Self cleaning screen

A self cleaning screen particularly for an engine cooling system comprises a housing having a screen front wall and a rear wall in which there is provided a circular opening. The housing is divided by divider plates connecting between the front and rear walls and extending outwardly from the circular opening to outer side edges of the housing. A baffle is mounted at the center of the opening and is rotatable by a fin or an electric motor. The baffle includes a triangular front plate for closing off a part of the screen aligned with the opening together with a side plate portion which closes off the area defined between the divider plates. As the baffle rotates therefore a portion of the screen extending radially from the centre of the opening to the side edge is closed off so that air does not flow through that area allowing filter debris to fall from the screen.

BACKGROUND OF THE INVENTION 
This invention relates to a self cleaning screen for use with an air flow 
which is particularly but not exclusively designed for use with an engine 
cooling system. 
Radiator type cooling systems of internal combustion engines used for 
example in an agricultural environment often require a screen upstream of 
the radiator so that air drawn through the radiator is filtered to extract 
dust and other particles in the air. In the agricultural environment the 
air drawn into the radiator carries dust, soil particles, plant materials 
such as chaff and other debris which must be separated to prevent clogging 
of the radiator with this material. Various proposals have previously been 
put forward for screen designs and it is of course essential that the 
screen be effectively self cleaning since the screen itself would 
otherwise become quickly clogged and valueless. 
In order to reduce air flow velocity through the screen to enable easier 
cleaning of the screen, it is often desirable to have a large screen which 
is significantly larger than the air intake. 
However, this causes difficulty in providing a necessary moving element 
which allows the portions of the screen to be cleaned on a regular basis. 
It is one object of the present invention therefore, to provide an improved 
design of screen which enables the screen to be manufactured to any 
required shape while allowing that screen shape to be simply and readily 
cleaned. 
According to the invention, therefore, there is provided a self cleaning 
screen for separating particles from an air stream comprising a housing 
defining a front surface which is covered by a filter screen having 
perforations sized to halt the particles while allowing the air stream to 
pass through, a rear surface spaced from the front surface and a 
surrounding side wall means extending between the front surface and the 
rear surface to cause all airflow exiting the rear surface to be drawn 
through the front surface and the screen, a plurality of divider plates 
each extending from a front edge of the plate at the screen in a rearward 
direction to a rear edge of the plate at said rear surface of the housing, 
said divider plates being spaced each from the next so as to divide the 
screen into plurality of separate screen elements, the air flow through 
the screen element being confined on respective sides by said divider 
plates, the rear surface of the housing having at least a portion thereof 
which is open to allow passage of the air through the screen and between 
the plates, and baffle means for halting flow of air through each one of 
said separate screen elements in turn to allow material collecting on said 
each element in turn to be discharged from the screen. 
Preferably the housing includes a back plate which has an opening smaller 
than the screen. A portion of the baffle within the smaller opening can 
then cooperate with the divider plates which direct the air toward the 
opening to close off the separate air channels defined by the divider 
plates in turn. 
This allows for example, a simple rotating vein type arrangement mounted in 
a circular opening in the back plate to control cleaning of a much larger 
screen of any desired shape for example, rectangular. 
With the foregoing in view, and other advantages as will become apparent to 
those skilled in the art to which this invention relates as this 
specification proceeds, the invention is herein described by reference to 
the accompanying drawings forming a part hereof, which includes a 
description of the best mode known to the application and of the preferred 
typical embodiment of the principles of the present invention, in which:

