PRIMARY / SECONDARY SECONDARY FUEL FILTER FIELD OF THE INVENTION The present invention relates generally to filters, and more particularly to fuel filters for diesel engines. BACKGROUND OF THE INVENTION Diesel engines are typically provided with a plenum pump, which extracts fuel from the fuel tank and provides the fuel under positive pressure to an injection pump. The injection pump is then provided for the sequential injection of the fuel into individual fuel injectors of the engine for proper regulation and combustion. The fuel in such a diesel engine is typically filtered in two different locations. A first or primary filter is normally provided upstream of the impeller pump, between the fuel tank and the impeller pump, to remove relatively large contaminants, and a second or secondary fuel filter is provided downstream of the impeller pump between the pump impeller and injection pump to remove finer contaminants, which could otherwise penetrate and detrimentally affect the fuel injectors of the engine. Since the primary filter is normally operated under a suction environment, negative, of relatively low pressure, the primary filtration medium must necessarily be made from a relatively coarse material, which provides relatively low flow resistance, but it is sufficiently dense to remove large contaminants. This is especially important under cold temperature conditions when the fuel can be particularly viscous and therefore tends to flow less easily. However, the fuel flow from the impeller pump is under a higher positive pressure and therefore can be forced through the secondary filtration medium, which in turn allows the secondary filtration medium to be made from a relatively fine filter medium and still allow adequate flow through it to penetrate the motor without loss of speed. Although such a two-filter system is provided for the adequate protection of contaminants, it is not without drawbacks, which expressly manifest themselves in the form of high manufacturing and maintenance costs. Since two separate fuel filters are provided, a separate tube kit is necessarily required to allow flow to and from the primary filter, as well as flow to and from the secondary filter. This - -
increases the total cost of the engine, as well as the space requirements of the engine. In addition, since there are two filters provided, the two filters need to be maintained, which causes the increase in labor costs for the removal and replacement of the separate filters. This requires a maintenance program, which ensures that both filters are replaced at appropriate intervals. The filtration industry has reduced the cost of labor for filter replacement by providing "in rotation" filter models, but since current systems that employ two different filters require a number of unacceptably high labor and time for maintenance and replacement of the two rotating filters. SUMMARY OF THE INVENTION It is therefore the main purpose of the present invention to combine the functions of the primary and secondary combustion filters towards a single, self-contained double fuel filter. It is an object of the present invention to provide a simple combustion filter, which is capable of performing both the upstream and downstream filtration function, i.e., filtering the fuel flow to the filter coming from a fuel tank to eliminate large pollutants, and in addition, filter the flow of fuel from an impeller pump to eliminate relatively small contaminants. It is another object of the present invention to provide a double-medium fuel filter, which is provided for proper sealing between the primary and secondary fuel filters, as well as between the fuel filters and the filter housing even under differential conditions of relatively large pressure. It is still yet another object of the present invention to provide the double-medium fuel filter in the form of a rotating filter design, which allows a single fuel filter to be easily and quickly removed and replaced, and perform both upstream and downstream filtration. It is still a further object of the present invention to provide a fuel filter with flow paths oriented therein to create a differential pressure, which acts as a pressure aid in the compression of the primary filter cartridge and the secondary filter cartridge and the seals between them to create an adequate seal in the filter, as long as the structural integrity of the filter is not destroyed. It is still a further object of the present invention to provide the upstream and downstream flow paths with a suitable cross-sectional area, and to make the filter medium from a sufficiently porous material in such a way that the motor is supplied with a adequate volume of fuel, under a range of pressure and temperature conditions, while still providing sufficient filtration of contaminants. It is an aspect of the present invention to carry out the above by providing the primary fuel filter and the secondary fuel filter in the form of different cartridges, which are compressively loaded into the filter housing and secured therein. by a base plate assembly. It is another aspect of the present invention to accomplish the foregoing by providing a manifold formed with the primary filter cartridge, which allows the flow of fuel from the fuel tank under negative pressure, and the flow of fuel out of the fuel cartridge. primary filter for introducing and removing the filter in radially inward positions, to