BACKGROUND OF THE INVENTION An oil filter assembly disclosed by Korean utility model laid-open publication No. 97-8238 on March 27,1997 and filed with Korean utility model application serial No. 95-20987 on August 16, 1995 by the present applicant) is briefly explained in the following with FIGs. 1 to 3b as the prior art oil filter assembly of a winding roll type. Referring first to FIG. 1, the oil filter assembly 10 comprises an inner tube 12 and an outer tube 11, an upper filter body 13 and a lower filter body 15 strongly inserted between the inner tube 12 and the outer tube 11, and moisture-removing filter layers 14,16 inserted between the upper filter body 13 and the lower filter body 15 and attached to the bottom surface of the lower filter body 15.

For example, the upper filter body 13 and the lower filter body 15 are formed of natural pulp material strip in a wound roll.

The moisture-removing filter layers 14,16 is made from woven or

non-woven cloth, compressed cotton, etc., particularly so as to remove moisture from the oil being filtered. And the outer tube 11 and the inner tube 12 may be formed of hard substance such as a hardboard.

In FIG. 2, the prior art oil filter assembly 10 having the above-mentioned construction is inserted into an housing 1, and then a cover 2 oil-tightly engages with the open end of the housing 1 using a fastening rod 3 with oil passageways 3a and 3b formed. Thus, the housing 1 is installed in the filtering apparatus or industrial applications and an inlet tube 100 and an outlet tube 200 from a filtering apparatus or industrial applications are oil-tightly connected to an inlet port 3c and an outlet port 1b of the housing 1 respectively.

When the housing 1 with the oil filter assembly 10 inserted is mounted to the filtering apparatus or industrial applications, the oil flows in from the inlet tube 100 to the upper space 5b through the oil passageways 3a and 3b and an annular passageway 5a between the inner tube 12 and the fastening rod 3 by the hydraulic pressure of a pressure source such as a pump (not shown). The oil in the upper space 5b flows down through the filter media along the upper filter body 13, the moisture-removing filter layers 14, the lower filter body 15 and the moisture-removing filter layers 16 in sequence, thus the contaminants contained in the oil are collected. Particularly, while the oil passes through the moisture-removing filter layers 14,16, the moisture is removed from the oil. Then, the filtered oil is collected in the lower space 5c and flows out through the outlet tube 200.

In FIG. sinue the outer tube 11 is made of the hard

material such as the hardboard, it is very difficult to obtain the complete sealing between the outer tube 11 and the inner wall surface of the housing 1. Therefore, the unfiltered oil seeps through a clearance 5d between the outer tube 11 and the inner wall surface of the housing 1 from the upper space 5b to the lower space 5c and the efficiency of the filtration is lowered. And, the particulates in the oil are collected from the circumference towards the inside on the upper surface of the upper filter body 13 and then the oil pressure become increased in the upper space 5b because of the smaller area of the upper surface of the upper filter body 13. The increased pressure generates cracks 13a in the upper filter body 13 as shown in FIG. 3b before the longevity of the filter body. The cracks 13a grow along the texture of the upper filter body 13 and the particulates pass through the cracks 13b, deteriorating the efficiency of the filtration abruptly and shortening the longevity of the oil filter assembly 10 and the oil.

Furthermore, it is required to heat the oil for increasing the temperature of the oil in the cold winter season and to cool the oil for decreasing the temperature of the oil in the hot summer season. The difference of temperature between the inside and outside of the lubrication system forms dew, thus a large quantity of the moisture becomes contained in the oil by the inside dew. Particularly, the oil filter assembly 10 of the above-mentioned type having the upper filter body 13 and the lower filter body 15 formed of natural pulp material sheet in a wound roll is very week in moisture in the side of its structure and characteristics, and so the above-mentioned problem is the more

severe in case of this structure.

In FIG. 3, the upper filter body 13 and the lower filter body 15 are wound similarly in density and the oil passes through the moisture-removing filter layer 14 from the upper filter body 13 toward the lower filter body 15 without staying at the moisture-removing filter layer 14 for a long time. Therefore, the removal of moisture is not sufficient, and the longevity of the oil filter assembly 10 and the oil are still more shortened.

