GB1582968A

GB1582968A - Air cleaners

Info

Publication number: GB1582968A
Application number: GB36489/77A
Authority: GB
Original assignee: Donaldson Co Inc
Current assignee: Donaldson Co Inc
Priority date: 1976-09-03
Filing date: 1977-09-01
Publication date: 1981-01-21
Also published as: JPS5651949Y2; FR2363360A1; JPS5336578U; ZA775329B; AU507283B2; DE2738521C2; IT1087357B; CA1069001A; JPS5332477A; BR7705797A; DE2738521A1; AU2793477A; FR2363360B1

Description

(54) IMPROVEMENTS IN OR RELATING TO AIR CLEANERS (71) We, DONALDSON COMPANY, INC., a corporation organised and existing under the laws of the State of Minnesota, United States of America, of 1400 West 94th Street, Minneapolis, Minnesota 55431, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention is generally related to apparatus for cleaning air, and is specifically directed to an air cleaner for use with internal combustion engines which are operated under extremely dusty conditions or in an environment containing substantial particulate matter of varying size. The invention also relates to separator/filter assemblies for use in such apparatus.

The conventional approach to the cleaning of intake air for intemal combustion engines is filtration; e.g., causing the air to flow through a porous medium to remove particles by interception, impaction and diffusion. Although filtration can be a highly efficient process in the cleaning of fluids, a problem does arise in extremely dirty environments because the filtered particulate matter tends to clog the filter element very quickly. This results in the frequent replacement or cleaning of the filter element, or an inadequate supply of fluid due to the increased pressure drop across the clogged element.

Because of this problem, it has long been the practice to preclean the air by separation, in which a force field is applied to a fluid containing particulate matter in such a way that the applied force can be overcome by the fluid, but not by some of the particulate matter. In this way, the efficiency of the filter element is prolonged, and the requirement for replacement or maintenance is less frequent.

More recently, air cleaners which utilize both separation and filtration in a single unit have been developed and advantageously used, and this invention is directed to an improvement in such devices. More specifically, we have been concerned with the development of an air cleaner in which air taken in from a dusty environment is more efficiently precleaned by separation, and then thoroughly filtered by passing it through a porous medium for delivery to an internal combustion engine. An additional and necessary objective, which arises from space limitations encountered in the area of use, is that the unit be of compact size without compromising its overall effectiveness.

It has been ascertained that maintaining the uncleaned air at a uniform or, preferably, increasing velocity as it passes through the separation stage enables separation to uniformly and effectively occur over the entire length of the separation stage. Although this has been recognised in prior art apparatus, the means for accomplishing a uniform or increasing velocity require an additional structural element which occupies a significant amount of space within the unit. In addition, the resulting unit is more difficult to assemble and more costly to manufacture.

Other prior art structures have recognized the need for both separation and filtration in a single unit, but this has been accomplished at the expense of separation of filtration efficiency, or without serious regard to economy or space limitations.

According to the present invention there is provided apparatus for cleaning air, comprising: (a) a casing defining an internal chamber and having an inlet for uncleaned air, a first outlet for discharging particulate matter and a second outlet for discharging cleaned air; (b) converging wall means disposed within the chamber in association with the inlet and defining a first flow path for inlet air which decreases in flow area from the inlet; (c) louver means formed in the converging wall means and defining a second flow path therethrough, the louver means being constructed to cause air to partially change direction in order to flow therethrough, thereby enabling the separation of particulate matter from the air; (d) means for establishing fluid communication between the converging wall means and the first outlet to discharge separated particulate matter therefrom; and (e) filter means disposed within the chamber between the converging wall means and the second outlet and tapering in the same direction with respect to said chamber as does the converging wall means, said filter means being for filtering air that passes through and leaves the louver means; (f) the second outlet being in fluid communication with the filter means to receive filtered air therefrom and to discharge the filtered air from the apparatus.

Preferred embodiments of the invention have features described or referred to hereinafter. The preferred embodiments show the advantages of separation and filtration in a single unit which is extremely compact in size.

