Composite planar and triangularly pleated filter element
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates in general to fluid filters and more particularly to a filter element having a filtering medium which is pleated or folded to give a large filtering area in a relatively small space. 
     II. Description of the Prior Art 
     It is known to form a filtering medium from a filtering material which is folded to include alternating top and bottom sections of generally triangular shape, the top sections tapering in one direction and the bottom sections tapering in the opposite direction, and side wall sections lying between the top and bottom sections and having their edges joined in the front and back at the apexes of the triangular top and bottom sections. 
     A filter element having a pleated filtering medium of the above described kind is disclosed in Japanese Provisional Utility Model Publication No. 62-132714 and also shown in FIGS. 13 and 14. 
     In the prior art filter element of FIGS. 13 and 14, the bottom sections 12 are completely coated with adhesive and bonded to a roughly flat filtering medium 13. The bottom sections 12 therefore cannot effect a filtering action. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an improved filter element which comprises a roughly flat filtering medium formed of filtering material and a pleated filtering medium placed upon the roughly flat filtering medium. The pleated filtering medium is formed of filtering material folded to include alternate top and bottom sections of roughly triangular shape, the top sections tapering in one direction and the bottom sections tapering in the opposite direction, and side wall sections lying between the top and bottom sections and having their edges joined in the front and back at the apexes of the triangular top and bottom sections. The bottom sections have edges defining an end of the pleated filtering medium and joined by seal to the roughly flat filtering medium only at and near the edges of the bottom sections. 
     The filter element of the above construction is effective for overcoming the above noted shortcoming of the prior art filter element. 
     It is accordingly an object of the present invention to provide an improved filter element of the kind having a plurality of pleated filtering mediums which can efficiently increase the filtering area without accompaniment of a substantial increase of the flow resistance. 
     It is another object of the present invention to provide an improved filter element of the above described character which requires a smaller amount of sealant adhesive as compared with a comparable prior art filter element. 
     It is a further object of the present invention to provide an improved filter element of the above described character which is compact in size but has a large filtering area. 
     It is a further object of the present invention to provide an improved filter element of the above described character which can be formed from a number of relatively shallowly pleated filtering elements without accompaniment of substantial increase of flow resistance and thereby making it possible to increase the structural strength. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective, partially cutaway view of a filter element according to an embodiment of the present invention; 
     FIG. 2 is an enlarged fragmentary exploded view of the filter element of FIG. 1; 
     FIG. 3 is a view similar to FIG. 14 but illustrates how a strip of filtering material is folded in forming a pleated filtering medium of the filter element of FIG. 1; 
     FIGS. 4 to 6 are enlarged fragmentary perspective views of filter elements according to modifications of the present invention; 
     FIG. 7 is a view similar to FIG. 1 but shows another embodiment of the present invention; 
     FIG. 8 is a fragmentary exploded view of the filter element of FIG. 7; 
     FIG. 9 is a fragmentary perspective view of a subassembly of pleated filtering medium and roughly flat filtering medium according to a further embodiment of the present invention; 
     FIG. 10 illustrates how the of FIG. 9 is rolled into a filter element of a frustoconical shape; 
     FIG. 11 is a partly sectional view of the filter element of FIG. 10 installed in a filter housing; 
     FIG. 12 is a view similar to FIG. 11 but shows a modification of the present invention; 
     FIG. 13 is a perspective view of a prior art filter element; and 
     FIG. 14 illustrates how a strip of filtering material is bent in forming a pleated filtering medium of the filter element of FIG. 11. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIGS. 1 to 6, a filter element according to an embodiment of the present invention is generally indicated by 20 and consists of a plurality of pleated filtering mediums 21, a plurality of generally or roughly flat filtering mediums 22 each interposed between the adjacent two pleated filtering mediums 21 in such a way as to form a laminated or honeycomb-like construction and a casing 23 of filtering material or sythetic resinous material surrounding the subassembly of filtering mediums 21, 22 except for the front and back through which fluid enters and exits from the filter element 20, as indicated by the arrows in FIG. 1, when the filter element 20 is in use. 