Further, it is very inconvenient to replace the oil filter assembly 10 with a new one because the oil filter assembly 10 is tightly inserted into the housing 1 and so the housing 1 should be in reverse for removing the oil filter assembly 10 from the housing 1.

And, besides the seeping of the unfiltered oil through a clearance 5d, when the oil filter assembly 10 is pulled out from the housing 1'for being replaced with a new one, the foreign particulates collected near the circumferential end of the upper surface of the upper filter body 13 inside of the outer tube 11 flow into the housing 1 along, and contaminate, the inner wall surface of the housing 1.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above described problems of the prior arts, and accordingly it is the principal object of the present invention to provide an oil filter assembly for industrial applications which effectively removes oil contaminants such as moisture, solid particulate from the oil and prevents the bypassing of the oil without being filtered and

contaminating the inside wall surface of the housing, thereby remarkably enhancing the efficiency of the filtration and the longevity of the oil filter assembly as well as readiness in handling the assembly for replacing it.

Also, it is a further object of the present invention to provide a method of manufacturing such a new and improved oil filter assembly.

To accomplish the aforementioned purpose, the present invention provides an oil filter assembly for industrial applications, which is inserted into the housing and comprises an inner tube, an outer tube, multiple layers of filter bodies inserted between the inner tube, and the outer tube for filtering foreign substance from the oil by passing through the filter body and at least one moisture-removing filter layer inserted between the multiple layers of the filter bodies, the improvement being characterized in that the filter bodies between which the moisture-removing filter layer is inserted, an upper filter body in the upper stream side of the moisture-removing filter layer being lower in density than a lower filter body in the lower stream side of the moisture-removing filter layer so as to stay at the moisture-removing filter layer for a longer time and sufficiently remove water or moisture from the oil.

Further, the present invention provides a method of manufacturing an oil filter assembly which comprises an outer tube, an upper filter body and a lower filter body inserted into the outer tube, a first inner tube and a second upper inner tube and a second lower inner tube into which the first inner tube is securely inserted and around each of which filter medium such as

natural pulp material strip is wound for forming the upper filter body and the lower filter body of a roll type, respectively, said method comprising the steps of: winding filter medium of natural pulp strip onto the second upper inner tube and the second lower inner tube, respectively for forming the upper filter body and the lower filter body; and pseudo-assembling the upper filter body and the lower filter body by means of the first inner tube by securely inserting the second upper inner tube and the second lower inner tube into the upper portion and the lower portion of the first inner tube, respectively, for making multiple layers of the upper filter body and the lower filter body.

These and other objects and advantages as well as these and other features will become apparent to those skilled in the art from the following detailed description of a preferred embodiment of the invention. especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of the prior art oil filter assembly; FIG. 2 is a longitudinal sectional view of a housing assembly in which the oil filter assembly in FIG. 1 is mounted; FIG. 3a is an enlarged partial section of the oil filter assembly in FIG. 1 for explaining one problem in the filtration of moisture when passing a moisture removing filter layer; FIG. 3b is a plan view of the oil filter assembly in FIG. 1

for explaining the other problem of the short life; FIG. 4 is a longitudinal sectional view of an oil filter assembly according to one embodiment of the present invention; FIG. 5 is a longitudinal sectional view of a housing assembly in which the oil filter assembly in FIG. 4 is mounted; FIG. 6 is an enlarged partial section of the oil filter assembly in FIG. 4 for explaining one feature of the present invention in the filtration of moisture when passing a moisture removing filter layer; and FIGs. 7 through 11 show various steps in manufacturing the oil filter assembly of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will now be described by way of example with reference to the accompanying drawings.