As pointed out above, maintaining uniform or increasing velocity throughout the separation stage gives rise to extremely efficient separation; and this is accomplished with structure which also uniquely enables the unit to be of lesser size than prior art devices. More specifically, in a preferred embodiment there is provided a cylindrical casing having an inlet for uncleaned air at one axial end and a first outlet for scavenged particulate matter at the opposite axial end. A generally frustoconical wall member is disposed within the casing defining a flow path for the inlet air which converges toward the outlet. A plurality of louvers are formed through the frustoconical wall member and spaced over its length. Each of the louvers extends radially inward and at the same time in the downstream direction, so that it is necessary for air to partially reverse its downstream direction in order to pass through the frustoconical wall member.

However, the particulate matter, which is of greater density than the air, builds up an inertial force which is of such magnitude as to preclude the particles from reversing direction as they pass through the converging flow path, and separation of the particulate matter from a substantial portion of the air is thus effected. The converging flow path maintains the air at a uniform or increasing flow velocity by compensating for the loss of air through upstream louvers, and this enables the spaced louvers to have equal effectiveness at any point on the frustoconical separation surface. As such, highly efficient separation occurs within a very small area, with the scavenged particulate matter passing out of the device through the axial outlet.

A filter element, preferably of the pleated dry porous paper type is disposed radially outward of the frustoconical wall member.

In order to take full advantage of the uniform flow velocity, the pleated filter element also takes a generally frustoconical form which receives the precleaned air from the spaced louvers and filters the air as it passes through the porous medium. As is well known in the art, the pleated medium substantially increases the filtration surface of the element as well as provides it with increased structural strength.

In the preferred embodiments, the pleated filter element includes an annular inner and outer perforate lining for additional support, and is integrally formed with the louvered frustoconical wall member into a separation, filtration element which is easily replaceable within the cylindrical casing.

The space defined between the outer surface of the pleated filter element and the inner surface of the cylindrical casing diverges or increases in flow area from the inlet end to the outlet end. This structural configuration is a space-saving feature since the resulting chamber has its smallest dimension closest to the inlet end, where a lesser volume of filtered air enters. By the same token, as this outlet chamber increases in size, it is capable of accommodating a greater volume of air as it leaves the pleated filter element. A second outlet is formed in the wall of the cylindrical casing in direct communication with this outlet chamber.

The unit may also advantageously include a safety filter element which is also frustoconical in shape and disposed within the outlet chamber immediately outward of the pleated filter element. The safety element can consist of inner and outer perforate frustoconical liners and a single layer of dry paper therebetween which is of greater porosity than that of the pleated element. As such, the safety filter element is capable of performing minimal filtration to protect the internal combustion engine should a breakage occur in the pleated element.

In another embodiment, the frustoconical separator is separate from the pleated filter element and formed from a stack of annular members of progressively decreasing diameter which are held in relative position by a plurality of longitudinal stringers. The relationship of the annular members one to another defines the desired louvered configuration.

The frustoconical separator can be constructed by other manufacturing methods, such as spiral winding, which simultaneously forms the louvers, or by molding the entire unit.

In further embodiments of the invention, a reversed outlet tube is provided for the scavenged particulate matter, and means including a high pressure nozzle are included in cooperation with the outlet tube to assist in the removal of scavenged matter.

There is now described, by way of example and with reference to the accompanying drawings, several embodiments of apparatus and separator/filter assemblies of the invention. In the drawings: Figure 1 is a view in side elevation of air cleaning apparatus embodying the subject invention, portions thereof broken away and shown in section; Figure 2 is an exploded perspective view of the replaceable separator/filter assembly for the air cleaning apparatus; Figure 3 is an enlarged end view of the frustoconical separator of the separator/filter assembly; Figure 4 is a fragmentary view in side ele vation of an alternative embodiment of the invention with portions thereof broken away and shown in section; Figure 5 is a side elevational view which is diminished in size of the frustoconical separator of the alternative embodiment; Figure 6 is an end view of the alternative frustoconical separator; and Figures 7-9 are views taken in longitudinal section of alternative embodiments of the invention, each of which specifically discloses the variation in the outlet treatment of scavenged particulate matter.

