GB1569991A - Oil filter - Google Patents

Description

(54) OIL FILTER (71) We, MONROE AUTO EQUIPMENT COMPANY, a Corporation organised under the laws of the State of Delaware, United States of America of One International Drive, Monroe, Michigan 48161, 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: This invention relates to an oil filter. Modern automotive vehicle engines are produced with circulating oil lubrication systems wherein oil is forced under pressure by means of the engine driven oil pump from the oil sump or pan through various lubricating passages to the critical points of lubrication of the engine. In order to remove or at least minimize oil contaminants within such engine lubrication system, it has been the practice to incorporate oil filters therein. It is usually the case that such filters are of the replaceable type and as such, the filters are periodically discarded and replaced, usually concurrently with the replacement of the engine lubricating oils.

Generally, oil filters produced and sold for both original equipment and replacement on auto motive vehicles operate on the same principle; namely, the filters are provided with a filtering medium or element and under normal operating conditions, oil enters at the top of the filter through a series of holes leading to the outer periphery of the filtering medium.

The oil then passes through the filtering medi um during which the oil contaminants are removed and the oil thereafter passes centrally through the filter element and exits through an outlet port, from where the oil is commu nicated back through the lubrication system of the vehicle engine. Frequently, antidrainback valves are used which prevent the oil from draining out of the filter after the engine has stopped operating, and in many instances, the filters are provided with pressure relief valves which provide means for bypassing the filter element or medium at such time as a predetermined pressure drop occurs across the filter element, i.e., when the lubricant is in a highly viscous state such as during low temperature operating conditions.

In order for the lubrication systems of the aforementioned type of engines to operate satisfactorily, the lubricant or oil must have certain properties that ensure both adequate system flow and at least a particular minimum performance after delivery. At the same time, the oil must not have any tendency to degrade the life or performance of any component parts of the vehicle engine with which it comes into contact. In light of these require ments, several categorical properties and their acceptable performance levels have been established. Such properties and performance levels include oil viscosity, oil oxidation rate, anti-wear properties, detergent and dispersant properties, and anti-corrosion properties.

More particularly, engine oil used in modern automotive, as well as light truck, engines are specified by two separate classifications.

The first is the engine service classification and relates primarily to the performance of the engine oil under simulated service operat ing conditions. Typical requirements are a maximum increase in viscosity which would indicate the presence of contaminants in the engine after certain sequential operations, the presence of scuffing and actual wear of certain parts of the oil testing apparatus (typically a specified type of engine), and the presence of other deposits, such as varnish and the like on engine piston rings. The second classification is based on the viscosity of the oil at OOF. and at 2100F., and engine oils are normally rated at either the 0 F. point, the 210 F. point or at both. For example, a typical specification would be 10W indicating a viscosity range at 0 F.; 30 indicating a viscosity range at 210 F. or 10W 30 indicating viscosity ranges at both 0 F. and 2100F.

Producers of engine oils have found that in order to meet the aforesaid classifications, petroleum oils by themselves are unsuitable.

Consequently, a typical engine lubricating oil contains between 10% and 20% by weight additives or non-oil components, in order to meet these classification requirements. Typical components needed to meet the classifications are detergents, dispersants, inhibitors, antiwear agents and anti-corrosive agents. Those lubricants of the multiple viscosity or multigrade type require an additive or component in them to provide for acceptable performance at the requisite viscosity levels. Such additives or components are know in the art as viscosity improvers or viscosity index (VI) improvers.

Unfortunately, however, many of the additive components of modern engine oils degrade with use, either because of (a) inherent defi ciences, or (b) because their function is, in fact, to be consumed or depleted to provide the necessary or desired feature in the lubricant. More particularly, oil viscosity improvers fall into category (a) since they consist of very large molecules which break up during use so that they can no longer perform their intended function. This breaking up of the VI molecules is referred to as shear-instability, which results from the fact that the molecules are unstable when subjected to high fluid shear rates. In the second category (b) are those types of oil additives which are sacrificed or which are purposely consumed during the service life of the oil. Examples of such sacrificial additives are anti-oxidants which funtion to prevent the deterioration associated with oxygen attack on the lubricant base fluid. Normally, anti-oxidants are provided in the oil for the purpose of absorbing any oxygen present and thus, among other things such additives prolong the resistance of the oil to form sludge.