FIG. 4 shows an oil filter assembly 20 according to one embodiment of the present invention. In FIG. 4, the oil filter assembly 20 comprises an outer tube 21, an first inner tube 22, a second upper inner tube 22a, a second lower inner tube 22b, a upper filter body 23, a lower filter body 25, a intermediate moisture-removing filter layer 24, and a lower moisture-removing filter layer 26. The upper filter body 23, the lower filter body 25, the intermediate moisture-removing filter layer 24, and the lower moisture-removing filter layer 26 comprise a multiple-layer filtration element made of filtration medium such natural pulp, etc.

As shown in FIG. 7, the upper filter body 23 is formed as a roll type by winding filtration medium of a strip structure such

as a natural pulp strip around the second upper inner tube 22a in a relatively low density. Also, the lower filter body 25 is formed as a roll type by winding filtration medium of a strip structure such as a natural pulp strip around the second lower inner tube 22b in a relatively high density. That is, on forming the lower filter body 25, the strip is wound under stronger tension than when the upper filter body 23 is formed, thereby the turns of winding being increased in the lower filter body 25.

In FIG. 4, the intermediate moisture-removing filter layer 24 is inserted between the upper filter body 23 and the lower filter body 25 and the lower moisture-removing filter layer 26 is disposed to be in contact with the lower surface of the lower filter body 25. Those moisture-removing filter layers 24 and 26 are particularly made of filtration medium such as woven or non-woven cloth, compressed cotton, etc., for removing moisture from the oil, and assembled by simply inserting the filtration medium of a circular sheet type with a hole into each lower end portion of the filtration-strip-wound second upper and lower tubes 22a and 22b as shown in FIG. 8.

The upper filter body 23 has a circumferential protrusion portion 23a projected circumferentially at the upper circumferential wall portion outside of the outer diameter of the upper filter body 23. When the oil filter assembly for industrial applications is inserted into the housing 1, the circumferential protrusion portion 23a is compressed by the inner wall of the housing 1 and ensures the complete sealing between the housing 1 and the oil filter assembly 20, as shown in FIG. 5. Therefore, the seeping of the unfiltered oil through a clearance 5d between the

housing 1 and the upper filter body 23 is prevented.

Also, foreign particulates collected near the circumferential end of the upper surface of the filter body inside of the housing 1 is prevented from flowing into the housing 1 along, and contaminating, the inner wall surface of the housing 1 when the oil filter assembly 10 is pulled out from the housing 1 for being replaced with a new one.

The circumferential protrusion portion 23a can be formed by inserting a pseudo-assembled upper and lower filter bodies into the outer tube 21 shorter than the whole height of the upper filter body 23 and the lower filter body 25, as after-mentioned in relation to FIG. 11.

Further, the present invention may comprise a strap 27 for easily handling and replacing the oil filter assembly, said strap 27 being securely inserted between the first inner tube 22, and the second upper inner tube 22a and the second lower inner tube 22b, and between the outer tube 21, and the upper filter body 23 and the lower filter body 25, as shown in FIG. 4. Said strap 27 may be covered by a strap cover 28 for preventing from becoming dangling and dirty. Preferably, the strap 27 is inserted with a thin non-woven cloth 28a, thereby being fixed strongly. Also, the thin non-woven cloth 28a maintains the more complete sealing condition between the first inner tube 22, and the second upper inner tube 22a and the second lower inner tube 22b.

Instead of the above stable strap fixing structure, the strap 27 may be inserted between the first inner tube 22, and the second upper inner tube 22a, and between the outer tube 21, and the upper filter body 23.

One method of manufacturing the oil filter assembly in accordance with one embodiment of the present invention is described hereinafter with FIGs. 6 to 11.

In FIG. 7, filter medium of natural pulp strip is wound around the second upper inner tube 22a and the second lower inner tube 22b, respectively for forming the upper filter body 23 and the lower filter body 25 as a roll type. On forming the lower filter body 25, the strip is wound under stronger tension than when the upper filter body 23 is formed, thereby the turns of winding and the density of the filtration medium being increased in the lower filter body 25.

In FIG. 8, moisture-removing filter medium is inserted around the second upper inner tube 22a and the second lower inner tube 22b respectively to come into contact with each bottom surface of the upper filter body 23 and the lower filter body 25 right after the winding step, thereby the moisture-removing filter layers 24,26 being formed.