With initial reference to Figure 1, an air cleaner embodying the inventive concept is represented generally by the numeral 11.

Cleaner 11 comprises a cylindrical casing 12 having a longitudinal axis, and which, in unassembled form, is open at both axial ends.

The inlet end (the right end of Figure 1) of casing 12 has an annular flange 13 secured thereto which receives an end cap 14 in a manner described in greater detail hereinbelow.

Cap 14 defines a central axial opening 15 which serves as the inlet for uncleaned air to the cleaner 11.

At the opposite or outlet end, a cap 16 is secured to the casing 12 as by welding, the cap 16 defining a central axial opening 17 of smaller diameter than opening 15, and which serves as an initial outlet for the device. The opening 17 empties into a cylindrical collector 18 of short axial dimension and which includes an outlet tube 19 which extends radially outward for venting scavenged particulate matter.

Casing 12 also has a large, generally circular opening formed through its side adjacent the outlet end to which an outlet 20 for clean air is rigidly and sealable secured.

With additional reference to Figures 2 and 3, a separator/filter assembly for the device 11 is represented generally by the numeral 21.

Assembly 21 comprises a separator 22 which is the innermost component. Generally speaking, separator 22 defines a wall or partition which converges from the inlet 15 to the outlet opening 17, thus presenting a flow path of progressively decreasing area to the uncleaned air entering the device. Specifically, separator 22 is a truncated cone formed from a plurality of frustoconical components 23. To this end, each of the components 23 is arcuate in section and tapered as a function of the progressively decreasing cone diameter. As best shown in Figure 3, each of the components 23 is formed with an upturned side 23a which in assembled form extends radially outward to form a longitudinal spacer rib. The opposite side of each segment is formed to define a step 23b which extends radially inward an amount approximating the thickness of the component so that it receives the opposite side of the adjacent component while at the same time continuing the circular configuration as viewed in transverse cross section. As constructed, the overlapping, fitted sides of adjacent components 23 are welded or joined together by means of epoxy resin to define the frustoconical shape.

With reference to Figures 1 and 2, each of the components 23 is formed with a plurality of louvers 24 which are disposed in two longitudinal rows. In assembled form, the louvers of each component 23 are aligned with the louvers of other components 23 to define circumferential rows. In the preferred embodiment, the louvers 24 are punched from the body of the component 23, thus creating edges which project radially inward. The resulting louver surfaces are inclined toward the outlet; or, stated otherwise, they converge in the general direction of uncleaned air flow. As shown in Figure 1, the flow of air through the louvers 24 is permitted only upon a partial reversal of flow direction. For a substantial amount of particulate matter, which is of greater density than the air, the buildup of inertia is too large to permit such partial reversal, and the particulate matter is thus swept through the entire length of the separator 22 for discharge through the outlet.

Separator/filter assembly 21 further comprises a pleated filter element 25 sandwiched between inner and outer liners 26, 27, respectively. Filter element 25 is made from porous paper, and, as is well known in the art, pleated to increase the filtraion surface as well as to strengthen the element itself. Inner and outer liners 26, 27 are made from thin metal or plastic to provide additional strength to the filter element 25, and include large perforations to permit the unobstructed flow of air.

As shown in Figure 1, the sandwich of filter element 25 and liners 26, 27 also takes the form of a truncated cone, although it diverges slightly with respect to the separator 22. This divergence may be observed with the increasing radial dimension of the single spacer side 23a shown in Figure 1. The divergence is included to increase the size of the inner diameter of the filter element 25, while at the same time permitting the outlet opening 17 to be small.

The opening 17 must be sufficiently small relative to the inlet 15 to permit sufficient convergence and thereby control the flow velocity, and the separator 22 must converge smoothly to the opening 17 without abrupt changes to ensure maximum effectiveness.

However, were the inner diameter of the smaller end of filter element 25 to correspond more closely to the outlet opening 17, the pleats would be too close together to permit full and efficient filtration, and the concentration of pleats could also create the possibility of structural defects. The spacing effect of the sides 23a thus enables the filter element 25 to assume more desirable dimensions.

