Abstract:
An automatic transmission fluid filter has a casing consisting of a main casing portion and a cap. Generally axial spigots, are provided on the casing portion and the cap for connection into a fluid line. Within the casing there is a disc-shaped magnet and a paper element cartridge the magnet being located adjacent the entry spigot such that all fluid flowing through the spigot passes within the effective range of the magnet. 
     A bypass valve may be provided in the paper element cartridge to allow fluid at a pressure above a predetermined level to bypass the paper filter.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a filter, and more particularly relates to a filter for removing solid particles from a fluid. 
     In fluid used to lubricate automatic transmissions, such as those connected to internal combustion engines, it has been found that metal particles which are shed by elements of the transmissions during normal wear and tear act in an abrasive manner and are therefore damaging to the transmission. 
     2. Description of the Prior Art 
     Prior art arrangements for removing such particles have included the location of a small magnet in the transmission housing. However, such an arrangement is capable of removing only a very small percentage of metal particles, as most of the fluid does not come within the effective range of the magnet. 
     The use of magnets in filters for the lubricating oil of internal combustion engines is known. In GB 2042360A, there is disclosed a disposable filter in which is located a magnet. However, the magnet is located in an area which is not subject to the full flow of the oil, and thus is not likely to be very effective in removing metal particles from the oil. In addition, the oil flow is not through the casing of the filter, but enters and leaves at the same end thereof. 
     For the abovementioned reasons, the filter of GB 2042360A would not be suitable for removing particles from automatic transmission fluid, as it is essential that such a filter rapidly removes metal particles in the fluid, to prevent damage occuring to complex automatic transmission equipment. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of this invention to produce an improved apparatus for filtering fluid, which will remove a much higher percentage of solid material from the fluid. 
     The invention provides a disposable filter for automatic transmission fluid comprising: 
     a casing, said casing being composed of casing elements which may be secured together to form said casing, there being fluid entry and exit ports located generally at either end of said casing; 
     mechanical filtration means located within said casing; and magnetic filtration means located within the casing, said means consisting of a disc-like magnet formed from a material in which is suspended magnetic particles; said magnet being located in said casing such that it is opposite said entry port, and such that all points of the fluid flow through said entry port pass within the effective range of said magnet, said fluid thereafter flowing, in use, through said mechanical filtration means to said exit port. 
     The invention further provides a disposable filter for automatic transmission fluid, including 
     a generally cylindrical casing formed from thermoplastic casing elements which have been sonically welded together said casing having axial entry and exit spigots; 
     mechanical filtration means located within said casing, said means comprising a generally cylindrical folded paper element held within circular caps; 
     fluid bypass means located in the upstream one of said caps, said bypass means including a spring-loaded valve element responsive to a predetermined pressure in said fluid upstream of said means; 
     and magnetic filtration means located opposite said entry spigot such that all points of the flow of said fluid pass within the effective range of said means, said means comprising an apertured disc-like magnet formed from a plastics material in which are suspended magnetic particles, said magnet being spaced from said one end cap by spacing means; 
     wherein said fluid normally flows over or through said magnet, between said casing and said mechanical filtration means and through said filter paper to said exit spigot. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded elevation of one embodiment of a filter according to the invention; 
     FIG. 2 is a longitudinal section through an assembled filter; and 
     FIG. 3 is an enlarged sectional view of the pressure relief valve of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The filter 10 comprises a casing 12 consisting of a main casing portion 14 and a cap portion 16. The casing portions 14,16 are injection moulded from plastics material which can be sonically welded together to form a sealed unit. 
     Casing portion 14 is generally cylindrical, with an open end 18; a generally closed end 20 and a casing side wall 82. Closed end 20 has a web 22, extending outwardly from which is a spigot 24, with an annular flange 26 at the end thereof. The spigot has an internal axial passage 28, which also passes through an internally extending tubular spigot 30, which connects the interior and exterior of the casing portion 14. 
     Cap portion 16 is generally circular, with an outwardly extending spigot 32 with an annular flange 33 at the end thereof, and with an axial passage 34 therein. The internal face 36 of cap portion 16 has four ribs 38 (two of which are shown in FIG. 2) each of which is located 90° from the next rib. 
     Seal 40 is adapted to be located within casing portion 14. It is a circular piece of plastic material with a central aperture, and is adapted to be located over spigot 30, against the internal face of web 22. 
     The paper element cartridge 42 has two ends 44,46, which are preferably metallic. Between ends 44,46 is located a paper filter 48, which has a generally tubular construction, with a folded, ribbed or concertina-type side wall 50. End 44 has a central aperture (not shown) which is adapted to receive spigot 30. End 46 has a smaller central aperture 52, which opens into a pressure relief valve arrangement 54. 
     Pressure relief valve arrangement 54 has a generally cylindrical housing 56 which has a shaft 64 passing through an internal annular abutment 66. A frusto-conical sealing member 58 is secured to shaft 64 by a circular lip 70. Sealing member 58 normally makes a seal with the edge 72 of the inner end of housing 62, under the force of a spring 60 which is retained between shaft flange 76 and abutment 66. 
     A magnet support member 78 is provided to locate a magnet 80 and space it from the side wall 82 of the casing 12. The member 78 has four legs, three of which are shown as 84,86 and 88. Each leg is angularly spaced 90° from the adjacent leg, and each leg has a foot (three of which are shown as 90,92 and 94) each of which extends generally at right-angles to the respective leg to both sides thereof. 
     Magnet 80 is generally in the shape of a flattened cylinder having opposing faces 80a and 80b and a perimeter 81. It is preferably formed from a plastic material, in which material is suspended magnetic particles. The magnet 80 is provided with four apertures (two of which are shown as 96,98 in FIG. 1) or may have a single aperture. 
     Cap portion 16 also has on its internal surface an annular groove 100 which is adapted to receive the circular edge of side walls 82 at open end 18 of portion 14. 
     The filter 10 is assembled by locating the various elements of FIG. 1 within casing portion 14, in the order in which they appear in the figure. Seal 40 and cartridge 42 slide over spigot 30. The feet 90,92,94 of spacing member 78 rest on end 46 of cartridge 42, and serves to space the end from the walls 82. 
     Magnet 80 is held within the other ends of feet 90,92,94 such that the opposing faces 80a, 80b are substantially perpendicular to the fluid flow from the passage 34, which defines a fluid entry. The feet provide that the magnet is spaced from the side wall 82 of the casing, as mentioned above, along the perimeter 81, thereby forming a gap 83. Lastly, cap portion 16 is fitted onto portion 14, is sonically welded (or otherwise attached) thereto, to provide the sealed unit of FIG. 2. 
     The filter 10 is intended to be placed in a fluid supply line of an automatic transmission, preferably before the radiator, by means of hoses which may be attached to spigots 24,33. 
     A used filter 10 may be removed from the hoses, be disposed of, and be replaced by another unit. 
     The automatic transmission fluid enters the filter 10 via the passage 34 in spigot 33. The fluid is forced to flow over the surface of magnet 80, and some of it will flow through apertures 96,98. The spatial location of the magnet 80 with respect to the wall 82 of the casing portion 14 and the internal face of cap portion 16, means that no point in the fluid can pass by the magnet at more than the effective range thereof. The fluid, after passing either across the magnet 80 and through the gap 83, or through magnet 80, flows over the external face of end 46 and/or between the end 46 and the wall 82. As seal 40 prevents fluid from passing directly into spigot 30, the fluid must then pass through filter paper 48 and then through passage 28 to the automatic transmission fluid line. Thus, a second, mechanical, filtration step takes place. 
     It is not envisaged that the filter will become so clogged that pressure will build up on the supply side of filter 10. However, in the event that this did occur, pressure relief valve 54 would operate, the pressure depressing sealing element 58 and allowing fluid to flow directly to spigot 30 through the centre of cartridge 42. 
     Tests have been carried out on the filter 10 of this embodiment. The tests involved measurement of the numbers of particles removed by the filter under normal operating conditions from a standard mixture of iron powder particles in oil. 
     The filter 10 (without a paper filter cartridge 42) was mounted horizontally after first removing air therefrom, and was subjected to a flow rate of 850 ml/min of Mobil Automatic Transmission Fluid 220, from an initial total volume of 3 liters at a temperature of 50° C. The iron particles were added to the fluid in the amount of 1 g/l. 
     20 ml samples were taken from a sump at time intervals indicated in Tables 1 and 2. Each sample was diluted with filtered kerosene to 200 ml, after which the diluted sample was subjected to analysis by a HIAC Particle Size Analyser. The channel settings were as follows: 
     1. 10-20 μm 
     2. 20-30 μm 
     3. 30-40 μm 
     4. 40-50 μm 
     5. 50-60 μm 
     6. 60+ μm 
     Tables 1 and 2 set out the results obtained, in two different ways. Table 1 is data corrected for background count, so that represents the introduced magnetic particles only. 
     