     More specifically, the subassembly of filtering mediums 21, 22 has a rectangular configuration and is surrounded at four sides except for the front and back by the casing 23 which is correspondingly rectangular in shape. 
     Each pleated filtering medium 21 is formed from a strip of filtering material folded and corrugated as described above with the folds or bends lying substantially in the direction of fluid flow. That is, as seen from FIG. 2, each pleated filtering medium 21 has triangular top sections 21a, triangular bottom sections 21b and side walls 21c lying between the top and bottom sections 21a and 21b. Specifically, the top and bottom sections 21a, 21b are shaped so as to be of the same isoceles triangle. 
     The folding and bending of filtering medium 21 will be clearer from FIG. 3, where pairs of edges of the side walls 21c to be joined together and sealed to each other by sealant adhesive are shown at 21d for the front of the filter element 20 and at 21e for the back of the filter element 20. 
     The pleated filtering mediums 21 are placed one upon another, i.e., superposed in such a way that the top and bottom sections 21a, and 21b are respectively aligned with one another and equally spaced. 
     Each pleated filtering medium 21 has a generally or roughly straight front end 21f constituted by the front edges 21g of the top sections 21a, i.e., constituted by the bases 21g of the isosceles triangular top sections 21a, and a generally or roughly straight rear end 21h constituted by the rear edges 21i of the base sections 21b, i.e., constituted by the bases 21i of the isosceles triangular base sections 21b. Each pleated filtering medium 21 is bonded and sealed with sealant adhesive 25 only at and near the front and rear ends 21f, 21h to the adjacent upper and lower roughly flat filtering mediums 22. That is, the front end 21f and its adjacent portion of the pleated filtering medium 21 is bonded and sealed to the lower surface front end of the upper roughly flat filtering medium 22, whereas the rear end 21h and its adjacent portion is bonded and sealed to the upper surface rear end of the lower roughly flat filtering medium 22. 
     The front end 21f of each pleated filtering medium 21 further has a pair of vertically bent sections 21j constituted by the front edges of the side walls 21c located most outwards. In this connection, the most outward bottom sections 21b are halved so that the lateral and rear ends of each pleated filtering medium 21 are fittingly received in the rectangular casing 23, which will be described and shown more in detail with reference to the embodiment of FIGS. 7 and 8. 
     In the foregoing, it is to be noted that the bottom sections 21b are bonded and sealed to the roughly flat filtering medium 22 only at and near the rear edges 21i so that fluid can flow not only through the top and side wall sections 21a, 21c but through the bottom sections 21b when the fluid is filtrated by the filter element 20, i.e., the bottom sections 21b can effect a filtering action. Accordingly, the filter element 20 according to an embodiment of the present invention can give a larger filtering area and at the same time can reduce the flow resistance as compared with the comparable prior art filter element shown in FIGS. 13 and 14. 
     It is further to be noted that the top sections 21a are bonded and sealed only at and near the front edges 21g to the flat filtering medium 22 so that the top sections 21a can effect a filtering action even when a plurality of pleated filtering mediums 21 and a plurality of generally or roughly flat filtering mediums 22 are arranged in a multilayered fashion. Accordingly, the present invention makes it possible to increase the filtering area without accompaniment of a substantial increase of the flow resistance. 
     It is further to be noted that the present invention is effective for increasing the structrual strength of the filter element by forming a filter element including a number of relatively shallowly pleated filtering mediums. In this connection, if the prior art filter element is provided with a number of pleated filtering mediums, not only the filtering area in a limited space is considerably reduced but the flow resistance is considerably increased. 