It is intended that the separator/filter assembly 21 be easily removed and replaced as a unit, and the several elements are therefore held in relative position by end caps 28, 29.

Each of the end caps 28, 29 is annular in shape and cupped to receive the element ends. The caps are secured to the elements by an adhesive material.

It is also preferable that the device 11 in dude a safety filter element, which is represented by the numeral 31 in Figure 1. Safety element 31 consists ofinner and outer linings 32, 33 which are similar to the linings 26,27 but for the difference in diameter. A single layer of paper 34 is sandwiched between the linings 32, 33, the porosity of which is greater than that of the filter element 25, but which is sufficient to perform minimal filtration should a break occur in the element 25. Safety element 31 further includes an annular cap 35 at its smaller end which is adhered to the elements 32-34. An end cap 36 having a radial flange is adhered to the larger end, the flange serving to mount the safety element 31 in proper position.

The separator/filter assembly 21 and safety element 31 are sealably mounted within the device 11 through the use of gaskets 37, which are adhesively secured to the respective end caps 14, 16 of the device for engagement with the end caps 28, 29 and 35, 36. For assembling purposes, the inlet cap 14 is removed, and the safety element 31 is initially inserted with its tapered sides in engagement with the cylindrical casing 12 at the inlet end (see Figure 1). This has the effect of centering the element 31, and the subsequent insertion of the separator/filter assembly 21 is thus centered by the engagement of its end caps with those of the element 31.

The cap 14 is then placed over the inlet end of the unit and secured in place with a nut and bolt assembly.

A bracket 39 is mounted to the casing 12 for mounting the device.

In operation, uncleaned air is admitted through the inlet 15, passing through the longitudinal flow path defined within the separator 22. Depending on the selected degree of convergence of the frustoconical separator, the flow of the air is maintained at a uniform or increasing velocity; and separation of a substantial amount of the particulate matter therefore occurs uniformly over its length. In this regard, we have found that optimum separation efficiency occurs when the flow velocity at the scavenge outlet is more than two times greater than the flow velocity at the dirty air inlet. As pointed out above, separation occurs because the particles are of greater density than the air, and are unable to reverse the essentially straight flow path due to the buildup of inertia. The scavenged particulate matter thus passes entirely through the separator 22, entering the collector 18 from the opening 17 and passing to atmosphere from the outlet tube 19.

That portion of the air flow which separates from the main stream by passing through the louvers 24 then moves essentially radially outward through the filter element 25. The precleaned and filtered air then passes through the safety element 31 and into an outlet chamber 40, from which it leaves through the outlet 20 for use in the internal combustion engine. The chamber 40 increases in size toward the outlet end of the device, commensurate with the volume of flow delivered from the assembly 21 over its length.

A vacuum assist may be used in conjunction with the outlet 19 to enhance the removal of particulate matter, and/or with the outlet 20 to assist in the separation and filtration processes.

With reference to Figures 4-6, an alternative air cleaning device is represented generally by the numeral 41. In these figures, like numerals represent structure identical to that of the device 11, and additional numerals represent new or modified structure.

The principal difference between devices 41 and 11 resides in the separation and filtration stages. Rather than an integral assembly, the device includes a separate separator 42 and a separate filter element 43, along with the identical safety element 31.

With specific reference to Figures 5 and 6, separator 42 comprises a plurality of annular rigid bands 44, each of which takes the form of a truncated cone having a large diameter as compared with its axial dimension. The rigid bands 44 are of progressively decreasing diameter in the direction of air flow; and, in order to define the necessary louvered passages, the smallest diameter of each band is smaller than the largest diameter of the adjacent band, thus creating a flow passage therebetween. The plurality of bands 44 are arranged in a stacked relationship and commonly secured by four longitudinal stringers 45.

At the inlet end of the separator 42, a larger rigid band 46 of greater axial dimension and converging in the opposite direction is secured to the first band 44 and defines an inlet for the separator 42. A cruciform 47, consisting of a pair of orthogonal blades 48, extends into the inlet of the separator 42 and is secured to the inner surface of the larger band 46. The cruciform 47 assists in maintaining straight, axial flow through the separator 42, which results in better separation of the particulate matter.