                                           TABLE 1__________________________________________________________________________Numbers of Particles by size range at particular timesSize (μm) Initial       10 min             20 min                   30 min                       45 min                           60 min                               90 min                                   120 min__________________________________________________________________________10-20 44030 32157 13587  0   0   0   0   020-30 4206  1950  1163  320 233 290 27  3330-40 726   433   270   43  220 90  129 10540-50 186   160   89    13  106 16  46   050-60 80    73    30     9   60 23  40   560+   40    26    43    20   46 26  26  13__________________________________________________________________________ 
    
     
                       TABLE 2______________________________________Number of Particles expressed as percentages of the initial numbers   10             30               90Size (μm)   min    20 min  min  45 min                             60 min                                   min  120 min______________________________________10-20   72.8   30.8    0    0     0     0    020-30   46.3   27.6    7.6  5.5   6.9   0.6  0.830-40   59.6   37.1    5.9  30.3  12.4  17.7 14.540-50   86.0   47.8    6.9  57.0  8.6   24.7 050-60   91.2   37.2    11.2 75    28.7  50   6.260+     65.0   107.5   50.0 115.0 65.0  65.0 32.5______________________________________ 
    
     From Table 1, it can be seen that: 
     (a) initial particle removal is very fast 
     (b) virtually all of the magnetic particles have been removed after 60 minutes of operation. 
     Table 2 illustrates the rapid decline in percentage with time. The numbers become a little erratic because of the small quantities involved, but the initial trend is clear.