Over the service life of the oil, however, the anti-oxidant additives become saturated and hence the resistance of the oil to form sludge gradually terminates. Anti-wear and anticorrosive additives or compounds are similar to anti-oxidants in that these additives are intended to be deposited on the engine surfaces.

Because of the washing action of the oil and the rubbing of the metal surfaces during opera- tion of the engine, however, such deposits do not remain on the critical surfaces and must be replenished at these points from the lubricant. When the concentration of these additives drops below a certain level, the additives can no longer be deposited and hence the engine components are subject to wear and corrosion.

In view of the finite life of the lubricant additives which are utilized in modern engine oils, either because of the inherent deficiences of such additives or because of their depletion (sacrificial) characteristics, it has heretofore been proposed to replace or replenish such additives and thereby extend the service life of the engine oils. The prior art is replete with a myriad of different ways of effecting such replacement of engine oil additives, and among such prior art suggestions are those methods disclosed in the specifications of United States Patents Nos. 2,302,552, 2,310,305, 2,435,707,2,898,902, 2,943,737, 3,314,884 and 3,749,247.

All of the various concepts disclosed in the aforementioned patents, while generally addressing themselves to the problems resulting from oil additive depletion, have not proved completely satisfactory due primarily to the complexity of the systems and methods proposed therein and the resultant difficulties of adapting such proposed systems in commercially acceptable filter units. Additionally, there is no single system or method proposed therein which provides for the replenishment of the three most important oil additives which become depleted throughout the service of the oil, namely, the viscosity index improvers, anti-oxidants, and anti-wear-anticorrosion compounds. Moreover, such heretofore proposed systems suffer the extremely important shortcoming of not assuring against over or underdosing of the additives, a characteristic which can be detrimental to the engine oil and engine component parts as the depletior of the original oil additives. For example, if the engine oil is provided with an overdose of a VI improver, there is a marked reduction in the low temperature performance of the oil which in turn results in engine starting difficulties at low operating temperatures.

The specification of United States Patent No. 3,336,223 discloses a system for prolonging the useful life of lubricating oils by providing an oil soluble solid thermoplastic polymer within an oil filter enclosure and causing the polymer to be contacted with the circulating oil, whereby oil additives which are compounded into the polymer will be gradually dispersed into the oil. The system disclosed in this patent does not, however, provide for the optimum rate of additive replenishment during the service life of the oil, and this particular shortcoming has been found to be extremely critical in ensuring optimum effective oil life.

In particular, it has been found that optimum oil life is achieved in those cases wherein the oil additives are replenished at a relatively uniform or linear rate so as thereby to replenish the original oil additives at essentially the same rate as they become depleted, thus positively ensuring against over or underdosing of the additives.

In our copending patent application No.

10,743/76 (Serial No. 1541051) we claim an oil filter for an engine having a circulating oil lubrication system, said filter comprising a generally cylindrically-shaped enclosure having a filter element therein, a base plate at one end of the enclosure having a centrally located oil outlet opening and at least one oil inlet opening spaced radially from the outlet opening, a first oil passage within the enclosure communicating the oil inlet opening with the upstream side of the filter element, a second oil passage within the enclosure communicating the downstream side of the filter element with the oil outlet opening, and a body comprising an oil-soluble material and having at least one oil improver property, said body being located within the enclosure at a position out of the direct flow path of oil from the inlet through the filter element to the outlet and at a location where it can only be contacted by a substantially stagnant volume of oil during use of the filter whereby oil flowing along such flow path during use of the filter will not impinge directly upon the body, and whereby the oil-soluble material of said body will dissolve at a substantially uniform rate during the life of the oil.

When referring herein to a body having at least one oil improver property we are referring to the body being comprised of one or more substances or additives which improve the viscosity, extreme pressure, anti-oxidant and/or other properties of oil when dissolved or dispersed in the oil.