At the outlet end of separator 42, a cylindrical outlet sleeve 49 is secured to the smallest rigid band 44. An annular flange 50 extends radially outward from the outlet sleeve 49. The outer diameter of sleeve 49 corresponds to the inner diameter of outlet opening 17, permitting a sliding relation. An additional gasket 37 is positioned on outlet cap 16 for sealing engagement with the flange 50, as shown in Figure 4.

With continued reference to Figure 4, the filter element 43 consists of the same pleated element 25 and liners 26,27, but includes modified end caps 52, 53 which do not acommodate the separator 42.

The construction of device 41 is otherwise essentially the same as device 11. The stacked construction of separator 42 creates an in creased louvered passage flow area. It will also be appreciated that the separate construction of the separator 42 and filter element 43 enables them to be individually removed and replaced from the device 41.

Figures 7-9 disclose three further embodiments which include means for assisting in the removal of scavenged particulate matter, and which are particularly useful in extremely dusty and dirty conditions. In Figure 7, an air cleaning device represented generally by the numeral 61 comprises a cylindrical casing 62 which is open at both ends and formed with a peripheral flange 63 at the inlet end. Casing 62 also includes an outlet 64 for cleaned air which opens from its side approximately the outlet end. A removaeble cap 65 is sealably secured to the casing 62 by nut and bolt assemblies 66 and an 0-ring 67. Inlet cap 65 is formed with a large inlet 68 which admits uncleaned air to the device 61.

An end cap 69 is permanently and sealably secured to the outlet end of casing 62. As shown, end cap 69 is formed with a cylindrical recess which receives the smaller end of a conical separator/filter assembly 71. The assembly 71 comprises a conical separator 72 having louvers 73 and a pleated dry paper filter element 74 which is also conical in shape. The separator 72 and filter element 74 are integrally held by end caps 75, 76, the former of which includes a peripheral flange which is clamped between the end cap 65 and flange 63 of casing 62. A flat annular seal 77 is disposed between end caps 76 and 69 for air tight operation. An outlet stack 78 is secured to and supported by the inlet cap 65, projecting virtually to the outlet end of the separator 72 to define a separation flow passage 79 and an outlet flow passage 80 which are concentric. It will be observed that the end cap 76 for the separator/filter assembly 71 is a solid circular cap, as distinguished from the annular configuration of end cap 75, so that the scavenged particulate matter and carrier air flow do not leave from the bottom of the device 61 as shown in Figure 7. The end cap 76 is formed with an annular, concave recess 76a which conforms generally to the annular, rounded lower end of the outlet stack 78, so that the scavenging air flow from separation passage 79 to outlet passage 80 is smoothly reversed.

It will be further observed that the outlet passage 80 initially assumes a constant diameter and then expands to a larger flow area before curving outwardly for issuance through the side of inlet cap 65. To this end, outlet stack 78 is formed from an outer lining 81 which is generally cylindrical and an inner lining 82 which defines the expanding flow passage. The connection between the linings 81, 82, designated by reference numeral 83, initially conforms to the shape of the lowermost louver 73 and is then rounded to effect the smooth reversal of flow as noted above.

To assist in the rapid and efficient removal of scavenged particulate matter, an air nozzle 84 is introduced through the end cap 76, projecting axially into the inlet of outlet passage 80. Air nozzle 84 is sealably clamped against the end cap 76 through the use of an 0-ring 85, and is adapted for connection to a high pressure air source through the use of an enlarged fitting 86.

Separation and filtration of the air cleaner 61 is much the same as air cleaner 11, although it will be noted that incoming air must pass around the outlet stack 78 into the annular separation flow passage 79. This passage is convergent to maintain a uniform flow velocity to achieve efficient separation.

As the particulate matter and its carrier flow leave the separation passage 79, a smooth flow reversal takes place which is significantly assisted by the high velocity flow issuing from air nozzle 84. Nozzle 84 creates a flow pressure within outlet passage 80 which is lower than that within separation passage 79, and which draws the scavenged particulate matter into the outlet passage and out of the outlet stack 78. This increased flow significantly improves the separation capability of the device 61 and is thus well adapted to extremely dusty environments.

