[01] The invention relates to air filtration systems which include a mesh screen protecting an inlet of an air flow channel, in particular, but not exclusively so, the invention relates to air filtration systems used in conjunction with vehicle cooling packages.

[02] Air filtration systems are known to include mesh screens either as a primary or preliminary means of removing particulate matter and unwanted material from an air stream. In dusty environments the mesh screen can quickly clog thus reducing the efficiency of the overall filtration system. When used in conjunction with cooling packages on vehicles, for example, the efficiency of the cooling package is also significantly reduced.

[03] Combine harvesters operate in such a dusty environment. Without means to remove collected dust, chaff and straw from the protective mesh screen then the efficiency of the associated cooling package is known to significantly decrease. Such reduction in efficiency comes from the need to increase the speed of the fan which drives the air flow through the mesh screen and cooling package. Any reduction in the free surface area of the mesh screen through blockage ultimately leads to an increase in power consumption of the fan and/or reduced cooling.

[04] Known mechanisms to remove material collected on the mesh screen of those employed on combine harvesters include the use of a wiper brush which moves across the mesh screen in a reciprocating motion. However, more commonly a rotating mesh screen is provided to utilise centrifugal forces to propel the collected material radially from the screen.

[05] Rotary screens are traditionally circular and therefore dictate the perimeter of the air inlet at the upstream side of an air flow channel. The circular air inlet is typically disposed immediately upstream of a heat exchange unit, which is rectangular due to ease of construction and availability of components. As a consequence a significant portion of the surface area of the heat exchanger, namely the corners, is not utilised thus reducing the efficiency thereof. [06] it is therefore an object of the invention to provide an air filtration system having improved efficiency both in relation to cleaning of the mesh screen and when used in conjunction with a vehicle cooling package.

[07] In accordance with the invention there is provided an air filtration system comprising a fan, a mesh screen, and an airstream which is cleaned as it passes through the screen, the screen having an area at least twice the size of an airstream inlet, wherein the screen area covers the airstream inlet and extends outside a perimeter of the inlet, the fan being arranged to drive the airstream by drawing air through the screen into, and through, a channel provided for the airstream, wherein the screen moves across the inlet to carry collected material away to a position outside said perimeter where the material is removed from the screen.

[08] By increasing the size of the mesh screen beyond the air passage inlet, a portion thereof is rendered redundant at ail times. The material previously stuck to said portion is therefore relieved of the fan suction. This allows the material to be easily removed either by gravity or other force.

[09] The invention involves the recognition that known mechanisms to remove material on the mesh screen must overcome the suction force of the air flow which inherently holds the material to the screen. By moving the mesh screen across the perimeter of the air flow channel inlet this barrier to removing the material is overcome thus making the material removal easier.

[10] The screen may move across the inlet at all times. Alternatively, movement of the screen may be enacted only when cleaning of the screen is required.

[11] In one example the screen moves relative to the inlet in a reciprocating motion. This may include the situation in which the overall area of the mesh screen remains substantially within a single plane. The reciprocating motion may be linear or pivoting around an axis which is perpendicular to the screen area.

[12] However, in a preferred embodiment the screen is belt-like and moves in a continuous loop being supported on a pair of rollers, each roller being position either side of the channel, the screen moving along a first path across the inlet in one linear direction and returning along a second path through the air stream downstream of the inlet, a clean air region being defined between the first and second paths, wherein the air stream forces the collected material away from the screen. Advantageously, the belt-like screen allows the redundant portion to be turned around by 180 degrees and passed again through the air stream, thereby utilizing the force of the fan to clean the screen. The screen is preferably made of a flexible material to enable the screen to flex around the rollers and provide a continuous loop. For example, the screen may be formed from a mesh of stainless steel or nylon wire.

[13] The invention improves design freedom by removing the need for a circular mesh screen. A profile may be selected which conforms better with the shape of the chosen cooling package. Therefore, a rectangular air inlet {which corresponds with a rectangular radiator) may be shielded by a rectangular portion of the overall mesh screen.

[14] Preferably the first and second paths are parallel which optimizes the impact force provided by the fan and the air flow.

[15] in one example the rollers may be disposed above and below the channel wherein the screen movement is a substantially vertical direction. Alternatively, the rollers may be transversely spaced either side of the channel, and the screen movement being in a substantially horizontal direction. It should be appreciated the that chosen position for the rollers will be selected dependent upon the application and specific construction in hand.

