread portion for engagement with the ground
and an intermediate portion which extends between the
tread portion and the base portion and which is
resiliently flexible so as to deflect under load.
The support means provided by the invention may
be a wheel, in which case the ground engaging elements
form a tire of the wheel. The support may be a wheel rim
or a circular band adapted to be fitted to a separate rim.
In an alternative embodiment applied to an endless track,
the support may be a flexible endless band or belt which
is guided around rollers or drums on the vehicle in use.
Preferably, the ground engaging elements are
arranged on the support in end-to-end relationship in the
said defined direction. In other words, each element
preferably occupies and defines the entire transverse
extent of the ground engaging portion of the support means
(e.g. the width of the tire where the support means is a
wheel). Preferably, the ground engaging elements are
identical with one another.
The fact that the tread structures of each
ground engaging element are spaced from one another
transversely of the support provides a distinct channel
along the tread surface formed by successive ground
engaging elements. It has been found that this tends to
have a "funnelling effect on mud over which the vehicle
may be moving, and keeps the mud within the footprint of
the tire or track. This contrasts with conventional
offroad type tires which are designed to push the mud
outwardly to the sides of the tire. This tends to cause
the tire to make a deep trough in the ground, which can
lead to difficulties in traction and the tire "bogging
down". The invention adopts the opposite approach of
attempting to keep the mud within the footprint.
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The fact that the tread structures are offset
from one another in the direction of movement of the tire
or the like tends to avoid mud building up on the
individual structures. In other words, the tire is to
some extent "self-cleaning~.
The respective tread structures of each ground
engaging element are preferably symmetrically disposed
about the longitudinal centerline of the element and the
structures themselves are preferably arranged in a
chevron-like configuration pointing in the direction of
movement of the tire or the like. The tire is then
directional.
The tread portions of the structures are
preferably tread bars that extend at least generally
transversely of the support and preferably in the said
chevron configuration so as to in effect provide paddle-
wheel like arrangement for good traction.
Resilient flexibility may be provided by
arranging for the intermediate portions of the respective
tread structures of each ground engaging element to be
hollow. Preferably, each intermediate portion has a
single hollow cavity that extends from end-to-end of the
structure (generally transversely of the element itself)
and which has front and rear side walls that are capable
of deflecting under load. Such deflection effectively
changes the shape of the cavity itself and tends to
squeeze out any mud that has entered the cavity. Since
the cavity is open-ended, some of this mud will squeeze
into the center channel of the tire or the like, which
further aids in keeping the mud within the tire footprint
as discussed previously. In very viscous mud or in water,
this has the effect of increasing the flotation effect of
the tire. In this respect, the effect is opposite the
effect desired with some prior art tires where the
intention is to decrease flotation in water.
Preferably, the ground engaging elements are
removably mounted on the support so that individual
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elements can be replaced in the event of damage or
deterioration.
Each element is preferably, integrally formed of
suitable resilient materials such as rubber. The rubber
will normally be moulded. The moulding preferably
incorporates bolt holes, bolts or other formations that
allow the element to be attached to the support.
BRIEF DESCRIPTION OF DRA~INGS
In order that the invention may be more clearly
understood, reference will now made to the accompanying
drawings which illustrate a particular preferred
embodiment of the invention by way of example, and in
which:
Fig. 1 is a perspective view from one end of
part of a mobile irrigation system provided with wheels in
accordance with the present invention;
Fig. 2 is a perspective view of one of the
wheels used in the system of Fig. 1;
Fig. 3 is a perspective view from above of a
ground engaging element of the wheel;
Fig. 4 is a perspective view of the element as
seen from one end and above;
Fig. 5 is a perspective view similar to Fig. 4
but from a lower elevation;
Fig. 6 is a plan view as seen from slightly to
one side;
Fig. 7 is a similar view as seen from the
opposite side; and,
Fig. 8 is an underneath plan view.
DESCRIPTIQN OF PR ~nn~ EMBQDIMENT
Fig. 1 shows part of a mobile irrigation system
which includes a pair of so-called irrigation pivots,
individually denoted by reference numeral 20. The pivots
are spaced from one another and act as supports for spray
equipment generally denoted 22. The irrigation system is
shown simply to illustrate a possible environment in which
the wheel provided by the invention may be used and forms
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no part of the present invention. Accordingly, neither
the irrigation system nor the individual irrigation pivots
will be described in detail. Suffice it to say that the
irrigation pivots are self-propelled and travel slowly in
synchronism on parallel paths while water is delivered
from the spray equipment 22. For the purposes of the
present invention, it is relevant to note only that the
individual pivots 20 are provided with wheels 24 that have
offroad-type tires 26 in accordance with the present
invention.
One of those wheels is shown individually in
Fig. 2 and comprises a rim 28 which is essentially of
conventional form and includes a cylindrical outer band 30
which supports the tire 26. The tire is formed by an
assembly of individual ground engaging elements 32 that
are bolted to the band 30. The elements are shown
individually in Figs. 3 to 8 (which will be described
later). With reference to Fig. 2, it is important to note
that the support formed by the rim 28 is movable in a
defined direction indicated by arrow 34 and that the
individual ground engaging elements 32 are arranged end-
to-end in a continuous assembly forming the tire with each
element defining the entire lateral extent of the tire.