Figure 8 discloses an air cleaner which is essentially the same as device 61, with the exception of a modified outlet stack 91. Stack 91 comprises an outer lining 92 which has a progressively increasing diameter as it approaches the lower end of the separator 72, thus increasing the degree of convergence of a separator flow passage 93. An inner lining 94 is cylindrical in shape, thus defining an outlet passage 95 of constant cross sectional area. The outlet end of stack 91 bends radially outward through the side of the inlet cap as shown.

In figure 9, an outlet stack 101 is defined by a cylindrical outer lining 102 and a cylindrical inner lining 103 to define a separator flow passage 104 having a lesser degree of convergence and an outlet passage 105 of constant cross sectional area. The upper end of outer lining 102 terminates in a dome 106 which is disposed in the inlet of the device to assist in smoothly dividing the flow into the annular separation passage 104. The inner lining 103 bends radially outward through the outer lining 102 and the side of the inlet cap to discharge the scavenged particulate matter.

The space defined between inner and outer linings 81-82, 92-94, and 102-103 is dead space and is not exposed to flow.

The embodiments of Figure 7-9 are somewhat schematic for purposes of clarity, and do not disclose any support for the outlet stacks 78, 91 and 106 other than the support provided by the associated inlet cap. It is possible to include radial struts between the stack and the inlet cap or associated separator if necessary for additional support.

Claims

WHAT WE CLAIM IS:

1. Apparatus for cleaning air, comprising: (a) a casing defining an internal chamber and having an inlet for uncleaned air, a first outlet for discharging particulate matter and a second outlet for discharging cleaned air; (b) converging wall means disposed within the chamber is associated with the inlet and de fining a first flow path for inlet air which de creases in flow area from the inlet; (c) louver means formed in the converging wall means and defining a second flow path therethrough, the louver means being construc ted to cause air to partially change direction in order to flow therethrough, thereby enabling the separation of particulate matter from the air (d) means for establishing fluid communica tion between the converging wall means and the first outlet to discharge separated particulate matter therefrom; and (e) filter means disposed within the chamber between the converging wall means and the second outlet and tapering in the same direc tion with respect to said chamber as does the converging wall means, said filter means being for filtering air that passes through and leaves the louver means; (f) the second outlet being in fluid com munication with the filter means to receive fil tered air therefrom and to discharge the filtered air from the apparatus.

2. Apparatus according to claim 1, wherein the casing as generally cylindrical, and the converging wall means and filter means are frusto conical in shape.

3. Apparatus according to claim 2, wherein the converging wall means and filter means are constructed as a separator/filter assembly, the assembly being removeably disposed in the cylindrical casing.

4. Apparatus according to claim 2 or 3, wherein the inlet and first outlet are disposed in the axial ends of the cylindrical casing, the converging wall means defining circular openings at each end thereof that correspond in size to the inlet and first outlet and are disposed in fluid communication therewith.

5. Apparatus according to claim 3 or 4, wherein the cylindrical casing has at least one removeable end cap to permit removal of said separator/filter assembly.

6. Apparatus according to claim 5, wherein the removeable end cap is disposed at the inlet end of the casing, said inlet being centrally disposed therein.

7. Apparatus according to any of claims 2 to 6, wherein the filter means comprises inner and outer frustoconical shells with a pleated filter element sandwiched therebetween.

8. Apparatus according to claim 7, wherein the converging wall means and filter means are disposed in concentric, spaced relation, and the separator/filter assembly has imperforate annular end caps secured to each end thereof.

9. Apparatus according to claim 8, which has gasket means disposed in sealing relation between each of the annular end caps and the casing.

10. Apparatus according to any of claims 3 to 9, which has a safety filter element of frustoconical shape disposed between the separator! filter assembly and the second outlet, the safety filter element being concentric with the separator/filter assembly and in sealable engagement with the ends of the casing.

