Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED CHIPPER SHREDDER SCREEN
Field of the Invention
This invention relates to an improved chipper
shredder and, more particularly in the preferred
embodiment, a chipper shredder having an improved shredder
screen.
Background of the Invention
Chipper shredders have been utilized in consumer
and professional applications for years. The purpose of
these chipper shredders is to translate the longitudinal
length and/or physical volume of various types of
vegetation into smaller pieces having lesser volume,
typically by chipping or shredding the incoming
vegetation. Examples include feeding a three inch
diameter tree limb into a chipper section in order to
reduce it to small wood chips and/or feeding many bushel
baskets of leaves or small sticks into the device
(normally via a separate shredding section in consumer
devices) so as to shred the same into small particles.
Typically, as the diameter of the branch is increased and
as the volume of the sticks/leaves increase, the power
requirements also increase dramatically. This can create
problems in that the chipper shredder unit preferably are
designed for worst case scenarios. This can be expensive.
Further to the above, chipper shredders are not known to
be the most aerodynamically efficient, frequently having
places of restriction in the airflow which impede
operation of the chipper shredder unit. This is
particularly true in respect to lightweight and/or high
velocity materials exiting the chipper shredder through
the screen at the discharge chute.
Objects and Summary of the Invention
It is the object of the present invention to
increase the volumetric efficiency of chipper shredders.
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It is another object of the present invention to
reduce the potential for debris build-up at the discharge
screen of chipper shredder units.
It is the object of the present invention to
reduce the horsepower requirements for chipper shredder
units.
It is another object of the present invention to
reduce the volume of residue produced by chipper
shredders.
It is yet another object of the present
invention to simplify the design of chipper shredders.
It is still another object of the present
invention to lower the cost of chipper shredders.
Other objects and a more complete understanding
of the invention may be had by referring to the following
description and drawings in which:
Brief Description of the Drawings
The structure, operation, and design of the
presently disclosed preferred embodiment of the invention
will become apparent on consideration of the following
description taken in conjunction with the accompanying
drawings wherein:
Figure 1 is a lateral side view of a chipper
shredder incorporating the present invention;
Figure 2 is an enlarged partial side view of the
discharge screen area of the chipper shredder shown in
Figure 1;
Figure 3 is a cross-sectional view of the
chipper shredder of figure 1 showing the cooperation of
the moving blades and fixed discharge screen of the
chipper shredder of figure 1 taken along lines 3-3; and,
Figure 4 is a cross-sectional view like figure 3
showing the cooperation of the moving inner blades to the
fixed teeth of the chipper shredder of figure 1 taken
along lines 4-4.
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Detailed Description of the Invention
This invention relates to an improved discharge
screen for a chipper shredder.
The invention will be described in a preferred
embodiment of an improvement to the MTD Models 648 and 645
chipper shredders, the structure of which is incorporated
by reference. These chipper shredders include a
horizontal shaft engine (not shown), a housing 11, and an
internal flail mechanism 20.
The engine provides the rotary power for the
system. This is typically a five or eight horsepower
horizontal shaft engine, directly bolted to the housing
11 .
The housing 11 provides an enclosure physically
containing the moving parts of the actual chipper shredder
unit and the vegetation actively modified and directing
the volume of air generated by the flail mechanism.
Typically, this housing 11 is a stamped steel
housing having a large lateral feed 12 for bulky objects,
such as small branches and leaves, and a smaller lateral
feed 13 for smaller more solid objects, such as branches
up to perhaps three inches in diameter (since the feed 13
of the preferred embodiment is on the opposite side of the
housing 11 from the feed 12, such feed 13 is shown in
dotted lines).
The particular housing disclosed comprises two
stamped parts 14, 15 bolted together at a central seam 16.
This housing has an inner chamber some 16" in diameter and
4" in depth (overall diameter of the connecting flanges 17
is about 19"). The larger lateral feed 12 is
approximately 5+1/4~ long and 3+1/4~ wide. The smaller
lateral feed 13 is approximately 2+1/4 long and 4" wide.
The larger lateral feed 12 is customarily a
simple opening into the side of the later described inner
flail 20. This feed 12 allows direct access to the blades
21 of the flail 20, promoting an aggressive shredding
action, aided by the later described additional teeth 35.
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The lateral feed 12 is located approximately 180 opposite
to the discharge opening 18.