allow the flow of fuel from the positive pressure pump to introduce the filter in a radially outward position, and to place the secondary filter towards the closed end of the housing of the filter. The fuel under positive pressure from the impeller tank is therefore radially out of the fuel under negative pressure and must cross to the closed end of the filter before passing through the secondary filter. This tends to compress the secondary filter cartridge relative to the primary filter cartridge and relative to the base plate, so as to adequately compress the sealing seals for increased sealing, and prevent the filter cartridges from being deflected outwardly and affecting thus detrimentally the structural integrity of the filter. It is another aspect of the present invention to provide an efficient method for manufacturing a primary and secondary double fuel filter, which locates the primary and secondary filter cartridges under compression. This is done by assembling the components in the following order: place the primary filter cartridge on top of the base plate, place the secondary filter cartridge on top of the primary cartridge, place a spring on top of the secondary cartridge, and then placing the filter container above the assembled base plate, the primary filter cartridge, the secondary filter cartridge, and the spring so as to compress the spring and allow a projection provided at the open end of the container to attach to a projection provided on the base plate. These and other objects and aspects of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial cross-sectional view of the present invention with the engine, which the present invention shows mounted schematically; Figure 2 is an enlarged cross-sectional view of the primary filter cartridge; Figure 3 is an enlarged cross-sectional view of the secondary filter cartridge; Figure 4 is a bottom view of a manifold; Figure 5 is a cross-sectional view of the manifold taken along line 5-5 of Figure 4; Figure 6 is an enlarged, fragmentary, cross-sectional view of the assembled filter shown in Figure 1 rotated through 90 ° and specifically showing the base plate, the manifold, and the flow paths to and from the filter; Figure 7 is an exploded view of a filter incorporating the present invention; Figure 8a is a fragmentary sectional view showing the protrusion of the container and the projection of the base plate before being joined together; Figure 8b is a sectional, fragmentary view showing the protrusion of the container and the projection of the base plate joined together. Although the present invention is susceptible to various modifications and alternative constructions, certain illustrated embodiments of these have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms set forth, but rather, the intention is to cover all modifications, alternative constructions and equivalents that fall within the spirit and scope of the invention as is defined by the appended claims. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring first to FIG. 1, the filter 20 is shown having a typical exterior appearance among the rotating type filters. This is that the filter 20 includes a container 22 having a generally cylindrical side wall 24 and an end wall 25 which closes one end of the container 22 to give the filter a conventional exterior appearance. The container is preferably designed from a steel sheet, and is provided with an open end 26 opposite the end wall 25. The open end 26 of the container is closed with a base plate assembly 28, which includes a mechanism for threading the filter into a motor block, as will be described in more detail herein. Although the outer appearance of the present invention is preferably conventional, Figure 1 also shows that the internal construction of the filter 20 provides a new installation of the primary filter 30 and a secondary filter 32 in the form of two completely independent filter elements, i.e. , the primary filter cartridge 34 and the secondary filter cartridge 64, are held within the container 22 by assembling the base plate 28. The structure and functionality of each of these components will be discussed individually in the following description. One of the challenges in the design of a fuel filter, which combines the primary filtration medium with a secondary filtration medium, is the design of the flow circuits through the filter, which allows the proper fuel not only be - -
filtered but also power the motor and therefore not underfed the motor. In addition, since the fuel flow to the primary filter is low suction or low negative pressure, and the fuel flow to the secondary filter is under positive, relatively high pressure or compression, it is necessary to design the flow paths in such a way that the The filter is not forced to separate, but preferably helps itself to create an autonomous unit, sealed, compressed. In accordance with these objects, the primary filter cartridge 34 is configured as shown in Figure 2. The primary filter cartridge 34 not only includes a paper filter means 36, but also provides a filter means 36 within a housing 37, which is attached to a manifold 56. This allows the primary filter cartridge to be formed complete with flow paths to and from the filtration means 36 prior to the final assembly of filter 20 as a hole, and provides a axial flow path completely separated therethrough for fluid communication between the secondary filter