11. Apparatus according to claim 9 or 10, wherein the second outlet is disposed in the side of the casing.

12. Apparatus according to any of claims 4 to 11, which has a collector cap connected to the outlet end of the casing in communication with the first outlet, the collector cap including an outlet tube which extends radially outward for venting particulate matter.

13. Apparatus according to any of claims 2 to 12, wherein the filter means diverges relative to the converging wall means in the downstream direction.

14. Apparatus according to any of claims 1 to 9, which has a second filter means disposed between the first named filter means and the second outlet.

15. Apparatus according to claim 14, wherein the second filter means converges in the same direction with respect to said chamber as does the converging wall means and first filter means.

16. Apparatus according to claim 15, wherein the casing is generally cylindrical, and the converging wall means and first and second filter means are frustoconcial in shape and concentrically disposed.

17. Apparatus according to any of claims 2 to 16, wherein the louver means comprises a plurality of louvers that project radially inward and converge in the direction of air flow in the converging wall means.

18. Apparatus according to claim 17, wherein the louvers are disposed in circumferential and longitudinal rows.

19. Apparatus according to any of claims 2 to 18, wherein the filter means comprises inner and outer frustoconical shells with a pleated filter element sandwiched therebetween.

20. Apparatus according to any of claims 2 to 16 and 19,wherein the converging wall means comprises a separator formed from a stacked plurality of frustoconically shaped, annular bands, the bands being of progressively decreasing diameter in the direction of air flow in the converging wall means, and the smallest diameter of each being smaller than the largest diameter of the adjacent band to define a louvered passage therebetween.

21. Apparatus according to claim 20, wherein the annular bands are interconnected by a plurality of longitudinal stringers.

22. Apparatus according to claim 20 or 21, wherein the separator further comprises a pair of orthogonal blades extending axially into its inlet for maintaining straight, axial flow therethrough.

23. Apparatus according to claim 1, which has nozzle means disposed in the region of the downstream end of converging wall means, adapted for connection to a source of fluid pressure for assisting in the removal of separated particulate matter from the apparatus.

24. Apparatus according to any of claims 1 to 3,5 to 11 and 13 to 23,wherein: (a) the converging wall means and louver means comprise a separator; (b) the separator and filter means are frustoconical in shape and concentrically disposed; (c) and the means for establishing fluid communication between the converging wall means and the first outlet comprises (i) an outlet tube disposed concentrically within the separator and having an inlet end and an outlet end; (ii) means for causing a reversal of air flow from the separator into the outlet tube; (iii) and the nozzle means is disposed proximate the inlet end of the outlet tube.

25. Apparatus according to claim 24, wherein the nozzle means comprises an air nozzle supported by the casing and projecting into the inlet end of the outlet tube.

26. Apparatus according to claim 24 or 25, wherein the outer surface of the outlet tube diverges relative to the convergence of the separator.

27. Apparatus according to claim 24, 25 or 26, wherein the inner surface of the outlet tube diverges relative to the first outlet.

28. Apparatus according to claim 24,25 or 26, wherein the inner surface of the outlet tube is cylindrical and of generally uniform diameter.

29. Apparatus according to claim 24 or 25 wherein the outer surface of the outlet tube is cylindrical and of generally uniform diameter.

30. Apparatus according to any of claims 24 to 29, wherein the first outlet is disposed in the casing side, and the outlet tube curves radially outward for fluid communication therewith.

Apparatus according to any of the preceding claims, wherein the converging wall means is constructed to effect a velocity of flow at the first outlet that is approximately the same as the velocity of flow at the inlet

32. Apparatus according to any of claims 1 to 30, wherein the converging wall means is constructed to effect a velocity of flow at the first outlet that is at least twice the velocity of flow at the inlet.

33. Apparatus according to claim 20, wherein each of said frustoconically shaped, annular bands has first and second longitudinal edges, the first edge being turned radially outward to form an elongated spacer rib, each rib being secured to an adjacent second longitudinal edge, the elongated spacer ribs together defining spacer means to space apart said filter means from the converging wall means.

34. Apparatus according to Claim 33, wherein each of said second longitudinal edges is formed to define a longitudinal step which is recessed radially inward an amount approximating the thickness of the annular band, said step receiving the first longitudinal edge in overlapping engagement.