The lateral feed 13 along the side of the inner
flail 20 allows direct lateral access to the side
chipper(s) 22 of the inner flail 20. While this promotes
less aggressive action than the flail blades 21, the side
chipper(s) 22 are designed for heavier duty cutting than
the r~m~;nAer of the inner flail 20 and thus can
accommodate greater diameter branches and/or more load
than the outer circumferential flail blades 21. In the
preferred embodiment the smaller chipper opening 13 is
located adjoining the discharge opening 18 and screen 30.
Any chips that bypass the screen 30 are further broken
down by the blades 21 of the flail 20 and the later
described additional teeth 35. In that the chips are
small, a high percentage are passed directly out of the
discharge opening 18.
In the conventional chipper shredder there is
frequently a reinforcing or blocking member located in the
immediate path of the discharge through the screen 30. An
example of this would be the chipper shredder shown in the
Hamlin Patent U.S. 3,817,462 -Shredder- Issued June 18,
1974 or certain other prior devices. In these devices,
there is typically a structural attachment or reinforcing
member for the discharge screen located inside of the main
volumetric airflow for the chipper shredder. An example
of this would be if a reinforcing member was located at
hypothetical position A in Figure 2 of this present
application. This reinforcing member A blocks the
cross-sectional extent of the discharge opening 18. Not
only does this reduce the volumetric efficiency of the
chipper shredder, but it also causes a location for debris
build-up immediately in front of the reinforcing member A.
The reason for this is that the radially extending blades
of the flail cannot overlap with reinforcing member
without physically contacting the same. There must
therefore be a small space between reinforcing member and
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the outer radial extent of the blades - a clearance which
along with the positioning of the member A in the
discharge stream can allow debris to build-up.
In the present application, the reinforcing
member 32 is located outside of the normal leading edge
tangential path 33 of the discharge airflow. Further, the
aggregate cross-sectional area for debris passage through
the screen is substantially equal to or greater than that
of the discharge opening 18, thus providing for a
relatively unrestricted passage of debris.
In the preferred embodiment, this is primarily
caused by shifting a section of the housing 11 radially
outwardly at the location of the entrance 19 to the
discharge chute 18, thereby assuring that the
cross-sectional area of such discharge 18 is not
compromised by the existence of the reinforcing member 32
for the discharge chute. Further, with the reinforcing
member in this location, the blades 21 interleave with the
screen 30 on the inside of the member 32, thereby keeping
the screen clear also insuring no operational reduction in
discharge cross-sectional area. Also in the preferred
embodiment disclosed, the cross-sectional area of the
discharge chute 18 is relatively enlarged outside of the
screen 30. This further increases volumetric efficiency
by lowering relative air pressure at this location.
Typically, the circumferential flail 20 has
external blades or extensions 21 which are interconnected
to a high mass central member 23 in order to pulverize
materials which are fed through the chute or feeds 12, 13.
Typically, these blades 21 are rotatively mounted to the
central member 23 of the inner flail 20 such that only
centripetal force maintains them extending outward of such
flail 20 (they could be fixedly or otherwise connected if
desired).
As set forth, these blades 21 also cooperate
with the screen 30 which is separately affixed to the
housing 11 adjacent to the discharge chute 18 in order to
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pulverize materials which are fed into the chipper
shredder.
Normally the blades 21 are interlineated with
fixed sections or bars 31 of the screen 30 allowing an
overlapping shredding action at this point (see fig 3).
By this it is meant that the outer diameter of the blades
21 is greater than the inner diameter location of the
screen 30, which difference in diameter produces an
overlap that allows for the pulverizing action there
between, and that the members are sequentially located to
allow for an effective shredding action. In the preferred
embodiment disclosed the displacement of the reinforcing
member 32 outside of the airflow, in addition to
increasing the cross-sectional area for passage of residue
through the screen 30, displaces the reinforcing member 32
relatively radially outward of the rotational access of
the flail 20. This allows the screen 30 to be located
relatively inward of the alternate designs because of the
removal of the issue of interference between such
reinforcing member and the blades 21 of the flail. This
has the effect also in the preferred embodiment of causing
the blades 21 of the flail to intersect the leading edge
of the screen 30 at an acute angle (at 37 in Fig 2). This
increases the relative power at this location, further
improving the discharge action of the shredder (especially
since the reinforcing member 32 is not tangentially
outside of this point to block air flow). It also
lengthens the screen 30, and lowers its longitudinal axis
into the flails 21, further lowering the forces on the
screen and increasing the effectiveness of the shredder.
