Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: TRACTOR-MOUNTED WEED TRIMMER WITH A
WINGNUT PLATE
FIELD OF THE INVENTION
This invention pertains to tractor-mounted weed trimmers, and more
particularly, it pertains to a weed trimmer in which the cutting blades are
replaceable by working a wingnut plate mounted above the blades.
BACKGROUND OF THE INVENTION
Walk-behind lawnmowers with weed trimmer attachments have been
known for some time. These weed trimmers are convenient for cutting
grass and weeds along a fence for example. These weed trimmers are
usually mounted to the forward corner of a lawnmower where they can be
easily seen and guided by the user of the lawnmower. A weed trimmer
mounted to a lawnmower is considered to be a very useful tool.
Examples of the weed trimmers mounted on walk-behind lawnmowers
have been found in the prior art and are listed herein below to show the
work of others in this field and the evolution of this technology:
US Patent 3,668,845 issued to James M. Parker on June 13, 1972;
US Patent 3,782,085 issued to James M. Parker et at., on January 1, 1974;
US Patent 4,152,882 issued to Tyson W. Howard on May 8, 1979;
US Patent 4,551,967 issued to Joseph S. Murcko on November 12, 1985;
CA Patent Appl. 2,002,351 issued to Glenn W. Gregory on Nov. 02, 1989;
US Des. Patent 304,728 issued to Peter V. Piorkowski on Nov. 21, 1989;
US Patent 4,896,488 issued to Larry A. Duncan et al. on January 30, 1990;
US Des. Patent 311,009 issued to Robert W. Wilkins on October 2, 1990;
US Patent 5,226,284 issued to John. C. Meehleder et al. on July 13, 1993;
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US Des. Patent 359,291 issued to Albert J. Tihonovich on June 13, 1995;
US Patent 5,966,914 issued to Thomas R. Reents on October 19, 1999.
The weed trimmers described in the above documents are mounted to
walk-behind lawnmowers. When a cutting blade on the weed trimmer
needs to the replaced, it is relatively easy to tilt the lawnmower on its
side;
take the weed trimmer head apart and to change the tines or the cutting
blades that are worn out.
Because of the way cutting blades are retained to a weed trimmer head, it
will be appreciated that the maintenance and repair of a weed trimmer
attachment becomes a challenge when it is permanently mounted to a lawn
tractor. A lawn tractor is relatively heavy and stable on the ground. It is
impractical to tilt a lawn tractor on its side to replace worn cutting blades
on a weed trimmer attachment. For that reason, basically, very few weed
trimmer attachments exist for mounting to a lawn tractor.
In spite of the above-mentioned inconveniences, the prior art includes at
least two examples of a weed trimmer mounted to a lawn tractor: US
Patent 5,167,108 issued to Joseph J. Bird on December 1, 1992. This
document describes a weed trimmer that is mounted to the side of a lawn
tractor. The document does not explain how the spool of whip line on this
weed trimmer is repaired or replaced.
US Patent 7,028,455 issued to Violet M. Liguras on April 18, 2006. This
document describes a mounting bracket for removably retaining a portable
weed trimmer to the side of a lawn tractor. The mounting bracket has a
pivot therein so that the weed trimmer can be guided by one hand in a
cutting position alongside the tractor by the operator sitting on the lawn
tractor. Maintenance of the cutting line is done by taking the weed
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trimmer altogether out of the mounting bracket and replacing the whip line
reel as one would normally do with any portable weed trimmers of that
type.
A search of the prior art has also shown weed trimmer heads in which the
cutting blades can be replaced when the weed trimmer heads are sitting low
on the ground without giving access under the sole plates of the devices.
The following four documents explain the structures of these weed trimmer
heads.
US Patent 6,119,350 issued to James W. Sutliff et al. on Sept. 19, 2000.
This cutting head has replaceable cutting blades that are mounted on pivot
pins. The pivot pins are retained fixed to a lower circular plate. An upper
plate has holes to register with the upper ends of the pivot pins. Latch
members are provided on the upper plate to engaged with the pivot pins.
In use, these latch members are held in place by centrifugal force. When
the latch members are disengaged, the upper plate may be lifted upward to
expose the end of the pivot pins so that the cutting blades can be removed
and replaced.
US Patent 7,614,153 issued to Lauro Guerra on November 10, 2009. This
document discloses a weed trimmer head wherein the cutting blades are
pivoted on pins affixed to a lower shell. An upper shell above the pins
keeps the blades captive on the pivot pins. This upper shell is retained to
a central housing by the engagement of fingers into corresponding notches.
A spring inside the upper shell must be compressed to disengage the fingers
from the notches and to expose the pivot pins so that the cutting blades can
be replaced.
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US Patent 7,878,097 issued to Gordon Strader on February 1, 2011; and
US Patent Application 2011/0232109 filed by Gordon Strader and
published on Sept. 29, 2011. These two documents describe various
aspects of a weed trimmer head wherein the blades are mounted to
respective pivot pins extending from a lower shell. A ring plate above the
blades and the lower shell retains the blades on the pivot pins. This ring
plate has slots in its circumference. The ring can be rotated to align and
register the slots over the pivot pins and to provide sufficient clearance to
remove the cutting blades from the pins and to replace the cutting blades.