     It is further to be noted that the filter element 20 according to an embodiment of the present invention requires a smaller amount of sealant adhesive 25 as compared with the comparable prior art filter element shown in FIGS. 13 and 14 since the pleated filtering mediums 21 are bonded and sealed only at and near the front and rear ends 21f, 21h to the adjacent upper and lower roughly flat filtering mediums 22. 
     Referring to FIG. 4, a spacer in the form of a strip of tape indicated by 26 is disposed between the top sections 21a of each pleated filtering medium 21 and the adjacent roughly flat filtering medium 22 so that the top sections 21a are held out of contact with the roughly flat filtering medium 22, i.e., a space is defined between the top sections 21a and the adjacent roughly flat filtering medium 22. Similarly, another spacer 26 is disposed between the bottom sections 21b of each pleated filtering medium 21 and the adjacent roughly flat filtering medium 22 so that the bottom sections 21b are held out of contact with the filtering medium 22, i.e., a space is defined beween the bottom sections 21b and the adjacent roughly flat filtering medium 22. More specifically, the spacers 26 are disposed adjacent to the front edges 21g of the top sections 21a and the rear edges 21i of the bottom sections 21b. The spacers 26 are effective for enabling the top and bottom sections 21a, and 21b of each pleated filtering medium 21 to effect an efficient filtering action. 
     As shown in FIG. 5, a pair of projections 27a, and 27b may be formed in each top section 21a and its adjacent roughly flat filtering medium 22 in place of the spacers 26 of FIG. 4. Similarly, another pair of projections 27a, and 27b may be formed in each bottom section 21b and its adjacent roughly flat filtering medium 22. More specifically, each top section 21a may have near the front edge 21g the upward projection 27a which is put into contact with the downward projection 27b formed in the adjacent roughly flat filtering medium 22. Similarly, each bottom section 21b may have near the rear edge 21i the downward projection 27b which is put into contact with the upward projection 27a formed in the adjacent roughly flat filtering medium 22. 
     As shown in FIG. 6, the roughly flat filtering medium 22 may be formed with alternate small ridges 22a and grooves 22b in place of being formed with such projections 27a, and 27b or in place of being provided with such spacers 26. In other words, a spacer means is constituted by the small ridges 22a and grooves 22b formed in the roughly flat filtering medium 22. Such alternate small ridges 22a and grooves 22b may also be formed in the casing 23 for the same end. 
     FIGS. 7 and 8 show another embodiment in which parts and portions similar to the previous embodiment of FIGS. 1 to 6 are designated by the same reference characters. As described with reference to the previous embodiment, the front end 21f of each pleated filtering medium 21 has the vertically bent sections 21j constituted by the front edges of the side walls 21c located most outwards. In this connection, as seen from FIG. 7, the most outward bottom sections 21c are halved so that each pleated filtering medium 21 has a predetermined rectangular plane figure or configuration, i.e. the pleated filtering medium 21 has lateral ends 21k which constitute together with the front and rear ends 21f, 21h a predetermined rectangular plane figure. 
     Each pleated filtering medium 21 is surrounded by a channel-shaped filtering medium 33 formed of filtering material except for the front, back and bottom. The channel-shaped filtering medium 33 consists of a top wall section 33a covering the top of each pleated filtering medium 21 and a pair of side wall sections 33b covering the opposite lateral ends of each filtering medium 21. The side wall sections 33b have at the lower ends thereof inwardly bent ends 33c. The top wall section 33a is bonded and sealed to the front end 21f of the pleated filtering medium 21 similar to the previous embodiment. The vertical bent sections 21j of the front end 21f, i.e., the front edges 21j of the most outward side wall sections 21c and the lateral ends 21k are bonded and sealed to the side wall sections 33b and the inwardly bent ends 33c with sealant adhesive 25. 