35. Apparatus for cleaning air, comprising: a) a generally cylindrical casing having first and second axial ends and defining an internal chamber, the cylindrical casing further comprising an inlet in the first axial end, a first outlet in the second axial end for discharging particulate matter, and a second outlet; b) a separator comprising (i) a hollow, frustoconical member disposed within the chamber with its larger end sealingly encircling the inlet and the smaller end sealingly encircling the first outlet to define a first flow path for inlet air which decreases in flow area from the inlet to the first outlet; (ii) louver means formed in the frustoconical member and defining a second flow path therethrough, the louver means being constructed to cause air to partially change direction in order to flow therethrough, thereby enabling the separation of particulate matter from the air; (c) a hollow, frustoconical filter element disposed in the chamber in concentric, encircling relation to said frustoconical member with its larger end sealingly engaging the first axial end of the casing and its smaller end sealingly engaging the second axial end of the casing, the frustoconical filter element diverging relative to said frustoconical member from said larger end to said smaller end define a first annular space therebetween; (d) the frustoconical filter element further defining a second annular space with the inner surface of the cylindrical casing that increases in flow area from the first axial end of the casing to its second axial end; (e) the second outlet being in fluid communication with the second annular space to receive filtered air from the filter element, and to discharge filtered air from the apparatus.

36. Apparatus according to any of the preceding claims, substantially as described herein with reference to the accompanying drawings.

37. Apparatus for cleaning air, substantially as described herein and substantially as shown in Figures 1 to 3 of the accompanying drawings.

38. Apparatus for cleaning air, substantially as described herein and substantially as shown in Figures 4 to 6 of the accompanying drawings.

39. Apparatus for cleaning air, substantially as described herein and substantially as shown in Figure 7 of the accompanying drawings.

40. Apparatus for cleaning air, substantially as described herein and substantially as shown in Figure 8 of the accompanying drawings.

41. Apparatus for cleaning air, substantially as described herein and substantially as shown in Figure 9 of the accompanying drawings.

42. An internal combustion engine equipped with apparatus as claimed in any of the preceding claims.

43. A replaceable separator/filter assembly for use in air cleaning apparatus as claimed in Claim 35, comprising: (a) a separator comprising (i) a hollow, frustoconical member having open axial ends and defining an air flow path that decreases in flow area from the larger open end to the smaller open end; (ii) louver means formed in the frustoconical member and defining a second flow path therethrough, the louver means constructed to cause air to partially change direction in order to flow therethrough, thereby enabling the separation of particulate matter from the air; (b) a hollow, frustoconical filter element disposed in concentric, encircling relation to said frustoconical member, the filter element diverging relative to said frustoconical member from the larger end to the smaller end of the frustoconical member to define a first annular space therebetween; and (c) an imperforate annular end cap secured to each axial end of said frustoconical member and filter element to hold them in assembled relation.

44. A separator/filter assembly according to Claim 43, wherein the filter element comprises inner and outer perforated frustoconical shells with a body of pleated filter material sandwiched therebetween.

45. A separator/filter assembly according to Claim 43 or 44, in which said frustoconical member is formed from a plurality of tapered frustoconical components.

46. A separator/filter assembly according to Claim 45, wherein each of said tapered frustoconical components defines first and second longitudinal edges, the first edge being turned radially outward to form an elongated spacer rib, each rib being secured to an adjacent second longitudinal edge.

47. A separator/filter assembly according to Claim 46, wherein each of said second longitudinal edges is formed to define a longitudinal step which is recessed radially inward an amount approximating the thickness of the tapered component, said step receiving the first longitudinal edge in overlapping engagement.

48. A separator/filter assembly according to any of Claims 43 to 47, wherein the louver means comprises a plurality of louvers disposed in circumferential and longitudinal rows, the louvers projecting radially inward and converging in the direction of downstream air flow.

49. A separator/filter assembly according to Claim 43, substantially as described herein with reference to the accompanying drawings.

50. A separator/filter assembly substantially as described herein and substantially as shown in Figures 2 and 3 of the accompanying drawings.