According to the present invention there is provided an oil filter for an engine having a circulating oil lubrication system, said filter comprising an enclosure having a filter element therein and provided with oil inlet and outlet ports for connection with the lubrication system of the engine, a first oil passage within the enclosure providing communication between the oil inlet port and the upstream side of the filter element and a second oil passage within the enclosure providing communication between the downstream side of the filter element and the outlet port, an annular body having a cylindrical outer surface, comprising an oil soluble material having at least one oil improver property and being mounted in the enclosure, and means for limiting the rate of dissolution of said body by restricting the proportion of the surface area of the body exposed to the oil which in use is flowing through the enclosure from the inlet port to the outlet port, the means for restricting the proportion of the surface area of said body exposed to the oil comprising a masking element within the enclosure, such masking element having a first portion disposed adjacent to and in surface to surface contact with a radially extending surface of the body and a second portion disposed adjacent to and in surface to surface contact with the cylindrical outer surface of said body.

The present invention will become further apparent from the following detailed description given by way of example with reference to the accompanying drawings, in which: Figure 1 is a transverse cross-sectional view of a vehicle engine filter as disclosed in the Specification of our above-mentioned copending Patent Application No. 10743/76; Figure 2 is a fragmentary cross-sectional view taken substantially along the line 2-2 of Figure 1; Figure 3 is a fragmentary view of a portion of a filter similar to the construction shown in Figure 1 but without the anti-drainback and pressure relief valves incorporated therein; Figure 4 is a graphic representation of the effect that a thermoplastics polymer utilized in accordance with the present invention has on oil circulating in a typical lubrication system; Figure 5 is an enlarged cross-sectional view similar to Figure 1 and illustrates a filter embodying the present invention; Figure 6 is a fragmentary view of a portion of the polymer body and associated support member of another embodiment of the filter; and Figures 7 and 8 are similar to Figure 6 and disclose still further embodiments of the filters.

Referring now in detail to the drawings and in particular to Figure 1 thereof, a filter unit 10 is shown as comprising a generally cylindrically shaped housing or enclosure 12 having a side wall 14 and a generally dome-shaped end section 16. The side wall 14 is formed with a plurality of flats 18 adapted to be engaged by a wrench and the lower open end of the enclosure 12 is provided with an annular closure plate 20 which is secured to the side wall 14 by means of a suitable rolled seam 22. The closure plate 20 is formed with an annular recess 24 which is defined by radially spaced wall portions 26, 28 and a wall portion 30.

Disposed within the annular recess 24 is a seal 32 which is adapted for sealing engagement with a suitable portion of an associated engine block 34 shown in phantom lines in Figure 1.

Secured to the interior side of the closure plate 20 is an annular base plate 36. The base plate 36 comprises a generally radially extending portion 38 which is secured, as by spot welding, to the closure plate 20, as best seen at 40. The base plate 36 is formed with a plurality of circumferentially spaced, axially extending inlet ports 42 and with a central axially extending flange 44 having an internally threaded inner periphery 46 defining an oil outlet port 48. The filter unit 10 is secured to the associated engine block 34 by being threadably received upon a suitable stand pipe or the like (not shown) which is threaded into the outlet port 48.

Disposed interiorly of the enclosure 12 is an annular filter element 50, which may be frabricated of any suitable filter medium and is representatively illustrated herein as being fabricated of pleated filter paper which is folded in a manner so as to provide a plurality of pleats or flutes 52 as best seen in Figure 2.

The filter element 50 is disposed between a pair of axially spaced end caps 54 and 56 which close the axially opposite ends of the flutes 52 so as to ensure that oil circulating through the unit 10 will pass radially through the filter element 50.

The filter unit 10 is provided with an anti-drainback valve 58 which is of a generally disc or ring-shaped configuration and is fabricated of a suitable oil impervious elastomeric material, such as synthetic rubber. The valve 58 is concentrically oriented relative to the oil outlet port 48 and has the inner periphery thereof retained against the interior side of the base plate 36 by means of a generally axially extending section 62 of an annular support flange 64. The flange 64 includes a radially extending portion defining a plurality of circumferentially spaced axially extending oil bypass ports 66.