     The subassemblies of pleated filtering mediums 21 and channel-shaped filtering mediums 33 are placed one upon another and joined in such a manner that the rear end 21h of the pleated filtering medium 21 of one subassembly is bonded and sealed with sealant adhesive 25 to the top wall section 33a of the cover 33 of another subassembly. By the repetition of the above procedure, a filter element 30 of a predetermined laminated structure is obtained. The bottom of the lowest subassembly of pleated filtering medium 21 and channel-shaped filtering medium 33 is covered by a generally or roughly flat filtering material 38 formed of filtering material. That is, the rear end 21h of the pleated filtering medium 21 of the lowest subassembly is bonded and sealed with sealant adhesive 25 to the flat filtering medium 38. The roughly flat filtering medium 38 is also bonded and sealed to the inwardly bent ends 33c of the channel-shaped filtering medium 33 of the lowest subassembly. 
     In the foregoing, it will be understood that the channel-shaped filtering medium 33 of one of the most outward subassemblies, the side wall sections 33b of the remaining channel-shaped filtering mediums 33 and the roughly flat filtering medium 38 constitute a casing means similar to the casing 23 of the previous embodiment of FIGS. 1 to 6. 
     It will be further understood that the top wall sections 33a of the channel-shaped filtering mediums 33 except that of the highest subassembly serve as a partition means similar to the roughly flat filtering mediums 22 of the previous embodiment of FIGS. 1 to 6. 
     Except for the above, this embodiment is substantially similar to the previous embodiment and can produce substantially the same effect. Futhermore, this embodiment can make the assembly of the filter element 30 easy and efficient. 
     FIGS. 9 to 11 show a further embodiment in which parts and portions similar to the previous embodiment of FIGS. 1 to 3 are designated by the same reference characters. In this embodiment, an originally roughly or generally flat filtering medium 42 is formed from a filtering material corrugated so as to have alternate small ridges and grooves (no numeral). The rear end 21h of the pleated filtering medium 21 is bonded and sealed with sealant adhesive 25 to the originally roughly flat filtering medium 42 in a similar manner to the previous embodiments. As shown in FIG. 10, the subassembly of originally roughly flat filtering medium 42 and pleated filtering medium 21 is coiled or wound about a center pipe 48 and formed into a round shape while at the same time the front end 21f of the pleated filtering medium 21 is bonded with sealant adhesive 25 to the originally roughly flat filtering medium 21 in a similar manner to the previous embodiments. 
     More specifically, by the above coiling or winding, the subassembly of originally roughly flat filtering medium 42 and pleated filtering medium 21 are formed into a frustoconical shape. This is because the circumferential length of the subassembly does not substantially change at the front but reduces at the rear due to the fact that the apexes of the top sections 21a are caused to come nearer by the coiling. In this instance, by the effect of the small ridges and grooves, the originally roughly flat filtering medium 42 expands a little at the front and contracts at the rear, whereby to make it possible to attain the rolling of the unit of filtering mediums 21, 42 with ease. The tendency of being formed into the frustoconical shape can be reduced by bonding the top and bottom sections 21a, 21b together at the additional places. In use, the frustoconical filter element 40 is disposed in a filter housing 49 as shown in FIG. 11. In the meantime, by using a suitable jig or the like means, the subassembly of originally roughly flat filtering medium 42 and pleated filtering medium 21 can be wound into a cylindrical shape for installation in a cylindrical casing 49 as shown in FIG. 12. 
     Except for the above, this embodiment is substantially similar to the previous embodiment of FIGS. 1 to 6 and can produce substantially the same effect. This embodiment is further advantageous since the small ridges and grooves of the originally roughly flat filtering medium 42 can serve as spacers for defining spaces between the top and bottom sections 21a, 21b. 
     In the foregoing, it is to be noted that the terms &#34;top&#34;, &#34;bottom&#34;, &#34;side&#34;, &#34;vertically&#34;, &#34;upper&#34;, &#34;lower&#34;, &#34;lowest&#34; and so forth are to be understood in this connection as conveniently indicating relative positions only and not that the element necessarily lies in any particular plane.