It is also useful to note from Fig. 2 that each element
has a generally chevron-like overall configuration and
includes a pair of similar tread structures 36 that are
spaced from one another transversely with respect to the
defined direction 34 and are offset from one another in
that direction. These features are shown in more detail
3-0 in Figs. 3 to 8, which will now be described.
Referring now more particularly to Fig. 3, one
of the ground engaging elements 32 is shown individually;
the same element is in fact shown in Figs. 4 to 8, as seen
from different viewpoints. In any event, with continued
reference to Fig. 3, the element is shown to comprise a
generally flat base portion 38 that has a somewhat
chevron-shaped overall configuration. The defined
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direction of movement indicated by arrow 34 in Fig. 2 is
similarly indicated in Fig. 3 and it will be seen that the
element is symmetrical about a median plane that is normal
to base portion 38 and that includes arrow 34.
The two tread structures 36 extend upwardly from
base portion 38 and are spaced from one another
transversely of the element, i.e. are on opposite sides of
the median plane of the element. The hollow structures
are spaced by an amount selected to provide a defined
channel along the centerline of the tire, as is generally
indicated at 39 in Fig. 2. In Fig. 3, the part of the
channel defined by the spacing between the two tread
structures 36 of the individual element 32, is similarly
denoted 39.
It is also clearly apparent from Fig. 3 that the
two structures 36 are offset from one another in direction
34 so that each structure extends over only slightly less
than half of the overall width of the element, with the
other half of the element being open. The elements are
mounted on rim 28 so as to "nest" into one another in end-
to-end relationship so that these open portions of the
elements remain unobstructed, as is apparent from Fig. 2.
Referring back to Fig. 3, the two tread
structures 36 are essentially identical with one another.
Each structure is of uniform cross-sectional shape
throughout its length and has an outer portion denoted 40
that forms a tread bar for engagement with the ground. It
will be seen that the two tread bars 40 of the respective
hollow structures extend generally transversely of the
tread of the tire but angled slightly towards one another
to reflect the overall chevron-like shape of the element,
while still presenting upright, laterally extending
surfaces of substantial extent for providing good
traction. It will be seen from Fig. 2 that these tread
portions are designed to impart to the overall tire a
paddle-wheel like overall configuration.
Each of the tread structures 36 also includes a
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hollow intermediate portion 42 between the tread bar 40
and the base portion 38 of the element. Portion 42 has a
generally arch-shaped configuration as seen in cross-
section with respective side limbs 42a that form sidewalls
of a cavity 44 that extends from end-to-end of the hollow
structure. The sidewalls are resiliently flexible so as
to deflect under load, imparting resilient riding
characteristics to the tire not unlike those that are
achieved with a pneumatic tire.
In this embodiment, the ground engaging element
is formed integrally from a material having appropriate
characteristics of resiliency to allow appropriate
deflection of the sidewalls 42a, while providing adequate
strength for the tread bars 40 and resisting undue
deflection of the base portion 38. In a specific example,
the ground engagement element is moulded in a rubber
material of appropriate hardness.
The exposed areas of the base portion 38
opposite the respective hollow structures 36 are provided
with openings 46 for receiving bolts for securing the
element to the rim 28. Two additional openings are
provided within the respective cavities (see Fig. 8).
In the tire that is formed by the assembly of
ground engaging elements 32 on the rim 28, the design
features of the elements described above tend to cause mud
that is encountered by the tire as it rotates to be
funnelled into the central channel 39 defined between the
spaced tread structures 36 of the respective elements.
This has the effect of keeping the mud within the
footprint of the tire instead of pushing the mud to the
side as in conventional offroad tires, and avoiding the
trough that is formed by the tire becoming too deep, which
can lead to the tire "bogging down". Mud that accumulates
within the cavities 44 of the respective tread structures
tends to be squeezed out into the center channel as the
cavities are distorted inwardly under load. At the same
time, the fact that the structures 36 are offset from one
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another in the direction of movement of the tire (34)
means that the tire to some extent tends to be self-
cleaning and does not clog up with mud.
It will of course be appreciated that the
preceding description relates to a particular preferred
embodiment and that many modifications are possible within
the broad scope of the invention. For example, the
particular chevron-like configuration of the element is
not essential. The tread bars or other ground engaging
formations could extend strictly transversely of the tire
surface. While the drawings show the ground engaging
elements exten~ing end-to-end in a single row for forming
the circumference of the tire, two or even more laterally
adjacent rows of elements could be provided if required by
particular applications for the tire.
It has also previously been mentioned that,
while specific reference has been made to a tire, ground
engaging elements of the form provided by the invention
can be used to form an endless track for a tracked
vehicle. In this case, the support for the ground
engaging elements, instead of being the wheel rim 28 shown
in Fig. 2 would be an endless belt or band on which the
ground engaging elements would be mounted.