The filter unit 10 is also shown as being provided with a pressure relief valve 68 which is fabricated of a suitable elastomeric material and is of a generally ring or disc-shaped configuration, as shown in Figure 1. The valve 68 is located adjacent one side of a support disc or ring 70 which is urged under the influence of a coil spring 72 toward a pair of concentric valve seats 74 on the support flange 64, whereby the relief valve 68 will normally be sealingly engaged with the seats 74 and hence block oil flow through the ports 66. Disposed interiorly from the relief valve 68 is a generally cupshaped spring retainer 76 which is formed with a central opening 78 and is provided with a generally radially arranged securing flange 80 that extends around the outer periphery of the support flange 64.

At such time as the associated engine is operating, oil will be circulated by the engine oil pump through the lubrication passages of the engine and will be communicated through the inlet ports 42 and then radially outwardly around the outer periphery of the filter element 50. The oil will then pass radially inwardly through the filter element 50 and be filtered thereby, after which time the oil will pass axially through the opening 78 and thereafter through the outlet port 48 back to the engine. When the engine is not operating, the anti-drainback valve 58 is disposed in the position shown in Figure 1, with the outer periphery of the valve 58 being movable axially away from the base plate 36, whereby to permit the aforesaid circulation of oil through the filter element 50, and at such time as the engine is shut off, the valve 58 will again seat against the base plate 36 to prevent any oil within the unit 10 from draining back into the engine. The pressure relief valve 68 is normally seated against the valve seats 74; however, at such time as the filter element 50 becomes clogged or for some other reason that an excessive pressure differential exists between the inlet ports 42 and outlet port 48, the valve 68 will move axially against the resistance of the spring 72, whereupon oil entering through the inlet ports 42 will be circulated through the bypass ports 66 and thereafter be returned through the outlet port 48 to the engine, thus circumventing circulation through the filter element 50.

Disposed between the dome-shaped section 16 of the enclosure 12 and the end cap 54 of the filter element 50 is a flat ring-shaped or annular body 82 of additive material. The body 82 is formed with a central opening 84 adapted nestingly to receive a central portion 86 of a retaining plate 88 which is disposed between the body 82 and the dome-shaped section 16. The retaining plate 88 may be provided with a generally axially extending annular lip to extend around the outer periphery 90 of the body 82. A suitable spring element 92 is provided interjacent the retaining plate 88 and the dome-shaped section 16 for resiliently urging the entire assemblage consisting of the plate 88, body 82, filter element 50 and end caps 54, 56 toward the base plate 36, whereby to ensure against any undesirable movement of these components within the enclosure 12.

The body 82 may consist of any one of a variety of high molecular weight polymers that are slowly dissolvable in oil and which are suitable to have the desired oil additives compounded therein, whereby when the oil contacts the additive polymer composition, the polymer will have a low rate of dissolution in the oil and will thereby be slowly dissolved into the oil. If the particular additives which are compounded into the polymer are oil soluble, such additives will dissolve slowly in the oil at essentially the same rate as the polymer itself. On the other hand, if the additives are oil insoluble when exposed to the oil, they will be carried along with the oil to perform their intended function. The polymer thus serves two essential purposes; it is the carrying medium for the additives and it also protects the additives from immediate contact with the oil. Accordingly, the polymer is preferably a thermoplastics polymer having a low rate of dissolution in oil and being of a sufficiently high molecular weight, preferably at least 60,000, so that the polymer and consequently the additives carried by it, is at least substantially solid at the temperature of oil contact.

Virtually any polymer that has the aforesaid properties may be used in practice such as, for example, ethylene-propylene copolymers ranging in molecular weight from 200,000 to 300,000; ethylene-ethylacrylate copolymers ranging in molecular weight from 200,000 to 300,000; polypropylene oxide having a mole; cular weight of about 500,000; and ethylenevinyl acetate copolymers ranging in molecular weight from 200,000 to 300,000. One polymer that has been found to be highly satisfactory and which is preferred is polyisobutylene ranging in molecular weight from approximately 600,000 to 135,000, and a preferred polyisobutylene is identified by the registered trandemark "VISTANEX" that is manufactured by the Enjay Chemical Company.