[16] Preferably the fan is located downstream of the clean air region. In this case the unwanted material removed from the screen passes through the fan itself before being ejected to the environment. A fan shroud is preferably provided to transition the air flow channel between the screen and the fan thereby channelling the air from the typically rectangular profile of an associated cooling package into a circular profile of the fan.

[17] Air extracting means may be provided to extract clean air from the clean air region. The extracted clean air may be utilised for an engine air intake or for other cooling or air conditioning applications.

[18] The invention lends itself particularly well to cooling systems wherein a heat exchange unit is positioned within the clean air region. As discussed above the perimeter of the air inlet may be tailored to the shape of the heat exchange unit thereby improving the efficiency of the heat exchange unit by utilising the full surface area.

[19] In a preferred embodiment guide means are provided to guide the screen and rollers into a lifted maintenance position wherein the heat exchange unit is exposed for cleaning or maintenance. Advantageously this permits easy access to the heat exchange unit thereby saving operator time.

[20] The invention lends itself well to cooling systems located on vehicles which may or may not operate typically in dusty environments, for example combine harvesters. In this case the heat exchange unit may be associated with the cooling of an internal combustion engine and/or air conditioning system located in a driver's cabin.

[21] Further advantages of the invention will become apparent from reading the following description of specific embodiments with reference to the appended drawings in which:-

[22] Figure 1 is a perspective isometric view of a cooling system in accordance with a first embodiment of the invention;

[23] Figure 2 is a side elevation view of a the cooling system of Figure 1 ;

[24] Figure 3 is a plan view of the cooling system of Figure 1 ;

[25] Figure 4 is a side elevation view of combine harvester which implements the cooling system of Figure 1 ;

[26] Figure 5 is a plan view of the combine harvester of Figure 4;

[27] Figures 6, 7 and 8 show various views of a cooling system in accordance with a second embodiment of the invention; and,

[28] Figures 9 and 10 show a cooiing system in accordance with a third embodiment of the invention. [29] With reference to Figures 1 , 2 and 3, a cooling system 10 comprises an air filtration system 12 and heat exchange unit 14. The filtration system comprises a fan 16 which rotates on an axis 17 and includes at least a pair of fan blades 18. The fan 16 is constructed using known techniques and, although not shown, is preferably mounted for rotation on a shaft driven by an electrical motor or an internal combustion engine via belts and pulleys for example.

[30] With particular reference to Figure 3 the fan 16 draws air from the environment on an input side 20 into an air flow channel to be described below and propels the air back to the environment on an output side 22. Working upstream from the fan 16, a fan shroud 24 is provided and which serves to transition the circular profile of the fan 16 to the rectangular profile of heat exchange unit 14. At its downstream end fan shroud 24 has a circular outlet 26 which is proximate to fan 18. At its upstream end fan shroud 24 has a substantially rectangular profile 28 which presents an inlet for the fan shroud 24.

[31] The rectangular inlet 28 of the fan shroud 24 provides a substantially rectangular cross-sectional area of an air flow generated by fan 6.

[32] The cooling system further comprises a belt-like mesh screen 30 which is supported at two ends by a pair of upright rollers 32, 33. The mesh screen 30 is formed from a suitable flexible material such as rubber or nylon and comprises a mesh which presents a percentage area through which air can pass appropriate to the application in hand. By way of example, in a combine harvester operating in a dusty environment between 40 and 60% exposed area of the mesh screen 30 is free for air to pass through.

[33] The upright rollers 32, 33 are supported on suitable shafts held in place by appropriate bearings (not shown) which allow full rotational movement. The rollers are driven by a suitable belt and pulley mechanism for example. Mesh screen 30 moves linearly in a continuous loop as indicated by arrow A across the upstream side of heat exchange unit 14 and returning on the downstream side of heat exchange unit 14.

[34] The profile of the air flow channel through which the air is guided is largely dictated by the upstream edge 28 of fan shroud 24. Although a bounded passage is not provided between the point at which the air is drawn through mesh screen 30 to the fan shroud 24, the significant force of air driven by fan 16 effectively presents an air inlet on the upstream side of belt 30 having a perimeter substantially conforming of the profile of fan shroud inlet 28 and as indicated by arrows X in Figure 3.