cartridge 64 and the motor. As shown in Figure 2, the filter means 36 is contained between the first cover 38 and the second cover 40, is formed in an annular manner, and includes an inner diameter having a tubular member 42 provided therein with a plurality of openings to allow the passage of fuel therethrough far from the filter means 36. In a practical implementation of the invention, the primary filter medium is preferably made from a folded paper having a total of 78 folds and an area of total filtration of 292.5 inches; Other sizes could be used, and other materials that include a metal filter. To provide integrity in the structure of the primary filter cartridge 34, the tubular member 42 substantially extends the length of the paper filter means 36. A first end cap 38 is provided with flanges 44 and 46 at sufficient distance to engage the outer diameter of the paper filter means 36 and the tubular member 42 respectively. An encapsulation compound 48 is then provided at a sufficient depth to seal the paper filter means 36, the tubular member 42, the first end cap 38, and the conical end 139 of the collector arm 135 together. In the preferred embodiment, plastisol is used as the encapsulation compound, but it should be understood that in alternative embodiments, other sealants and encapsulation compounds could be used. A second end cap 40 with the encapsulation compound 48 is similarly provided for sealing - 1 -
the end torus of the primary filter cartridge 34. However, the second end cap 40 cooperates additionally with the manifold tube 52, and the outer capsule 54 to provide the seal. As best seen in Figure 2, a second end cap 40 is provided at a diameter substantially greater than the first end cap 38 and an outer capsule 54 with an outer diameter substantially equal to the outer diameter of the second cap 40 is provided. , the first end cap 38, the second end cap 40, the tubular member 42, and the outer capsule 54, are all manufactured from a steel sheet in the preferred embodiment, although the collector 56 is made of plastic. As best shown in Figure 2, the first end cap 38 is provided adjacent the end plate 58 of the collector 56 and the outer capsule 54 is wound around the end plate 58. By curing the encapsulation compound 48 of the second cap end 40 and by winding the outer capsule around the end plate 58, the primary filter cartridge 34 is formed towards an autonomous unitary piece. It can further be seen in Figure 2 that the sealing rim 60 of the outer capsule 54 is provided with an annular groove 61 formed to frictionally engage the annular sealing ring 62 therein. The sealing ring 62 is adapted to engage the assembly of the base plate 28 and can be fabricated from any suitable elastomeric sealing material, such as neoprene. As mentioned, supra, one of the challenges in designing such a double-medium filter is to create flow paths within the filter, which are not only provided with a cross-sectional area large enough to allow sufficient fuel to pass through. It is also installed in order to create a differential pressure through the filter, which acts as a pressure aid when compressing the filters and the shutter between them. For a better extension, these objectives are carried out through the new use of the collector 56, shown in detail in FIGS. 4 and 5, and by providing a collector 56 with the apertures appropriately positioned for fuel communication to and from the filter. First of all, the fuel enters the primary filter cartridge 34 from the fuel tank (see Figure 6) through the inlet pipes 110 provided in the manifold 56 and passes between the inner surface 55 of the outer capsule 54 and the flange 44 of the first end cap 38 as shown by the directional arrow A, before passing through the paper filter means 36 and towards the impeller 112 of the primary filter cartridge 34. As shown in Figure 4, the inlet tube 110 comprises a plurality of openings 114 provided radially around the end plate 58 of the collector 56. Each opening 110 is separated by means of a support beam 116 and is located between the outer support ring 118 and the ring medium support 120. As best shown in Figure 4, the outer support ring 118 is concentric with the medium support ring 120, and is provided with a substantially larger diameter. After passing through the filtration means 36, the fuel passes through the impeller 112 and exits through the filter 20, as shown by way of the directional arrow B through the outlet pipe 122 is also provided in the collector 56. Similar to the inlet tube 110, the outlet tube 122 is provided in the form of a plurality of circumferentially disposed openings 124 spaced apart by support beams 116. The openings 124 are provided between the middle support ring 120 and the ring 120. inner support 126. The inner support ring 126 is provided with a plurality of elastically deformable edges 127, which allows the manifold 56, which is formed by injection molding, to be more easily removed from a mold after being formed, and which cooperates with the wall 135 and for supporting the annular obturator 133. Similarly, the medium support ring 120 includes a plurality of elastically deformable edges. 