The additives which are compounded into the above discussed polymer can be in liquid or solid form; and as previously mentioned, they can be oil insoluble, or they can range in oil solubility from partially to completely soluble. As used herein, the term "additive" includes all materials which can be compounded or admixed with the polymer and which in any way impart beneficial properties to the oil being circulated through the filter unit 10.

It is important to note that the polymer itself will tend to improve the viscosity properties of the oil as the polymer goes into solution.

The particular additives to be admixed or compounded with the polymer will, of course, depend on the type and magnitude of additive replenishment which is being sought. For example quality crankcase lubricants contain detergent additives such as the metal sulphonates, metal phenates, metal phosphenates and derivatives of alkenyl succinimides.

Suitable oxidation inhibitors that can be included as additives are the metal dithiophosphates and metal dithiocarbonates. One particular anti-oxident additive that has been found to be highly satisfactory and is preferred in the polymer is a phenolic anti-oxidant, 4,4' -methylenebis (2,6-di-tert-butylphenol) that is commercially available under the tradeanem Ethyl 702 manufactured by Ethyl Corporation. Extreme pressure (EP) and oiliness additives, such as sulphor, metal naphthenates, phosphate esters and sulphurized hydrocarbons, may be admixed with the polymer, and one highly satisfactory and preferred EP additive which also is highly satisfactory as a bearing corrosion inhibitor is zinc dibutyldithiocarbamate that is commercially available under the registered trademark BUTYL ZIMATE manufactured by the R.T. Vanderbuilt Company.

Of course, additional additives may be admixed or compounded with the polymer and the aforesaid list of such additives is merely intended to be exemplary of the various additives that may be used alone or in combination. Particular details of acceptable ways of compounding or admixing the additives and polymers is described in the specification of the aforementioned United States Patent No.

3,336,223. Additional exemplary additives and polymer compositions are also set fourth in that patent specification which may be used in making the body.

In order to provide for the optimum linear or uniform rate of dissolution of the polymeradditive composition constituting the body 82 over the desired life of the oil, i.e., a drain interval of between 3,000 and 7,500 vehicle miles, and thereby ensure against over or underdosing of the additives that are replenishing the original depleted additives in the oil, it has been discovered that it is extremely important that the body 82 be located at a position within the enclosure 12 where a minimum amount of oil circulation of flow occurs, i.e., at a location wherein the oil within the enclosure 12 is substantially stagnant during use of the filter, whereby there is no direct impingement of flowing oil on the body and no contact of turbulent oil with the body 82. Thus, it is desirable that the oil is out of the path of oil circulating through the filter unit 10 so that the oil does not in any way impinge directly upon the body 82.

Such direct oil impingement would result in turbulent circulating oil contacting the body 82 and hence result in an undersirable and accelerated rate of dissolution of the polymer and consequential premature release of the additives admixed or compounded therein.

Figure 4 demonstrates a derived linear rate of dissolution by showing the uniform rate of increase in the viscosity of a test oil that is caused by the dissolution of a VI (viscosity improver) in a test apparatus that does not subject the oil to modes of degradation found in normal engines, but which duplicates the normal drain interval by means of controlling flow rates and temperatures. It will be noted that because of homogenous mixture of the polymer and additives throughout the body, the polymer and all additives are replenished at constant related rates. It may be noted that an additional feature comprises locating the body 82 in the position shown in Figure 1 of the drawings, namely upstream from the filter element 50, which arrangement ensures against any of the polymer body migrating into the lubrication system of the associated engine in the event any portion of the body 82 becomes separated therefrom. In other words, if a part of the body 82 migrates away or is separated from the main body thereof, such migrating portion will be trapped by the filter element 50 and thus be prevented from flowing through the outlet port 48 into the associated lubrication passages or the like of the engine block 34.

Figure 3 illustrates a fragmentary portion of a filter unit 10' which may be identical in construction and operation to the filter unit 10 hereinabove described, with the exception that the unit 10' is not provided with either an anti-drainback or pressure relief valve, and it is to be noted that the present invention is equally applicable to filter units that are not provided with such valving arrangements, or are provided with only one of such valves. In addition, the filter unit 10' has the filter seal 32' located radially outwardly from the position shown by the analogous seal 32 of the filter unit 10, thereby rendering the filter unit 10' adapted for application on certain types of vehicle engines presently being produced.