In this respect, while it is technically
possible to locate the trailing edge reinforcing member 33
in a manner similar to the leading reinforcing member 32
(by example creating a small pocket in the trailing edge
of discharge chute), it was found that it was important
for the teeth 21 to cleanly sweep this area and merge
seamlessly with the housing 11 at this location. This is
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believed to be more preferable from a design standpoint
than the lateral displacement of such reinforcing member
in the matter similar to the reinforcing member 32. For
this reason, the trailing edge reinforcing member 33 is
displaced outwardly of the extent of rotation 34 of the
blades 21 of the flail with the minimum restriction in
cross-sectional discharge area created at this location
made up for by the strength of the merger between the
teeth from the screen 30 to the housing 11 at this
particular location. The reinforcing member 33 also aids
in physically protecting this location. (The increased
cross-sectional area relative to the leading edge of the
screen 30 aids in this respect by compensating for the
area occupied by the reinforcing member 36).
In the preferred embodiment, the blades 21
comprise three outward extensions off of a central member
26, each tooth some 1" wide, 1/4" thick and 2+1/4" long.
The center lines of teeth are spaced by the extreme ends
of the blades 21 and are cut away at the corners on a 1/4"
radius to improve efficiency and extend operational life.
These blades 21 intervene with the four bars 31 of the
cast screen 30, themselves some 10" long, 1+1/3" wide
spaced from each other by 1" (center to center). The
inner edge of the screen 30 is spaced 7" from the center
of the housing 11 so as to provide an overlap of about
7/8ll with the blades 21. Both reinforcing members 32, 33
are displaced relatively outward of the blades 21 so as to
not interfere therewith. Further, as previously
mentioned, the reinforcing member 32 is, in addition,
displaced outwardly of the leading tangential edge 33 of
the flail so as to enlarge the effective cross-sectional
area available for air passage at this location, most
particularly, by removing the reinforcing member 32 from
being a impediment to relative airflow through the
discharge 18. The leading edges of the screen 30 are
radiused with a contour so as to facilitate the operation
of the unit. The central member 23 has an overall
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diameter of 13+1/2" with the blades 21 connected at a
5+1/2" radius.
Due to the rotative connection between the
blades 21 and the central member 23 of the flail 20, any
major impediments will cause the blades 21 to rotate about
their interconnection axis, and thus reduce the load on
the engine and not cause any stalling or damaging torque
increase on the engine 10. Further, due to the increase
in relative cross section of the discharge 18 in respect
to alternate designs, the longitudinal extent of contact
between the screen 30 and the teeth 21 is extended so as
to allow for a more efficient sheading action. There is
also no location for blockage of the airflow at leading
edge of the screen 30, thus insuring a good airflow and
shredding action at this particular location. Also, at
the trailing edge of the screen, any debris will be
carried smoothly around the diameter of the housing
without having any significant outward impact forces on
such housing (and the trailing reinforcing member 36 will,
as previously discussed, also strengthen this critical
location).
Customarily, in the prior chipper shredder art,
a significant amount of the shredding action occurs
between the blades 21 and the screen 30. This
concentrates most of the torque at this location. In
addition due to the carry over of vegetation, the screen
30 must be very strong in order to absorb very high impact
loadings. These are inefficient and damaging.
In the preferred embodiment of the present
application, there is an outer blade having a series of
inwardly extending teeth 35 located somewhere within the
shredding compartment. This could include being
incorporated on the screen 30 at the discharge opening 18.
These teeth 35 are set forth in more detail in the U.S.
Application 08/382,483 filed February 1, 1995 the contents
of which are incorporated by reference.
These additional teeth 35 break up the
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vegetation carried about the circumference of the housing
11 by the blades 21, thus providing an additional location
of shredding for the device. In this respect it is noted
that in the prior art devices this vegetation would
acquire a high kinetic energy due to its being carried at
high speed in clumps by the blades 21 about the
circumference of the device (wet leaves are particularly
troublesome). In specific, in the prior art devices,
there is a tendency for the vegetation to accumulate in
clumps along the inner circumferential surface of the
housing 11. These clumps typically continue to travel
about such circumference surrounding the blades 21 driven
thereby. This accumulation dramatically increases the
impact forces on the screen 30, as well as the steady
state loading on the engine. This increase in loading
requires an increase in engine horsepower as well as an
increase in screen 30 strength. Not only did this kinetic
energy reduce the effectiveness of the shredding action at
the screen but, in certain instances, it could even
physically deform the screen 30. The present invention
avoids this build-up, thus increasing both effectiveness
and longevity of the associated chipper shredder as well
as increasing the volumetric efficiency of the chipper
shredder. This is in addition to the effect previously
set forth due to the revised location of the leading
reinforcing member 32 and its synergetic effect with the
rem~;n~er of the device.