Then, as shown in FIG. 9, the handling strap 27 is inserted into the second upper inner tube 22a and the second lower inner tube 22b, and the first inner tube 22 is inserted through the non-woven cloth 28a into the second upper inner tube 22a and the second lower inner tube 22b in press-fit, thus the upper filter body 23 and the lower filter body 25 are pseudo-assembled by means of the first inner tube 22.

In FIG. 10, the strap 27 may be preferably fixed to the outer periphery of the upper filter body 23 and the lower filter body 25 by means of a stapler 29.

After this, a strap cover 28 larger than the inner diameter

of the outer tube 21 is disposed between the outer tube 21 and the pseudo-assembled upper and lower filter bodies as shown in FIG.

11. Then, the pseudo-assembled upper and lower filter bodies are horizontally compressed by means of a lateral compression tool 31 such as multiple jaws and an omitted aerodynamic or hydraulic cylinder so as to reduce the outer diameter of the pseudo-assembled upper and lower filter bodies so that the pseudo-assembled upper and lower filter bodies can be inserted into the outer tube 21. While maintaining the horizontal-compressing step, the pseudo-assembled upper and lower filter bodies are inserted into the outer tube 21 with the strap cover 28 by vertically compressing the pseudo-assembled upper and lower filter bodies against a base 30 by means of a upper compression tool 32 and an omitted aerodynamic or hydraulic cylinder.

In the vertical compressing and inserting step, the circumferential protrusion portion 23a is formed by inserting the pseudo-assembled upper and lower filter bodies into the outer tube 21 shorter than the whole height of the upper filter body 23 and the lower filter body 25. That is, the upper end portion of the upper filter body 23 above the upper end of the outer tube 21 is projected in the whole periphery.

Thus, the oil filter assembly 20 is simply manufactured and assembled according to one method of the present invention.

The features of the above-mentioned oil filter assembly 20 are described hereinafter with FIGs. 5 to 6.

In FIG. 5, when the oil filter assembly 20 is inserted into the housing 1, there is no clearance between the inner wall

surface of the housing 1 and the improved circumferential protrusion portion 23a, thereby ensuring the complete sealing between the housing 1 and the filter body. Therefore, the seeping of the unfiltered oil between the inner wall surface of the housing 1 and the filter body is prevented, and also, the whole oil is filtered through the whole section area of the upper and lower filter body 23 and 25 with far less foreign particulates collected near the circumferential end of the upper surface of the upper filter body 23 inside of the housing 1, the efficiency of filtration being improved. Also, the inner wall surface of the housing 1 is not contaminated by the less collected foreign particulates even, because the inner surface of the housing 1 is washed by the circumferential protrusion portion 23a and so basically the collected foreign particulates cannot flow in along the inner surface of the housing 1 when the oil filter assembly 20 is taken out from the housing 1.

In FIG. 6, because the upper filter body 23 is lower in density than the lower filter body 25, the oil filtered by the upper filter body 23 flows in to the lower filter body 25 with a decreased flow rate and is distributed in the radial and/or circumferential directions at the moisture-removing filter layer 24, thereby water or moisture completely being removed from the oil and the efficiency of filtration being further improved. After passing through the moisture-removing filter layer 24, even though the upper filter body 23 is damaged by the moisture and so the foreign particulates pass through the upper filter body 23 to the lower filter body 25, the foreign particulates is thoroughly filtered from the oil by means of the lower filter body 25 of the

high density, thus the complete rupture or damage of the whole oil filter assembly 20 is extended and the longevity is far more increased.

Further, the oil filter assembly 20 comprises the strap 27 at the low cost structure, thereby the handling and replacing of the oil filter assembly being facilitated.

As described above, the oil filter assembly 20 of two filter body layers and its manufacturing method according to the present invention are disclosed by way of examples only, but not limit the present invention.

It should be clear to one skilled in the art that the present solutions can be altered and applied without any limitation to the aforementioned embodiments of the present invention and within the scope of the present invention's spirit.