The rate of dissolution of the polymer body may be limited by restricting the surface area of the body with which the oil circulating through the filter unit comes into contact.

Thus, the rate of dispersion of the additives in the body can be limited by restricting the proportion of the surface area of the body which the oil contacts. For example, the filter unit shown in Figure 1 may have the polymer body 82 therein dissolve at a somewhat slower or lesser rate by having the outer peripheral portion of the retaining plate 88 cover and be in surface to surface contact with not only the upper radial surface of the body 82, but also a portion of the axially extending radially outer surface thereof. Toward this end, attention is directed toward the modified construction of the filter unit as shown in Figure 5 which is, in many ways, identical to the unit shown in Figure 1 and is identified to a similar numerals having a primed (" " ') suffix. In this unit, the retaining plate 88" " ' is formed with a down- wardly extending peripheral lip portion 200 which is disposed directly adjacent to and in surface to surface contact with the outer peripheral surface of the body 82" " ' and hence will limit the amount of oil circulating through the unit which comes into contact with the body 82" " '. The magnitude of the surface area covered or "masked" from the oil may be varied, as indicated in Figure 6 wherein the lip portion 200a extends axially the entire thickness of the associated body 82 " Instead of varying the size of the so-called masking element which functions to limit oil contact with the polymer body, such masking element may be formed with various openings or apertures, the size and number of which are selected so as to provide the desired degree of oil contact and hence rate of polymer dissolution. For example, the downwardly depending lip 200b in Figure 7 may be formed with a plurality of circumferentially spaced openings or apertures 202. Alternatively, the downwardly depending lip 200c shown in Figure 8 may be formed with a plurality of cut-away portions or notches 204. Of course, various other alternative arrangements will work just as satisfactorily, provided that the amount of surface area of the body that is masked from the oil is correlated to the rate of dispersion which is to be achieved, i.e.

correlated so that the polymer dissolves at some predetermined rate relative to the lif

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. addition, the filter unit 10' has the filter seal 32' located radially outwardly from the position shown by the analogous seal 32 of the filter unit 10, thereby rendering the filter unit 10' adapted for application on certain types of vehicle engines presently being produced. The rate of dissolution of the polymer body may be limited by restricting the surface area of the body with which the oil circulating through the filter unit comes into contact. Thus, the rate of dispersion of the additives in the body can be limited by restricting the proportion of the surface area of the body which the oil contacts. For example, the filter unit shown in Figure 1 may have the polymer body 82 therein dissolve at a somewhat slower or lesser rate by having the outer peripheral portion of the retaining plate 88 cover and be in surface to surface contact with not only the upper radial surface of the body 82, but also a portion of the axially extending radially outer surface thereof. Toward this end, attention is directed toward the modified construction of the filter unit as shown in Figure 5 which is, in many ways, identical to the unit shown in Figure 1 and is identified to a similar numerals having a primed (" " ') suffix. In this unit, the retaining plate 88" " ' is formed with a down- wardly extending peripheral lip portion 200 which is disposed directly adjacent to and in surface to surface contact with the outer peripheral surface of the body 82" " ' and hence will limit the amount of oil circulating through the unit which comes into contact with the body 82" " '. The magnitude of the surface area covered or "masked" from the oil may be varied, as indicated in Figure 6 wherein the lip portion 200a extends axially the entire thickness of the associated body 82 " Instead of varying the size of the so-called masking element which functions to limit oil contact with the polymer body, such masking element may be formed with various openings or apertures, the size and number of which are selected so as to provide the desired degree of oil contact and hence rate of polymer dissolution. For example, the downwardly depending lip 200b in Figure 7 may be formed with a plurality of circumferentially spaced openings or apertures 202. Alternatively, the downwardly depending lip 200c shown in Figure 8 may be formed with a plurality of cut-away portions or notches 204. Of course, various other alternative arrangements will work just as satisfactorily, provided that the amount of surface area of the body that is masked from the oil is correlated to the rate of dispersion which is to be achieved, i.e. correlated so that the polymer dissolves at some predetermined rate relative to the life of the oil. Such rate of dispersion can be linear or in certain instances it may be desirable to have a non-linear rate of dispersion so that a greater or lesser amount of additives may be dispersed into the oil in the early or late stages of. the service life thereof wbdeh variations in the rate of dispersion can, through suitable testing and eeiirnentation, be achieved with different degrees of polymer masking. It is to be further noted that the abovedescribed naskisE or blocking of surface area of the polymer body achieves an extremely important, additional function. In particular, by suitably covering certain portions of the polymer body by a suitable masking element undesirable migration of broken off pieces of the polymer body is achieved by the masking element physically restraining the polymer body in a predetermined location within the filter housing. Thus, the masking element prevents portions of the polymer body froni bealiing away and moving toward some undesirable location within the filter housing during dissia-i-ion of the body which might adversely affect either the operation of the filter unit per se or result in an undesirable rate of dispersion of additives into the oil being filtered by the unit. It wili be seen from the foregoing that there has been described a filter unit wherein through proper placement or location of the body at a location out of any direct impinge ment of oil circulating through the unit, unifonn or linear additive dispersion will occur, thereby ensuring against over or underdosing of additives into the oil, and providing for optimum additive replenishment over the service life of the oil in the associated lubrication system. VHAT WE CLPAiA IS:-