129, which facilitate the removal of a mold, and which cooperate with the wall 137 to support the annular obturator 131. Although the description above provides the structure by which the fuel is initially filtered, the creation of the flow paths to and from the primary filter cartridge 134 is only a demand for a double-medium filter. The primary filter allows fuel from the tank to be initially filtered before entering the pump, but additional means are needed for finer filtration before the fuel can communicate with the injectors. This finer filtration is provided in the form of the secondary filter cartridge 64, shown in detail in Figure 3. The secondary filter cartridge 64 is provided with a paper filter medium 66 contained between a third end cap 68 and the fourth. end cap 70. Both the third end cap 68 and the fourth end cap 70 are provided with an encapsulation compound 48 as a sealant. In addition, similar to the primary filter cartridge 34, the tubular member 74 is provided in the inner diameter of the paper filter means 66, which extends from the third end cap 68 to the fourth end cap 70. In the preferred embodiment, the secondary paper filter means 66 is formed with a total of 67 folds and provides 770.5 square inches of a cross-sectional area through which the fuel is filtered. However, it should be understood that the alternative embodiments could certainly include secondary filtration means made from different materials and provided in different configurations and dimensions. Similar to the primary filter cartridge 34, the secondary filter cartridge 64 is manufactured by providing an annular paper filter means 66 around a tubular member 74 and by placing a third annular metal end cap 68 at one end and a fourth cover 70 metal ring end at the other end. Both the third end cap 68 and the fourth end cap 70 are provided with an encapsulation compound 48, which is then cured to provide a secondary, tubular, self-contained filter cartridge 64. It should be understood that prior to the method by which the fuel is communicated to and from the secondary filter cartridge 64, the assembly of the base plate 28, shown in detail in Figure 6, is described. It is a base plate assembly 28, which cooperates with the -
collector 56 to create the necessary flow paths to and from the secondary filter cartridge 64. The base plate assembly 28 is comprised primarily of a metal base plate 76, on which the metal attachment edge 78 is attached. attachment edge 78 is preferably fabricated from a sheet of metal and formed within an annular groove 80 sized sufficiently to receive the outer seal 82 and in the pre-wrapping state best shown in FIG. 8a, is provided with a flange 84 extending radially to attach to the open end 26 of the container 22 as described in more detail herein. The base plate 76 is provided with a plurality of openings 86, which allow the fuel to be filtered as it passes through them. The base plate 76 is also provided with an annular edge 88, which is provided with a plurality of threads 90 adapted to be attached to the motor block schematically shown at 92. It can therefore be observed that when the filter 20 is fastened to a In the case of a motor, the fuel coming from the pump passes under a relatively high positive pressure towards a secondary filter 32, as shown by the directional arrow C, through the openings 86 provided in the base plate 56 (See Figure 6). In the preferred embodiment, eight openings 130 are circumferentially provided around the base plate 76 although a different number of openings are certainly possible. From the openings 86, the fuel passes between the inner surface 132 of the container 22 and the outer surface 133 of the outer capsule 54. Since the primary filter cartridge 34 is sealed, the fuel can not enter the primary filter cartridge, and since the primary filter cartridge 34 is separated from the secondary filter cartridge 64 by an inner sealing plug 98, the fuel coming from the plenum pump passes directly to the secondary filter cartridge 64, as best shown in Figure 1. As shown by the directional arrow D, the fuel passes directly through the paper filter means 66 and into the inner impeller 136 through the openings 138 provided in the tubular member 74. From the inner impeller 136, the fuel passes to the reduced impeller 140 provided in the inner diameter of the primary filter cartridge 34 and from there to the engine (shown schematically ) through the outlet pipe 141. In current practice, the fuel would then pass to an injection pump, which could sequentially inject the fuel to the fuel injectors for proper synchronization of the operation - -
the motor. Therefore it can be seen that the fuel under positive pressure enters the filter 20 at the end of the outer diameter of the filter and towards the end wall 25 before leaving the filter through the center. On the other hand, the fuel under negative pressure enters the filter 20 towards the inside diameter of the filter 20 towards the open end 26 of the filter 20 and radially inward from the highly pressurized fuel coming positively from the impeller pump. This positive pressure therefore creates a differential pressure through the filter 20, which tends to compress the two filter cartridges and acts in conjunction with the bypass force of the shock absorber 94 to deflect the filters towards the base plate 76. This does not it only provides a pressure aid by properly compressing the shutters out of the filter 20 and thereby providing a proper seal, but also prevents the filter cartridges from being deflected externally and potentially damaging the filter 20. For example, if the primary filter was positioned towards the end wall 25 and the