Although the weed trimmers of the prior art that are susceptible of
mounting to a lawn tractor deserves undeniable merits, it is believed that
these devices contain many movable parts requiring a certain amount of
clearance to operate satisfactorily. Because of these clearance, basically,
these devices are subject to vibration in use, and accelerated wear due to
this vibration. Therefore, it is believed that there is a market need for a
sturdier weed trimmer head with less moving parts and less clearance
between the parts. It is believed that there is a market demand for a weed
trimmer head that is sturdy, easily maintained and more compatible to a
mounting to a lawn tractor.
SUMMARY OF THE INVENTION
In the present invention, there is provided a new and improved weed
trimmer head in which the cutting blades can be replaced while the lawn
tractor on which the weed trimmer head is mounted sits evenly on the
ground in a normal position. The elements of the weed trimmer head are
held against each other without clearance, in a pre-stressed manner so that
vibration amplitude in these elements is reduced.
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In one aspect of the present invention, there is provided a weed trimmer
head comprising a sole plate having a diameter; a circumference; a plurality
of pivot pins extending upwardly therefrom near the circumference. The
sole plate also has a driving shaft extending upwardly therefrom from a
center thereof. The driving shaft has a threaded segment thereon. A
plurality of cutting blades are pivotally mounted to the plurality of pivot
pins. A wingnut plate is also provided. This wingnut plate has a disc-like
portion and wing blades extending on an upper side thereof The wingnut
plate has a threaded hole in its disc-like portion. The threaded hole is
mounted to the threaded segment of the driving shaft and the wingnut plate
is movable along the threaded segment for selectively contacting or
exposing the ends of the pivot pins.
The cutting blades of the weed trimmer head can be replaced by turning the
wingnut plate about the driving shaft using an impact implement or by
hand, for distancing the wingnut plate from the pivot pins until sufficient
clearance is obtained above the pivot pins for replacing the cutting blades.
In another aspect of the present invention, there is provided a lawn tractor
having a lawnmower deck and the above-mentioned weed trimmer head
mounted to the lawnmower deck. The lawnmower deck has a bracket and
bearing assembly attached to a side thereof and the aforesaid driving shaft
of the weed trimmer head is movably mounted to that bracket and bearing
assembly. The cutting blades of the weed trimmer head can be replaced
while the tractor sits evenly on the ground in a normal position.
In yet a further aspect of the present invention, the weed trimmer head is
driven by a separate belt and a belt tightener. The mounting of the weed
trimmer on the lawnmower deck is such that the footprint of its core lies
withing a track width of the lawnmower deck. The weed trimmer and the
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lawnmower deck can thereby be used independently or together.
The weed trimmer head according to the present invention is susceptible of
a low cost of manufacture with regard to both materials and labour and
which accordingly is then susceptible of low prices of sale to the consumer,
thereby making such mounting joint economically available to the public.
This brief summary has been provided so that the nature of the invention
may be understood quickly. A more complete understanding of the
invention can be obtained by reference to the following detailed description
of the preferred embodiment thereof in connection with the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention is illustrated in the
accompanying drawings, in which like numerals denote like parts
throughout the several views, and in which:
FIG. 1 is a side view of a lawn tractor having the weed trimmer head
according to the preferred embodiment of the present invention mounted
thereto;
FIG. 2 shows a perspective view of the preferred weed trimmer head
shown with the wingnut plate retracted, and one of the cutting blades being
removed;
FIG. 3 shows a side view of the preferred weed trimmer head with the
wingnut plate shown in cross section and in a down position;
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FIG. 4 shows another side view of the preferred weed trimmer head with
the wingnut plate shown in cross section and in an upper position with a
cutting blade being removed;
FIG. 5 illustrates a plan view of the belt arrangement driving the lawn
mover deck and the preferred weed trimmer head.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring firstly to FIGS. 1 and 2, the preferred weed trimmer head 20 is
mounted to the front left side of the mower deck 22 of a lawn tractor 24.
A mounting to the right side is also possible.
The weed trimmer head 20 has a sole plate 26 with three pivot pins 28
extending upward from the sole plate 26. Each pivot pin 28 has a shoulder
30 thereon next to the sole plate 26. These shoulders 30 constitute bearing
seats on which the cutting blades 32 sit and pivot. Each cutting blade 32
has a hole in its end to pivot freely on one of the pins 28.
The sole plate 26 also has a driving shaft 36 extending upward therefrom.
The driving shaft 36 is shown shorter than in reality, for convenience of the
drawing. It will be appreciated that the upper end of the driving shaft 36
is movably mounted in a bracket and bearing assembly 40 and it has a
pulley 42 mounted to its upper end, as shown in FIG. 1.
The driving shaft 36 has a threaded portion 44 there along and a wingnut
plate 50 is threaded to the threaded portion 44. The wingnut plate 50 has
disc-like portion that has a similar overall diameter as the sole plate 26,
such that it covers the heads of the pivot pins 28.