DETAILED DESCRIPTION 
The self cleaning screen comprises a housing defined by a flat back plate 
10 and four upstanding side walls 11, 12, 13 and 14 arranged at right 
angles to define a rectangular box. In one example, the back plate and the 
side walls are formed of metal welded to form a rigid box structure. 
However other materials such as molded PVC are possible. The front surface 
of the housing is defined by a sheet 15 of a filter screen material which 
is attached to the side walls 11, 12, 13, 14 by a suitable fastening (not 
shown). The screen thus covers the whole of the front of the housing so 
that any air entering the housing must pass through the screen to carry 
out a filtering action. 
The size of the perforations of the screen are chosen in accordance with 
the requirements and in one example the screen can comprise a simple mesh 
screen suitable for extracting dust, chaff and soil particles which will 
otherwise clog the radiator of the cooling system in an internal 
combustion engine. The size of the housing can be selected in accordance 
with the size of the inlet area available and can be flat as shown or can 
be curved as necessary to follow the curvature of the vehicle to which it 
is intended to be attached. 
The back plate 10 has an opening 16 in the form of a circular hole simply 
cut into the back plate at a suitable location on the back plate. The hole 
defines the outlet for air entering the housing with the hole being 
suitably located on the housing to direct the air onto the equipment with 
which the filter screen is associated. In the example shown the hole is 
offset slightly to one side. This position can be modified in accordance 
with the design requirements of the vehicle concerned. 
The size of the hole can also vary but is preferably significantly smaller 
than the size of the back plate. The relative dimensions of the hole on 
the back plate are preferably coordinated with the proportion of opening 
of the screen material and in many cases this approximates to fifty 
percent of the screen material so that an opening which is fifty percent 
of the back plate is desired. However, it will be appreciated that a 
larger back plate relative to the size of the opening 16 will reduce the 
velocity of air flow through the screen. 
From the opening a plurality of divider plates 17 are provided which extend 
from the opening to the side walls. The divider plates as best shown in 
FIG. 3 have a front edge in contact with the screen 15 and a rear edge in 
contact with or welded to the back plate 10. This acts to define the 
screen into separate screen elements with the air which passes through 
that screen element passing through the channel defined by the divider 
plates toward the opening and through a rectangular area 18 bounded by the 
divider plates on the respective sides and the screen and the back plate 
at the front and rear respectively. 
A baffle member indicated at 20 is shaped in plan view as a sector of the 
circle defined by the opening 16. Sides 21 and 22 of the sector are 
arranged to be spaced by the same angular distance as four of the divider 
plates 17. The baffle further includes a surface 23 lying at right angles 
to the upper surface in the shape of the sector so that the surface 23 is 
curved about the centre of the circular opening 16. The baffle is 
rotatable about the centre of the circle on an axle 24. As the baffle 
rotates, the wall 23 of the baffle passes closely adjacent the inner edges 
of the divider plates 17 at the periphery of the opening 16. The front 
surface of the baffle lies closely adjacent to or in contact with the rear 
surface of the screen 15 so that it prevents air from flowing directly 
through that portion of the screen which is shaped in the sector of the 
circle defined by the front surface of the baffle. The side wall 23 of the 
baffle as shown in FIG. 1 covers three of the air flow passages defined 
between the divider plates 17 so that in that position the baffle halts 
flow of air through the screen into the air flow passage and along the 
passage way to the opening 16. This position is best shown in FIG. 3 where 
the face 23 of the baffle is visible through three of the air passage 
ducts while the fourth air passage duct is open to allow passing through 
the screen element associated with that passage duct to pass toward the 
opening 16 and through the opening 16. 
Thus as the baffle rotates, it halts air flow through one portion of the 
screen so while the air flow is halted through that portion, any material 
collecting on the outside surface of the screen can fall from that portion 
to be discharged since the suction acting to hold the material against the 
screen is removed as the air flow is halted. 
The drive force for rotating the baffle is provided firstly by a fin 30 
which is shaped so that air passing through the opening provides a 
rotational force onto the fin and thus on the baffle which is connected to 
the fin. The shape of the fin is shown only schematically since this will 
be apparent to one skilled in the art and can be modified in accordance 
with requirements. In addition the force controlling the rotation is 
provided by an electromagnetic control device indicated at 31. The control 
device can either provide a rotational force or it can be controlled to 
provide repeated halting forces at spaced positions around the axle. Thus 
a plurality of magnets can be provided around the axle which are actuated 
sequentially temporarily halting the baffle at each space location around 
the periphery. This ensures a rotation rate of the baffle of the order of 
one to five rpm which gives a period during which the air stream is halted 
which is sufficient to allow the collected material to fall from the 
screen. The control device 31 is mounted upon a bearing 32 carrying the 
axle 24 with the bearing being supported upon a spider assembly 33. 
In an alternative arrangement (not shown), the opening can be rectangular 
with the divider plates extending transversely across the screen from one 
side to the other side. In this case the baffle can be formed as a strip 
across the rectangular opening movable in a vertical direction so as to 
gradually move from the top of the opening to the bottom of the opening. 
In addition the baffle has side pieces corresponding to the surfaces 23 
which cooperate with the divider plates to halt air flow moving across the 
screen between the divider plates. 
In a yet further alternative arrangements (not shown) each air passage 
between two divider plates is associated with a pivotal louvre arrangement 
which can be moved from an open position in which the air is allowed to 
flow through the screen element associated with those divider plates to a 
closed position in which the air flow is closed off through that screen 
element to allow material collected to be discharged. Each louvre element 
in turn is therefore operated to be moved to the closed position and then 
reopened. 
Since various modifications can be made in my invention as hereinabove 
described, and many apparently widely different embodiments of same made 
within the spirit and scope of the claims without departing from such 
spirit and scope it is intended that all matter contained in the 
accompanying specification shall be interpreted as illustrative only and 
not in a limiting sense.