1. An oil filter for an engine having a r,}rculating oil lubrication system, said filter comprising an enclosure having a filter elenien- therein and provided with oil inlet and outlet ports for connection with the lubrication sys-fea of the engine, a first oil passage within the enclosure providing communication between the oil inlet port and the upstream side of the filter element and a second oil passage within the enclosure providing communication between the downstream side of the filter element and the outlet port, an annular body having a cylindrical outer surface, comprising an oil soluble material, having at least one oil improver property and being mounted in the enclosure, and means for limiting the rate of dissolution of said body by restricting the proportion of the surface area of the body exposed to the oil which in use is flowing through the enclosure from the inlet port to the outlet port, the means for restricting the proportion of the surface area of said body exposed to the oil comprising a masking element within the enclosure, such masking element having a first portion disposed adjacent to and in surface to surface contact with a radially extending surface of the body and a second portion disposed adjacent to and in surface to surface contact with the cylindrical

outer surface of said body.

2. An oil filter as claimed in Claim 1, wherei said body is of a flat ring-shaped configuration, and wherein said first portion of the masking element extends across one entire radially extending surface of said body and the second portion extends at least partially along and adjacent the cylindrical outer surface of said body.

3. An oil filter as claimed in Claim 1 or 2, wherein said second portion of the masking element has parts thereof removed to provide for restricted access of oil to contact the surface of the body.

4. An oil filter as claimed in Claim 3, wherein said second portion of the masking element has a plurality of openings therein.

5. An oil filter as claimed in Claim 3, wherein said second portion of the masking element has a plurality of notches therein.

6. An oil filter as claimed in any preceding claim, wherein said second portion of said masking element comprises a downwardly depending lip arranged circumjacent the outer periphery of said body.

7. An oil filter for an engine having a circulating oil lubrication system, said filter comprising a generally cylindrically-shaped enclosure having an annular filter element therein; a base plate at one end of said enclosure having a centrally located oil outlet opening and at least one oil inlet opening spaced radially from said outlet opening; a first oil passage within said enclosure for communicating the oil inlet opening(s) with the outer periphery of the filter element; a second oil passage within said enclosure communicating the inner periphery of said filter element with said oil outlet opening; an annular body comprising an oil soluble polymer and having at least one oil improver property, said body being of a flat ring-shaped configuration having upper and lower radially extending ends and inner and outer cylindrical sides; and a masking element disposed in the enclosure and adjacent said body and comprising a radial portion extending adjacent to and in surface to surface contact with said upper end of said body and an axial portion comprising a downwardly depending lip disposed adjacent to and in surface to surface contact with said outer cylindrical side, said masking element limiting the amount of surface area of said body exposed to the oil.

8. An oil filter constructed and arranged substantially as herein described with reference to and as illustrated in Figure 5, 6, 7 or 8 of the accompanying drawings.