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The wingnut plate 50 has a pair of large wing blades 52 one on each side
of the driving shaft 36. Both wing blades 52 jointly extend the full
diameter of the wingnut plate 50, and have a substantial thickness to resist
impacts by hammer for example for turning the wingnut plate 50 about the
driving shaft 36. For example purposes, the wingnut plate 50 is made of
steel or aluminum or other strong and resilient material, and the wing
blades 52 have a thickness of about one-quarter inch. Because of this
structure, the wingnut plate 50 can be easily rotated about the driving shaft
36 by the use of light blows with a striking implement for example.
Referring now to FIGS. 3 and 4, the preferred trimmer head 20 will be
further explained. The wingnut plate 50 has a threaded hole in its center.
The wingnut plate 50 is threaded to the threaded portion 44 of the driving
shaft 36. The wingnut plate 50 has a downward-facing surface that is made
of a raised annular portion 54 along the circumference thereof and a hollow
central portion 56.
In operation, the wingnut plate 50 is turned on the threaded portion 44 of
the driving shaft 36 until its raised annular portion 54 is held tight against
the head ends of the pivot pins 28. In that position, the cutting blades 32
are held captive about their respective pivot pins 28. The pivot pins 28 are
long enough to provide a loose running fit between the wingnut plate 50
and the shoulder 30.
The hollow central portion 56 is provided in the central underside portion
of the wingnut plate 50 so that tightening of the wingnut plate 50 beyond
a contact with the head ends of the pivot pins 28 causes a slight downward
deflection along the diameter of the wingnut plate 50 as illustrated in an
exaggerated manner in FIG. 3.
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Because the sole plate 26 has a uniform thickness, an excessive stress along
the driving shaft 36, such as by the over-tightening of the wingnut plate 50
as explained above, causes this sole plate 26 to bow slightly upward also
as illustrated in an exaggerated manner in FIG. 3. The deflections in each
of the wingnut plate 50 and in the sole plate 26 cause a pre-stressing of the
elements of the weed trimmer head 20 to reduce the amplitude of any
vibration that might occur in the weed trimmer head 20 during use.
Such vibration might be caused by an unbalance or by a natural frequency
of any element of the weed trimmer head 20 at or near the rotational speed
of the weed trimmer head. By keeping the elements under a pre-stressed
manner as described above reduces the amplitude of vibration or dampens
the amplitude of a vibration that might occur. Such a reduction of
vibration is beneficial for reducing wear on all parts of the weed trimmer
head 20.
This pre-stressing of the weed trimmer head 20 is also beneficial for
locking the parts in place against relative movement during use. This is
considered as a major improvement over the weed trimmer heads of the
prior art having moving parts therein and clearances between these moving
parts.
As it can be seen in FIG. 4, the cutting blades 32 can easily be replaced
when the wingnut plate 50 is moved upward along the driving shaft 36.
The cutting blades 32 can be replaced without having to tilt or to otherwise
raise the weed trimmer head 20 up from the ground.
Referring now to FIG. 5 the weed trimmer head is permanently fastened
to the mower deck 22 by means of a bracket and bearing assembly 40. A
pulley or sheave 42 is mounted to the end of the driving shaft 36 as
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mentioned earlier. This sheave 42 is driven by a belt 60 which is threaded
on the double-groove power-take-off sheave 62 of the tractor. Of course,
the other groove on the output sheave 62 drives another belt 64 to the
lawnmower deck 22.
The tension in the belt 60 driving the weed trimmer head 20 is controlled
by a belt tightener assembly 66. This belt tightener assembly 66 has a pull
cable system 68 connected to it such that the tension of the belt 60 can be
controlled from the tractor's dashboard by the tractor operator, to engage
or to disengage a rotation of the weed trimmer head 20.
The use of a double-groove sheave 62, a separate belt 60 and belt tightener
assembly 66 allows for the weed trimmer head 20 to be operated
independently or at the same time as the lawnmower deck 22. Similarly, the
lawnmower deck 22 may be operated independently or at the same time as
the weed trimmer head 20. The clutch system on the lawnmower deck 22
has not been illustrated because these mechanisms are well known in this
field and are not the focus of the present invention.
In order to facilitate the use of the preferred weed trimmer 20 or the
lawnmower deck 22 in an independent manner, the bearing assembly 40 is
mounted at a location on the lawnmower deck 22 that places the core of the
weed trimmer 20, that is the sole plate 26 and the wingnut plate 50, within
a track width of the lawnmower deck 22. The track width of the
lawnmower deck 22 is illustrated by dashed line 70 in FIG. 5 extending
tangent to the lawnmower deck 22. The footprint of the weed trimmer 20
inside this track width 70 is illustrated by label 72.
When the lawnmower deck 22 is used independently, the blade 32
extending to the left of the weed trimmer 20 folds backward and rests
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within the track width 70 of the lawnmower deck 22 as it may be
understood from FIG. 5.
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