negative pressure flow paths were located on the outer diameter of the container 22, and the secondary filter cartridge was positioned towards the open end 26 with the positive pressure on the inside, the positive pressure would therefore act in a radially inward direction, and not only would it tend to resist the compression deviation of the damper 94, it would also tend to cause the container 22 to move outward and potentially be damaged. The inventive aspects of the present invention also include the efficient method, by which the double-medium, pressure-assist, sealed, and stand-alone filter 20 is manufactured. In an effort to explain that method, reference is now made in particular to Figures 7, 8a, and 8b. Since all of the aforementioned components are contained within the container 22 and deflected outwardly by the biasing damper 94, it is necessary to compress the bumper 94 before the radial flange 84 of the bonding edge 78 is proximate the circumferential rim 106. of the container 22 for joining the two metal components. The present invention is therefore combined in the following manner. After the base plate 76 is attached to the binding edge 78, the assembly of the base plate 28 is located on a work surface (not shown) in such a manner that the attachment edge 78 rests on the work surface and the base plate 76 is projected upwards. The primary filter cartridge 34 is then located on the upper part of the base plate assembly 28 such that the annular sealing ring 62 rests on the upper part of the base plate 76 and the second end cover 40 projects upwardly. . An inner sealing plug 98 is then provided in the annular groove 100 of the second end cap 40. The secondary filter cartridge 64 is then located on top of the primary filter cartridge 34 such that the third end cap 68 is located adjacent the second end cap 40. The third end cap 68 is similarly provided with the annular groove 102 for receiving the inner seal plug 98 therein. The fourth end cap 70 is therefore projected upward, as best shown in Figure 1, and is provided with an interior cavity 104 having an outside diameter sufficient to receive the damper 94. The damper 94 is then located within of the inner cavity 104 and the container 22 is then lowered onto the upper part of the assembly. The end wall 25 engages the shock absorber 94 and compresses the shock absorber 94 to a sufficient extent to allow the circumferential flange 106 to abut the radial flange 94 of the bonding edge 78 as best shown in Figure 8a. The contiguous flanges 84 and 106 are then joined together in a conventional manner resulting in a rolled joint 108 as best shown in Figure 8b. Thus, the filter 20 is provided in a stand-alone unit where the secondary filter cartridge 64 is deflected in the direction of the primary filter cartridge 34, which in turn deviates in the direction of the assembly of the base plate 28. that the assembly of the base plate with threads 90 is provided, the filter 20 can be easily secured through rotation to the motor block 92 of a motor, and removed with the same ease. From the foregoing, it can be seen that the present invention provides a fuel filter, which combines the functions of the primary filter and the functions of a secondary filter in a single autonomous unit. This is opposite to the prior art installations where separate primary and secondary filters would be provided, and therefore a separate pipe to and from the engine, and therefore the impeller pump would need to be provided. Such prior devices not only increase the costs resulting from the engine and filtration equipment, but also increase the maintenance required in those two separate filters, which not only have to be maintained in the supply, but replaced periodically. The present invention, on the other hand, allows a single filter to combine the functions of filtering fuel from the fuel tank and introducing it to the impeller pump, and filtering the main fuel from the impeller pump and into the injection pump and the injectors. When giving the viscosity of the fuel under cold temperature conditions, and the fact that the fuel is introduced to the impeller pump under negative pressure, low (approximately -3 psi) the filtration medium between the fuel tank and the impeller pump needs be relatively thick to allow a large cross-sectional flow area. This will remove relatively large pollutants to protect the impeller pump, while still allowing the right fuel to enter the impeller pump even under cold conditions when the fuel is viscous. After leaving the impeller pump the fuel will necessarily be heated and less viscous, and under increased positive pressures (approximately 70 psi). The secondary filter can therefore be manufactured from a finer filtration medium to allow fuel to be forced through it. This finer filtration medium will be able to remove relatively small contaminants, which is essential for the proper operation of fuel injectors, which have relatively narrow machine tolerances and which can not accept large contaminants. After the filter life has ended, the filter 20 can be easily moved by rotating the filter 20 with respect to the threaded flywheel of the engine block and installing a new one. The present invention therefore provides a more efficient, more cost-effective, more compact, and more compact fuel filter, which combines the primary and secondary conventional fuel filter functions into a single, stand-alone unit.