Means for emptying a filter box

An improved means is provided for emptying dust and debris accumulated in the air filter box of a surface maintenance machine having vacuumized dust control.

BACKGROUND 
U.S. Pat. No. 4,557,739 to Fortman et al is assigned to the assignee of the 
present application, and is incorporated by reference into this 
specification. It describes a baffle precleaner which may be 
advantageously used in a sweeper having a vacuumized dust control system. 
This precleaner has been applied in a number of different sweeper models, 
where it has successfully fulfilled the objective of reducing dust load 
going to the related air filters. This has permitted extending the time 
between filter cleanings, which has reduced the wear and tear on the 
filters and the mechanisms for cleaning them. Thus the precleaner has 
proven to be a useful device, and it seems assured of a place in future 
generations of sweepers. 
However, several years of field experience with this precleaner have 
revealed a problem that arises in its operation. The device is comprised 
of metal sheets with slotted openings in them through which the air stream 
passes. These slots are large enough to pass small pieces of solid debris 
as well as dust. For example, broken fragments of dry leaves, tiny scraps 
of paper, bits of thread or string and similar small items will pass 
through the precleaner. They lodge on the filters, and when these are 
cleaned such debris items fall to the bottom of the filter box and mix 
with the dust that is also dislodged from the filters. 
This mixture of dust and debris accumulates and periodically must be 
emptied. The precleaner is often applied in a high dump sweeper which is 
dumped by tilting the hopper and filter box forward and emptying them 
through a dump door in the front of the hopper, as described in connection 
with FIG. 1 of the '739 patent. In this configuration, during the dumping 
operation the dust in the filter box slides forward along the bottom of 
the box and falls through the slots in the precleaner, after which it 
mixes with debris from the hopper and passes out through the dump door in 
the front of the hopper. Pure dust will do this without any trouble. 
However, when small debris items as described above are mixed with the 
dust, they tend to bridge across the precleaner slots and obstruct the 
dust from falling through the precleaner. This has made it necessary to 
manually clean out such debris, which is a dirty, time-consuming job. 
There is a need for a better way of emptying dust and debris from the 
filter box of such sweepers. 
SUMMARY OF THE INVENTION 
The present invention provides a highly reliable, completely automatic 
means for emptying such filter boxes that avoids the problem described 
above. This is done by providing the filter box with a front wall, so 
located in the debris hopper that there is space for the airflow to 
circulate in front of it. A precleaner as described in the '739 patent may 
be installed in the upper part of this wall, and air is drawn through it 
and through one or more air filters inside the filter box. However, the 
precleaner is high enough above the bottom of the filter box that there is 
room below it for a generous opening in the lower part of the front wall 
essentially across its full width. When the filter box is tilted forward, 
the dust and debris on the floor of the box slide forward and readily 
empty out through this opening. At least the part of the front wall 
containing this opening is essentially vertical. The opening is covered by 
a simple door which operates by gravity alone to swing open when the 
hopper and filter box are tilted forward and to swing closed when the 
hopper and filter box are tilted back to their normal operating positions. 
No auxiliary operating devices or latches are needed or used. Gravity 
alone also holds the door shut in its closed position. Then the airflow 
can only enter the filter box and filters through the precleaner, which of 
course is the intended condition during normal sweeping operation. 
The effect of the invention, then, is to provide a simple, highly reliable 
and fully automatic gravity operated device for emptying a filter box such 
as described when it and a related debris hopper are tilted for dumping, 
and for also closing any air inlet to the filter box during normal 
sweeping operation except through a related desired inlet.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 is shown the forward portion of a direct forward throw sweeper. 
In principle and general construction it is similar to sweepers shown in 
FIGS. 2 and 5 of previously mentioned U.S. Pat. No. 4,557,739. However, 
there are significant differences between this design and the '739 patent, 
as will be seen by the following description of the present invention. 
In FIG. 1 the hopper assembly of a direct forward throw sweeper is shown at 
10. The term "hopper assembly" is generally taken to comprise the debris 
hopper 12, the filter box 14, the filter or filters 24 and other mechanism 
contained therein, such as, for example, a filter shaker 26 and other 
related parts which together comprise the unit that is tipped for dumping, 
as shown in dashed lines in FIG. 1. The hopper assembly is supported by 
the sweeper's two front wheels 16 (only one shown) and one or more rear 
wheels (not shown). Dirt and debris are thrown into hopper 12 by a 
sweeping brush (not shown) through opening 13 in the rear of the hopper, 
or at its right hand end as shown in the solid line portion of FIG. 1. 
A sweeper stirs up dust when it is working, and it is objectionable for 
this to spread to the surroundings. To control it a suction blower 18 is 
installed. It pulls dusty air as indicated by the arrows 20 from the 
vicinity of the sweeping brush through the hopper 12 and through a baffle 
precleaner 22 which is described in the '739 patent, and which removes a 
portion of the dust from the airstream. Next the air passes through one or 
more filters 24. These are shown in FIG. 1 to be as described in U.S. Pat. 
No. 5,013,333 to Beaufoy et al, which is also assigned to the assignee of 
the present invention. However, the design of the filters is not part of 
the present invention, and any suitable filter design may be used. 
Practically all of the remaining dust and debris entrained in the 
airstream lodge on the filters, so that essentially clean air passes out 
of the filters and through duct work to the suction blower 18, where it is 
exhausted to atmosphere. 