Preferably the location of the additional teeth
35 is displaced from the location of the screen 30 and
between the shredding opening 12 and the discharge 18.
The displaced location facilitates operation of the device
by spreading the shredding action about the device
circumference. The between location further facilitates
shredding by allowing sequential operation. This also
acts to equalize the torque loading on the device.
In the preferred em~odiment disclosed, teeth 35
are set forth in multiple pairs interleaved with the
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blades 21 at a location between the input 12, 13 and the
screen 30 and discharge opening 18.
In the preferred embodiment, the additional
fixed teeth 35 act to break up the accumulation,
preferably at a location displaced from the screen 30.
This reduces the loading of the device while increasing
its efficiency. It also adds to the volumetric efficiency
by causing smaller particles to be present for discharge
out of the increased cross-sectional area screen 30 and
discharge chute 18.
The fixed teeth 35 connected to the housing 11
cooperate with the blades 21 of the inner flail 20 to
pulverize vegetation which is fed into the chipper
shredder. These teeth 35 thus also act to improve the
efficiency of the chipper shredder by allowing for a more
complete shredding of the vegetation prior to the
discharge thereof through the output chute. Although the
teeth are shown fixed to the housing in two rows,
alternate methods of mounting including resiliently biased
movable teeth and other shapes, numbers, and orientations
could be utilized without departing from the invention.
In the preferred embodiment disclosed, the
blades 21 are three in number for the inner flail 20 while
the teeth 35 of the housing are arranged in two pairs of
five tooth units. The teeth of the inner housing are
interleaved with the blades of the flail such that the
blades 21 and teeth 35 cooperate to pulverize and
vegetation caught there between. Further to the above,
the preferred teeth 35 have a inclined leading edge 36
which causes any vegetation which is circulated by the
blades 21 to be moved inwardly, thus increasing the
efficiency of the pulverizing process in addition to
reducing parasitic loading. In addition due to the inward
forces, the mass of any vegetation that is carried to and
past the four section screen 30 in contact therewith is
reduced, thus lowering the kinetic energy available
parasitic power loss and for possible deformation of the
- 10 -
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screen 30. Further, the teeth 35 cooperate with the
outward spirals 24 of the flail 20 by tossing material
back and forth to further shred the input materials.
In the preferred embodiment disclosed the teeth
35, some ten in number, are located in two sections in
aggregate extending some 19" about the outer circumference
of the housing 11 with the base of the teeth at an 8+2/5"
radius from the center line of the housing 11. This
substantially matches the inner radius of the housing 11.
This provides for about 3/4" over lap with the blades 21.
Each individual tooth is 1/8" thick and extends slightly
over 1+1/8" into the housing in staggered formation with
the two banks of teeth displaced 1/2" from the center line
of the housing 11. The leading edge 36 of each tooth is
angled, 46 shown, in order to increase the overall
efficiency of the shredding action (as well as displacing
any accumulated vegetation inward). The inner diameter of
the teeth 35 is such in respect to the outer diameter of
the flail blades 21 such that the two over lap, about 3/4"
in the preferred embodiment disclosed. Although not
necessary to performance, the inward tips 37 of each tooth
are radiused (.38 shown) to increase the operational life
of the teeth 35.
In the preferred embodiment, the multiplicity of
the teeth 35 allows for a sequential pulverization of the
vegetation as such vegetation is circulated throughout the
inner circumference of the housing 11. This multiplicity
of teeth further increases the efficiency of the
pulverizing action of the improved chipper shredder.
Further to the above, the fact that three flail blades 21
interleave with four bars 31 at the screen 30 earlier and
longer than before in addition to the two sets of teeth 35
of the housing 11, the overall efficiency of the device is
increased through lateral displacement of forces. This
also m;n;m;zes the residue that otherwise might
continually travel about the device. In the preferred
embodiment, the shredding action occurs over 180 of the
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housing 11 (120 teeth 35; 60+ screen 30). This is
preferred for allowing some momentum to build up on the
blades 21 prior to driving engagement of material to the
teeth 35. The preferred embodiment also allows for a
recovery period between initial material contact (for
example feed 12) and engagement of material to the teeth
35. Up to 360 of shredding action is possible through
the inclusion of additional teeth 35.
Although the invention has been disclosed as
preferred embodiment with a certain degree of
particularity, it is to be understood that numerous
changes can be made without deviating from the invention
as hereinafter claimed.