[35] To summarise the passage of air from inlet side 20 to outlet side 22 of the environment, dirty air is drawn through an inlet XX of an effective air flow channel which is defined on the upstream side 30a of mesh screen 30 as indicated by arrows B. Material is collected by mesh screen 30 and the resulting clean air is conveyed through heat exchange unit 14. From here the air passes once again through mesh screen 30 but on a downstream side 30b before passing through fan shroud 24 and out to the output side 22 of the environment via fan 16 as represented by arrows C.

[36] The material such as straw, dust and chaff held to the upstream side 30a of mesh screen 30 moves with the mesh screen around roller 33 and to the downstream 30b. Some of the material may fall away from the screen under the influence of gravity once moved outside of the air stream. The air flow exiting the clean air region in which heat exchange unit is located propels any remaining material away from the surface of the mesh screen, the material being conveyed back to the environment.

[37] The continuous movement of mesh screen 30 in a loop as described provides a continuous cleaning process in which particulate matter drawn through the mesh screen 30 is cleared away. This improves the efficiency of the overall cooling system and maintains an optimal surface through which air can pass. Furthermore, the construction described allows the effective air inlet XX to conform with the profile of heat exchange unit 14 thereby maximising the use thereof and presenting a significant improvement over known cooling systems employing rotary screens.

[38] The embodiment described with reference to Figures 1 to 3 shows upright rollers 32, 33 being disposed either side of the air flow channel wherein the movement of screen 30 is in a substantially horizontal direction. In an alternative arrangement not shown, the rollers may be positioned above and below the channel respectively, resulting in vertical movement of the mesh screen. To clarify, in this case the rollers would rotate on a substantially horizontal axis and the mesh screen would move up and down. [39] Although not shown, it is envisaged that the filtration system 12 which includes the upright rollers 32, 33 and mesh screen 30 may be provided with guide means to guide the screen 30 into a Sifted maintenance position thereby exposing the heat exchange unit for maintenance and cleaning.

[40] The cooling system 10 described above lends itself particularly well to implementation in combine harvesters as illustrated in Figures 4 and 5. As in known combine harvesters, the cooling system 10 is positioned on one side of the machine. This allows an unobstructed intake of air from the environment. Preferably, the positioning is chosen so as to also leave an unobstructed passage for the propelled air on the outlet side so that the removed particulate material can pass back to the environment via the fan.

[41] Figures 6, 7 and 8 illustrate a second embodiment of the invention wherein the belt-like screen 30 described above is replaced by a substantially flat mesh screen 60 which moves in a linear direction across the air flow channel inlet in a reciprocating manner. It should be understood that, for clarity, features of the second embodiment which are common to the above-described first embodiment will share like reference numerals.

[42] Mesh screen 60 covers the upstream side 14a of heat exchange unit 14 as in the previous embodiment. Air drawn in (arrows B) from the input side 20 of the environment passes through the mesh screen 60 through the heat exchange unit 14 and through fan shroud 24 before being expelled to the outlet side 22 of the environment. The mesh screen 60 passes across the upstream side 14a of the heat exchange unit 14 in a linear reciprocating motion so that material collected on the surface thereof is carried away from the influence of the air stream thereby allowing the collected matertal to fall under gravity. With reference to Figure 8, arrow Y shows the direction of motion of screen 60.

[43] Advantageously, the provision of a substantially planar mesh screen 60 allows rigid materials to be used thereby increasing the design freedom.

[44] Figures 8 and 9 show a third embodiment of the invention in which another substantially flat screen is employed but is moved in a pivoting motion around an axis in a reciprocating motion indicated by arrow Z. In this embodiment the principle behind cleaning mesh screen 90 is similar to that as described above with reference to mesh screen 60 wherein collected material is carried to a position outside the parameter of the channel inlet so as to be away from the influence of the air flow driven by fan 16. This permits the collected material to fall under gravity away from the surface of screen 90.

[45] In all embodiments described the fan 16 is located downstream of the clean air region. However it is envisaged that the fan may instead be located inside the clean air region without deviating from the scope of the invention. Alternatively, although not preferred, the fan may be located even upstream of the inlet to the air flow channel, that is on the outside of the mesh screen.

[46] Although a heat exchange unit is shown in ail embodiments, it is envisaged that, instead, clean air may be extracted from the clean air region without deviating from the invention. In this case appropriate ducting may be provided to draw clean air from the clean air region. However, a fan is still required to drive the main air stream.

[47] Although having particular benefits when applied to combine harvesters it is envisaged that the air filtration system of the present invention may be implemented in a host of different applications including utility vehicles or air conditioning systems in buildings for example.