As dust and debris accumulate on filter 24 it gradually becomes obstructed 
and offers increasing resistance to the passage of air. This progressively 
reduces the airflow until it becomes inadequate for effective dust 
control. The filter is then cleaned by a shaker mechanism indicated 
generally at 26, which may be as described in U.S. Pat. No. 5,013,333, or 
may be some other cleaning system. Wide variations are possible in the 
design of filters and filter cleaners for use with this invention. But in 
any case the filter will be periodically cleaned to re-establish its 
porosity and restore the airflow through it, and the dust and debris 
dislodged from it will fall to the floor of filter box 14 and accumulate 
there as indicated at 28. It is necessary to periodically empty the 
accumulated dust and debris from the filter box, and the apparatus for 
doing this is the subject of this invention. 
During normal sweeping the debris hopper 12 becomes filled with the debris 
swept up from the surface being swept, and must be periodically emptied or 
dumped. This is done by raising the hopper assembly 10 to a desired 
height, tipping it forward, and opening a hopper dump door 30. Of course, 
this action also tips filter box 14 forward, and in addition, as the 
hopper assembly 10 moves up, the air duct to suction blower 18 will be 
separated at doughnut seal 17. All of this is shown by dashed outline in 
FIG. 1. The details of this action will be omitted, as this method of 
dumping a sweeper hopper is entirely conventional and is well known. 
In the lower part of the front wall 36 of filter box 14 there is an opening 
37 provided for emptying dust and debris out of the filter box. This 
opening preferably extends across the width of the filter box, which is 
essentially the transverse width of the sweeper, but may be less wide than 
that. It commences at or near the floor of the filter box and extends up 
far enough to provide an adequate opening for emptying the dust and debris 
accumulated in the filter box. For example, it may be on the order of four 
inches high. Opening 37 is fitted with a filter box door assembly 32, best 
seen in FIG. 2. This door assembly is comprised of a flexible flap 34, 
which may be made, for example, of one-eighth inch thick fabric reinforced 
neoprene sheet material. A steel angle 38 or other structural shape 
extends essentially across the width of the flap 34, and is attached to it 
near its lower edge as seen in FIG. 2, typically with conventional 
fasteners and a backing strip 40. The upper edge of flap 34 as seen in 
FIG. 2 is attached to the filter box front wall 36 with conventional 
fasteners and another backing strip 40. 
Steel angle 38 serves several purposes. For one thing it keeps the lower 
part of flap 34 straight so it seals properly against the edge of the 
filter box floor. Also, it provides a weight which has its center of 
gravity offset somewhat from the center of gravity of flap 34. It will be 
realized that this offset weight tends to swing the lower edge of flap 34 
to the right as seen in FIG. 2, so the weight of the angle 38 serves to 
hold flap 34 in contact with the edge of the floor of filter box 14. This 
closes the opening 37 in the front wall of filter box 14 during normal 
sweeping operation so that the only inlet for air into the filter box is 
through the baffle precleaner 22, which is the desired condition. A third 
purpose of angle 38 is realized when the hopper 12 and filter box 14 are 
tipped forward for dumping. Then the weight of angle 38 helps pull flap 34 
away from the filter box, thus assuring a wide open exit from the filter 
box for dust and debris to flow through. This may be seen in the dashed 
line portion of FIG. 1, where a series of arrows 44 indicate the path of 
dust and debris falling out of the filter box 14 and the hopper 12 during 
a dump operation. The purpose of the invention is thus fulfilled, i.e. the 
dust and debris 28 in the bottom of filter box 14 are automatically 
emptied through opening 37 without passing through precleaner 22 during a 
dump operation, and when hopper 12 and filter box 14 are returned to 
normal sweeping position the opening 37 is automatically closed and held 
closed by door assembly 32. 
A deflector strip 42 extends essentially across the transverse width of the 
filter box 14, and is attached to the under side of the filter box floor 
by welding or other means as best shown in FIG. 2. It serves to stiffen 
the filter box floor so it presents a true edge to flap 34. It also serves 
to deflect debris that the main sweeping brush might throw in this area 
and which otherwise might strike the lower edge of flap 34 and swing it 
open, or lodge between the flap and the edge of the filter box floor. 
ALTERNATIVE EMBODIMENTS 
The foregoing discussion describes a sweeper having a single filter box 
with one or more filters in it. U.S. Pat. No. 5,013,333, which was 
previously mentioned, describes a sweeper having two side by side filter 
boxes, each with a filter in it. Such a configuration can be accommodated 
by the present invention by giving both filter boxes a common vertical 
forward wall with an opening as at 37 extending across the transverse 
width of both boxes. Then a door assembly as at 32 can close both filter 
boxes except when they are being dumped, as described above for the 
present invention. Or if preferred, two openings and two doors could be 
used, an opening and a door for each filter box. 
The normal operating air inlet opening to the filter box has been described 
as occupied by precleaner 22. It should be realized that some other 
structure, or no structure at all, could occupy the air inlet opening and 
the operation of the dump door assembly 32 would not be affected. 
Some direct forward throw sweepers are dumped by tipping their hoppers 
backward and emptying debris out of the hopper entrance opening, rather 
than by tipping forward as described above. A person familiar with 
sweepers will realize that in such a case the present invention can be 
used by providing an opening equivalent to 37 in the rear wall of the 
filter box, with some space beyond the wall opening into the debris 
hopper. Such an opening could be covered by a door assembly as at 32 in 
the present invention and would provide the previously described 
advantages of the invention in a sweeper with a rear dump hopper.